Behaviour of ilmenite as a gangue mineral in the benzohydroxamic flotation of a complex pyrochlore-bearing ore

One challenge identified in the flotation of niobium bearing minerals with hydroxamates is the recovery of gangue minerals which can result in concentrate grade dilution. Micro-flotation of single and mixed minerals and bench scale flotation tests on a low-grade complex pyrochlore-bearing ore were conducted to assess the flotation behavior of ilmenite as a gangue mineral in the flotation of pyrochlore using benzohydroxamic acid (BHA) as a collector and sodium hexametaphosphate (SHMP) as a dispersant/depressant. In micro-flotation, high dosages of BHA resulted in high pyrochlore recovery and low ilmenite recovery at pH 8. It was observed that the order of addition of SHMP in relation to BHA had a strong effect on pyrochlore recovery, with high recovery maintained only when SHMP was added after BHA. When ilmenite and pyrochlore were floated in the same system, it was found that reagent addition order played an important role in selective flotation of pyrochlore. Flotation of pyrochlore was more selective over ilmenite when SHMP was added before BHA, similar to a cleaner flotation stage in real-ore flotation. Contrary to micro-flotation results titanium recovery was high (more than 60% TiO2 recovery in most cases) under similar pulp conditions in bench scale flotation, an indication that to some extent titanium minerals were recovered by a mechanism other than genuine flotation. Similarly, in mixed mineral micro-flotation, the recovery of ilmenite increased in the presence of pyrochlore. Two possible scenarios, one physical and the other chemical in nature, have been proposed to explain this observed phenomenon. First, it is possible that moderately floatable titanium mineral particles were recovered in the froth by association with highly floatable pyrochlore, particularly at starvation levels of a dispersant (SHMP) through the hydraulic entrainment of fines. The second possibility is that titanium minerals experienced inadvertent activation in multi-mineral systems, perhaps with metal-hydroxamates as the activating species, forming hydroxamate complexes involving ferric and/or niobium species. This research area is under further investigation. (C) 2017 Published by Elsevier Ltd.