Abstract
The combination of lead nitrate and benzohydroxamic acid (BHA) has succeeded in the commercial flotation of wolframite for years, regardless of the detrimental effects of Pb2+ on environment. In this work, a clean flotation technology was developed to remove the use of lead nitrate. The oxidation flotation with sodium hypochlorite (NaClO) and N-[(3-hydroxyamino)-propoxy]-N-hexyl dithiocarbamate (HAHD) achieved an effective separation and enrichment of wolframite from calcite, while NaClO and BHA combination delivered an inefficient floatation recovery of wolframite. The flotation mechanism in the HAHD-NaClO-wolframite system was further explored by in situ AFM, FTIR, UV and XPS. The findings deduced that NaClO treatment increased the proportion of Fe(III) and Mn(IV) species in wolframite interface, which benefited the chelation of HAHD’s hydroxamic group with Fe(III) and the oxidation of HAHD’s dithiocarbamate group by Mn(IV). Thus, with the help of NaClO, HAHD was changed into (HAHD)2 thiuram disulfide which anchored on wolframite surface through its double hydroxamate groups, leaving the two hexyl groups and the thiuram structure outward for attaching air bubbles. As a result, the hydrophobicity and floatability of wolframite significantly strengthened.
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