Capture and storage of CO2 into waste phosphogypsum: the modified Merseburg process

We evaluated the chemical sequestration of carbon dioxide into the phosphogypsum from the Lowveld region of South Africa. The phosphogypsum was converted to saleable ammonium sulphate and precipitated calcium carbonate in a modified Merseburg process. The heat from the ammonium carbonate formation exothermicity increased the temperature in the gypsum conversion reactor contents by 35 K, significantly reducing the heating requirements to achieve the reaction temperature of 343 K. The modified process will lower capital layout but no fundamental energy superiority or inferiority to the original Merseburg process. The gypsum conversion efficiency of 95 % was achieved. The purity of the ammonium sulphate produced is comparable to the chemical grade, commercially available in South Africa. The calcium carbonate precipitated as calcitic scalenohedral polymorphs with a mean size of 3.4 μm in diameter. The economic feasibility study must be done to determine the cost implication of the omission of the carbon dioxide scrubbing towers in the modified Merseburg process.