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Recovery of Sulphur from Gypsum by Reaction with Sodium Carbonate: Production of Sodium Sulphate

Samarendra Karmakar*
Bose Centre for Advanced Study and Research, Department of Applied Chemistry, Dhaka University

Nurul Hoque Bhuiyan
Bose Centre for Advanced Study and Research, Department of Applied Chemistry, Dhaka University

Abstract/ Executive Summary:

The reaction between gypsum, a waste product of the TSP Factory in Chittagong and solid sodium carbonate was studied under different conditions. The products were sodium sulphate and calcium carbonate. Under optimum conditions about 94% yields of both sodium sulphate and calcium carbonate were obtained at 600⁰C within half an hour.

Keywords: Calcium carbonate, Gypsum, Plaster of Paris, Sodium sulphate.

Location: Bose Centre for Advanced Study and Research, Department of Applied Chemistry, Dhaka University

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Sulphur

Objectives:

Gypsum, the waste product of the TSP Factory, has been produced industrially and is a problem for its disposal. It is important for an industry to use the waste by-product, which motivated the authors to undertake the study for its better utilization into valuable chemicals which have also demand in other industries. The main objective of this study is to utilize industrially gypsum waste of the TSP Factory by conversion of its sulphur and metal components into useful products economically. Most of the processes mentioned above are lengthy, time-consuming, and less cost-effective. The reaction between gypsum and sodium carbonate was chosen for the production of Na2SO4, which is an important chemical for the paper industry, and CaCO3 which is used in the cement and lime industries; the reaction is less time consuming and cost-effective. The Pilot Plant Study was made with higher amounts of the reactants so that the production can be made industrially.

Methodology:

2.1 Purification of gypsum A weighed amount of gypsum was treated with 100 ml of 0.5 M sulphuric acid solution. It was stirred thoroughly and the supernatant liquid was decanted off. The process was repeated five times. The residue left was washed with distilled water repeatedly until it was free from acid. It was then treated with rectified spirit and finally dried at 110⁰C in an electric oven for 2 hours. The gypsum was then converted to Plaster of Paris by heating the sample at 120-150⁰C for 2 hours (Shreve, 1956). After analysis, Plaster of Paris was found to have a purity of 99.56%. The dehydration reaction is:

CaSO4.2H2O → CaSO4.1/2H2O + 3/2H2O at 120-150⁰C

All the reactions were carried out with this sample of gypsum thus purified.

A weighed amount of Plaster of Paris, CaSO4.1/2H2O, was thoroughly mixed with a definite proportion of anhydrous sodium carbonate and transferred onto a silica boat. The boat was placed in the middle part of a reaction tube which, in turn, was introduced into an electric furnace. The reaction tube was then connected to a nitrogen cylinder on one hand and to a bubbler containing water on the other hand. Nitrogen gas was passed through the system for some time. The temperature of the furnace was raised to the desired point and the reaction was carried out for a certain period. The furnace was then switched off and allowed to cool down to room temperature in a slow stream of nitrogen. The reaction boat was taken out, and the solid reaction products were leached with boiling water, cooled and filtered. Sulphate present in the filtrate was quantitatively estimated (Vogel, 1962) and the amount of sodium sulphate was calculated. No trace of calcium sulphate was found in the filtrate. The amount of carbon dioxide evolved from the residue by the action of hydrochloric acid and the total amount of calcium carbonate were also calculated.

Na2SO4 + BaCl2 = 2 NaCl + BaSO4 (White ppt. of Barium Sulphate)

The solution of the product when treated with hydrochloric acid gave effervescence of CO2 gas which turned lime water milky. The presence of Ca ion was tested by adding Sodium Oxalate, which formed white precipitation of Calcium oxalate, indicating the presence of calcium:

CaCl2 + Na2C2O4 = CaC2O4 (White ppt.) + 2 NaCl

Source of Information: Journal of Engineering Science 09(1), 2018, 71-76

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

From the study of the present work, it is clear that the reaction between Calcium sulphate hemihydrate obtained from gypsum and anhydrous sodium carbonate takes place very rapidly even in presence of air. The reaction is very simple and takes short time to complete and requires no costly apparatus, and the yield is very high. About 94% sodium sulphate can be obtained by heating a mixture of purified gypsum and sodium carbonate in 30 minutes. Thus, gypsum, a waste product of the TSP Factory, can be utilized for making calcium carbonate and sodium sulphate both of which are important raw materials for many industries in Bangladesh.

Knowledge Management: Journal