Environmentally friendly ionic liquid medium based on dicyanamide anion for leaching gold from e‐waste CPUs by iodination

Abstract

BACKGROUD The large and growing amount of electronic waste (e‐waste) caused by the rise of the electronics industry has negatively impacted the environment and secondary resource utilization. Thus, research on the recovery, recycling, and reuse of valuable metals from e‐waste has attracted considerable attention. In this study, a novel leaching system based on dicyandiamide ionic liquids (ILs): 1‐ethyl‐3‐methylimidazolium dicyandiamide, 1‐butyl‐3‐methylimidazolium dicyandiamide, and 1‐hexyl‐3‐methylimidazolium dicyandiamide were used to evaluate the effectiveness of leaching gold from typical e‐waste CPUs by iodination. RESULTS The response surface experiment and analysis of variance (ANOVA) for the results showed that the optimal gold leaching efficiency reached 93.81% after 170 min under a rotational speed of 300 rpm, temperature of 32 °C, and iodine dosage of 1.15%. The mechanism of reaction was determined and the main reaction products were Au[IN(CN)2]− and Au[N(CN)2]2−. Moreover, the kinetic behavior of gold leaching showed a good correlation with the Avrami model and the activation energy value was 14.01 kJ·mol−1. The comparison of iodine consumption between aqueous medium and ILs showed that the required amount of iodine (calculated by ionic iodine) decreased by a factor of six times in ILs. CONCLUSION The iodine dosage, leaching temperature, and time had significant effects on the gold leaching efficiency in the IL leaching system. The reaction of gold leaching was jointly controlled by diffusion and chemical reactions. The coordination groups [N(CN)2]22− and [IN(CN)2]2− in the pregnant solution formed stable complexes with Au(I). The consumption of iodine in ILs decreased remarkably, showing the significant practical value of ILs. © 2022 Society of Chemical Industry (SCI).