title: Synthesis of high-purity precipitated calcium carbonate during the process of recovery of elemental sulphur from gypsum waste.
abstract: We recently showed that the production of elemental sulphur and calcium carbonate (CaCO3) from gypsum waste by thermally reducing the waste into calcium sulphide (CaS) followed by its direct aqueous carbonation yielded low-grade carbonate products (i.e. <90 mass% as CaCO3). In this study, we used the insight gained from our previous work and developed an indirect aqueous CaS carbonation process for the production of high-grade CaCO3 (i.e. >99 mass% as CaCO3) or precipitated calcium carbonate (PCC). The process used an acid gas (H2S) to improve the aqueous dissolution of CaS, which is otherwise poorly soluble. The carbonate product was primarily calcite (99.5%) with traces of quartz (0.5%). Calcite was the only CaCO3 polymorph obtained; no vaterite or aragonite was detected. The product was made up of micron-size particles, which were further characterised by XRD, TGA, SEM, BET and true density. Results showed that about 0.37 ton of high-grade PCC can be produced from 1.0 ton of gypsum waste, and generates about 0.19 ton of residue, a reduction of 80% from original waste gypsum mass to mass of residue that needs to be discarded off. The use of gypsum waste as primary material in replacement of mined limestone for the production of PPC could alleviate waste disposal problems, along with converting significant volumes of waste materials into marketable commodities.
authors: DST/CSIR National Centre for Nanostructured Materials, Council for Scientific and Industrial Research, PO Box 395, Pretoria 0001, South Africa; Centre for Research and Continued Engineering Development (Pretoria), North-West University, South Africa. Electronic address: mdebeer@csir.co.za.
authors: M
authors: M
authors: de Beer
authors: Council for Geoscience, Private Bag X112, Pretoria 0001, South Africa. Electronic address: fdoucet@geoscience.org.za.
authors: F J
authors: FJ
authors: Doucet
authors: Department of Environmental, Water and Earth Science, Faculty of Science, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa.
authors: J P
authors: JP
authors: Maree
authors: Centre for Research and Continued Engineering Development (Pretoria), North-West University, South Africa.
authors: L
authors: L
authors: Liebenberg
mesh_terms: D002119:Calcium Carbonate / Q000032:analysis; D002133:Calcium Sulfate / Q000737:chemistry*; D003252:Construction Materials / Q000032:analysis*; D007220:Industrial Waste / Q000032:analysis*; D059027:Recycling; D013455:Sulfur / Q000737:chemistry*; D018505:Waste Management
chemical_list: D007220:Industrial Waste; D013455:Sulfur; D002119:Calcium Carbonate; D002133:Calcium Sulfate
keywords: Calcium sulphide; Gypsum waste; Indirect carbonation; Precipitated calcium carbonate; Valorisation