Recycling of ZnS from wastes and its utilization as an electrode material in supercapacitors

Ferrochrome and electric arc furnace flue dusts, that are among the wastes generated in the metallurgy industry, contain valuable metal oxides as well as compounds that are harmful to the environment and human health, making recycling of these wastes essential from both an economic and environmental perspective. Additionally, it is known that the utilization of metal sulfides as electrode materials in the new generation energy storage systems has been intensively investigated in recent years. The aim of the study is to develop an efficient hydrometallurgical process to generate ZnS with high purity from flue dusts and to use the generated ZnS as an electrode material in asymmetric type coin cell supercapacitors. In the scope of the study, leaching experiments were conducted at varying liquid-solid ratios, acid concentrations and durations with sulfuric acid and nitric acid solutions. Four optimum parameters were determined to recover Zn from these solutions selectively. By addition of sodium sulfide to optimum solutions, it was ensured that, Zn ions in the solutions were precipitated as ZnS. After determination of the optimal parameters for precipitation, it was revealed that ZnS can be recovered from the leach solutions with an efficiency of about 99%. The electrochemical behavior of the asymmetric type coin cell supercapacitors produced

with the obtained ZnS from ferrochrome flue dust and electric arc furnace dust wastes were investigated in a two-electrode system at a scanning rate of 10 mVs-1, and the specific capacitance of 1723.57 Fg-1 and 1293.94 Fg-1 was achieved, respectively. Additionally, it has been determined that the supercapacitors retain 92.82% and 79.33% of their capacity in the end of 1000 cycles, respectively. Obtained results demonstrate that, ZnS may be recovered from flue dusts effectively and the utilization of the recovered ZnS to be used as electrode materials in supercapacitor applications is promising.