FIELD OF INVENTION:
[0001]. The present invention relates to a method for producing multiple value added
products from LD slag fines which can be advantageously used in ceramic, cement making
process, gypsum boarded industry agriculture and other industries.
[0002]. Further, the present disclosure also provides different value added novel
products like 1st Product (limegyp), 2nd Product (dologyp) and 3rd Product (finegyp)
composition, which are mainly combination of mixture produced from LD slag fines after
reaction with an acid and can be used as sulphate fertilizer, soil conditioner and source of
carbon and micro-nutrients and have a wide use in the field of agriculture.
BACKGROUND AND PRIOR ART:
[0003]. With the increased costs for disposing of wastes and the decrease of available
places to send wastes, converting the wastes that need to be discarded in to valuable products
by utilising another waste liquid is more important. Non-hazardous wastes and hazardous
wastes each have its own set of problems. Issues such as toxicity, harm to the environment,
and the amount of waste created cause problems for those with these types of wastes that need
to be discarded. For example, waste sulphuric acid is toxic and is regulated as a hazardous
waste. The primary way to dispose of waste sulphuric acid is to have it incinerated.
Incinerating waste, or spent, sulphuric acid is expensive and there are many regulatory
requirements associated with the disposal of it.
[0004]. Various methods have been used to produce or recover reusable compounds
from waste materials, which in turn reduces the amount of waste that needs to be disposed off
and decreases raw material costs for the reusable compound. Waste Recycling Plant (WRP)
fines is one such type of waste that is produced during the recovery of metallic Iron from LD
Slag produced during steel manufacturing process from LD Converters. Attempts have also
been made to recover valuable and rare metal compounds like Vanadium from the LD Slag,
in land filling and for acidic soil conditioning which decrease the amount of LD Slag that has
to be discarded.
[0005]. Natural gypsum, by-product gypsum from the manufacture of phosphoric
acid fertilizer, or synthetic gypsum prepared from waste sulphuric acid and limestone, etc.,
have been here to fore main sources of the gypsum, and have been used all in a powdery state.
However no efforts have been made till now to utilize the 1st Product (limegyp) product

produced from LD Slag fines which is an waste containing mixture of di-calcium silicate,
calcite and calcium hydroxide generated from LD process of steel making
[0006]. Phospho-gypsum produced as a byproduct from a phosphoric acid plant is of
acidic in nature and finds majority of its use only in cement industry as the acidic nature of it
is not suitable for all the soils in common and can be applied only in limited quantity to
alkaline soil. Its usage in agriculture is also limited due to the fact that the phospho-gypsum
contains hazardous elements like radio-active substances and heavy metals.
[0007]. But the naturally available mined gypsum, mainly finds its usage is cement
industry and its agriculture usage is not really encouraged due to the huge consumption by
cement producers in the country and it doesn’t contain any plant beneficial micro nutrients
apart from Sulphur and calcium.
[0008]. One such example of making a reusable compound from waste materials can
be found in U.S. Pat. No. 4,049, 462, issued to Cocozza. The Cocozza patent relates to the
chemical fixation of industrial desulfurization residues by forming a mixture of the residue,
such as a flue gas desulfurization sludge, with an alkaline calcination stack dust, such as CKD
in the presence of water. The pH of the mass is adjusted with sulphuric acid to a value of
below about 7.0. The mixture is then dried into a shaped article to produce a solid, cement-
like fixed product. Stack dust contains constituents such as calcium, silicon, aluminium, iron,
magnesium, sodium, potassium and associated constituents found in cement making and
similar stack dust, for example, in the form of oxides and salts. The industrial waste residue
can be any such residue or sludge as, for example, is produced in the after-removal of
pollutants, such as sulphur constituents from the effluent or flue gas of basic manufacturing
processes, such as fossil fuel consumption reaction or cement making or ore roasting reaction
processes. These manufacturing processes often generate sulphur oxides, especially sulphur
dioxide, which must be removed from the reaction effluent by scrubbing or absorbing
techniques before venting to the atmosphere in order to avoid environmental pollution. An
advantageous source of sulphuric acid is a spent industrial waste acid liquor, such as a spent
pickle liquor of about 3-10% concentration.
[0009]. Another example of trying to recover reusable products from CKD can be
found in U.S. Pat. Nos. 4,716, 027, and 4,915,914, both issued to Morrison. These patents
describe neutralizing cement kiln dust so that it is suitable as a feed stock to the cement kiln
and at the same time scrubbing the exhaust fumes to reduce SO2 levels. The precipitate from

the neutralization process is suitable as kiln feed stock. The precipitate is sent to a kiln with
other raw materials, where the raw materials are heated and produce clinker. The clinker from
the kiln is then ground and mixed with gypsum to form cement. The alkali salt solution from
the neutralization process is dried and forms a fertilizer. This process decreases the amount
of waste that is produced due to use of a kiln during the cement manufacturing process.
[00010]. Another example is the process for production of Gypsum from Sulphuric acid
containing waste streams (WO9851616). This invention provides a process for the production
of gypsum from a waste stream containing sulphuric acid including: (A) adding calcium
containing basic material to said waste stream to bring pH within the range of from about 2.0
to 2.7 to precipitate gypsum, and recovering the precipitated gypsum from the waste stream,
and (B) adding basic material to the waste stream to bring pH within the range of from about
3.0 to 3.4 to precipitate impurities, and removing the precipitated impurities from the waste
stream, and (C) adding calcium containing basic material to said waste stream to bring pH
within the range of from about 4 to 6 precipitate gypsum, and recovering the precipitated
gypsum from the waste stream.
[00011]. Another process for the recovery of purified gypsum product (FR2761357) , a
process for the recovery of sulphate ions and, if need be, metallic ions from industrial effluents
containing sulphate ions, Fe(III) and Cr(III) ions, is claimed. It comprises the reaction of the
SO4<2-> charged effluent with a solution containing Ca<2>+ ions(Ca<2+> solution) to
precipitate SO4 <2-> ions as gypsum at a pH of suitable acidity: this is carried out after the
separation of most of the Fe and Cr ions such that the residual content of the precipitated
gypsum (possibly washed) are less than 100 ppm (or even less than 50 ppm) to enable
vaporisation of the gypsum for industrial use. Preferably the process comprises: (a) a prior
selective separation from the liquid phase of most of the metallic ions Fe(III) and Cr(III) in
conditions which retain the sulphate ions in solution (i.e., in the absence of Ca<2+> ions in
solution); (b) reaction of the effluents thus depleted in Fe(III) and Cr(III) ions with a Ca<2+>
solution charged with calcium ions and precipitation of gypsum at a suitable acid pH ; (c)
recovery of the resulting insoluble purified gypsum. The Ca solution is calcium chloride. This
can partly be obtained as a product of the re-dissolving of sludges from effluents neutralised
with calcium hydroxide in acid solution (other than H2SO4) such as HCl, the Ca solution itself
being freed from most of the Cr and Fe ions.
[00012]. Preparation of gypsum hemihydrate with thermal waste, aqueous H2SO4 and
sulphuric acid salts (DE3117641) Alpha-gypsum hemihydrate is an important building

material, which is obtained especially by calcination of calcium sulphate dihydrate, which
arises in the desulphurisation of a power station flue gas or in the chemical sector, for example
in the manufacture of phosphoric acid.
[00013]. A particularly advantageous calcination process comprises first preparing a
dispersion of calcium sulphate dihydrate and aqueous sulphuric acid solution in the presence
of sulphuric acid salts and then heating this dispersion, while maintaining a predetermined
heating-up rate, to about 373 K together with industrial, dust-free thermal waste, whereupon
the solid constituents are then separated off from the aqueous sulphuric acid and dried. Due
to the combination of aqueous sulphuric acid solution and sulphuric acid salts, the result of
this process is an alpha-gypsum hemihydrate virtually without fractions of anhydrite II, which
substantially facilitates the processing thereof. Apart from the negligibly small fraction of
anhydrite II, the alpha-gypsum hemihydrate product is distinguished, if magnesium oxide is
added, by high fineness and absence of any efflorescence phenomena.
[00014]. Process for manufacturing CaSO4.2H2O, (KR8100800) CaSO4.2H2O, useful
as bean curd coagulant having high purity, solubility and ultra fine particle crystal structure,
was manufactured by reacting sulphuric acid with calcium salt soln. which was obtained by
reacting CaCO3 with acid. For e.g., excess CaCO3 was put-in 2N-HNO3 500ml for 1-2hrs. to
give Ca (NO3)2 soln., wherein 64% H2SO4 46L was put-in and dehydrated to give pure
CaSO4.2H2O 64kg and the filtrated 2N-NHO3 was recovered.
[00015]. Hence, a need always exists for a process that will reduce the amount of LD
Slag Waste that needs to be disposed off and produce a product that is reusable in the cement
production process or as a fertiliser in the agriculture or a raw material for gypsum board
industry. It is an object and a goal to convert a waste product to a desirable product,
particularly one that currently is purchased to reduce raw material costs in the cement
production process and also as an alternative to costlier fertilisers.
[00016]. The present invention meets the long felt need.
OBJECTS OF THE INVENTION
[00017]. It is therefore an object for the present invention to provide a method for
producing various value added products from LD slag fines, which can be used mainly in
paint, ceramic, cement making process, gypsum board industry, agriculture and other
industries.

[00018]. Another object of the present invention to recover multiple value added
products having industrial importance from waste, produced during the recovery of metallic
iron from LD slag by continuous hydro metallurgical process.
[00019]. Yet another object of the present invention to provide a method for producing
various value added products from LD slag fines, which provides utilization of sulphuric acid
and low quality lime stone, dolomite and lime fines are also produced during the production
of lime from limestone.
[00020]. Further object of the present invention to provide different value added
products including calcium sulphate in anhydrite forms, ferric sulphate, 2nd Product
(dologyp), 1st Product (limegyp) and 3rd Product (finegyp) composites.
[00021]. Still object of the present invention to provide a method for producing various
value added products from LD slag fine, which can remove alkali as Na2O and sodium oxide.
[00022]. Yet, another object of the present invention to provide a 1st Product (limegyp)
or 2nd Product (dologyp) or 3rd Product (finegyp) composition produced from LD slag fines
to be used as sulphate fertilizer and soil conditioner in the agricultural field.
[00023]. Further object of the present invention to provide a 1st Product (limegyp) or
2nd Product (dologyp) or 3rd Product (finegyp) composition produced from LD slag fines,
which can used as a source of carbon to the soil as well as a source of silicon to the plants.
[00024]. Another object of the present invention to provide a 1st Product (limegyp) or
2nd Product (dologyp) or 3rd Product (finegyp) composition produced from LD slag fines,
which is produced from LD slag of size -2.0 mm separated by means of sieving of 0-6 mm
nonmetallic LD slag fines.
[00025]. Still another object of the present invention to provide a 1st Product (limegyp)
or 2nd Product (dologyp) or 3rd Product (finegyp) composition produced from LD slag fines,
which can combine the advantages of micro nutrients like, Iron, Magnesium, Manganese and
phosphorus to all kinds of soils and crops.
[00026]. Another object of the present invention to provide a 1st Product (limegyp) or
2nd Product (dologyp) or 3rd Product (finegyp) composition produced from LD slag fines,
which can provide the low alkali and low chloride content product as a soil conditioner for
salt affected soils as the calcium replaces the sodium and makes the land alkali free when
applied.

[00027]. Yet, another object and goal is to decrease the amount of LD Slag Waste that
needs to be disposed off and recovering a useful product from the LD Slag produced during
the steel making process.
[00028]. It is yet another object and goal to provide a use for lime fines generated in
lime making process.
[00029]. Another object and goal is to remove and recover the Iron, Phosphorus,
Aluminium, Titanium from the Waste.
[00030]. It is yet another object and goal to provide a use for sulphuric acid which is an
hazardous byproduct in copper concentrate smelting industries.
SUMMARY OF INVENTION
[00031]. While the embodiments of the disclosure are subject to various modifications
and alternative forms, specific embodiment thereof have been shown by way of the figures
and will be described below. It should be understood, however, that it is not intended to limit
the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover
all modifications, equivalents, and alternative falling within the scope of the disclosure.
[00032]. The present invention relates to the method of treatment of LD slag of produce
various value added composites comprises the steps of: i) taking LD slag in a reactor and
mixing with sulfuric acid solution and water while maintaining a suitable temperature to brake
the calcium silicate into calcium sulphate and silica; ii) reaching definite a pH value of product
slurry once reaction completes and then the slurry is allowed to cool for sufficient residence
time (half an hour to one hour) within the reactor; iii) after the discharge, the product slurry
conveyed to pumping for removal of excess water; iv) filtering of slurry either by filter press
or drum filter producing calcium sulphate and then dried at a suitable temperature depending
upon production of calcium sulphate in different form such as dehydrate or hemihydrate or
anhydrate; v) neutralization of filtrate with different neutralizing agent such as powdered lime
stone, dolomite and lime fines to produce 3rd Product (finegyp), 2nd Product (dologyp) and
1st Product (limegyp); vi) evaporation of filtrate containing soluble sulphate to produce ferric
sulphate; vii) filtration of product slurry to produce iron rich ammonium sulphate fertilizer
and iron rich calcium sulphate and then subjected to drying between 50 to 100ºC depending
upon the procuring of calcium sulphate in dehydrate or hemihydrate or anhydrate form

alongwith other sulphates of iron, phosphorous, titanium, aluminium and excess sulphuric
acid.
[00033]. In another aspect, the present invention also provides different novel value
added composite such as 1st Product (limegyp), 3rd Product (finegyp) and 2nd Product
(dologyp).
[00034]. In another aspect, the 1st Product (limegyp) composite comprises
CaSO4.2H2O : 55.84
Calcite: 37.00
FeO: 2.46
SiO2: 1.44
P2O5: 0.42
Al2O3: 0.64
TiO2: 0.089
Others: 1.11
[00035]. In another aspect, the 2nd Product (dologyp) composite comprises
CaSO4.2H2O+MgSO4.H2O (Gypsum + Epsum): 47.40%
Dolomite: 42.50%
FeO: 2.20%
SiO2: 5.60%,
P2O5: 0.53%
Al2O3: 1.10%
TiO2: 0.067%
Others : Traces
[00036]. The 3rd Product (finegyp) composite comprises
CaSO4.2H2O: 89.50
Calcite: 4.17

FeO: 2.46
SiO2: 0.28
P2O5: 0.48
Al2O3: 0.52
TiO2: 0.12
MgO: 1.37
[00037]. Various objects, features, aspects, and advantages of the inventive subject
matter will be more apparent from the following details of preferred embodiments, along with
the accompanying drawing figures.
[00038]. It is to be understood that the aspects and embodiments of the disclosure
described above may be used in any combination with each other. Several of the aspects may
be combined to form a further embodiment of the disclosure.
[00039]. The foregoing summary is illustrative only and is not intended to be in any
way limiting. In addition to the illustrative aspects, embodiments, and features described
above, further aspects, embodiments will become apparent by reference to the drawings and
the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
[00040]. The illustrated embodiments of the subject matter be best understood by
reference to the drawings. The following description is intended only by way of example, and
simply illustrates certain selected embodiments of method, systems, that are consistent with
the subject matter as claimed herein, wherein:
[00041]. Figure 1 illustrates is a simplified flow diagram of a process of producing
different value added products in the combination of Anhydrite and Ferric Sulphate or
Anhydrite and 1st Product (limegyp) or Anhydrite and 2nd Product (dologyp) or Anhydrite
and 3rd Product (finegyp).
[00042]. The figure depict embodiments of the disclosure for purposes of illustration
only. One skilled in the art will readily understand from the following description that
alternative embodiments of the structures and methods illustrated herein may be employed
without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE PRESENT INVENTION WITH PREFERRED
EMBODIMENTS:
[00043]. One or more drawbacks of conventional method for treatment of LD slag fines
for removal of value added products in steel industry are overcome, and additional advantages
are provided through the method as claimed in the present disclosure, additional features and
advantages are realized through the technicalities of the present disclosure. Other
embodiments and aspects of the disclosure are described in detail herein and are considered
to be part of the claimed disclosure.
[00044]. It is to be noted that a person skilled in the art would be motivated from the
present disclosure to arrive at an methodology for production of different value added
products and different novel composites. Such method may vary based on configuration of
one or more ingredients. However, such modifications should be construed within the scope
of the disclosure. Accordingly, the drawings illustrate only those specific details that are
pertinent to understand the embodiments of the present disclosure, so as not to obscure the
disclosure with details that will be clear to those of ordinary skill in the art having benefit of
the description herein.
[00045]. As used in the description herein and throughout the claims that follow, the
meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates
otherwise.
[00046]. The terms “comprises”, “comprising”, or any other variations thereof used in
the disclosure, are intended to cover a non-exclusive inclusion, such that a method, LD slag,
steel, slurry, filtrate that comprises a list of components does not include only those
components but may include other components not expressly listed or inherent to such
method. In other words, one or more elements in a method proceeded by “comprises…..a”
does not, without more constraints, preclude the existence of other elements or additional
elements in the method.
[00047]. Hereinafter, a description of an embodiment relates to novel method of
producing various value added products from LD slag fines.
[00048]. A description of an embodiment related to a method for producing multiple
value added products from LD slag fines produced in steel industry after recovery of metallic
iron.

[00049]. In more specific aspects, the invention advantageously provides a method for
producing various value added products such as calcium sulphate in anhydrate form alongwith
other products viz 1st Product (limegyp), 2nd Product (dologyp) and 3rd Product (finegyp)
composites depending on the choice of neutralization agent. This invention includes a process
of treating LD Slag through a leaching process with sulfuric acid, and/or commercially
available sulfuric acid solution or oleum, resulting in a blend of pure calcium sulphate with
silica and Ferrous sulphate solution.
[00050]. In order to meet one or more of the identified objects, the present invention
advantageously includes a method for treating LD slag fines in the size range of 0-6mm left
after the recovery of metallic iron with sulphuric acid to form Calcium Sulphate in anhydrite
form and leach liquor left after the production of the said product is utilised for producing
ferrous or ferric sulphate or / and other multi-neutrient products such as 1st Product (limegyp),
3rd Product (finegyp) and 2nd Product (dologyp) which can be effectively used as soil
fertilizer or as soil conditioner.
[00051]. LD slag contains highest level of calcium as calcium silicate, free lime and
calcite along with impurities like Iron, Titanium, Magnesium, Aluminium etc., The calcium
sulphate product can include calcium sulphate dihydrate (CaSO4.2H2O), anhydrite forms, co-
products, and intermediates. The method disclosed can produce pure Calcium Sulphate
product in anhydrite form along with other products such as either ferrous sulphate or 1st
Product (limegyp) or 2nd Product (dologyp) or 3rd Product (finegyp) (trademark products)
materials. The sulphuric acid solution reacts with calcium silicate, calcite and calcium
hydroxide forming calcium sulphate. This can be used in cement manufacturing process and
as a raw material in Gypsum board industry and in Agriculture as a sulphate fertilizer.
[00052]. The present disclosure uses LD slag having a composition of 60.06 – 37.35%
CaO, 26.51 – 10.97% SiO2, 6.16 – 0.12%MgO, 28.67 – 10.10% Fe, 5.65 – 2.06% P2O5, 3.76
– 0.52% Al2O3, 4.41 – 0.18% MnO, in a preferred range of 0-6 mm, which contains the highest
level of calcium mainly as Calcium Silicate, Calcium carbonate and Calcium hydroxide on a
weight basis.
[00053]. The principal components of LD Slag are calcium silicate, calcium carbonate,
calcium hydroxide and free lime put together which accounts between 35% and 60% by
weight. Other compounds can vary in similar fashion due to the composition of feed materials
to the LD converter, operating temperatures and the time of Slag generation during the steel

making process. An averaged X-ray fluorescence (XRF) analysis for last one year samples of
LD Slag taken randomly heat wise from the applicant is provided in Table – 1.

[00054]. The chemical analysis of the LD Slag of -60mesh taken for the study is given
in the Table – 2.



[00055]. Fig 1 illustrates a simple flow diagram of the process of producing different
value added products as claimed hereinafter.
[00056]. The oversized LD slag i.e., + 2.0 mm LD slag is grinded or crushed and
subjected to sieve to produce LD slag of size – 2.0 mm.
[00057]. In this embodiment, LD Slag of -2.0mm is mixed with water and sulphuric
acid in a reactor at a temperature of about 100 – 110ºC for about 2 Hrs to form a Slurry (04)
whose composition is given in Table – 3.



[00058]. A method of treatment of LD slag to produce various value-added composites,
comprising the steps of:
i) taking non-metallic LD slag fines in a reactor;
ii) mixing with sulfuric acid solution with a concentration 98% and water in a ratio
1:2:10;
iii) maintaining a pH of 2-4 to break the calcium silicate into calcium sulphate and
silica and forming a product slurry;
iv) filtration of the filtrate from the product slurry to make a solid cake and neutralizing
the filtrate with different neutralizing agents;
v) heating of solid cake to produce various forms of calcium sulphate in dihydrate,
hemihydrate or anhydrate form.
[00059]. In this method, LD slag, sulphuric acid and water are mixed in a ratio of 1:2:10
respectively. The chemicals used for neutralisation of filtrate includes lime stone , dolomite
and lime fines etc. to have different composites such as 1st Product, 2nd Product and 3rd Product.
[00060]. The powdered lime stone is added till the pH reaches 5-6 and further lime fines
is added to attain the pH 7-8 to form a 1st product.
[00061]. The powdered dolomite is added till the pH reaches 5-6 and further lime fines
is added to attain the pH 7-8 to form a 2nd product.
[00062]. The lime fines are added till the pH attains 7-8 to form a 3rd product.
[00063]. The chemical composition of 1st Product (limegyp), 2nd Product (dologyp) and 3rd
Product (finegyp) are provided in table 4, 5 and 6 respectively.

[00064]. Table 7 provides the typical composition of ferric sulphate composition of
ferric sulphate produced from the leachate.


[00065]. The chemical composition of calcium sulphate anhydrate is provided in Table

[00066]. The residue is filtered by using centrifuge (18) and the solid ferric sulphate
crystals (19) is formed and taken out for bagging whose typical composition is given in the
Table – 7. The liquid from centrifuge (18) which is acidic in nature can be reused in the
digestion process in the reactor (08).
[00067]. The chemical composition of filtrate has given in table 9.



[00068]. The second filtrate-2 is neutral in nature, which can be reused in the reactor
(8), whose properties and composition is provided in Table 10.

[00069]. The calcium sulphate ejected from the belt filter press (11), it is typically
conveyed to a dryer, which is preferably a rotary drum type dryer for removal of excess
moisture and then is granulated using a granulator machine (with no binder required) to form
granules.
[00070]. . The rotary drum dryer step drives off residual moisture from the wet filter
calcium sulphate cake (15), or moist pellet, to a desirable level for pneumatic conveying and
storage. The dryer (14) can be by-passed to allow blending of the filter calcium sulphate cake
(13) with previously dried calcium sulphate cake product (15). The dried calcium sulphate
product (15) is then combined with a binding agent for extraction and forming pellets or other

suitable form. The dried calcium sulphate product (15) can also be sent to off-site for disposal
in a land-fill as a non-toxic byproduct if it is not utilized for other purposes.
[00071]. The amount of sulfuric acid required to reduce the pH on the average 10gms
of LD Slag solution with a PH of 11.0+/-0.5 to 2.0+/-0.5 is 20 ml+/-0.14 along with 100ml of
water for a 2Hr digestion at 100 – 110ºC. The results of Table - 8 are based upon ten digestions
of -2.0mm LD Slag using sulphuric acid and water at 100 – 110ºC. to collect the calcium
sulphate residue the through a 2.5 µm filter paper using a 150 mm diameter Buchner funnel
operating under 20cm Hg vacuum. The operating parameters are summarized in Table – 11.

[00072]. The method as claimed hereinafter though described as a batch process, but
process modification can be possible to make the present method as a continuous operation
without departing from the scope of the present invention. The process modifications required
for continuous operation will be known to those skilled in the art.
[00073]. For example, it is envisioned that the process can be carried out in batch
operations or on a continuous operation basis with only the reactors working in a batch mode.

Other variations, such as different types of process equipment, can be utilized and are to be
considered within the scope of the present invention
[00074]. The range of calcium oxide and its associated oxide, silicate and hydroxide
concentrations in the LD Slag (02), the amount of dry weight sulfuric acid required within the
sulfuric acid solution (06) to achieve the conversion to Calcium Sulphate product varies
according to stoichiometry. The reactions of Sulphuric acid (06) with the calcium compounds
present in LD Slag (02) yield the following
CaSiO4 + H2SO4 = CaSO4 + SiO2 + H2O + O
Ca(OH)2 + H2SO4 = CaSO4 +2 H2O
CaCO3 + H2SO4 + H2O = CaSO4.2H2O + CO2
[00075]. Since the composition and amount of calcium within LD Slag varies because
of presence of various types of oxide along with calcium, a more accurate manifestation of the
reaction, based upon experimentation, is as follows


[00076]. In accordance with an embodiment of the present disclosure, the precipitation
reaction between the hydrogen iron and calcium oxide molecule results in liberation of various
vapours.
[00077]. The primary reaction between the hydrogen ion from the sulfuric acid and the
metal oxides in an aqueous environment produces Oxygen gas and the associated metal ion
complex. The metal ion complex then forms an ionic bond with the resulting sulphate ion from
the dissociation of the sulfuric acid in solution. The result is an often hydrated metal ion
sulphate. When the metal oxide is calcium, the result is Calcium Sulphate, calcium sulphate
di-hydrate, as the lower energy more stable monoclinic crystal structure of the hydrate is
formed. Other metal oxides, hydroxides and carbonates react with the sulfuric acid solution
but are considered side reactions for the purpose of this invention and forms soluble sulphates
with the exception of calcium oxide and calcium hydroxide. These soluble sulphates are
filtered and washed (11) residue is dried (14) and the product anhydrite calcium sulphate (15)
is formed which contains calcium sulphate along with silica
[00078]. Besides carbon dioxide, the various vapours (08b) that are emitted during the
reaction can also include water vapor, sulfuric acid mist, and inherent volatile organic
compounds from the slurry (08). The sulfuric acid mist contained within the vapor stream (08c)
contains traces of organic vapours, which can be neutralized by sending the vapor stream (08c)
to a caustic/lime scrubber/mist eliminator system (08d).
[00079]. In accordance with another embodiment of the present invention there is
provided different functional roles and structural properties of the calcium sulfate.
[00080]. Calcium sulphate has three functional roles when blended with clinker for
(Portland) cement production. The first function is its role as a retardant in preventing flash
set. The second function is as an accelerator by increasing the rate of strength development in
the cement mixture. The third function is as a modifier of the volume change characteristics of
cement. Calcium sulphate can exist in any of the following four forms: gypsum, hemihydrate,
water soluble anhydrite and water insoluble natural anhydrite. When gypsum is exposed to
temperatures over 262° F. over short periods of time or even lower temperatures over longer
periods of time, the chemical water of hydration is liberated to form a hemihydrate. If the
hemihydrate form of calcium sulphate is heated to temperatures about 325° F., chemical waters
of hydration will be liberated and soluble anhydrite form of calcium sulphate results. Over a
prolonged period of time and at high temperatures, insolubles of natural anhydrite can be

formed. It is believed that LD Slag derived calcium sulphate product (15) contains calcium
sulphate anhydrite.
[00081]. The presence of significant amounts of calcium sulphate anhydrite, as a
replacement to mined gypsum, does not significantly affect setting time nor the expansion and
contractions of the concrete made from these corresponding cement blends. The blends of
mined gypsum and anhydrite exhibit near identical properties to that of mined gypsum under
the same SO3 content. Based upon the results from Table - 2, the average gypsum purity of the
LD Slag -derived calcium sulphate product is 86 %+/-5 from the process (I). Furthermore, any
of the forms of calcium sulphate, gypsum, hemihydrate, soluble anhydrite and natural
anhydrite can be used to control the rates of setting and hardening of cement pastes. Problems
associated with the rehydration of soluble anhydrite and hemihydrate in the cement paste can
be overcome with continuously working the batch to prevent the possibility of false set, which
can occur locally with using high levels of hemihydrate or soluble anhydrite.
[00082]. The purity of the Anhydrite calcium sulphate derived from the process of
reacting LD Slag using sulphuric acid solution varies directly with the corresponding
abundance of silica in the LD Slag sample as silica remains insoluble along with calcium of
LD Slag and decreases the purity of Anhydrite calcium sulphate formed. Table – 8 illustrates
the ICP spectrometry of Calcium Sulphate product produced in accordance with the present
invention, in which the Calcium Sulphate product was produced using the same sample used
in Table 2. LD Slag samples with high weight percent calcium values tend to produce the
highest purity of Calcium Sulphate product. The presence of excess water above that required
for stoichiometric conversion favours the formation of the hydrate over that of the anhydrite
form of calcium sulphate.
[00083]. In accordance with an embodiment of the present invention, three novel
composites or products are formed such as 1st Product, 2nd Product and 3rd Product from the
LD slag fines.
[00084]. The 1st Product (limegyp) produced is a mixture of calcium silicate, calcite,
calcium hydroxide and other compounds, or more particularly combination of various form of
calcium sulphates, i.e., calcium sulphate dehydrate (CaSO4.2H2O), calcium sulphate
hemihydrate (CaSO4.1/H2O) and calcium sulphate anhydrate (CaSO4).
[00085]. The 1st Product (limegyp) composition can be used as as a sulphate fertilizer,
soil conditioner, source of carbon to the soil and as well as a source of silicon to the plants thus

also acting as silicon fertilizer. The 1st Product (limegyp) purity can be varied to chosen
composition by means of process adjustments.
[00086]. The 1st Product (limegyp) composition comprised of :
50 – 60% as CaSO4.2H2O,
30 – 40% as Calcite,
1 – 5% as MgO,
1 – 5% as Silica,
2 – 3% as FeO,
0.5 – 2.0% as Al2O3,
0.05 – 0.10% as TiO2,
1.0% Max as P2O5 and
traces of manganese, titanium and chromium.
[00087]. In the 1st Product (limegyp) composition , iron is present as FeO varies in the
range of 2 – 3%, SiO2 in the range of 1 – 5%, Magnesium as MgO in the range of 1.0 – 5.0%,
Phosphorus as P2O5 in the range of Max 0.25% (0.25 – 1%), Aluminum as Al2O3 in the range
of 0.05 – 0.10% .
[00088]. The trace elements are manganese, titanium and chromium. Manganese is
present as MnO in the range of 0.03 - 0.30 %, Titanium as TiO2 in the range of 0.05 – 0.1%
and Chromium (Cr) in the range of maximum 150 ppm (50 – 150 ppm).
[00089]. 1st product having a surface area of 33.198m2/gm, True density:2.6154 g/cm3, and
Bulk density:0.7111 g/cm3.
[00090]. Apart from that, the 1st Product (limegyp) composition also incorporates
sodium as Na2O and potassium as K2O in less than 0.10% for each.
[00091]. In addition to the constituents already mentioned, the 1st Product (limegyp)
composition may further comprise other constituents such as boron, copper, nickel etc., in
traces which are also serves as a important micro nutrients to the plants.
[00092]. The total chemical composition has been given in table 12



[00093]. The pH value of the 1st Product (limegyp) composition is neutral and varies
between 6.5-7.5. Though pH is neutral, it can be adjusted on acidic as well as basic sides to
match the different soil requirements and thus it can be used for all kinds of soils like acidic,
alkaline and salt affected soils for agriculture application.
[00094]. The 1st Product (limegyp) composition has been tested for presence of
different hazardous metals and substances like lead, arsenic, mercury, cadmium etc. The
results are satisfactory and meets the TCLP norms of phospho gypsum in its original
composition itself as given in the Table – 13.
[00095]. Table 13: Trace and heavy metal content in 1st Product (limegyp) and its
comparison with TCLP norms for phospho gypsum


[00096]. Further, the 1st Product (limegyp) composition has also gone through checking
as per EU 2016 norms for soil conditioners and growing media respectively is provided in the
Table – 14.
[00097]. Table – 14: 1st Product (limegyp) typical composition for trace and heavy
metals compared with IS & EU norms.

[00098]. From table 14, it can be concluded that the 1st Product (limegyp) composition
meets the norms of IS (Awasthi) 2000 & EU 2002 as stated in the Table – 14 for use in
agriculture as soil amendment.
[00099]. 2nd Product (dologyp) is another important composite produced from the LD
slag fines. The 2nd Product (dologyp) produced is a mixture of calcium sulphate, magnesium
sulphate, Dolomite and calcite in varying proportion alongwith other ingredients.
[000100]. The 2nd Product (dologyp) composite can be used as a soil sulphate fertilizer
soil condition for the salt affected soils as the calcium replaced the sodium and makes the land
alkali free when applied.
[000101]. The detailed 2nd Product (dologyp) composite is given in Table 15


[000102]. The alkali content i.e., sodium and potassium as Na% & K% in 2nd Product
(dologyp) component is less than 0.10% for each.
[000103]. The pH value of 2nd Product (dologyp) composite is neutral i.e., 6.5 to 7.5 and
hence it can be used for all kinds of soils for agriculture application.
[000104]. The 2nd Product (dologyp) composition has been tested for presence of
different hazardous metals and substances like lead, arsenic, mercury, cadmium etc. The
results are satisfactory and meets the TCLP norms of phospho gypsum in its original
composition itself as given in the Table – 16.
[000105]. The 2nd product having a surface area of 13.914m2/gm, True density: 2.5958
g/cm3, and Bulk density: 0.9186 g/cm3.
[000106]. Table – 16: Trace and heavy metal content in 2nd Product (dologyp) and its
comparison with TCLP norms for phospho gypsum


[000107]. Further, the 2nd Product (dologyp) composition has also gone through
checking as per EU 2016 norms for soil conditioners and growing media respectively is
provided in the Table – 17.
[000108]. Table – 17: 2nd Product (dologyp) typical composition for trace and heavy
metals compared with IS & EU norms


[000109]. From table 17, it can be concluded that the 1st Product (limegyp) composition
meets the norms of IS (Awasthi) 2000 & EU 2002 as stated in the Table – 17 for use in
agriculture as soil amendment.
[000110]. The 3rd product having a surface area of 10.591 m2/gm, True density: 2.7435
g/cm3, Bulk density: 0.8965 g/cm3.
[000111]. The non-limiting advantages of the present invention is as follows:
1. LD Slag of -6mm is regulated as a non-hazardous waste byproduct from the steel
industry. This invention or process allows for the transformation of LD Slag from a highly
alkaline disposal problem. The result of this process to the Portland cement industry will be a
significant reduction in the use of commercially mined gypsum incorporated in Portland
cement manufacturing.
2. Sulfuric acid is regulated as a hazardous waste by-product. This invention or
process allows for the transformation of sulfuric acid from a highly hazardous disposal problem
to a recoverable addition to the cement process used primarily to make gypsum ranging in
purity from 30% to 90%. The result of this process to the Portland cement industry will be a
reduction in the amount of spent sulfuric acid discarded for disposal.

3. The advantages of this invention apply to both the producers of LD Slag and the
producers of by-product sulfuric acid solution.
4. To the cement manufacturers, the LD Slag derived Calcium Sulphate product from
process (I) will offset costs associated with purchasing commercially mined or by-product
gypsum as a functional retarding and strengthening agent in Portland cement manufacturing.
5. In the agriculture industry, the LD Slag derived Calcium Sulphate product from
process (I) will offset costs associated with purchasing commercial fertilisers. The calcium
sulphate produced by the Process (I) contains macro nutrients like Calcium, Sulphur and can
be used as sulphate fertilizer.
[000112]. Each of the appended claims defines a separate invention, which for
infringement purposes is recognized as including equivalents to the various elements or
limitations specified in the claims. Depending on the context, all references below to the
“invention” may in some cases refer to certain specific embodiments only. In other cases, it
will be recognized that references to the “invention” will refer to subject matter recited in one
or more, but not necessarily all, of the claims.

[000113]. Groupings of alternative elements or embodiments of the invention disclosed
herein are not to be construed as limitations. Each group member can be referred to and claimed
individually or in any combination with other members of the group or other elements found
herein. One or more members of a group can be included in, or deleted from, a group for
reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the
specification is herein deemed to contain the group as modified thus fulfilling the written
description of all groups used in the appended claims.
Equivalents:
[000114]. With respect to the use of substantially any plural and/or singular terms herein,
those having skill in the art can translate from the plural to the singular and/or from the singular
to the plural as is appropriate to the context and/or application. The various singular/plural
permutations may be expressly set forth herein for sake of clarity.
[000115]. It will be understood by those within the art that, in general, terms used herein,
and especially in the appended claims (e.g., bodies of the appended claims) are generally
intended as “open” terms (e.g., the term “including” should be interpreted as “including but
not limited to”, the term “having” should be interpreted as “having at least”, the term
“includes” should be interpreted as “includes but is not limited to”, etc.). It will be further
understood by those within the art that if a specific number of an introduced claim recitation
is intended, such an intent will be explicitly recited in the claim, and in the absence of such
recitation no such intent is present. For example, as an aid to understanding, the following
appended claims may contain usage of the introductory phrases “at least one” and “one or
more” to introduce claim recitations. However, the use of such phrases should not be construed
to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits
any particular claim containing such introduced claim recitation to inventions containing only
one such recitation, even when the same claim includes the introductory phrases “one or more”
or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should
typically be interpreted to mean “at least one” or “one or more”); the same holds true for the
use of definite articles used to introduce claim recitations. In addition, eve it a specific number
of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that
such recitation should typically be interpreted to mean at least the recited number (e.g., the
bare recitation of “two recitations”, without other modifiers, typically means at least two
recitations, or two or more recitations).

[000116]. The above description does not provide specific details of the method of the
various parameters. Those of skill in the art are familiar with such details, and unless departures
from those techniques are set out, techniques, known, related art or later developed designs
and materials should be employed. Those in the art are capable of choosing suitable
manufacturing and design details.
[000117]. The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of the present disclosure. It will be
appreciated that several of the above-disclosed and other features and functions, or alternatives
thereof, may be combined into other methods or applications. Various presently unforeseen or
unanticipated alternatives, modifications, variations, or improvements therein may
subsequently be made by those skilled in the art without departing from the scope of the present
disclosure as encompassed by the following claims.
[000118]. The claims, as originally presented and as they may be amended, encompass
variations, alternatives, modifications, improvements, equivalents, and substantial equivalents
of the embodiments and teachings disclosed herein, including those that are presently
unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and
others.
[000119]. While various aspects and embodiments have been disclosed herein, other
aspects and embodiments will be apparent to those skilled in the art. The various aspects and
embodiments disclosed herein are for purposes of illustration and are not intended to be
limiting, with the true scope and spirit being indicated by the following claims.

WE CLAIM:
1. A method of treatment of LD slag to produce various value-added composites,
comprising the steps of:
i) taking non-metallic LD slag fines in a reactor;
ii) mixing with sulfuric acid solution with a concentration 98% and water in a
ratio 1:2:10;
iii) maintaining a pH of 2-4 to break the calcium silicate into calcium sulphate
and silica and forming a product slurry;
iv) filtration of the filtrate from the product slurry to make a solid cake and
neutralizing the filtrate with different neutralizing agents.
2. The method as claimed in claim 1, wherein reaction of the non-metallic LD slag fines,
water and sulphuric acid is maintained in the reactor at temperature 100 - 110ºC for a duration
of 1.5 to 2 hours.
3. The method as claimed in claim 1, wherein nonmetallic LD slag is of size -2.0mm.
4. The method as claimed in claim 1, wherein the nonmetallic LD slag comprises 60.06
– 37.35 CaO, 26.51 – 10.97 SiO2, 6.16 – 0.12 MgO, 28.67 – 10.10 Fe, 5.65 – 2.06 P2O5, 3.76
– 0.52 Al2O3, 4.41 – 0.18 MnO (all in wt%).
5. The method as claimed in claim 1, wherein the solid cake is heated at temperature
50ºC -150ºC to produce various forms of calcium sulphate in dihydrate, hemihydrate or
anhydrate form.
6. The method as claimed in claim 1, wherein filtering of the product slurry is by filter
press or drum filter.
7. The method as claimed in claim 1, wherein neutralizing agent is a powdered lime
stone.
8. The method as claimed in claim 1, wherein neutralizing agent is dolomite.
9. The method as claimed in claim 1, wherein neutralizing agent is lime fines.
10. The method as claimed in claims 1, wherein the powdered lime stone is added till the
pH reaches 5-6 and further lime fines is added to attain the pH 7-8 forming a 1st product.

11. The method as claimed in claim 1, wherein the size of the powdered lime stone and
lime fines are 100 microns – 1mm.
12. The 1st product as claimed in claim 10, comprises Gypsum: 50 – 60%, Calcite: 30 –
40%, MgO: 1 – 5%, SiO2: 1 – 5%, FeO: 2 – 3%, Al2O3: 0.5 – 2.0%, TiO2: 0.05 – 0.10%,
P2O5: 1.0 Max%, MnO: 0.03 – 0.30%, Cr2O3: 150 ppm Max%, Na2O: 0.10 Max%, K2O: 0.10
Max%.
13. The 1st product as claimed in claim 10, comprises CaSO4.2H2O: 55.84, Calcite: 37.00,
FeO: 2.46, SiO2: 1.44, P2O5: 0.42, Al2O3: 0.64, TiO2: 0.089, Others: 1.11.
14. The 1st product as claimed in claim 10, having a surface area of 33.198m2/gm, True
density:2.6154 g/cm3, and Bulk density:0.7111 g/cm3.
15. The method as claimed in claims 1, wherein the powdered dolomite is added till the
pH reaches 5-6 and further lime fines is added to attain the pH 7-8 forming a 2nd product.
16. The method as claimed in claim 1, wherein the size of the powdered dolomite and the
lime fines is 100 microns – 1mm.
17. The 2nd product as claimed in claim 15, comprises Gypsum+ Epsom: 45 – 55,
Dolomite: 40 – 50, P2O5: 1.0 Max, SiO2: 4 – 7, FeO: 2 – 3, Al2O3: 1 – 2, TiO2: 0.05 – 0.10,
MnO: 0.03 – 0.30, Cr: 150ppm Max, Na2O: 0.10, K2O: 0.10.
18. The 2nd product as claimed in claim 15, comprises CaSO4.2H2O, +MgSO4.H2O,
(Gypsum + Epsum): 47.40%, Dolomite: 42.50%, FeO: 2.20%, SiO2: 5.60%, P2O5: 0.53%,
Al2O3: 1.10%, TiO2: 0.067%, Others: Traces.
19. The 2nd product as claimed in claim 15, having a surface area of 13.914m2/gm, True
density: 2.5958 g/cm3, and Bulk density: 0.9186 g/cm3.
20. The method as claimed in claim 1, wherein the lime fines are added till the pH attains
7-8 forming a 3rd product.
21. The method as claimed in claim 1, wherein the size of the lime fines is 100 microns
to 1mm.
22. The 3rd product as claimed in claim 20, comprises CaSO4.2H2O: 89.50, Calcite: 4.17,
FeO: 2.46, SiO2: 0.28, P2O5: 0.48, Al2O3: 0.52, TiO2: 0.12, MgO: 1.37.

23. The 3rd product as claimed in claim 20, having a surface area of 10.591 m2/gm, True
density: 2.7435 g/cm3, Bulk density: 0.8965 g/cm3.