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, North-West University, Pretoria, South Africa.
Department of Environmental, Water and Earth Science, Faculty of Science, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa.
Waste Manag. 2014 Nov;34(11):2373-81. doi: 10.1016/j.wasman.2014.07.010. Epub 2014 Aug 13.
The production of elemental sulphur and calcium carbonate (CaCO3) from gypsum waste can be achieved by thermally reducing the waste into calcium sulphide (CaS), which is then subjected to a direct aqueous carbonation step for the generation of hydrogen sulphide (H2S) and CaCO3. H2S can subsequently be converted to elemental sulphur via the commercially available chemical catalytic Claus process. This study investigated the carbonation of CaS by examining both the solution chemistry of the process and the properties of the formed carbonated product. CaS was successfully converted into CaCO3; however, the reaction yielded low-grade carbonate products (i.e. <90 mass% as CaCO3) which comprised a mixture of two CaCO3 polymorphs (calcite and vaterite), as well as trace minerals originating from the starting material. These products could replace the Sappi Enstra CaCO3 (69 mass% CaCO3), a by-product from the paper industry which is used in many full-scale AMD neutralisation plants but is becoming insufficient. The insight gained is now also being used to develop and optimize an indirect aqueous CaS carbonation process for the production of high-grade CaCO3 (i.e. >99 mass% as CaCO3) or precipitated calcium carbonate (PCC).
从石膏废料中生产元素硫和碳酸钙（CaCO3）可以通过将废料热还原为硫化钙（CaS）来实现，然后将其进行直接的水碳化步骤，以生成硫化氢（H2S）和 CaCO3。随后，可以通过商业上可用的化学催化克劳斯（Claus）工艺将 H2S 转化为元素硫。本研究通过考察该过程的溶液化学和形成的碳酸化产物的性质，研究了 CaS 的碳化。CaS 成功转化为 CaCO3；然而，该反应生成的碳酸化产物品位较低（即<90 质量%为 CaCO3），其由两种 CaCO3 多晶型体（方解石和文石）以及源自起始原料的痕量矿物质组成。这些产品可以替代 Sappi Enstra CaCO3（69 质量% CaCO3），它是造纸工业的副产品，用于许多全规模 AMD 中和工厂，但现已不足。目前，所获得的见解也正在用于开发和优化间接水合 CaS 碳化工艺，以生产高品位 CaCO3（即>99 质量%为 CaCO3）或沉淀碳酸钙（PCC）。
