Thiourea compounds with diverse hydrophobic group used as selective flotation collectors for galena

Hydrophobic group is a crucial yet underutilized component of a collector molecule. Herein we examine the flotation behaviors of thioureas with various hydrophobic groups for a galena/sphalerite mixed flotation system and compare them with sodium ethyl-xanthate (SEXT). Flotation experiments show that thiourea collectors with shorter alkyl chain and less nucleophilic amine nitrogen display better separation performance. Larger contact angles and adsorption capacities between the thiourea collectors and galena are the key to the enhanced selectivity. In the homogeneous Zn2+/Pb2+ mixed solution, thiourea collectors exhibit strong coordination ability with Pb2+, and their selectivities are noticeably higher than that of SEXT. FTIR and single crystal X-ray diffraction studies prove that thiourea collectors coordinate with metal ions through the S atom only. DFT calculations reveal how side-chain size and type can affect the selectivity.