FIELD OF THE INVENTION
The present invention generally relates to an apparatus for producing yellow
gypsum lumps by reaction of non metallic portion of LD Slag fines of
particular size with sulfuric acid at a particular range of temperature followed by neutralisation using an agent of suitable substance, drying and filtration. More particularly, the invention relates to an apparatus for producing yellow gypsum cake from non metallic LD Slag fines
BACKGROUND OF THE INVENTION
Natural gypsum, by-product gypsum from the manufacture of phosphoric acid fertilizer, or synthetic gypsum prepared from waste sulphuric acid and limestone, have remained heretofore the main sources of the gypsum, and all of these been used in a powdery state. For example, explanation will be made of gypsum from the manufacture of phosphoric acid fertilizer. However no efforts have been made till now to manufacture yellow gypsum / calcium sulphate 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.
With the increased costs for disposing of wastes and with the decrease of available dump-yard for the wastes, converting of the wastes which otherwise need to be discarded, into valuable products by utilising another waste liquid is more economic. 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 stuck-up with such 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 restrictions associated with the disposal of it.
Various methods have been used in prior art, 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. Waste Recycling Plant (WRP) fines of an integrated steel plant 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 WRP fines, in land filling and for acidic soil conditioning which decrease the amount of WRP fines that has to be discarded.
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.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process and apparatus for producing yellow gypsum of varying purity from LD Slag fines of -2.0mm by reacting with varying quantity of excess sulphuric acid and neutralising with lime fines slurry.
Another object of the present invention is to utilise the another waste viz. lime fines generated at lime calcination plant of an integrated steel plant.

SUMMARY OF THE INVENTION
Rephrase it in the form of Product claim According to the present invention, yellow gypsum of varying purity can be produced in a cake state in a batch process by reacting LD Slag fines and sulphuric acid in a reactor, while rotating or giving turning movement or stirring movement to reactants resulting in the formation of gypsum slurry wherein calcium is converted into calcium sulphate which is insoluble along with silica present in the LD Slag fines which also remains insoluble and all other metal oxides forms soluble sulphates which will be precipitated by raising the PH of the slurry to neutral by adding the lime slurry with continuous stirring.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Now, the present invention will be explained in detail by way of the accompanying drawings:
Figure – 1 shows a schematic diagram of an apparatus for the production of yellow gypsum.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure 1, the apparatus according to the invention consists of a reactor vessel [A] made up of stainless steel and line inside with a rubber lining consists of a stirrer made up of stainless steel. It has four outlets, three at the top of the reactor[A] for feeding LD Slag fines, water and an outlet for

fumes generated during the reaction. Storage tank [B] for storing H2SO4 (98%) is also made up of stainless steel lined inside with a rubber liner of thickness 5mm and is called as Sulphuric acid tank[B]. Another tank [C] made up of stainless steel is fitted with a stirrer for keeping the lime slurry mixed condition which is called as lime tank[C]. Both tanks [B] and [C] are connected to main reactor vessel[A] through a flow meter for adding the required quantity of sulphuric acid and lime slurry.
Reactor vessel is having the capacity of 2000 litres and its inner rubber lining is having the capacity of withstanding the temperature up to 250 – 300 deg. Cent.
The main reactor vessel [A] is also fitted with a oil jacket / steam jacket for maintaining the temperature of the reactants. The stirrer is fitted with a motor having a rpm of 1450 for mixing the reactants. The bottom opening of reactor vessel [A] is having a valve which discharges the product slurry into a filtration unit which is connected to a vacuum pump. Filtration unit
The required quantity of sulphuric acid (98%) is added to the reactor vessel [A] sulphuric acid tank[B] followed by -2.0mm LD Slag fines through a opening provided on the top of the reactor[A]. After adding the LD Slag fines, much heat is released by the reaction between LD Slag fines and sulphuric acid and temperature of the reaction mixture partially exceeds 100°C. Sulphuric mists are evolved from the reactor[A] by the vigorous reaction, which starts just after the mixing of reactants. The mist are separated in a separator and only the gas is allowed to pass through. A pressure increase in the system can be avoided by providing this system which removes the sulphuric acid mist. The reaction continues for an hour with continuous stirring and temperature of the mixture is also maintained just below 100°C.

After an hour lime slurry (20 kg lime fines in 100 litre water) is added through lime tank[C] and PH of the slurry is adjusted to 7.0 through continuous slow addition followed by continuous stirring
Once the PH of the slurry is brought to 7, the resulting product slurry is stirred for a while and transferred to filtration unit through bottom discharge valve. The filtrate is taken out from the bottom of the filtration unit and yellow gypsum cake is taken out from the top of the filtration unit.
The yellow gypsum cake produced is having the free moisture of around 40-50 % which will be taken to a drying unit, where the cake is spread and dried at a temperature below 60 °C.
The dried lumps of yellow gypsum were crushed using suitable means and sieved to required size and packed for use at customer end
The flow of sulphuric acid from tank [B] and lime slurry flow from tank[C] are through gravitational force only as they were placed at an elevated place as compared to the main reactor [A].The filtration system is also located below the main reactor, the flow of slurry to filtration system is also through gravity thus helps in reducing the energy consumption.
The different types of yellow gypsum produced by using -2.0mm LD Slag fines and varying the quantity of sulphuric acid and thereby the lime slurry are provided in the table – 1 & 2.


Further the particle sizes of LD Slag fines of -2.0mm as a raw material exerts substantially no influence upon the properties of yellow gypsum formed although the particle size exerts a substantial influence upon the reaction time. Reaction is retarded with an increase in particle size, and thus the LD Slag fines inevitably remains in an unreacted state for a longer period of time.

Consequently, the reactants and products in the reactor will be harder to handle since the intermediate reaction stage in which the materials are in a sticky state will last for a longer time. The particle sizes, which are easiest to handle, are about 100 to 200 mesh pass.

WE CLAIM :
1. An apparatus for producing yellow gypsum cake from non-metallic LD
slag fines, the apparatus comprising:
a cylindrical reactor body with a rubber lining inside having a plurality of inlets on an upper portion of the body for supplying LD Slag fines, Water, sulphuric acid and lime slurry; and an outlet at a lower portion of the cylindrical reactor body for discharge of a neutralized slurry to a filtration unit for producing yellow gypsum cake;
the filtration unit with a rubber lining having a full opening at the top with a perforated sheet for filtering the neutralized slurry received, the opening below the perforated sheet is connected to a vacuum pump for sucking the neutralized slurry forcibly to enhance the separation of the yellow gypsum cake and water, and a bottom portion of the filtration unit is having a discharge valve for removing the water collected during the filtration
2. The apparatus as claimed in claim 1, wherein cylindrical reactor body comprises a stirrer for desired mixing of the input materials.
3. The apparatus as claimed in claim 2, wherein the stirrer is made up of stainless steel.

4. The apparatus as claimed in claim 1, wherein the cylindrical reactor body comprises an opening for removal of fumes generated during the reaction.
5. The apparatus as claimed in any of the preceding claims, wherein the purity of produced yellow gypsum with various combinations of LD Slag, sulphuric acid and lime fines is between 78% to 90%.
6. The apparatus as claimed in claim 1, comprising an externally disposed heating jacket, wherein the heating can be done by using steam or by circulating hot oil.
7. The apparatus as claimed in claim 6, wherein the heating jacket can achieve and withstand the temperature of 250 - 300°C which can transfer the heat to the reactants of the cylindrical reactor body and achieve a temperature of more than 100°C.