Factors affecting crystallization of copper sulfide in fed-batch fluidized bed reactor

• Cu2 + in aqueous solution was well crystallized into CuS in a fed-batch FBR.
• Larger CuS crystals were produced using Na2S·5H2O due to lower surface charge.
• CuS fines developed into larger star-shaped crystals using Ca-coated sand.
• Resting height and seed type were major factors affecting CuS crystallization in FBR.

This work has assessed factors affecting crystallization of copper sulfide (CuS) under batch conditions and in fed-batch fluidized bed reactor (FBR) using calcium-coated sands as a seed material. Compared with using sodium sulfide nonahydrate as a sulfidation reagent, larger CuS crystals were produced from sodium sulfide pentahydrate, most likely because of the lower surface charge. Due to the partial oxidation of sulfide in the pentahydrate form, the optimum molar ratio of Cu2 + to S2 − was found to be 1:2, higher than the theoretical ratio. Crystal growth and aggregation were further increased by using calcium ion as a cross-linker among the CuS fines (< 100 nm), resulting in an additional 30% decrease in Cu2 + concentrations from the effluent of fed-batch FBR. The efficacy of CuS crystallization was also remarkably dependent on the operating factors, i.e., the resting height of the seed material and recirculation rate. Under optimal conditions, > 95% of the initial Cu2 + (100 mg Cu2 +/L) was successfully transformed to CuS crystals within 120 min. The size and crystallinity of the star-shaped CuS crystals were confirmed by FEG–SEM and XRD analyses, respectively. Principal component analysis indicated that the resting height and the seed type were the primary parameters affecting CuS crystallization in the fed-batch FBR.