FIELD OF THE INVENTION
The present invention relates to a process for removing chloride, fluoride and
sulphate from industrial waste effluent water containing harmful complex organic
compounds and toxic metal. More particularly, the present invention relates to a
single-stage process of removing chloride, fluoride and sulphates from industrial
waste water using amphotaric salt acting as a complex metric agent.
BACKGROUND OF THE INVENTION
The known industrial wastewater management basically emphasizes on pollution
prevention both by source reduction/clean technologies through closed water
systems, in which water recycling plays a major role. Industrial water constitutes
22% of the total water used worldwide. Cooling water discharges are major
environmental problems, constituting from 60 to 90% by volume of industrial
discharges. Heat, toxic chemicals, and organic and inorganic materials are
contained in these discharges. Furthermore, cooling water contributes he highest
single water demand in industry, which accounted for 49% of all water
withdrawals in 1990.
The need for pollution control, water conservation, and reduced costs are the
major influencing factors to control the disadvantages of increased recycle of
cooling water. The major limitations to increased cooling water recycle are
associated with water quality problems. The underlying cause of these problems
is the continuous evaporation of water in the cooling tower that concentrates
nonvolatile compounds that enter the system in the makeup water. These higher
concentrations cause increased corrosion, biological, and scale formation on heat
transfer surfaces. Such fouling can substantially decrease the heat transfer
efficiency of the system and shorten the equipment life. To prevent scaling and
corrosion on the metal heat transfer surfaces, various chemicals are added to the
cooling water.
To increase the recycle of cooling water a need exits to control pollution, put
emphasis on water conservation and const reduction. However, the underlying
cause of these problems is the continuous evaporation of water in the cooling
water. The concentrates in the form of non volatile compound enter the system
leading to higher concentration of non-volatile compound in the make up water
which interaiia increases corrosion, biological growth scale formation, and heat
transfer/ surface. All these fouling substantially decrease the heat transfer
efficiency of the system. In order to prevent the scaling and corrosion on the
metal heat transfer surface, various chemicals are added to the cooling water,
which shortens the operating life of the equipment.
Several methods have been devised to remove anionic radicals such as C-I, F &
SO4"2 as exemplified in literature. The various known technologies used for
chloride removal from industrial cooling waters are noted below :
• Ion Exchange
• Reverse Osmosis
• Electrodialysis
Ion exchange resins are insoluble, cross linked, long chain polymers with a micro
porous structure and the functional groups attached to it are responsible for ion
exchange properties. Resins containing acidic functional group are capable of
exchanging their H+ ions with other cations which come in contact with them
whereas those containing basic functional groups are capable of exchanging their
anions with other anions which come in their contact.
Types of Ion Exchange Resins:
Ion exchange resin can be broadly divided into two catergories :
• Cation exchange resin : These are mainly styrene divinyl benzene
copolymers which on sulphonation or carboxylation become capable of
exchanging their hydrogen ion with the cations in the water.
• Anion exchange resin: These are styrene divinyl benzene or amine
formaldehyde copolymer which contain amino or quaternary phosphonium
or tertiary sulphonium groups as an intergral part of resin matrix. These
resins after treatment with dil. NaOH solution become capable to
exchange there OH group with anions in water.
Cation exchange and anion exchange resins can be again divided into following
categories:
Strong Acid Cation Resins
Strongly acidic cation resins derive their functionality from the sulfonic acid
groups. These strong acid exchangers operate at any pH, split all salts, and
require substantial amounts of regenerate. This is the resin of choice for most
softening applications and as the first unit in a two bed demineralizer or as the
cation component of a mixed bed.
Weak Acid Cation Resins
The weakly acidic cation resins have carboxylic groups as the exchange site. The
resin is highly efficient, for it is regenerated with nearly 100% stoichimatetric
amount of acid, as compared to the 200-300% required for strong acid cations.
The weak acid resins are subject to reduced capacity from increasing flow rate,
low temperatures, and a hardness-to-alkalinity ratio below 1.0. They are used
very effectively in conjunction with a strong acid cat ion resin operating in the
hydrogen form, in either a separate bed or stratified bed configuration. In both
cases, the influent water first contacts the weak acid resin where the cations
associated with alkalinity are removed. The remaining cations are removed by
the strong acid cation resin. The weak acid cation resin is regenerated with the
waste acid from the strong acid unit, making for a very economical arrangement.
Strong Base Anion Resins
Strongly basic anion resins derive their functionality from quaternary ammonium
exchange sites. The two main groups of strong base anion resins are Type 1 and
Type 2, depending on the type of amine used during the chemical activation
process. Chemically, the two types differ by the species of quaternary
ammonium exchange sites they exhibit: Type 1 sites have three methyl groups;
in Type 2 an ethanol group replaces one of the methyl groups. Type 1 resins are
suitable for total anion removal on all waters. They are more difficult to
regenerate and they swell more from the chloride form to the hydroxide form
than Type 2. They are more resistant to high temperatures and should be used
on high alkalinity and high silica waters.
Type 2 resins also feature removal of all anions, but they can be less effective in
removing silica and carbon dioxide from waters where these weak acids
constitute more than 30% of the total anions. Type 2 anions give best results on
waters that predominately contain free mineral acids.
Chlorides and sulfates - as in the effluent from a cation unit followed by a
decarbonator. Type 2 anion resins operating in the chloride form are typically
used in dealkalizers.
Weak Base Anion Resins
Weakly basic anion resins contain the polyamine functional group, which acts as
an acid adsorbed, removing strong acids (free mineral acidity), form the cation
effluent'stream. This weakly ionized resin is regenerated efficiently by nearly
stoichiometric amounts of base - such as sodium hydroxide - which restore the
exchange sites to the free base form. The regeneration step is essentially a
neutralization of the strong acids that are collected on the resin and it can use
waste caustic from a strong base anion unit to enhance economics. Weak base
anion resins should be used on waters with high levels of sulfates or chlorides or
where removal of alkalinity and silica are not required.
In order to overcome the prior art disadvantages, the effects of insitu addition of
aluminum alum and lime with the degradation of target pollutants in industrial
wastewater under various reaction conditions, were studied by the inventors.
The experiments were performed in a bench-scale reaction mixture so that they
could be easily controlled. The results of the chemical tests in this study can
serve as a reference for evaluating the effectiveness of wastewater and the
combination of treatment systems for practical applications.
OBJECT OF THE INVENTION
It is therefore, an object of the invention to propose environmentally sustainable
and economically viable chemicals/processes for removal of chloride and
sulphate from industrial waste water and mines processing water.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides an improved complex formation
process for treating wastewaters containing pollutants like cyanides and complex
organic compounds. The process enables an effective separation of
chloro/sulphate complex without adding any flocculent. Finally the sludge
products materials produced from the process are used as a precursor to cement
making.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 is a process flow chart of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The UHLA process of the invention exhibits excellent potential for efficiently
using industrial water and achieving zero discharge. The high pH and calcium
concentration found in first stage in the two stage configuration of the invention
shown in figure 1, allows removal of sulphate by precipitation as calcium sulfo
aluminate (Ca6AI2(SO4)3(OH)12). Furthermore, the conditions found in the first
stage of UHLA are suitable for removing chloride by precipitation as calcium
chloraluminate (Ca4AI2Cl2(OH)12). The present invention makes the UHLA
process more economically attractive by reducing the cost of reagents. This is
accomplished by using waste alum sludge from water treatment plants. This
sludge contains approximately 39% aluminum by weight. Every day about
10,000 tons of alum sludge are generated from water treatment plants and
disposed. Development of the UHLA process does not require development of
new equipment. In fact, the existing lime softening plants are enabled to convert
to UHLA with minor modifications.
Sulfate Removal in the UHLA Process:
Sulfate removal is required to facilitate recycle of cooling water. An important
source of information about the behavior of sulfate at high pH is the chemistry of
hydrated Portland cement and concrete. Sulfate is known to precipitate in
cement pore waters in the form of a calcium sulfoaluminate called ettringite
(Ca6(SO4)3AI2(OH)12). Ettringite is produced when gypsum (or gypsum saturated
solutions) reacts with a phase such as tri calcium aluminates, calcium aluminates
sulfate, or another source of calcium and aluminates ions. Ettringite was found to
be stable in low silica and low carbon dioxide activity environments. Ettringite is
stable above a pH of 10.7 UHLA treatment is capable of removing sulfate by
precipitation of calcium sulfoasluminate (Ca6(SO4)3Al2(OH)12) or calcium
sulfoferrate (Ca6(SO4)3Fe2(OH)12). The high pH and calcium concentration found
in the first stage of the two-stage configuration shown in Figure 2 allows for
removal of sulfate by precipitation as calcium sulfoaluminate.
It is known that when sufficient calcium is available, the molar ratio of sulfate to
aluminum removal is 1.5, which is in agreement with theoretical stoichiometry.
The kinetics of sulfate removal by precipitation of calcium sulfoaluminate is found
to be rapid enough for practical application. Furthermore, aluminum has been
found to promote silica removal by precipitation and adsorption mechanisms.
Chloride removal in the UHLA Process :
The UHLA process has demonstrated the ability to achieve high sulfate removal
efficiency. By expanding the process to remove chloride, the UHLA process acts
as a low-cost tool for improved industrial water management- The conditions
found in the first stage of ultra-high lime process allow for removal of chloride by
precipitation as calcium chloroaluminate (Ca4Cl2Al2(OH)12). Limited knowledge
exists on the formation of calcium chloroaluminate in aqueous solution. Most of
the previous research has focused on its chemistry in concrete and hydrated
Portland cement due to the effect of chloride on the corrosion of reinforcing steel
in concrete.
Preparation of reagents for UHLA method:
(1) Preparation of (N/10) 250 ml silver nitrate solution
Approximately 4.25 g of silver nitrate was dissolved by distilled
water in 250 ml volumetric flask.
(2) Preparation of calcium hydroxide solution
Calcium oxide ie lime is dissolved in distilled water.
1. Experimental procedure:
The experiment was done with 250 Lt chlorinated water, calcium hydroxide and
sodium aluminates added to this chlorinated water with molar ration 2:1 and pH
was maintained at a particular value and allowed it to stir for 1/2 hours. Then
calcium choloaluminateformed ultimately the chlorinated water was filtered and
concentration of water in the remaining solution was determined by the Mohr's
method.
2. Determination of chloride concentration :
Mohr's method :
In this method, concentration of chloride ion is determined by the precipitation
and titration with standard silver nitrate solution and potassium chromate is used
as indicator. End point is titration is obtained by the precipitation of silver
chromate, it is brown colored precipitate. So the end point color change is white
to brown. pH is maintained at the time of titration 6-9, because at low pH
chromate ion is converted into dichromate ion and at high pH silver ion of silver
nitrate solution from silver hydroxide black colored precipitate.
WE CLAIM :
1. A process for removing halides from waste water effluents comprising :
reduction of chloride compounds from industrial effluents by addition of
aluminum compounds at pH 12 at different temperature;
subjecting the compounds to a step of removing and followed by filtration
in a mix reactor; wherein the step of reduction of chloride compounds
constitutes chemo-precipitation by preparing slurry of chemicals dissolved
in waste water in a ratio from 1:5 to 1:20 at a reaction speed of 800 to
900 rpm in the mix reactor for a period of maximum 30 minutes to form
insoluble calciumaluminochloro complex precipitant.
2. The process as claimed in claim 1, wherein the step of filtration is
carried out for a period of 1 hour at temperature of 30°C, 50°C, 70°C and 90°C
respectively with sequential sampling for checking halide and sulfate contents.
3. The process as claimed in claim 1, wherein the chloride/sulfate used in the
step of removal is selected form of calcium-aluminum materials and rejects
calcium hydroxide materials.
4. The process as claimed in claim 1, wherein the chloride/sulfate content is
400PPM to 10,000PPM.
5. The process as claimed in claim 1, wherein the concentration of the solution
after filtration comprises reagent to water 1:40 by weight.
6. The process as claimed in claim 1, wherein t he 85-90% of chloride/sulfate
e compounds is removed.
7. The process as claimed in claim 1, wherein the sludge formed is 100%
reusable.

The invention relates to a process for removing halides from waste water
effluents comprising : reduction of chloride compounds from industrial effluents
by addition of aluminum compounds at pH 12 at different temperature;
subjecting the compounds to a step of removing and followed by filtration in a
mix reactor; wherein the step of reduction of chloride compounds constitutes
chemo-precipitation by preparing slurry of chemicals dissolved in waste water in
a ratio from 1:5 to 1:20 at a reaction speed of 800 to 900 rpm in the mix reactor
for a period of maximum 30 minutes to form insoluble calcium alumino chloro
complex precipitant.