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.
Council for Geoscience, Private Bag X112, Pretoria 0001, South Africa.
Waste Manag. 2015 Dec;46:619-27. doi: 10.1016/j.wasman.2015.08.023. Epub 2015 Aug 24.
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.
我们最近表明，通过将石膏废料热还原为硫化钙（CaS），然后直接将其进行碳酸化反应，从石膏废料中生产元素硫和碳酸钙（CaCO3），可以得到低品位的碳酸盐产品（即 <90%的质量为 CaCO3）。在本研究中，我们利用之前工作中的经验，并开发了一种间接的硫化钙碳酸化工艺，用于生产高品位碳酸钙（即 >99%的质量为 CaCO3）或沉淀碳酸钙（PCC）。该工艺使用酸性气体（H2S）来提高 CaS 在水中的溶解度，否则 CaS 的溶解度很差。碳酸盐产物主要为方解石（99.5%），含有微量的石英（0.5%）。获得的碳酸钙多晶型物仅为方解石；未检测到文石或霰石。产物由微米级颗粒组成，进一步通过 XRD、TGA、SEM、BET 和真密度进行了表征。结果表明，1.0 吨石膏废料可生产约 0.37 吨高品位 PCC，产生约 0.19 吨残渣，与原始石膏废料质量相比，残渣质量减少了 80%。将石膏废料作为主要原料替代开采的石灰石来生产 PCC，可以缓解废物处理问题，并将大量废物转化为有市场价值的商品。
