Study of the Mechanism of the Fe-BHA Chelates in Scheelite Flotation

Abstract

Scheelite associated with calcium-containing minerals such as calcite and fluorite is difficult to separate by flotation because of the Ca ions contained in the mineral lattices, which cause scheelite to have similar surface properties and floatability to gangue minerals. Traditional collectors such as oleic acid need to add a large amount of sodium silicate as gangue inhibitors, which causes difficulties for the settlement of tailings. In addition, the use of benzohydroxamic acid (BHA), which needs the addition of Pb(NO3)2 as the scheelite activator, can also cause environmental pollution. In this paper, Fe-BHA, a new collector containing the iron complex, was studied to investigate its flotation ability of scheelite, as well as its BHA/FeCl3 ratio on scheelite flotations. In the single mineral flotations, the Fe-BHA showed a significant difference in the flotation recoveries of scheelite and calcite, with a scheelite recovery of 77.03% at pH 8.0 and calcite recovery of 16.69% at the same pH. The results of the roughing tests of Xianglushan actual ore showed that the scheelite with Fe-BHA (500 g/t BHA and 200 g/t FeCl3) and 40 g/t oleic acid as collectors obtained satisfactory flotation results with a WO3 grade of 1.56% and WO3 recovery of 65.52%, which were much higher than those of scheelite with BHA or oleic acid as the collector, but there was still a gap with those of scheelite using Pb(NO3)2 as activation and BHA as the collector. The UV-Vis curves of the Fe-BHA with different BHA/FeCl3 ratios indicated that the Fe-BHA chelates might have several different structural forms, and the single mineral tests of the BHA/FeCl3 ratios showed that when the molar ratio of benzohydroxamic acid to FeCl3 was about 1.2:1, the best scheelite flotation result was obtained in this test. In addition, the XPS analyses proved that the adsorption of the Fe-BHA on the scheelite surface occurred, and by fitting the peaks of Ca 2p and O 1s of scheelite, it was found that the mechanism of the Fe-BHA acting on the Ca sites of the scheelite surface was through the removal of H2O from the Ca-OH of scheelite and Fe-OH from Fe-BHA to form Fe-O-H.