Utilization of Waste Calcium Chloride (CaCl2) for the Synthesis of Useful Chemicals

Abstract

Calcium chloride is waste of Solvay process, a process for manufacturing of sodium carbonate (soda ash) which is important raw material for many chemical industries. The discharged calcium chloride is either dumped to open land sites or is liquidated to the rivers where it causes environmental pollution. Calcium chloride discharge from the Solvay process can be used to produce calcium sulfate whiskers (CSWs). Environment friendly, cost effective and thermally stable CSWs have gained much attention as they are being extensively used as reinforcing material in pulp and paper, rubber, plastics and polymer composite materials. In the first part, CSWs were prepared using sodium sulfate (Na2SO4) and calcium chloride (CaCl2) discharged from the soda ash plant, by hydrothermal method. The study of different process parameters i.e. reaction temperature, molar ratio of reactants and mixing methods of reactants, was carried out and conditions were optimized for synthesis of CSWs. Based on these optimized conditions CSWs with high aspect ratio were made. The experimental results revealed that CSWs with length of 150-200 μm and width of 0.5 - 8 μm were produced by hydrothermal treatment of precursors that were formed by precipitation of Na2SO4 and CaCl2 at temperature of 25 oC, having molar ratio of Na2SO4 to CaCl2 0.5:1and by adding Na2SO4 to CaCl2. The morphology of whiskers was examined with the scanning electron microscope (SEM). The phase structures were identified by powder X-ray diffractometer (XRD). SEM results exhibited good morphology of CSWs and XRD provided phase identification. In the second part, polycaprolactone-calcium sulfate whiskers (PCL-CSWs) composites were prepared to study reinforcing properties of CSWs in the polymer composites. Co-precipitation method was used for the synthesis of PCL-CSWs composites. The CSWs were added in different wt. percentages i.e. 5%, 10%, 15% and 20% to study the enhancement of mechanical properties of composite. The PCL alone was also used separately for comparison with the composites. To examine the mechanical strength two tests i.e. tensile test and flexural property test were performed by electronic universal testing machine (UTM). Mechanical test results were excellent and were comparable to literature. Process study provided optimum utilization of CaCl2 to form CSWs that can be used as reinforcing material in polymer composites.