Probe into hydrophobic mechanism of solid-liquid interface during separation recovery of Zn from Fe and Cd by sulfide precipitation flotation with a novel “plane” collector

Abstract

Sulfide precipitation flotation process is one of the effective methods to recover heavy metal ions from wastewater, nevertheless, the selectivity and collection ability for flotation process are limited by the structure of collector group currently. While, the original collectors with novel minerophilic groups have been hardly reported. In this sense, a novel “plane” chelating collector 5-heptyl-1,3,4-oxadiazole-2-thione (HpODT) containing N-, O- and S-donor ligands was prepared and first used for selective flotation of Zn from Fe and Cd by sulfide precipitation flotation. Micro-flotation showed that HpODT exhibited stronger hydrophobization and selectivity to zinc sulfide and achieved higher flotation recovery than sodium isobutyl xanthate (SIBX). ζ-Potential revealed that HpODT might attached to the zinc sulfide surface by chemical adsorption. UV spectra of HpODT with metal ions suggested that HpODT had chemical interaction with Zn2+, accompanying with the release of H+. According to FTIR, XPS and DFT calculation results, a four-membered HpODT-Zn chelating structure was proposed and predicted, meanwhile the hydrophobic HpODT-Zn surface compound was covered on zinc sulfide surface under the action of ZnS and ZnN bonds. Considering the above results, the surface hydrophobicity of zinc sulfide improved obviously after attached with HpODT, thereby promoting the flotation recovery and selectivity of Zn2+, which is significant for effective recovery of zinc from wastewater of complex metal species.