Removal of residual benzohydroxamic acid-lead complex from mineral processing wastewater by metal ion combined with gangue minerals

Benzohydroxamic acid-lead (BHA-Pb) complex reagent is a commonly used collector for the flotation of oxidized ores such as tungsten ore, cassiterite, and ilmenite, but the BHA-Pb complex remaining in the mineral processing wastewater (MPW) after flotation is economically and efficiently difficult to remove. At present, the treatment technology usually starts from the treatment of MPW at a wastewater treatment station. However, the treatment cost is inevitably high due to the huge amount of MPW. In this study, a new process of removing residual BHA-Pb complex reagent from MPW in one-step using metal ions combined with gangue minerals in tailings pulp was proposed. It started from tailings pulp treatment and taking tailings reservoir as the main reaction site. The basic issues related to the new process were mainly studied. The concentration of BHA was characterized using chemical oxygen demand (COD). The results show that when Ca2+, Fe3+, or Al3+ was added to the BHA-Pb solution, only Fe3+ could effectively remove the COD of the BHA-Pb solution, while Ca2+ and Al3+ could not. This is because the BHA-Pb complex can be preferentially transformed into the BHA-Fe complex, and the COD of the BHA-Fe complex solution is most easily removed. However, BHA-Fe complex systems have dark colors and are difficult to settle. When gangue minerals are added to the BHA-Fe complex system, gangue minerals can play the role of coarse particles carrying fine particles settling, which is helpful to the sedimentation of the BHA-Fe complex system. The transformation mechanism between BHA-Pb and BHA-Fe complexes was explained by the conditional stability constants and Gibbs free energy changes analysis. In addition, the sedimentation mechanism of the BHA-Fe complex system was analyzed by zeta potential and scanning electron microscope-energy dispersive spectrometer. This study provides a new idea for removing residual organic flotation reagents from MPW starting from tailings pulp treatment.