Synthesis of robust insoluble anhydrite whiskers from desulphurization gypsum containing organic matter via improved hydrothermal‐calcination process for the removal of lead and zinc ions

Abstract Background An improved hydrothermal‐calcination method was used to convert desulphurization gypsum containing organic matter (OM‐gypsum) to insoluble anhydrite (II‐CaSO 4 ) whiskers, where OM‐gypsum was directly transformed to soluble anhydrite ( γ ‐CaSO 4 ) whiskers via the hydrothermal method followed by calcination. The synthesized II‐CaSO 4 whiskers were applied for the removal of lead ion (Pb(II)) and zinc ion (Zn(II)). Results The synthesized II‐CaSO 4 whiskers possessed a smooth surface, large aspect ratio, and high whiteness of above 90%. The mother liquor after synthesis could be recycled. The synthesized II‐CaSO 4 whiskers exhibited maximum adsorption capacities of 641.03 mg/g and 14.00 mg/g for Pb(II) and Zn(II), respectively, under optimal adsorption conditions. The pseudo‐second‐order model and Langmuir isotherm model were appropriate for describing the adsorption process of II‐CaSO 4 whiskers. Compared with II‐CaSO 4 whiskers calcined from hemihydrate gypsum and the short and columnar II‐CaSO 4 crystals, the synthesized II‐CaSO 4 whiskers in this work possessed a superior adsorption performance. Conclusion The improved hydrothermal‐calcination process could completely remove the organic matter from OM‐gypsum, and the direct formation of γ ‐CaSO 4 intermediate helped avoid the lattice collapse caused by the removal of water molecules during calcination. The excellent adsorption performance of the synthesized II‐CaSO 4 whiskers in this work could be attributed to their large negatively charged surface areas, which were formed by the large aspect ratio and excellent stability. This work provides a practical method for the comprehensive utilization of chemical gypsum containing organic impurities. © 2022 Society of Chemical Industry (SCI).