DESALINATION SYSTEM AND METHOD
FIELD OF THE INVENTION
[0001] The present disclosure relates to desalination systems and methods
using a desalination device, for example an electrodialysis reversal (EDR) unit, preferably in combination with a precipitation device, for product water recovery.
BACKGROUND
[0002] In industrial processes, large amounts of wastewater, such as aqueous
saline solutions are produced. Generally, such saline solutions are not suitable for
direct consumption in domestic or industrial applications. In view of limited eligible
water sources, de-ionization of streams, such as wastewater, seawater or brackish
water, commonly known as desalination, becomes an option to produce eligible water
for direct consumption in domestic or industrial applications.
[0003] Wastewater generated from mining, such as acid mine drainage,
mineral processing and metal production industries often contains elevated levels of
calcium and sulfates, as well as metal ions (such as Fe, Mn, Al, Mg, Cu, and/or Zn).
High levels of sulfates are also found in ground water in many parts of the world.
Deionization of solutions with elevated levels of sulfates, and especially of solutions
with high concentrations of less soluble salts (for example: sulfates of calcium,
barium and strontium) are limited by precipitation and scaling of such salts.
[0004] Due to relatively higher efficiency and higher recovery of product
water, electrodialysis reversal units have been employed for desalination of such streams. During operation, such streams are introduced into the EDR units for desalination for product water recovery.
[0005] The metals ions present in the wastewater produced by mining,
mineral process and metal production cause scaling in the EDR membranes. This results in decreased water recovery and low membrane life and increased operational

expenses. Typically, precipitation units are employed to circulate liquids into the
respective EDR units during desalination of the streams. This circulated liquid
concentrates the charged species removed from the EDR-treated streams. However,
the concentration of salts or other impurities in the liquids increases with the
circulation of the liquids between the EDR units and the respective precipitation
units. This results in particle precipitation occurring in the precipitation units. The
resulting particles may be brought into the EDR units by the recirculated liquids and
the resulting scaling or fouling may damage the EDR apparatuses.
[0006] There have been attempts to avoid introducing the particle
precipitation into the EDR apparatuses. For example, cartridge filters may be disposed between the precipitation units and the respective EDR units to filter the particle precipitation before the liquids are introduced into the EDR apparatus. However, the cartridge filters suffer from low efficiency and high replacement frequency, which results in increased operation cost.
[0007] Alternatively, the precipitation units may be made sufficiently large to
provide additional settling areas for solid-liquid separation, which reduces the possibility of introducing the particles into the EDR units during the circulation of the liquids. However, the large sizes of the precipitation units may result in increased installation space, capital cost and assembly difficulty, which may prohibit them from being widely implemented.
[0008] The product water from EDR units may have higher dissolved solids
in comparison to other desalination systems, such as reverse osmosis and distillation. Thus product water from EDR units may not meet discharge or re-use regulations in many regions.
[0009] There is a need for a new and improved EDR-based desalination
system and method.

SUMMARY
[0010] Wastewater from mining, mineral processing and metal production
industries may include levels of calcium, sulfates, and metal ions (such as Fe, Mn, Al, Mg, Cu, and/or Zn) that cause fouling in EDR membranes. The amount of iron, manganese and aluminum may be as high as a few thousand of ppm. Total dissolved solids may be in excess of 3000 ppm.
[0011] Additionally, if the concentrations of sulfate and calcium ions are not
substantially equal and they are not removed from the desalination system, either ion
can combine into scale forming salts. The presence of scale forming salts limits
recovery in desalination processes. If the wastewater to be treated is high in sulfate
and low in calcium (for example in wastewater generated from mining, mineral
processing or metal production, which may have, for example, greater than about 500
ppm calcium and greater than about 2000 ppm sulfate), it is desirable to remove the
sulfate in order to reduce scaling in an electrodialysis reversal (EDR) unit.
[0012] The recovery of the EDR-based systems depends on the removal of
insoluble salts in the precipitation unit, which in turn depends on the ionic balance of
the feed stream. For example, a stream with high sulfates and low calcium cannot
generate sufficient calcium sulfate salts to be removed, particularly in a pretreatment
step. This leads to a decrease in the product water recovery of the overall system. It is
desirable to reduce the levels of calcium, sulfates and/or metal ions in order to protect
desalination equipment, such as electrodialysis reversal units.
[0013] Treatment of the EDR feed stream to remove calcium, sulfates and/or
metal ions, in combination with nanofiltration of a recycled EDR output stream to
remove sulfates and other multivalent ions, reduces the amount of sulfate ions being
processed by the EDR unit, thereby reducing scaling and increasing the recovery rate.
[0014] The specification describes a desalination system that includes a
desalination unit that receives a first stream for desalination and a second stream to carry away ions removed from the first stream. A precipitation unit is in fluid

communication with the desalination unit and circulates the second stream to the desalination unit. The system also (a) includes a pre-treatment unit upstream of the desalination unit that receives a feed stream and at least one pre-treatment chemical, and produces an ion-reduced first stream for the desalination unit; (b) adds lime into the precipitation unit, or into the second stream passing through the precipitation unit; and/or (c) includes a membrane-based purification device that receives a desalinated output stream from the desalination unit.
[0015] The desalination unit is preferably an electrodialysis reversal unit.
[0016] The desalination system preferably desalinates a wastewater that
includes acid mine drainage, or that is rich in sulfate ions but has a calcium concentration that is less than the sulfate concentration on a molar basis, for example less than one half of the sulfate concentration.
[0017] Optionally, more than 90% of the concentrate from a desalination unit
can be recycled to a pre-treatment reactor. In particular, liquid produced after
dewatering precipitator sludge may be returned to the pre-treatment reactor.
[0018] This specification also describes a process that includes desalinating a
first stream in a desalination unit by removing ions from the first stream using a
second stream. The second stream is circulated from a precipitation unit to the
desalination unit. The process also includes: (a) treating a feed stream with at least
one pre-treatment chemical before desalinating the treated feed stream; (b) adding
lime into the precipitation unit, or into the second stream passing through the
precipitation unit; and/or (c) purifying a desalinated output stream from the
desalination unit using a membrane-based purification device.
[0019] This specification also describes a process in which feed water is
treated in a desalination unit with concentrate recycled through a precipitation unit wherein lime is dosed into the precipitation unit. The process may be used, for example, to treat acid mine drainage, or another feed water that is rich in sulfate ions but has a calcium concentration that is less than one half of the sulfate concentration.

The lime dosing helps remove magnesium and other residual metals as well as sulfates.
[0020] This specification also describes a process in which feed water is
treated in a desalination unit with concentrate recycled through a precipitation unit
wherein desalination product water is further treated in a reverse osmosis (RO) or
nanofiltration (NF) membrane unit. The membrane unit helps meet stringent
discharge regulations. Optionally, membrane unit concentrate may be recycled to a
pre-treatment reactor. The membrane unit is preferably an NF unit, particularly when
the feed water is acid mine drainage, or another feed water that is rich in sulfate ions
but has a calcium concentration that is less than one half of the sulfate concentration.
[0021] This specification also describes a desalination system that includes a
pre-treatment unit that receives a feed stream and at least one pre-treatment chemical, and produces an ion-reduced first stream and an ion-concentrated discharge stream. This desalination system includes a desalination unit that receives the first stream from the pre-treatment unit for desalination. The at least one pre-treatment chemical includes a base and an oxidant.
[0022] This specification also describes a desalination method that includes
pre-treating a feed stream with at least a base and an oxidant before passing the treated stream through a desalination unit for desalination.
[0023] This specification also describes a composition for treating wastewater
that has iron ions in a concentration over 100 ppb, aluminum ions in a concentration over 100 ppb, and manganese ions in a concentration over 50 ppb. The composition includes: a base; an oxidant; and a water-soluble, branched, polymeric dithiocarbamic acid salt.
[0024] Other aspects and features of the present disclosure will become
apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Embodiments of the present disclosure will now be described, by way
of example only, with reference to the attached Figures.
[0026] FIG. 1 is a schematic diagram of one portion of a desalination system
according to the present disclosure.
[0027] FIG. 2 is schematic diagram of another portion of the desalination
system.
[0028] FIG. 3 is a schematic diagram of a precipitation device that may be
used in a desalination system according to the present disclosure.
[0029] FIG. 4 is a graph illustrating the concentration of Fe, Mn and Al ions
in the effluent of samples of acid mine drainage treated with limestone and sodium
hypochlorite.
[0030] FIG. 5 A is a graph illustrating the concentration of Fe, Mn and Al ions
in the effluent of samples of acid mine drainage treated with different pre-treatment
compositions.
[0031] FIG. 5B is a graph illustrating the concentration of Fe, Mn and Al ions
in the effluent of samples of acid mine drainage treated with different pre-treatment
compositions.
[0032] FIG. 5C is a graph illustrating the concentration of Fe, Mn and Al ions
in the effluent of samples of acid mine drainage treated with different pre-treatment
compositions.
[0033] FIG. 6 is a schematic diagram of an exemplary desalination system
according to the present disclosure.
[0034] FIG. 7 is an illustration of a method according to the present
disclosure.
[0035] FIG. 8 is an illustration of an optional portion of the method.

DETAILED DESCRIPTION
[0036] Generally, the present disclosure provides a desalination system that
includes a desalination unit, preferably an electrodialysis reversal (EDR) unit. An electrodialysis reversal unit is an electrochemical separation device that uses anion exchange membranes and cation exchange membranes to remove ions or charged species from water and other fluids under DC current with periodic polarity reversal. Although the present disclosure refers to electrodialysis reversal units, other electrochemical separation devices, such as an electrodialysis (ED) unit or supercapacitor desalination (SCD) device, may be used. However, EDR is a proven technology that is less susceptible to scaling, and so is preferred over other electrochemical separation devices. In another alternative, the desalination unit may be a membrane-based purification device such as a reverse osmosis (RO) or nano-filtration (NF) device. However, a membrane-based purification device is likely to produce slightly less recovery in the exemplary system and so the EDR device is also preferred over membrane-based purification devices.
[0037] In the context of the present disclosure, addition of a chemical or
composition to a feed or input stream results in a treated feed or input stream with the noted concentration of the chemical or composition. For example, the expressions "treated with 50 ppm of compound X" and "adding 50 ppm of compound X" refers to the addition of sufficient amounts of compound X to result in 50 ppm of compound X in the treated input stream. Similarly, the expressions "dosed with 100 ppm of compound Y" and "a dosage of 100 ppm of compound Y" refer to the addition of sufficient amounts of compound Y to result in 100 ppm of compound Y in the treated input stream.
[0038] The desalination system is illustrated in FIG. 1. The desalination
system includes an electrodialysis reversal (EDR) unit 10 and a precipitation unit 11 in fluid communication with the EDR unit 10. The EDR unit 10 is also in fluid communication with a pre-treatment unit 12. One example of a pre-treatment unit is

discussed in greater detail below with respect to FIG. 2. The pre-treatment unit 12 accepts a saline feed stream and at least one pre-treatment chemical, generating an ion-reduced first stream 13.
[0039] As discussed above, when treating wastewater from mining, mineral
processing and metal production industries, it is desirable to reduce the amount of sulfate and calcium in the saline feed stream, for example to approximately equal concentrations, so that formation of scale can be reduced. It is also desirable to reduce the amount of metal ions (such as least iron, manganese and aluminum) from the saline feed stream to reduce fouling of the EDR unit.
[0040] The pre-treatment unit 12 removes metal ions from the saline feed
stream in order to reduce scaling in the EDR unit. Metal ions may be removed in the pre-treatment unit 12 by forming insoluble precipitates of the ions. This may be achieved by supplying hydroxyl ions (OH") to the saline feed stream, thereby forming insoluble metal hydroxides which precipitate out of water. Accordingly, the at least one pre-treatment chemical may include a base, such as lime, for example quick lime, slaked lime or limestone. Using lime may produce undesirable amounts of sludge that need to be disposed. It may be desirable to add one or more additional pre-treatment chemicals to remove the dissolved metals while reducing the amount of solids produced. Specific examples of pre-treatment chemicals which may be used are discussed in greater detail below.
[0041] The EDR unit 10 is configured to receive the first stream 13 from the
pre-treatment unit 12, and to receive a second stream 14 from the precipitation unit
11. The EDR unit generates an ion-reduced first output stream 15 and an ion-
concentrated second output stream 16, as discussed in greater detail below.
[0042] The precipitation unit 11 precipitates salts in the second output stream
16, producing a precipitation discharge stream 17. The precipitation unit 11 recirculates the supernatant back to the EDR unit 10 as the second stream 14. The recirculated supernatant is used in the EDR unit to accept the ions removed from the

EDR feed stream, as discussed in greater detail below. A portion of the first stream 13 may be added to the second stream 14 in order to make up for solution removed in the precipitation discharge stream 17.
[0043] When desalinating a feed stream that is high in sulfate and low in
calcium, it is desirable to further purify the first output stream 15, or a portion
thereof, by: (a) recycling at least a portion of the first output stream 15 to the pre-
treatment 12, (b) passing the first output stream 15, or portion thereof, to one or more
electrical or electrochemical separation units for further desalination, or (c) both. The
one or more electrical or electrochemical separation units may recycle concentrated
discharge back to the pre-treatment unit 12. As noted above, treatment of the output
stream 15 in the pre-treatment unit 12 to remove sulfate ions in combination with
nanofiltration of output stream 15 reduces the amount of sulfate ions being processed
by the EDR unit, thereby reducing scaling and increasing the recovery rate.
[0044] The electrical or electrochemical separation unit may include a
nanofiltration unit 19, as discussed in greater detail below. The nanofiltration unit 19 passes monovalent ions into the nanofiltration permeate 20 and discharges the permeate 20, for example with the first output stream 15, preventing their buildup in the system. Nanofiltration concentrate 21 may be recycled back to the desalination system, for example to the pretreatment unit 12, to increase the overall recovery. The first output stream 15 and/or permeate 20, make up the purified discharge stream 22. The nanofiltration unit 19 may be replaced with a reverse osmosis unit. The purified discharge stream 22 may be discharged as the final effluent from the desalination system or it may be treated further if required to meet any particular discharge or reuse requirements.
[0045] Electrodialysis Reversal Unit. In some non-limiting examples, an
EDR unit 10 includes a pair of electrodes configured to act as an anode and a cathode, respectively. The electrodes may include electrically conductive materials, which may or may not be thermally conductive, and may have particles with smaller

sizes and large surface areas. In some examples, the electrode may be stainless steel
plate, titanium plate or platinum coated titanium plate. In other examples, the
electrically conductive material may include one or more carbon materials. Non-
limiting examples of the carbon materials include activated carbon particles, porous
carbon particles, carbon fibers, carbon aerogels, porous mesocarbon microbeads, or
combinations thereof. In other examples, the electrically conductive materials may
include a conductive composite, such as oxides of manganese, or iron, or both, or
carbides of titanium, zirconium, vanadium, tungsten, or combinations thereof.
[0046] The EDR unit includes a plurality of alternating anion- and cation-
exchange membranes disposed between the anode and the cathode to form a plurality of alternating dilute and concentrate channels therebetween. The anion exchange membrane(s) are passable only for anions. The cation exchange membrane(s) are passable only for cations. The anion exchange membrane may include a polymeric material that includes quaternary amine groups. The cation exchange membrane may include a polymeric material that includes sulfonic acid groups and/or carboxylic acid groups.
[0047] The EDR unit may include a plurality of spacers disposed between
each pair of the membranes, and between the electrodes and the adjacent membranes.
The spacers may include any ion-permeable, electronically nonconductive material,
including membranes and porous and nonporous materials.
[0048] During operation, when the EDR unit is in a normal polarity state,
while an electrical current is applied to the EDR unit, liquids, such as the first and
second streams 13 and 14 pass through first valves and along first input pipes to enter
into the respective alternating dilute and concentrate channels, respectively.
[0049] In the dilute channels, cations in the first stream 13 migrate through
the cation exchange membranes towards the cathode to enter into the adjacent channels. The anions migrate through the anion exchange membranes towards the anode to enter into other adjacent channels. In the adjacent channels (concentrate

channels) located on each side of a dilute channel, the cations may not migrate through the anion exchange membranes, and the anions may not migrate through the cation exchange membranes, even though the electrical field exerts a force on the ions toward the respective electrode (e.g. anions are attracted to the positively charged anode). Therefore, the anions and cations remain in and are concentrated in the respective concentrate channels. As a result, the second stream 14 passes through the concentrate channels to carry the concentrated anions and cations migrating from the dilute channels out of the EDR unit.
[0050] During operation, the first and second streams 13 and 14 may enter the
EDR unit along respective first and second input pipes and the first output stream 15 and the second output stream 16 may be discharged from respective first and second output pipes. The first output stream 15 has a lower concentration of ions than the first stream 13, and the second output stream 16 has a higher concentration of ions than the second stream 14.
[0051] The polarity of the electrodes of the EDR unit 10 may be reversed, so
as to reduce the scaling and fouling tendency in the EDR apparatus. In the reversed polarity state, the dilute channels from the normal polarity state may act as the concentrate channels to receive the second stream 14, and the concentrate channels from the normal polarity state may function as the dilute channels to receive the first stream 13.
[0052] For the arrangements of the disclosed system, it should be noted that
the EDR unit is not limited to any particular electrodialysis reversal (EDR) unit for processing a liquid.
[0053] Precipitation Unit. The precipitation unit 11 separates solid
precipitate from supernatant. Pre-treatment chemicals, for example lime, may be added into the precipitation unit 11, or otherwise into the second output stream 16 passing through the precipitation unit 11, to increase the amount of solids removed in the discharge stream 17 and reduce the amount of ions, such as sulfate, recirculated in

the concentrate second stream 14. A dosage of lime, for example slaked lime, in the range of about 100-1000 ppm may be used. In an example described further below, a dosage of 445 ppm of slaked lime is used.
[0054] The precipitation unit 11 may include a precipitation zone,
alternatively called a reactor, and a solid-liquid separation zone, for example a
clarifier. Solids are precipitated in the reactor and are separated from the liquid in the
solid-liquid separation zone. A suitable precipitation unit 11 is the precipitation
device shown in US Patent Application Publication No. US 2011/0114567 Al, which
is incorporated by reference. Another suitable precipitation unit 11 is the brine
concentration unit of an AquaSel™ system available from GE Water & Process
Technologies. The pre-treatment chemicals added to the pre-treatment unit 12,
discussed in greater detail below, may be added to the precipitation unit 11, or
otherwise into the second output stream 16 passing through the precipitation unit 11.
[0055] The precipitation device described in Figure 1 of US 2011/0114567 is
the same as the precipitation device illustrated in FIG. 3. The precipitation device 38 includes a precipitation element 40 disposed within a vessel 42 and configured to define a precipitation zone 44 and a solid-liquid separation zone 46 between the precipitation element 40 and the vessel 42. The precipitation zone 46 is configured to receive a first stream of saline liquid 48 and precipitate solids (not shown) from the saline liquid. The solid-liquid separation zone 46 is configured to settle the solids by gravity. An exit port 50 is located in an upper portion 52 of the vessel and is configured for exit from the solid-liquid separation zone 46 of a second stream 54 of liquid of lower salinity than the first stream.
[0056] The salinity of the second stream 54 of liquid is affected by many
factors, e.g., construction of the precipitation device 38. The precipitation element 40 and the upper portion 52 of the vessel 42 have hollow cylindrical shapes. The precipitation element 40 comprises a lower opening 56 in communication with the vessel 42. Additionally, an upper opening 58 in communication with the lower

opening 56 of the precipitation element 40 may or may not be provided to communicate with the vessel 42. In some exemplary precipitation units, a flow rate per unit cross-sectional area in the solid-liquid separation zone is about 0.12 to about 0.48 gallons per minute per square foot cross-sectional area (gpm/ft2), or about 8.2xl0~5 to about 3.3><10~4 cubic meter per second per square meter cross-sectional area (meter/sec). A ratio of a diameter D of the upper portion 52 of the vessel 42 to a diameter Dl of the precipitation element 40 ranges from about 1.5 to about 2.8, or preferably from about 1.6 to about 2.2. In a specific exemplary precipitation device, the lower portion of the vessel 42 is cone-shaped having a taper angle a of from about 60 to about 120 degrees. A ratio of a height H to the diameter D of the vessel 42 is not less than 0.2.
[0057] In some non-limiting examples, the vessel 42 may have other shapes,
such as whole cylindrical shapes. Similarly, the precipitation element 40 may also comprise other shapes, such as cone shapes.
[0058] For the precipitation device 38 illustrated in FIG. 3, a confining
element 60 is provided to define a confinement zone 62 with at least a portion thereof disposed within the precipitation zone 44 and in communication with the precipitation zone 44 and the solid-liquid separation zone 46. As one example, the confining element 60 may comprise two open ends and have a hollow cylindrical shape having a uniform diameter.
[0059] The precipitation unit 11 is configured to recycle the supernatant, as
the second stream 14, into the EDR unit 10. The second stream 14 is preferably filtered, for example through an ultrafiltration unit, before being passed through the EDR unit 10. Acid, as sulfuric acid, may be added to the second stream. Addition of acid reduces the pH and reduces scaling in the filtration membranes of the EDR unit 10. As discussed above, the second stream 14 concentrates the charged species removed from the first stream 13 so as to produce the second output stream 16. As the circulation of the liquid 14 continues, the concentration of the salts or other

impurities continually increases until the liquid 14 is saturated or supersaturated. As a result, the degree of saturation, or the super saturation, may reach a point where particle precipitation occurs in the liquid 14 over time.
[0060] The precipitation of the salts or other impurities may not occur until
the degree of saturation is relatively high. Accordingly, seed particles may be added
(not shown) into the precipitation unit 11 to induce the precipitation at a lower degree
of saturation. In certain applications, the seed particles may include solid particles
including, but not limited to CaSC>4 particles and their hydrates.
[0061] The precipitation unit may have an upper portion that has a hollow
cylindrical shape and a lower portion that is cone-shaped. Alternatively, the precipitation unit may have other shapes, such as cylindrical or rectangular shapes. In non-limiting examples, a portion of the upper portion of the precipitation unit 11 may act as a solid-liquid separation space for facilitation of separation of the particle precipitation from the second stream (liquid) 14. During operation, the second stream 14 may be provided or extracted from an upper portion of the solid-liquid separation space of the precipitation unit 11. In other examples, the solid-liquid separation space may or may not be defined.
[0062] Thus, during introduction of the second output stream 16 into the
precipitation unit 11 from the upper end thereof, at least a portion of the particle precipitation may be separated from the liquid 14 (or from the second output stream 16) in the precipitation unit 11. In some examples, the particle precipitation with diameters larger than a specified diameter may be kept within a defined area (not shown) of the precipitation unit 11 or settle down in the lower portion of the precipitation unit 11. Other particle precipitation with diameters smaller than the specified diameter may be dispersed in the liquid 14.
[0063] In certain applications, the second output stream 16 is not redirected
directly into the precipitation unit 11, and a liquid source (not shown) is provided to introduce the liquid 16 into the precipitation unit 11.

[0064] In some applications, when the liquid 14 is introduced into the EDR
unit 10 from the precipitation unit 11 without filtration of the particle precipitation dispersed therein, the dispersed particle precipitation may enter into the EDR unit 10 to cause fouling or scaling issues. In order to avoid damages to the EDR unit 10 during desalination a backwashable filter may be disposed between the EDR unit 10 and the precipitation unit 11 to filter the liquid 14 and remove at least a portion of the particle precipitation from the liquid 14 before the liquid 14 is introduced into the EDR unit 10 from the precipitation unit 11.
[0065] As used herein, the term "backwashable filter" means a regenerable
filter, which may be reused after being flushed by a washing fluid, for example, flushing the filter in a direction opposite to a normal flow direction for filtration of a liquid to be filtered. In one example, the backwashable filter may be sold by Pall Corporation in Port Washington, New York, U.S.A. Compared to conventional desalination systems employing once-through filters, such as cartridge filters, the backwashable filters have a higher tolerance of loading of the particle precipitation. Using backwashable filters may improve the system efficiency and reduce the cost due to relatively higher replacement frequency of the cartridge filters in the conventional desalination systems.
[0066] Operation of the precipitation unit generates a precipitator discharge
stream 17. In certain examples, a certain amount of a stream 18 may be removed as a "blow down" from the liquid 14 in the precipitation unit 11 to maintain a constant volume and/or reduce the degree of saturation or supersaturation of some species in the precipitation unit 11. The stream 18 may be mixed with a stream removed from the lower portion of the precipitation unit 11 to form the precipitator discharge stream 17. The discharge stream may be further filtered to form a filtration discharge stream that includes the precipitated species. Depending on the chemical composition of the raw saline feed stream, the precipitator discharge stream 17 and the filtration discharge stream, may include solid or dissolved Ca, Mg, and/or S04 salts.

[0067] Pretreatment Unit. The pre-treatment unit 12 removes metal ions
from the saline feed stream in order to reduce scaling in the EDR unit. The pre¬
treatment unit 12 may include: a clarifier configured to produce a clarified stream and
a clarified discharge stream; and a filter unit in fluid communication with the clarifier
to receive the clarified discharge stream, the filter unit configured to circulate a
filtrate stream to the clarifier and to produce a filtration discharge stream. The pre¬
treatment unit may further include: an ultrafiltration unit in fluid communication with
the clarifier to receive the clarified stream, and configured to produce a pre-treated
liquid filtrate. Acid, as sulfuric acid, may be added to the clarified stream. Addition of
acid reduces the pH and reduces scaling in the filtration membranes of the EDR unit.
[0068] One example of a pre-treatment unit 12 is illustrated in FIG. 2. As
illustrated, the pre-treatment unit includes a clarifier 23 that accepts an input saline feed stream 24. As discussed above, in some saline feed solutions, for example wastewater generated from mining, mineral processing and metal production industries, it is desirable to reduce the amount of sulfates and other metal ions (such as Fe, Mn, Al, Ca, and/or Mg) from the input saline feed stream 24 in order to reduce the burden on the EDR unit 10 and thereby increase recovery.
[0069] The pre-treatment unit 12 treats the input stream 24 with lime 25 (such
as quick lime, slaked lime or limestone) or another base (such as: calcium magnesium carbonate, or "dolomite"; or caustic soda) to reduce the amount of heavy metals (such as aluminum, iron and manganese) and sulfate. For example, the input stream may be treated with 100 ppm lime. The input stream is preferably also treated with an oxidant, such as sodium hypochlorite. The input stream 24 may be additionally treated with one or more additional pre-treatment chemicals 26 to further reduce the levels of sulfates and/or other metal ions. For example, the input stream 24 may be further treated with, a polymer for improving removal of heavy metals, a flocculant, a coagulant, or any combination thereof. An added pre-treatment chemical may have a plurality of functions. For example, FeCl3 may act as a flocculant, a pH control agent,

a precipitation catalyst for dissolved metals and metalloids, or any combination thereof. FeCb aids in precipitation of dissolved metals and metalloids (such as arsenic). The combination and dosage of the treatment chemicals to be used depends on the composition of the input stream to be treated, and may be determined through testing of the input stream. For example, in an input stream with silica as well as iron, manganese, aluminum, calcium, and magnesium ions, it may be desirable to use a combination with Metclear™ 2405 and Dolomite. Metclear™ 2405 effectively removes iron, manganese and aluminum ions, but is less effective at removing calcium and magnesium. Dolomite effectively removes silica as well as calcium and magnesium ions, but does not significantly remove iron, manganese or aluminum ions.
[0070] When the input stream is acid mine drainage, pre-treatment of the
input stream with a base and an oxidant removes sufficient sulfate, calcium, Mn, Al,
and Fe ions to make the discharge acceptable to be fed to the desalination unit, such
as to a reverse osmosis unit, a nanofiltration unit, or an electrodyalysis reversal unit.
An acceptable level of Fe, Al and Mn for a reverse osmosis or nanofiltration
feedwater may be, for example: less than about 100 ppb, less than about 100 ppb, and
less than about 50 ppb, respectively. Acceptable levels for feedwater for an EDR unit
may be, for example 300 ppb of Fe, 100 ppb of Mn and 100 ppb of Al.
[0071] Testing the ability of pre-treatment compositions to reduce the amount
of metal ions in samples of acid mine drainage (which includes 540 ppm Ca ions; 2400 ppm SO4 ions; 74 ppm Na ions; 250 ppm Mg ions; 7 ppm Mn ions; 16 ppm Al ions; 21 ppm Fe ions; 3500 ppm total dissolved solids; and a pH of 3.5) indicated that limestone, at a dosage of 400 ppm or more, effectively removed Fe and Al. Increased removal of Fe and Al ions was seen as the concentration of limestone was increased up to 1000 ppm limestone, though limestone was not effective in removal of Mn even at dosages of up to 5000 ppm. Adding 50-100 ppm of sodium hypochlorite (hypo) to either 800 or 100 ppm limestone provided almost complete Mn removal, but over 150

ppm sodium hypochlorite showed reduced Al removal. Combined dosages of about 400-1000 ppm limestone and 50-150 ppm sodium hypochlorite provide a preferred composition for removing Fe, Al and Mn from the acid mine drainage. Compositions with dolomite at 200-400 ppm or slaked lime (Ca(OH)2) at 100 ppm produced results similar to compositions with 400 ppm limestone. Quick lime (CaO) may also be used since it forms slaked lime when added to water. Treatment of the acid mine drainage with these compositions results in an effluent that is acceptable to be fed to the desalination unit.
[0072] For example, treatment with a composition having 800 ppm limestone
and 100 ppm sodium hypochlorite results in an effluent having about 100 ppb Fe,
about 90 ppb Al and about 20 ppb Mn. This is shown in FIG. 4.
[0073] Although sodium hypochlorite was tested, the inventors expect that
other oxidants could be used. The oxidant may be, for example, sodium hypochlorite,
chlorine gas, CIO2, KMn04, hydrogen peroxide, or any combination thereof.
[0074] Testing the ability of pre-treatment compositions to remove metal ions
on samples of acid mine drainage indicated that adding 2 ppm of Metclear™ 2405 allowed about a 25% reduction in the amount of limestone used to meet target concentrations of 100 ppb Fe, 100 ppb Al, and 50 ppb Mn. These results are illustrated in FIG. 5 A.
[0075] A two stage process, in which all of the Metclear™ 2405, less than
25% of the limestone, and about half of the sodium hypochlorite are used in the first stage, with the balances being used in the second stage, allowed a further reduction in limestone usage (to 400 ppm) meet the target concentrations of Mn and Fe, but not Al. These results are illustrated in FIG. 5B where samples I-VI were tested in two stages. Within the first stage, the Metclear™ 2405 is added after lime, the preferred order of addition in the first stage being lime or another base, oxidant, Metclear™ 2405 or another base, and then any other coagulants or flocculants. Metclear™ 2405

can optionally be added in the second stage as well although in the experiments
shown in Figure 5B it was not.
[0076] Sample I corresponds to dosages of: 75 ppm limestone, 0 ppm sodium
hypochlorite and 2 ppm Metclear™ 2405 in the first stage; and 325 ppm limestone,
100 ppm sodium hypochlorite and 0 ppm Metclear™ 2405 in the second stage. The
pH was 7.89.
[0077] Sample II corresponds to dosages of: 75 ppm limestone, 50 ppm
sodium hypochlorite and 2 ppm Metclear™ 2405 in the first stage; and 325 ppm
limestone, 50 ppm sodium hypochlorite and 0 ppm Metclear™ 2405 in the second
stage. The pH was 7.98.
[0078] Sample III corresponds to dosages of: 75 ppm limestone, 100 ppm
sodium hypochlorite and 2 ppm Metclear™ 2405 in the first stage; and 325 ppm
limestone, 0 ppm sodium hypochlorite and 0 ppm Metclear™ 2405 in the second
stage. The pH was 8.01.
[0079] Sample IV corresponds to dosages of: 50 ppm limestone, 0 ppm
sodium hypochlorite and 2 ppm Metclear™ 2405 in the first stage; and 350 ppm
limestone, 100 ppm sodium hypochlorite and 0 ppm Metclear™ 2405 in the second
stage. The pH was 7.78.
[0080] Sample V corresponds to dosages of: 50 ppm limestone, 50 ppm
sodium hypochlorite and 2 ppm Metclear™ 2405 in the first stage; and 350 ppm
limestone, 50 ppm sodium hypochlorite and 0 ppm Metclear™ 2405 in the second
stage. The pH was 7.85.
[0081] Sample VI corresponds to dosages of: 50 ppm limestone, 100 ppm
sodium hypochlorite and 2 ppm Metclear™ 2405 in the first stage; and 350 ppm
limestone, 0 ppm sodium hypochlorite and 0 ppm Metclear™ 2405 in the second
stage. The pH was 7.98.
[0082] Adding chitosan, at about 20-200 ppm, in addition to 400 ppm
limestone, 100 ppm sodium hypochlorite and 2 ppm Metclear™ 2405 further reduced

the concentration of all three metal ions. These results are illustrated in Table 1, below.
Table 1

Treatment Al (ppb) Fe(ppb) Mn (ppb)
Untreated acid mine drainage 16500 20800 7120
Acid mine drainage treated with base composition (400 ppm limestone +100 ppm sodium hypochlorite + 2 ppm MetClear™ 2405) 164.4 41.02 28.68
Acid mine drainage treated with base composition +10 ppm Tannin 232.9 386.7 97.3
Acid mine drainage treated with base composition +100 ppm Tannin 48.7 67 3320.4
Acid mine drainage treated with base composition +10 ppm Chitosan 162.0 127.6 30.7
Acid mine drainage treated with base composition +100 ppm Chitosan 126.4 95.1 20.6
[0083] Adding 50 ppm of FeCb, in addition to 400 ppm limestone, 100 ppm
sodium hypochlorite and 2 ppm Metclear™ 2405, reduced the Al ion concentration with an acceptable increase in the Fe concentration. These results are illustrated in FIG. 5C, where Sample I corresponds to acid mine drainage dosed with 400 ppm limestone, 100 ppm sodium hypochlorite and 2 ppm Metclear™ 2405; Sample II corresponds to acid mine drainage dosed with 400 ppm limestone, 100 ppm sodium hypochlorite, 2 ppm Metclear™ 2405 and 50 ppm FeCb; and Sample III corresponds to acid mine drainage dosed with 400 ppm limestone, 100 ppm sodium hypochlorite, 2 ppm Metclear™ 2405 and 100 ppm FeCb. Treatment to result in an input stream having 400 ppm limestone, 100 ppm sodium hypochlorite, 2 ppm Metclear™ 2405

and 50 ppm FeCb reduces the Fe, Al and Mn to below the levels desired for reverse osmosis feedwater.
[0084] In view of the results described above, and considering that different
acid mine drainage may have different levels of metal ions, a preferred pre-treatment composition is added to result in a treated input stream having: a base, for example lime, limestone or dolomite, in an amount of about 100-1000 ppm; an oxidant, for example sodium hypochlorite, in an amount of about 50-200 ppm; and Metclear™ 2405, in an amount of about 1-5 ppm. Chitosan, in an amount of about 20-200 ppm is also beneficial, but not required, if additional reduction in the concentration of Al, Mn and Fe is desired. FeCb may also be added to result in an input stream having about 25-75 ppm FeCl3.
[0085] Metclear™ 2405 is a water soluble, branched, polymeric
dithiocarbamic acid salt (DTC) described in U.S. Patent No. 5,658,487, which is incorporated by reference. Water soluble, branched, polydithiocarbamic acid salts described in U.S. Patent No 5,658,487 have the formula:
R3f-R!—Z-f-CH2—CH—CH2—N—R1—N^-H
OH R2 R2
[0086] wherein R1 is independently an organic radical or
4-R*—N—R4fe I R2
[0087] wherein R4 is independently an organic radical and x=l to 5; R2 is
independently -H or -CS2R5, R5 is independently H or a cation; R3 is N or a

substituted organic radical; Z is independently N-R2, O or S; the sum of n is an
integer greater than 10; and m is an integer greater than 2.
[0088] In a preferred example of such a polydithiocarbamic acid salt, R1 is an
ethylene radical, the sum of n is greater than 10, m=3, R3 =N, >50% of R2 are -
CS2R5, R5 is an alkali metal and Z is N-R2.
[0089] In a particularly preferred example of such a polydithiocarbamic acid
salt, R1 is an ethylene radical, the sum of n is greater than 25, m=3, R3 =N, >50% of
R2 are -CS2R5, R5 is an alkali metal and Z is N-R2.
[0090] In another particularly preferred example of such a polydithiocarbamic
acid salt, R1 is an ethylene radical, the sum of n is greater than 25, m=3, R3 =N, >79%
of R2 are -CS2R5, R5 is an alkali metal and Z is N-R2.
[0091] Metclear™ 2405 is a DTC polymer prepared by reacting poly[ethyl-
eneimine] (PEI) with carbon disulfide (CS2) in the presence of a base, with 80% CS2
functionalization and a molecular weight of about 170,000.
[0092] The polymer for improving removal of heavy metals may be anionic
polymer that uses sulfur-containing functional groups to precipitate heavy metals.
Examples of such a polymer include MetClear™ 2405 and MetClear™ 2410,
developed by BetzDearborn Research and Development. Other exemplary polymers
are discussed in U.S. Patent No. 5,658,487, filed Nov. 1, 1995. MetClear™ 2405
preferentially precipitates heavy metals, such as cadmium, chromium, copper, lead,
mercury, nickel and zinc. It is also effective in precipitating aluminum, cobalt, iron,
manganese, silver, tin and vanadium.
[0093] The flocculant may be, for example: an anionic polymer, such as AP
1120 (a product from GE Water & Process Technologies, Trevose, PA); a cationic
flocculant, such as CE2666; a tannin-based flocculant; a chitosan-based flocculant; or
a non-polymeric flocculant, such as FeCb. The anionic polymer, for example AP
1120, may be used at a concentration of about 3 ppm. The cationic flocculant, for
example CE2666, may be used at a concentration of about 3 ppm.

[0094] For the clarification of the input stream 24, in particular examples it is
preferable to use a combination of limestone (400 ppm), sodium hypochlorite (100
ppm), MetClear™ 2405 (2 ppm), and a polymeric flocculant (3 ppm). This preferred
combination may additionally include FeCb (50 ppm). In this example, the pH of the
input stream is about 3.5. Using this preferred combination of chemicals is
advantageous as it allows removal of at least iron, manganese and aluminum in a
single step, which would otherwise be difficult since these metals precipitate at a
different pH ranges. For example, iron precipitates around 3.5, manganese
precipitates above 10, and aluminum precipitate around 6-9. Using the preferred
combination reduces the level of dissolved metals with a single step.
[0095] In other examples, it is preferable to use a combination of limestone
(800 ppm), and hypochlorite (100 ppm). In other examples, it is preferable to use limestone (600 ppm), hypochlorite (100 ppm), and Metclear™ 2405 (2 ppm). In yet other examples, it is preferable to use limestone (400 ppm), hypochlorite (100 ppm), Metclear™ 2405 (2 ppm), and FeC^ (50 ppm). In yet other examples, it is preferable to use dolomite (400 ppm), hypochlorite (100 ppm), and Metclear™ 2405 (2 ppm). In still other examples, it is preferable to use limestone (400 ppm), hypochlorite (100 ppm), Metclear™ 2405 (2 ppm), and chitosan (100 ppm). In still other examples, it is preferable to use slaked lime also known as calcium hydroxide (100 ppm), hypochlorite (100 ppm), and Metclear™ 2405 (2 ppm). These combinations were tested successfully with coal mine drainage water having about 20 ppm iron ions, 7 ppm manganese ions and 16 ppm aluminum ions.
[0096] It may be preferable to add the coagulant(s), flocculant(s), or both,
after the base and optional oxidant are added.
[0097] The nanofiltration concentrate 21 from the nanofiltration unit 19 may
be accepted by the pre-treatment unit 12 as a feed to the clarifier 23, resulting in treatment of the nanofiltration concentrate 21 with the lime 25 and additional pre-treatment chemicals 26.

[0098] The input stream 24 is clarified in clarifier 23 to produce clarified
stream 27, which may be filtered in an ultrafiltration unit 28. The resulting pre-treated
liquid filtrate 29 is accepted by the EDR unit 10 as the first stream 13.
[0099] The clarifier 23 also produces a clarifier discharge stream 30, which
includes precipitated, coagulated and/or flocculated products. The clarifier discharge
stream 30 may be may be filtered by filter unit 31 to form a filtration discharge
stream 32, which includes the solid species, and a filtrate stream 33. The filtrate
stream 33 may be recycled to the clarifier 23, resulting in treatment of the filtrate
stream 33 with the lime 25 and additional pre-treatment chemicals 26. Depending on
the chemical composition of the raw feed, the solid species may include solid or
dissolved Fe, Mn, Al, Ca, Mg, and/or S04 or C03 salts thereof.
[00100] The pre-treatment may be operated as a two-stage process. In a two-
stage process, the treatment chemicals are added at desired dosages in two steps. For example, 50 ppm of limestone, 50 ppm of sodium hypochlorite and 2 ppm of Metclear™ 2405 are added in the first stage, and 350 ppm limestone and 50 ppm sodium hypochlorite are added in the second stage. Adding the treatment chemicals in two stages, in contrast to adding them in a single stage, results in a more basic pre-treatment process which may aid in precipitation of, for example, Al, Mn and Fe salts. The two stage process allows less lime to be used to produce the same treated water quality.
[00101] Nanofiltration. The nanofiltration unit 19 includes a nanofiltration
membrane element, which has the ability to reject multivalent anions, and to reject cations depending on shape and size. Nanofiltration membranes which may be used in filtration systems according to the present disclosure may reject as much as 90% of divalent ions (for example rejecting 99% of sulfate, calcium and magnesium), while allowing at least 50% of monovalent ions (for example as much as 50-80% of sodium, potassium and chloride) to pass through the membrane, thereby reducing scale formation downstream of the nanofiltration membrane.

[00102] In particular examples, nanofiltration membranes are preferred over
reverse osmosis membranes due to the former's ability to reject multivalent ions while passing the monovalent ions in the permeate stream. This results in a slight increase in the product water salinity and reduction in the salinity of the nanofiltration concentrate stream 21 that may be recycled back to the treatment system to increase the water recovery.
[00103] Nanofiltration membranes known in the art may be used. In particular
examples, a membrane with at least 90% rejection of multivalent ions and at most 50% rejection of monovalent ions is preferred.
[00104] Exemplary membrane elements may have a molecular weight cut-off
of about 150 to about 300 daltons for uncharged organic molecules. Rejection of divalent and multivalent ions by such membrane elements would be dependent on feed concentration and composition. Exemplary nanofiltration membrane elements may be operated at about 70 to about 300 psi, or even as high as about 600 psi. The nanofiltration membrane elements may operate at a flux of about 10 to about 20 gallons per square foot of membrane per day (GFD). The exemplary nanofiltration membrane elements may operate at a pH of about 3.0 to about 9.0. Specific examples of such nanofiltration membrane elements include those produced by GE Water & Process Technologies as model HL8040F-400, which has an active area of about 37.2 m2 and an average permeate flow of about 43.5 m3/day (when tested with 2000 ppm MgS04 at 100 psig); and those sold as Seasoft™ 8040.
[00105] The salts present in the saline feed stream may include charged ions,
such as magnesium (Mg2+), calcium (Ca2+), sodium (Na+), potassium (K+), barium (Ba2+), strontium (Sr2+), chlorine (CI"), sulfate (S042"), and/or other ions. In certain applications, the first stream 13 and the second stream 14 may or may not comprise the same salts or impurities, and may or may not have the same concentration of the salts or the impurities. The concentration of the salts or impurities in the second stream 14 may or may not be saturated or supersaturated.

[00106] Exemplary System. An exemplary system according to the present
disclosure was modeled. The feed stream in the model represents acid mine drainage with a total dissolved solids (TDS) of about 3000 ppm and a pH of about 3.5. The feed stream is rich in calcium and sulfate ions, but the concentrations of sulfate and calcium ions are not substantially equal. The sulfate concentration is more than twice as much, and even more than four times as much, as the calcium concentration (about 2400 ppm vs. about 500 ppm, respectively). Significant metals ions include iron, manganese, aluminum and zinc. The feed stream is pre-treated with a mixture of 100 ppm of lime, 100 ppm of sodium hypochlorite, 5 ppm of MetClear™ 2405, and sufficient quantities of coagulants and flocculants. The second output stream 16 was also treated with pre-treatment chemicals.
[00107] An illustration of the modeled system is shown in FIG. 6, showing the
fluid and solid flows. The components of this exemplary desalination system interact as discussed above. The system includes pre-treatment unit 12, EDR unit 10, precipitation unit 11, and nanofiltration unit 19. The first output stream 15 was treated with the nanofiltration unit 19, and nanofiltration concentrate 21 was recycled to the pre-treatment unit 12. Lime was dosed into the reactor of the precipitation unit 11. The product flows encircled in a dashed line highlight the products produced by the desalination system. The modeled system includes an ultrafiltration unit 34 to filter the second stream 14; and a filter unit 35 to filter the precipitation discharge stream 17. The filter unit 35 separates solid that is discharged from the system from liquid that is mixed in mixer 36 with a portion of the second stream 14. The mixed liquid is recycled back to the clarifier 23 via clarifier recycle stream 37. A portion of the mixed liquid is discharged from the system as "blow down" stream 18. Acid, as sulfuric acid, is added to the clarified stream 27 and to the second stream 14 that is discharged from the ultrafiltration unit 34. Addition of acid reduces the pH and reduces scaling in the filtration membranes of the EDR unit 10.

[00108] The precipitation unit 11 in the modeled system is the precipitation
device shown in US Patent Application Publication No. US 2011/0114567 and
illustrated in FIG. 3.
[00109] The mathematical model results in the following stream properties:
[00110] The mathematical model of the exemplary system was compared to a
mathematical model of a system without pre-treatment of the saline feed stream, without pre-treatment of the raw feed, without chemical addition to the precipitator, and without the nanofiltration. This model used identical starting parameters and calculated that the treatment of the raw feed resulted in the following stream properties:

[00111] As evidenced from the comparison between the two mathematical
models, the exemplary system provided improved recovery for this calcium deficient feed water and reduced sulfate concentration in the product water. The inventors believe that it is beneficial to use a desalination system that includes one or more of (a) pre-treatment, for example with a mixture of about 100 ppm of lime, about 100 ppm of sodium hypochlorite, about 5 ppm of MetClear™ 2405, and sufficient quantities of coagulants and/or flocculants, (b) lime dosing in a precipitator and (c) a nanofiltration unit 19 when the desalination system is used to treat a feed stream whose sulfate and calcium ions are not substantially equal. Other mixtures of pre-treatment chemicals, as discussed herein, may also provide the desirable removal of sulfates, calcium and metal ions. Although lime consumption increased with the exemplary system, the increase in recovery more than offsets these increases in terms of total operating expense. Further, the lime consumption and solid production are less than a three stage RO process configured to give similar recovery.

[00112] Composition for treating wastewater. According to a further aspect
of the present disclosure, there is provided a composition for treating wastewater, for example wastewater generated from mining, such as acid mine drainage, mineral processing and metal production. These wastewaters contain elevated levels of calcium and sulfates, as well as levels of metal ions (such as Fe, Mn, Al, Mg, Cu, and/or Zn) that make the wastewater undesirable to use directly in a desalination unit. These wastewaters often contain a concentration of sulfate that is more than twice the concentration of the calcium.
[00113] It is desirable to reduce the concentration of Fe, Al and Mn to levels
that are acceptable to a desalination unit, such as to a reverse osmosis unit, a nanofiltration unit, or an electrodyalysis reversal unit, by treating the wastewater with a chemical composition in the absence of other treatment steps. Treating the wastewater in such a manner would allow the wastewater to separate into: an effluent having levels of Fe, Al and Mn below target concentrations for the desalination unit, and a sludge. The effluent may be treated in the desalination unit without further treatment steps.
[00114] Compositions according to the present disclosure may be used to
reduce the concentration of Fe, Al and Mn in an input stream. Preferred compositions may be used to reduce the concentration of acid mine drainage to below the target concentrations of 100 ppb Fe, 100 ppb Al, and 50 ppb Mn for reverse osmosis feedwater.
[00115] The composition includes: a base and an oxidant. The base is
preferably added at a dose of between about 50 and about 1000 ppm. The oxidant is preferably added at a dose of between about 50 and about 200 ppm. The composition may further include an anionic polymer that includes sulfur-containing functional groups for precipitating heavy metals. The composition may further include a flocculant.

[00116] The composition may include one or more chemicals that have a
plurality of functions. For example, FeCb may act as a flocculant, a pH control agent,
a precipitation catalyst for dissolved metals and metalloids, or any combination
thereof.
[00117] The base may be: lime, calcium magnesium carbonate (dolomite),
caustic soda (sodium hydroxide), or any combination thereof. The oxidant may be:
sodium hypochlorite, chlorine gas, C102, KMn04, hydrogen peroxide, or any
combination thereof. The anionic polymer that includes sulfur-containing functional
groups for precipitating heavy metals may be: MetClear™ 2405. The flocculant may
include: a polymeric flocculant. The lime may be: quick lime (calcium oxide), slaked
lime (calcium hydroxide) or limestone (calcium carbonate).
[00118] In specific examples, the base is: limestone; the oxidant is: sodium
hypochlorite; the anionic polymer that includes sulfur-containing functional groups
for precipitating heavy metals is: MetClear™ 2405; the flocculant is: a combination
of a polymeric flocculant and FeCb.
[00119] In a preferred composition, the limestone is added to the wastewater in
an amount of at least about 800 ppm. The sodium hypochlorite is added to the
wastewater in an amount of at least about 100 ppm.
[00120] In another preferred composition, the limestone is added to the
wastewater in an amount of at least about 600 ppm. The sodium hypochlorite is
added to the wastewater in an amount of at least about 100 ppm. The MetClear™
2405 is added to the wastewater in an amount of at least about 2 ppm.
[00121] In a preferred composition, the limestone is added to the wastewater in
an amount of at least about 400 ppm. The sodium hypochlorite is added to the
wastewater in an amount of at least about 50 ppm. The MetClear™ 2405 is added to
the wastewater in an amount of at least about 2 ppm. The FeCb is added to the
wastewater in an amount of about 50 ppm. In the preferred composition, a polymeric
flocculant may is added to the wastewater in an amount of at least about 1 ppm.

[00122] In yet other examples, it is preferable to use dolomite (400 ppm),
hypochlorite (100 ppm), and Metclear™ 2405 (2 ppm). In still other examples, it is preferable to use limestone (400 ppm), hypochlorite (100 ppm), Metclear™ 2405 (2 ppm), and chitosan (100 ppm). In still other examples, it is preferable to use slaked lime also known as calcium hydroxide (100 ppm), hypochlorite (100 ppm), and Metclear™ 2405 (2 ppm).
[00123] As discussed above with respect to FIGs. 4, 5 A, 5B and 5C, these
combinations were tested successfully with coal mine drainage water having about 20
ppm iron ions, 7 ppm manganese ions and 16 ppm aluminum ions.
[00124] This preferred composition is particularly advantageous for treating
wastewater that includes iron, manganese and aluminum as it allows removal of at least iron, manganese and aluminum in a single step, which would otherwise be difficult since these metals precipitate at a different pH ranges. For example, iron precipitates around 3.5, manganese precipitates above 10, and aluminum precipitate around 6-9. Using the preferred combination reduces the level of dissolved metals with a single step. As noted previously, wastewater from mining, mineral processing and metal production industries may include iron, manganese and aluminum at concentrations as high as a few thousand of ppm.
[00125] Desalination Method. In another aspect, the present disclosure
provides a desalination method. A desalination method according to the present disclosure is illustrated in FIG. 7. The method includes: passing a feed stream and at least one pre-treatment chemical though a pre-treatment unit 64 for producing an ion-reduced first stream and an ion-concentrated discharge stream; passing the first stream through an electrodialysis reversal unit 65 for desalination; and passing a second stream through the electrodialysis reversal unit via a precipitation unit 66 to carry away ions removed from the first stream.

[00126] The at least one pre-treatment chemical may include lime, such as
quick lime, slaked lime or limestone. The at least one pre-treatment chemical may include limestone, sodium hypochlorite, MetClear™ 2405, FeCl3, and a polymeric flocculant.
[00127] The method may further include passing a first output stream from the
electrodialysis reversal unit to a nanofiltration unit or a reverse osmosis unit 67. The method may further include passing a concentrate stream from the nanofiltration unit to the pre-treatment unit 68.
[00128] Passing the feed stream and at least one pre-treatment chemical though
the pre-treatment unit may include (as illustrated in FIG. 8): passing the feed stream
through a clarifier 69 to produce a clarified stream and a clarified discharge stream;
and passing the clarified discharge stream through a filter unit and circulating a
filtrate stream to the clarifier 70. Passing the feed stream and at least one pre-
treatment chemical though the pre-treatment unit may further include: passing the
clarified stream to an ultrafiltration unit 71 to produce a pre-treated liquid filtrate.
[00129] In the preceding description, for purposes of explanation, numerous
details are set forth in order to provide a thorough understanding of the examples. However, it will be apparent to one skilled in the art that these specific details are not required. The above-described examples are intended to be exemplary only. Alterations, modifications and variations can be effected to the particular examples by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

WE CLAIM:
1. A desalination system, comprising:
a desalination unit configured to receive a first stream for desalination and a second stream to carry away ions removed from the first stream;
a precipitation unit in fluid communication with the desalination unit and configured to circulate the second stream there between;
and at least one of:
(a) a pre-treatment unit upstream of the desalination unit and
configured to:
receive a feed stream and at least one pre-treatment chemical, and
produce an ion-reduced first stream for desalination in the desalination unit, and an ion-concentrated discharge stream;
(b) the desalination system being configured to add lime into the precipitation unit, or into the second stream passing through the precipitation unit; and
(c) a membrane-based purification device configured to receive a desalinated output stream from the desalination unit.

2. The desalination system according to claim 1, wherein the desalination unit is an electrodialysis reversal unit.
3. The desalination system according to claim 1 or 2, wherein the precipitation unit comprises a precipitation device having a precipitation zone and a solid-liquid separation zone.

4. The desalination system according to claim 3, wherein the precipitation unit provides the second stream from an upper portion of the solid-liquid separation zone.
5. The desalination system according to any one of claims 1 to 4, wherein the desalination system desalinates a wastewater that includes acid mine drainage, or that is rich in sulfate ions but has a calcium concentration that is less than one half of the sulfate concentration.
6. The desalination system according to any one of claims 1 to 5, wherein the desalination system comprises the pre-treatment unit upstream of the desalination unit.
7. The desalination system according to claim 6, wherein the at least one pre-treatment chemical includes a base.
8. The desalination system according to claim 7, wherein the base is quick lime, slacked lime, limestone, or dolomite, added to result in about 50 to about 1000 ppm base.
9. The desalination system according to claim 7 or 8, wherein the at least one pre-treatment chemical includes an oxidant.
10. The desalination system according to claim 9 wherein the oxidant is sodium hypochlorite, added to result in about 50 to about 200 ppm sodium hypochlorite.

11. The desalination system according to claim 9 or 10 wherein the at least one pre-treatment chemical includes a water soluble, branched, polymeric dithiocarbamic acid salt.
12. The desalination system according to claim 11, wherein the polymeric dithiocarbamic acid salt is Metclear™ 2405 added to result in about 1 to about 5 ppm Metclear™2405.
13. The desalination system according to claim 11 or 12 wherein the at least one pre-treatment chemical includes chitosan added to result in about 20 to about 200 ppm chitosan.
14. The desalination system according to claim 11 or 12 wherein the at least one pre-treatment chemical includes FeCl3 added to result in about 25 to about 75 ppm FeCl3.
15. The desalination system according to any one of claims 6 to 14, wherein the pre-treatment unit comprises:
a clarifier configured to produce a clarified stream and a clarified discharge stream; and
a filter unit in fluid communication with the clarifier to receive the clarified discharge stream, the filter unit configured to circulate a filtrate stream to the clarifier and to produce a filtration discharge stream.
16. The desalination system according to claim 15 wherein at least 90% of the
filtrate stream from the filter unit is recycled back to the clarifier.

17. The desalination system according to claim 15 or 16 wherein the pre-treatment unit comprises an ultrafiltration unit in fluid communication with the clarifier to receive the clarified discharge stream, and configured to produce a pre-treated liquid filtrate for the desalination unit.
18. The desalination system according to claim 17 where at least a portion of the pre-treated liquid filtrate accepted by the desalination unit is accepted as a portion of the second stream.
19. The desalination system according to claim 17 or 18 wherein the system is configured to accept an acid into the ultrafiltration unit, or into the clarified discharge stream passing through the ultrafiltration unit.
20. The desalination system according to any one of claims 1 to 19, wherein the system is configured to add lime into the precipitation unit, or into the second stream passing through the precipitation unit.
21. The desalination system according to claim 20, wherein the system is configured to add the lime into a precipitation element disposed within a vessel of the precipitator.
22. The desalination system according to claim 20 or 21, wherein the lime is added in an amount sufficient to reduce the amount of sulfate ions in the second stream circulated from the precipitation unit to the desalination unit.
23. The desalination system according to any one of claims 20 to 22, wherein the system comprises a filter unit to filter a precipitation discharge stream from the precipitation unit.

24. The desalination system according to claim 23 wherein at least a portion of the filtrate from the filtration unit is recycled back to the desalination system.
25. The desalination system according to any one of claims 20 to 24 wherein the system comprises an ultrafiltration unit to filter the second stream being circulated to the desalination unit.
26. The desalination system according to claim 25, wherein the system is configured to accept an acid into the ultrafiltration unit, or into the second stream passing through the ultrafiltration unit.
27. The desalination system according to any one of claims 20 to 26 wherein at
least a portion of the second stream is recycled back to the desalination system.
28. The desalination system according to any one of claims 1 to 27 wherein the system comprises the membrane-based purification device configured to receive a desalinated output stream from the desalination unit.
29. The desalination system according to claim 29, wherein the membrane-based purification device is a nanofiltration device.
30. The desalination system according to claim 28 or 29, wherein the membrane-based purification device produces a concentrate stream and a permeate discharge stream, at least a portion of the concentrate stream is recycled back to the desalination system, and at least a portion of the permeate stream is discharged from the desalination system as the purified discharge stream.

31. The desalination system according to any one of claims 28 to 30, wherein at least a portion of the desalinated output stream from the desalination unit is recycled back to the desalination system without passing through the membrane-based purification device.
32. The desalination system according to any one of claims 28 to 31, wherein the membrane-based purification device produces a permeate stream and at least a portion of the desalinated output stream from the desalination unit is discharged from the desalination system along with the permeate stream as the purified discharge stream.
33. A desalination system, comprising:
a pre-treatment unit configured to:
receive a feed stream and at least one pre-treatment chemical, and produce an ion-reduced first stream and an ion-concentrated discharge stream; and
a desalination unit configured to receive the first stream from the pre-treatment unit for desalination;
wherein the at least one pre-treatment chemical includes a base and an oxidant.
34. The desalination system according to claim 33, wherein the base is quick lime, slacked lime, limestone, or dolomite.
35. The desalination system according to claim 34, wherein the base is added to result in about 50 to about 1000 ppm base.

36. The desalination system according to any one of claims 33 to 35, wherein the oxidant is sodium hypochlorite.
37. The desalination system according to claim 36, wherein the sodium hypochlorite is added to result in about 50 to about 200 ppm sodium hypochlorite.
38. The desalination system according to any one of claims 33 to 37, wherein the at least one pre-treatment chemical includes a water soluble, branched, polymeric dithiocarbamic acid salt.
39. The desalination system according to claim 38, wherein the polymeric dithiocarbamic acid salt is Metclear™ 2405.
40. The desalination system according to claim 39, wherein the Metclear™ 2405 is added to result in about 1 to about 5 ppm Metclear™ 2405.
41. The desalination system according to any one of claims 33 to 40 wherein the at least one pre-treatment chemical includes chitosan.
42. The desalination system according to claim 41 wherein the chitosan is added to result in about 20 to about 200 ppm chitosan.
43. The desalination system according to claim any one of claims 33 to 42 wherein the at least one pre-treatment chemical includes FeCl3.
44. The desalination system according to claim 43 wherein the FeCl3 is added to result in about 25 to about 75 ppm FeCb.

45. The desalination system according to any one of claims 33 to 44 wherein the
pre-treatment unit comprises:
a clarifier configured to produce a clarified stream and a clarified discharge stream; and
a filter unit in fluid communication with the clarifier to receive the clarified discharge stream, the filter unit configured to circulate a filtrate stream to the clarifier and to produce a filtration discharge stream.
46. The desalination system according to claim 45, wherein the pre-treatment unit
further comprises:
an ultrafiltration unit in fluid communication with the clarifier to receive the clarified stream, and configured to produce a pre-treated liquid filtrate.
47. The desalination system according to any one of claims 33 to 46, wherein the desalination unit is an electrodialysis reversal unit, a reverse osmosis unit, a nanofiltration unit, an electrodialysis unit, or a supercapacitor desalination unit.
48. The desalination system according to any one of claims 33 to 47, wherein the desalination system desalinates a wastewater: that includes acid mine drainage; that is rich in sulfate ions but has a calcium concentration that is less than one half of the sulfate concentration; or that includes iron ions, aluminum ions and manganese ions in concentrations that are above a level acceptable to the desalination unit.
49. The desalination system according to claim 48 wherein the wastewater includes iron ions in a concentration over 100 ppb, aluminum ions in a concentration over 100 ppb, and manganese ions in a concentration over 50 ppb.

50. The desalination system according to any one of claims 33 to 49 wherein the desalination unit receives the first stream from the pre-treatment unit without additional treatment of the first stream.
51. A desalination method, comprising:
passing a first stream through a desalination unit for desalination; passing a second stream through the desalination unit via a precipitation unit to carry away ions removed from the first stream; and at least one of:
(a) passing a feed stream and at least one pre-treatment chemical through a pre-treatment unit to produce the first stream for desalinating in the desalination unit, and to produce an ion-concentrated discharge stream;
(b) adding lime into the precipitation unit, or into the second stream passing through the precipitation unit; and
(c) passing a desalinated output stream from the desalination unit through a membrane-based purification device to produce a purified discharge stream.

52. The desalination method according to claim 51, wherein the first and the second streams are passed through an electrodialysis reversal unit.
53. The desalination method according to claim 51 or 52, wherein the method includes precipitating in a precipitation unit that includes a precipitation device having a precipitation zone and a solid-liquid separation zone.
54. The desalination method according to claim 53, wherein the method includes passing the second stream to the desalination unit from an upper portion of the solid-liquid separation zone.

55. The desalination method according to any one of claims 51 to 54, wherein the desalination method desalinates a wastewater that includes acid mine drainage, or that is rich in sulfate ions but has a calcium concentration that is less than one half of the sulfate concentration.
56. The desalination method according to any one of claims 51 to 55 wherein adding lime into the precipitation unit comprises mixing at least lime with a desalinated output stream from the desalination unit and passing the mixture though a reactor and a clarifier in the precipitation unit to generate the second stream.
57. A desalination method for the treatment of wastewater, comprising:
passing a feed stream and at least one pre-treatment chemical through a pre-
treatment unit to produce an ion-reduced first stream and an ion-concentrated discharge stream;
passing the first stream through a desalination unit for desalination;
wherein the at least one pre-treatment chemical includes a base and an oxidant.
58. The desalination method according to claim 57, wherein the base is quick lime, slacked lime, limestone, or dolomite.
59. The desalination method according to claim 58, wherein the base is added to result in about 50 to about 1000 ppm base.
60. The desalination method according to any one of claims 57 to 59, wherein the oxidant is sodium hypochlorite.

61. The desalination method according to claim 60, wherein the sodium hypochlorite is added to result in about 50 to about 200 ppm sodium hypochlorite.
62. The desalination method according to any one of claims 57 to 61 wherein the wastewater includes iron ions in a concentration over 100 ppb, aluminum ions in a concentration over 100 ppb, and manganese ions in a concentration over 50 ppb.
63. A composition for treating wastewater having iron ions in a concentration over 100 ppb, aluminum ions in a concentration over 100 ppb, and manganese ions in a concentration over 50 ppb, the composition comprising:
a base;
an oxidant;
a water soluble, branched, polymeric dithiocarbamic acid salt; and
a flocculant.
64. The composition according to claim 63, wherein
the base is: lime, calcium magnesium carbonate, caustic soda, or any combination thereof;
the oxidant is: sodium hypochlorite, chlorine gas, CIO2, KMn04, hydrogen peroxide, or any combination thereof;
the water soluble, branched, polymeric dithiocarbamic acid salt: MetClear™ 2405;and
the flocculant comprises: a polymeric flocculant.
65. The composition according to claim 64 wherein:
the base is: limestone;
the oxidant is: sodium hypochlorite;

the water soluble, branched, polymeric dithiocarbamic acid salt is: MetClear™ 2405; and
the flocculant is: a combination of a polymeric flocculant and FeCl3.
66. The composition according to claim 65 wherein:
the limestone is added to the wastewater to result in at least about 400 ppm;
the sodium hypochlorite is added to the wastewater to result in at least about 50 ppm;
the MetClear™ 2405 is added to the wastewater to result in at least about 2 ppm;
the polymeric flocculant is added to the wastewater to result in at least about 1 ppm; and
the FeCb is added to the wastewater to result in about 50 ppm.