Process for decreasing the heavy metal contents in

LD slag based Yellow Gypsum

ABSTRACT
A method for producing Yellow Calcium Sulphate (Yellow Gypsum) from LD Slag fines,
with 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, after the
recovery of metallic Iron from LD Slag, along with a further decrease in the content of heavy
metals, especially chromium using an organic masking agent. The invention advantageously
reduces heavy metal contents in the Yellow Calcium Sulphate which finds use in mainly
agriculture, cement making process, ceramic and other industries.

BACKGROUND OF THE INVENTION

[0001] Field of the Invention:

This application generally relates to utilisation of LD Slag produced in steel industry
processes. The invention relates to series of methods of producing Yellow Calcium Sulphate
from LD Slag waste produced during the recovery of metallic Iron from LD Slag. The
invention also relates to alternative methods for utilisation of sulphuric acid and lime fines
produced during the production of lime from limestone. Moreover the concentration of heavy
metals, especially chromium, has been further reduced to increase product quality for various
applications.

[0002] Description of the Prior Art:

With the increased costs for dumping the wastes to valuable products is gradually becoming
more important. Non-hazardous as well as hazardous wastes have their own set of problems.
Issues such as toxicity, pollutants to the environment, and the sizeable amount of wastes
generated cause problems with these types of wastes that need to be addressed. For example,
sulphuric acid waste is toxic and is regulated as a hazardous waste. The primary way to
dispose of sulphuric acid is to have it incinerated. Incinerating waste, or spent, sulfuric acid is
expensive and there are many regulatory requirements associated with its disposal.
[0003] 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 of and
decreases raw material costs for the reusable compound. LD slag 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 oxide from the LD Slag, in land filling
and for acidic soil conditioning which decrease the amount of LD Slag fines that has to be
discarded.

[0004] As compared to blast furnace slag which has 100% utilization as a road construction
aggregate and in cement production, LD slag has little utilization due to its highly basic
nature. LD slag cannot be used as a proper road construction aggregate because of the
presence of high quantity of iron which tends to agglomerate in presence of moisture.

[0005] One such example of making a reusable compound from waste materials can be
found in use of Red Gypsum produced as waste in Titanium dioxide industry in land
application (The Science of Total Environment, Elsevier PII S0048-9697(96)05179-0)

[0006] High levels of heavy metals pose threat to humans, plants and animals alike causing
diseases like stunted growth and tapered roots in plants and cancer on humans. Suitable
methods need to be adopted to keep a check on the heavy metal content in products resulting
from LD slag so as not to cause a stir in the environment.

[0007] A need exists for a process that will reduce the amount of LD Slag waste that needs
to be disposed of and produce a product that is reusable. It is an object and a goal to convert a
waste product to a desirable product, to reduce manufacturing costs in industries where the
invented product may be used as raw material source. Another object and goal is to decrease
the amount of LD slag waste that needs to be disposed of and recovering a useful product.
Another objective is to provide a use for lime fines generated in lime making process and also
to provide a use for sulphuric acid which is a hazardous by-product in copper concentrate
smelting industries. Moreover, a reduction in the cost of raw materials while also adding
more quality to the soil conditioner is also an important goal.

[0008] The invention aims at further decreasing the content of heavy metals in the soil
conditioner, especially chromium. The objective is to increase the quality of the product so as
to be made suitable for use in countries where permissible limits on heavy metals in soil is
very low, for example Finland, Canada, Denmark etc. The object and goal is also to decrease
the cost of raw materials required for the process while also adding nutritious value to the
product. Another objective is to reduce the concentration of chromium in the soil conditioner
as it is toxic and carcinogenic, therefore harmful to the soil as well as the plants and
microorganisms that thrive in soil, indirectly causing toxicity to humans as well as animals.

SUMMARY OF THE INVENTION

[0009] In order to meet one or more of the identified objects, the present invention
advantageously includes a method for treating LD Slag waste fines in the size range of below
6mm left after the recovery of metallic iron with sulphuric acid to form slurry containing
insoluble calcium sulphate, excess unreacted sulphuric acid and other soluble metal
sulphates. Ascorbic acid is added to the slurry and the contents of the beaker are allowed
about 1-2 hours’ time for acid digestion. LD Slag waste contains highest level of calcium as
calcium silicate and also as free lime and also as calcite along with metals like Iron,
Titanium, Magnesium, Aluminium etc. The slurry is further neutralised using the lime fines
and filtered and dried to produce the Yellow calcium sulphate. The Yellow calcium sulphate
product can include calcium sulphate dihydrate (CaSO4.2H20), anhydrite forms, co-products
(like Iron Sulphate, Aluminium Sulphate). The method disclosed can produce a Yellow
calcium sulphate product with decreased levels of heavy metals, especially chromium. The
sulphuric acid solution reacts with calcium silicate, calcite and calcium hydroxide forming
the slurry containing the insoluble calcium sulphate and soluble other metal sulphates. This
can be employed in various industries like cement manufacturing, agriculture and ceramic.

[0010] Other embodiments of the present invention are also provided, all of which are
believed to improve the quality of the Yellow Calcium Sulphate. As one of the alternate
embodiments, the invention advantageously includes sweetening the LD Slag waste with
calcium rich by-products or limestone, shale or dolomite ores to enhance the calcium oxide
equivalent available to the sulphuric acid for reaction. Another important embodiment is the
ascorbic acid, or vitamin C, which adds nutritious value to the product and makes it even
more suitable for application in soil.

BRIEF DESCRIPTION OF THE DRAWING

[0011] So that the manner in which the features, advantages and objects of the invention, as
well as others which will become apparent, can be understood in more detail, more particular
description of the invention briefly summarized above can be had by reference to the
embodiment thereof which is illustrated in the appended innovative manufacturing flow
diagram, which form a part of this specification. It is to be noted, however, that the
innovative manufacturing flow diagram illustrate only a preferred embodiment of the
invention and is therefore not to be considered limiting of the invention's scope as it can
admit to other equally effective embodiments.

[0012] Figure - 1 shown below is a simplified flow diagram of a process of producing a

Yellow calcium sulphate product with decreased heavy metal content from LD Slag Waste
fines generated by steel plant according to the present invention.

DETAILED DESCRIPTION

[0013] The present invention advantageously provides a method for producing Yellow
calcium sulphate product from LD Slag waste, such that the product contains considerably
low levels of heavy metals. This invention includes a process of treating LD Slag waste
through a digesting process with sulphuric acid along with the addition of a very small
amount of ascorbic acid, resulting in a slurry, followed by neutralisation with lime fines and
filtering and drying resulting in a yellow calcium sulphate product, for the subsequent use in
all industries like cement manufacturing, agriculture and ceramic industry where this may be

FIGURE 1 : Flow diagram of process A

used. The product is specifically well suited for agricultural use due considerable decrease in
the quantity of heavy metals plus increase in nutritional value because of the ascorbic acid.
[0014] LD Slag fines is a mixture of compounds comprised of some or all of the following
chemical groupings: carbonates, Silicates of calcium, Magnesium, Oxides of Iron,
Aluminium, Phosphorus, hydroxides of calcium and some amount of free lime. LD Slag fines
can contain very low concentrations of heavy metals including, cadmium, chromium, lead,
mercury, nickel, platinum and palladium. They produces a highly alkaline solution (pH 11-
13.5) when mixed with water. This alkalinity is primarily due to the presence of calcium
hydroxide in the LD Slag fines or as the slacking of calcium oxide occurs in the solution. LD
Slag fines are being generated during the recovery of metallic Iron from LD Slag at Waste
recycling plant.

[0015] The LD Slag fines in the size of -6mm contains the highest concentration of calcium
majorly as Calcium Silicate, Calcium carbonate and Calcium hydroxide.

[0016] The principal components of LD Slag fine are calcium silicate, calcium carbonate,
calcium hydroxide and free lime put together which accounts for between 45% and 55% by
weight of LD Slag fine. Other compounds can proportionately vary due to the composition of
feed materials to the LD converter, operating temperatures the time of Slag generation during
the steel making process. An averaged X-ray fluorescence (XRF) analysis of LD Slag fines
taken randomly is provided in Table – 1.

TABLE-1

LD SLAG FINES
Components Weight %

Average Min Max Variance

CaO 51.36 37.35 60.06 7.79

SiO2 15.71 10.97 26.51 2.10
MgO 2.09 0.120 6.16 0.58
Al2O3 0.931 0.520 3.76 0.05
TiO2 1.14 0.600 2.43 0.03
Fe 18.20 10.10 28.67 7.64
S 0.016 0.005 0.177 0.01
MnO 0.446 0.180 4.41 0.03
Cr2O3 0.156 0.04 0.220 0.00
P2O5 3.24 2.06 5.65 0.16
[0017] The chemical analysis of the LD Slag fines of -0.60mesh (-0.25mm) taken for the
invention is given in the Table – 2

Table - 2
LD Slag fines composition, -60mesh

[0018] Yellow Calcium Sulphate product can be produced from LD Slag fines of -60 mesh
(-0.25mm) by several different methods. One preferred embodiment ‘A’ of the method of
producing Yellow Calcium Sulphate product is illustrated in Figure – 1.

[0019] In this embodiment A, LD Slag fines of -60mesh (02) is mixed with water (03a),
sulphuric acid (03c) and ascorbic acid (03b) in a reactor (03) at a temperature of about 100 –
1100C until a slurry of chemical composition(Table – 3) is developed (04).This Slurry (04) is
neutralised (05) using lime fines followed by filtration (06). The residue is dried (07) and
solid-1 (08) with chemical composition as shown in table – 4 is formed. The filtrate (09) can
be reused back in the process at reactor (03).

[0020] the percentage chemical composition of major elements present in solid-1 (08) is
shown in the table – 4.

Table -3 : Chemical composition of major components of slurry

 Table -4 : Chemical composition of yellow gypsum produced from process of
figure – 1.

[0021] The oversize +60mesh LD Slag fine (01c) grinded to -60mesh (01d) is sieved to
produce -60mesh LD Slag fine (02).

[0022] Given the range of calcium oxide and its associated oxide, silicate and hydroxide
concentrations in the LD Slag fine (02), the amount of dry weight sulfuric acid required
within the sulfuric acid solution (03c) to achieve the conversion to Calcium Sulphate product
varies according to stoichiometry. The reactions of Sulphuric acid (03c) with the calcium
compounds present in LD Slag fine (02) yield the following:

CaSiO4 + H2 SO4 →CaSO4 +SiO2 +H2 O + O

Ca(OH)2 + H2 SO4 →CaSO4 +2H2 O

CaCO3 + H2 SO4 →CaSO4 .2H2 O + CO2

The reaction of excess sulphuric acid left after the digestion of LD SLAG fines with lime
fines to neutralise the latter is given below

[0023] Since the composition and amount of calcium within LD Slag fines 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:
[0024] The chromium (III) ions present in the LD slag are masked due to the presence of
Ascorbic acid. The acid binds with the chromium ions to form a supra molecule, chromium
ascorbate according to the following reaction:

Cr+3 C6 H8 O6 →[C6 H7 O6 ]3 Cr
(Chromium ascorbate)

[0025] The purity of the Yellow Calcium Sulphate product derived from the process of
reacting LD Slag fine using sulphuric acid solution varies directly with the corresponding
abundance of silica in the LD Slag fine sample as silica remains insoluble along with calcium
of LD Slag fine and decreases the purity of Calcium sulphate formed. Also it depends on the
quantity of sulphuric acid used for digestion. The yellow colour to the calcium Sulphate
produced from process is due to the presence of Iron sulphate along with Calcium sulphate
and the colour turns to red as the Iron increases and decrease to pale yellow with decrease in
the Iron content in LD Slag fine. Table – 6 illustrates the ICP spectrometry of Yellow
Calcium Sulphate product produced in accordance with the present invention in which the
Yellow Calcium Sulphate product was produced using the same sample used in Table – 2.
LD Slag fine samples with high concentration of calcium tended to produce the highest purity
of Yellow 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 yellow calcium sulphate and also in dissolving the soluble compounds formed during
the reaction.
[0026] Once the LD Slag fine (02) is in the reactor (03), it reacts with the sulphuric acid
solution (03c) as well as the ascorbic acid (03b). The reactor (03) is preferably agitated and
maintained at a temperature between 100 – 110OC to allow for optimum reaction conditions
for a particular time preferably 2 hours till the Calcium silicate breaks in to insoluble Calcium
sulphate and Silica by the reaction with sulphuric acid and other impurities forms the soluble
sulphates. The reaction is complete once the product slurry (04) reaches the preferable pH
range, which is preferably in the range of about 2.0 to about 4.0 pH. Once the reaction halts,
the product slurry (04) is allowed sufficient residence time within the reactor (03) to cool.
The product slurry (04) is discharged from the reactor (03) once it is cooled and taken to
neutralisation tank (05). While the present invention is described as a batch process, process
modifications can be made to perform the present invention 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. The liberation of
various vapours 03d occurs as a result of the precipitation reaction between the hydrogen ion
and calcium oxide molecule. This 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 sulphuric acid in solution. The result is an
often hydrated metal ion sulphate. When the metal oxide is calcium, the result is Calcium
Sulphate, calcium sulfate di-hydrate, as the lower energy more stable monoclinic crystal
structure of the hydrate is formed. Other metal oxides, hydroxides and carbonates react with
and forms soluble sulphates with the exception of calcium oxide and calcium hydroxide.
These soluble sulphates along with excess sulphuric acid are neutralised with lime fines,
filtered(06), residue is dried(07) and solid – 1 (08) formed is Yellow Calcium sulphate along
with silica and other impurities.

[0027] Chromium in LD slag is present in the form of Cr2O3 (mol. wt. = 152g) and has a
52
percentage concentration of around 68.4 % (152 × 100 = 68.4 %). Upon masking,

chromium ion binds with 3 molecules of ascorbic acid which has a molecular weight of 176g.
The supra molecule chromium ascorbate has a net molecular mass of 577g and consequently
the percentage concentration of chromium decreases to 9.01 % since the denominator now
52
increases from 152 to 577 thus decreasing the overall fraction (577 × 100 = 9.01 %).

[0028] Besides carbon dioxide, the various vapours (03d) that are emitted during the
reaction can also include water vapour, sulphuric acid mist, and inherent volatile organic
compounds from the slurry (04). The sulfuric acid mist contained within the vapour stream
(03d) contains traces of organic vapours, which can be neutralized by sending the vapour
stream (03d) to a caustic / lime scrubber/mist eliminator system (03e).

[0029] The product slurry (04) is then conveyed, preferably by pumping, to neutralisation
step (05) for neutralization with lime fines. The LD Slag fines derived Yellow Calcium
Sulphate product slurry is filtered and dried between 50 – 100 deg cent depending upon the
requirement as Yellow calcium sulphate should be in dihydrate or hemihydrate or anhydride
(08) form. The filtrate – 1 (09) from the belt press step(06) is then again can be reused back
in the process in the reactor (03).

[0030] After the Yellow Calcium Sulphate filter cake (08) is ejected from the belt filter
press (06), it is typically conveyed to a dryer (07), which is preferably a rotary drum type
dryer. The rotary drum dryer step drives off residual moisture from the wet filter yellow
calcium sulphate cake (06a), or moist pellet, to a desirable level for pneumatic conveying and
storage. The dryer (07) can be by-passed to allow blending of the wet filter yellow calcium
sulphate cake (06a) with previously dried yellow calcium sulphate cake product (08). The
dried yellow calcium sulphate product (08) is then combined with a binding agent for
extraction and forming pellets or other suitable form. The dried yellow calcium sulphate
product (08) 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.

[0031] In the original process of manufacture of yellow gypsum, the amount of sulphuric
acid required to reduce the pH on the average 21gms of LD Slag fines solution from PH
11.0±0.5 to 2.0±0.5 is 24 ml±0.14 along with 86ml of water for a two Hr digestion at 100 –
110oC. The sample of LD Slag fines and other reagents and parameters used are as shown in
Table 9. The results of Table – 7 are based upon ten digestions of -60mesh LD Slag fines
using sulphuric acid and water at 100 – 110oC and neutralisation with lime fines to collect the
yellow calcium sulphate residue the through a 2.5 µm filter paper using a 150 mm diameter
Buchner funnel operating under 20 cm Hg vacuum.
 Table – 5

Sr No Materials Quantity

1 LD SLAG fines 21gm

2 Sulphuric acid (1.84 SpGr) 34ml

3 Water 86ml

4 Temperature 100 – 110 oC

5 Duration of digestion 2Hrs

6 Filter paper porosity 2.5µm

7 Vacuum 20 cm Hg

8 Lime fines 35gms (Approx) / Up to

neutralization

9 Ratio: LD Slag(gm):H2SO4(ml):H2O(ml) 21:34:86

[0032] Process optimization however suggests a decrease in the quantity of sulphuric acid
taken for digestion of slag along with the use of a very small amount of ascorbic acid to not
only reduce raw material cost but also decrease the concentration of heavy metals (especially
chromium) and increase the quality of the yellow gypsum produced in terms of the nutritional
value added in the form of vitamin C. Table 10 shows the various parameters considered
during optimization.
 Table – 6

Sr Materials Quantity
No

1 LD SLAG fines 21gm

2 Sulphuric acid (1.84 SpGr) 30ml

3 Water 86ml

4 Ascorbic acid 40 mg

5 Temperature 100 – 110 oC

6 Duration of digestion 2Hrs

7 Filter paper porosity 2.5µm

8 Vacuum 20 cm Hg

9 Lime fines 35gms (Approx) / Up

to neutralization

10 Ratio:LD Slag(gm):H2SO4(ml): C6 H8 O6 (mg):H2O(ml) 21:30:40:86

[0033] Table – 5 shows the original method for yellow gypsum preparation having
composition as shown in table – 7. However, when synthesis is done according to parameters
listed in table – 6, the composition of yellow gypsum changed to as shown in table – 4. The
chromium content increased upon decreasing the quantity of sulphuric acid used. However
the addition of only 40 mg ascorbic acid decreased the chromium content by 24% resulting in
0.0488% of Cr2O3.
Table -7 : Chemical composition of yellow gypsum prepared from parameters of
Table – 5.

[0034] One limitation to the treatment of LD Slag fines with sulphuric acid to manufacture
yellow calcium sulphate by process mentioned in Fig – 1 is the quality of the Calcium
Sulphate produced. Due to the nature of LD Slag fines, the constituents of the LD Slag fines
vary both qualitatively and quantitatively and also depends up on the quantity of sulphuric
acid used for treating the LD slag fines. Increase in the quantity of Sulphuric acid needs more
quantity of Lime fines for neutralisation in the process.

[0035] 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 sulfate is heated to temperatures about 325° F., chemical waters
of hydration will be liberated and soluble anhydrite form of calcium sulfate results. Over a
prolonged period of time and at high temperatures, insolubles of natural anhydrite can be
formed. It is believed that LD Slag fines derived yellow calcium sulphate product Solid – 1
contains gypsum, hemihydrate and soluble forms of calcium sulfate anhydrite.

[0036] The presence of significant amounts of calcium sulfate 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 fines
-derived yellow calcium sulphate product is 86 %+/-5. Furthermore, any of the forms of
calcium sulfate, 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

[0037] LD Slag fines 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 fines 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.

[0038] Sulphuric 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.

[0039] The advantages of this invention apply to both the producers of LD Slag fines and
the producers of by-product sulfuric acid solution.

[0040] To the agriculture industry, the LD Slag fines derived Yellow Calcium Sulphate
product from process mentioned in Fig – 1 will offset / reduce costs associated with
purchasing commercially available fertilisers as it is a very good Sulphate fertiliser, substitute
for other fertilisers derived from gas. It contains macro nutrients like Calcium, Iron, Sulphur,
Magnesium and other micro nutrients like Phosphorus etc.,

[0041] While the invention has been shown or described in only some of its forms, it should
be apparent to those skilled in the art that it is not so limited, but is susceptible to various
changes without departing from the scope of the invention.

[0042] 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.
What is claimed is:

1. A method of producing Yellow Calcium Sulphate from LD Slag fines of -6mm after
recovering the metallic iron , the method comprising the step of: reacting LD Slag
fines, water, and a sulfuric acid solution at a range of temperature and for stipulated
time and neutralise the slurry with lime fines to produce a Yellow calcium sulphate
product by process as shown in the Fig – 1
2. The method of claim 1, wherein the sulfuric acid solution comprises Sulphuric acid
(98%, SpGr 1.84)
3. The method of claim 1, wherein the sulfuric acid solution comprises dilute Sulphuric
acid. (14%(v/v))
4. The method of claim 1, further including the step of mixing the LD Slag fines of -
60mesh (-0.25mm) with water prior to addition of sulphuric acid solution
5. The method of claim 1, further including the step of heating mixture of LD Slag fines,
water and Sulphuric acid at temperature of 100 – 110oC
6. The method of claim 1, further including the step of ratio of LD Slag fines(gm),
Sulphuric acid(ml), ascorbic acid (mg) and water(ml) in the ratio of 2.1 : 3 : 4 : 8.6
respectively.
7. The method of claim 1, further including the step of heating up 1.5 – 2.5 Hrs to break
the calcium compounds present in the LD Slag fines to insoluble Calcium sulphate
and converting other metal oxides to soluble sulphates
8. The method of claim 1, further includes the step of adding calcium rich compound to
the Slurry product to bring the PH to 7.0 – 7.1 to neutralize the excess un reacted
sulphuric acid
9. The method of claim 8, where in the calcium rich compound selected lime fines.
10. The method of claim 8, where in the alkaline solution selected is liquor ammonia
(25%) or lime fines solution (20%) prepared by mixing lime fines with water
11. The method of claim 1, further comprising drying the Yellow Calcium Sulphate
product
12. The method of claim 10, where in the step of drying of Yellow Calcium Sulphate
product further comprises removing a filtrate from the wet yellow calcium sulphate
product
13. The method of claim 12, where in the filtrate is reused back in the process.
14. Chromium concentration in yellow gypsum is reduced by almost 24% upon adding 40
mg of ascorbic acid.
15. The cost of raw materials is considerably reduced due to reduction in the volume of
sulphuric acid used.
16. Ascorbic acid is produced naturally in the soil by various micro-organisms. By
providing ascorbic acid to the soil through yellow gypsum, the production by
microorgnisms is sped up.
17. The method of claim 16, plants take up nutrients that are either water soluble or
organic acid soluble. Increasing the concentration of ascorbic acid in the soil,
increases the solubility of nutrients which are then taken up by the roots of the plants.
18. Increased uptake of nutrients results in fast growing as well as healthy crops therefore
increasing the yield.
19. The soil conditioner prepared from method of claim 1 can be used to treat degraded
soil which occurs as a result of acidity, alkalinity, heavy rainfall, improper cultivation
and other reasons.
20. Ascorbic acid is an important dietary element for plants, humans as well as animals.
21. Ascorbic acid being a strong anti-oxidant, reduces oxidative stress in plants which
occurs due to release of reactive oxygen species.
***************