A lead-free flotation process for enriching wolframite with H2O2 and dithiocarbamate-hydroxamic acid

The green and eco-friendly flotation process to enrich wolframite under lead-free pulp is an attractive issue, which is promising to be broken through an innovative oxidation flotation approach with H2O2 and N-[(3hydroxyamino)-propoxy]-N-hexyl dithiocarbamate (HAHD). The flotation results indicated that in comparison to the traditional technology with lead ion pre-activation and benzohydroxamic acid (BHA) collection, the new approach with H2O2 oxidation and HAHD flotation dramatically promoted the floatability of wolframite. In situ AFM showed that H2O2 eroded wolframite surface and effectively enhanced the adsorption of HAHD. XPS proved that H2O2 treatment increased the proportion of Fe(III) on/in wolframite interface. Interestingly, the dithiocarbamate group (-C(=S)S-) of HAHD was confirmed to be oxidized to the thiuram structure of -C(=S)-S-S-(S=) C-, i.e., HAHD was oxidized to (HAHD)2 on wolframite surface. Thus, the two hydroxamate groups of (HAHD)2 combined with two Fe(III) sites, leaving the thiuram structure and two hexyl groups outward for attaching air bubbles. The "H" configuration of (HAHD)2 adsorption model intensified the hydrophobicity of wolframite, which returned the high flotation recovery. Therefore, the lead-free flotation of wolframite was achieved.