Abstract
The flotation separation of scheelite from calcite is problematic, where sodium silicate modified by polyvalent metal ions has shown some advantages for selective depression. In this study, an Al-Na2SiO3 polymer was used as the depressant for the flotation separation of scheelite from calcite using a lead complex of benzohydroxamic acid (Pb-BHA) as the collector. Furthermore, a number of measurements were conducted to investigate the structure of the Al-Na2SiO3 polymer and its adsorption behavior with Pb-BHA complexes on the mineral surface. Flotation experiments indicated that the Al-Na2SiO3 polymer shows good selectivity for the flotation separation of scheelite from calcite at pH 8, where the optimum ratio of sodium silicate to aluminum sulfate was 2:1. Fourier-Transform Infrared (FTIR) and solution chemical analyses revealed that aluminum hydroxide complexes and the hydroxy moiety of silicic acid are able to self-assemble via condensation affording an Al-Na2SiO3 polymer, i.e., a composite aluminosilicate polymer. The zeta potential measurements and adsorption capacity measurements indicated that, upon adsorption of the Al-Na2SiO3 polymer and Pb-BHA complexes on the mineral surface, the Al-Na2SiO3 polymer had less influence on the adsorption of Pb-BHA complexes on the scheelite surface, while the opposite was true for calcite. Therefore, more Pb-BHA complexes and fewer Al-Na2SiO3 polymers were deposited on the scheelite surface, while fewer Pb-BHA complexes and more Al-Na2SiO3 polymers were adsorbed on the calcite surface. The selective separation of scheelite from calcite was attributed to the cooperative selectivity of the Pb-BHA complexes and Al-Na2SiO3 polymer.
Highlights
The flotation separation of scheelite from other calcium-containing minerals is problematic due to their similar physicochemical characteristics and flotation behavior [1,2,3,4,5,6]
Pb-benzohydroxamic acid (BHA) complexes have proven to be selective for calcium mineral flotation, demonstrating good collecting ability toward scheelite
The optimum concentration of Al-Na2 SiO3 polymer for scheelite flotation using Pb-BHA complexes as the collector was determined as 100 mg/L
Summary
The flotation separation of scheelite from other calcium-containing minerals is problematic due to their similar physicochemical characteristics and flotation behavior [1,2,3,4,5,6]. The selective adsorption of sodium silicate on minerals is significantly improved by modification with polyvalent metal ions, such as Fe(II), Pb(II), Cu(II), Mg(II), and Al(III) [10,12,14,15,16], especially for application in scheelite flotation. In contrast to fatty acid flotation processes requiring large masses of sodium silicate (e.g., 1–3 kg/t), little amounts of Al-Na2 SiO3 polymer (e.g., 0.1–0.3 kg/t) are enough and effective for Pb-BHA flotation, indicating that the combined utilization of Pb-BHA complexes and such an Al-Na2 SiO3 polymer exhibits absolute specificity toward scheelite, contributing to efficient and clean scheelite flotation processes. The competition between the Al-Na2 SiO3 polymer and Pb-BHA complex on the minerals surface remains unclear; their adsorption behavior on scheelite and calcite requires further investigation to uncover the mechanism behind the superior selectivity of the Al-Na2 SiO3 polymer during Pb-BHA flotation
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