The efficient separation of scheelite from calcium-bearing minerals, especially calcite, remains a challenge in practice. In this work, a novel reagent scheme incorporating a depressant of sodium hexametaphosphate (SHMP) and a collector mixture of octyl hydroxamic acid (HXMA-8) and sodium oleate (NaOl) was employed in both single and mixed binary mineral flotation, and it proved to be highly effective for the separation. Furthermore, the role of the pH value in the separation was evaluated. Additionally, the mechanism of the selective separation was investigated systemically via zeta potential measurements, fourier transform infrared (FTIR) spectroscopy analysis, X-ray photoelectron (XPS) spectroscopy analysis and crystal chemistry calculations. It turns out that the selective chemisorption of SHMP on calcite (in the form of complexation between H2PO4−/HPO42− and Ca2+) over scheelite is ascribed to the stronger reactivity and higher density of Ca ions on the commonly exposed surfaces of calcite minerals. The intense adsorption of HXMA-8 on scheelite over calcite due to the match of the O O distances in WO42− of scheelite and CONHOH of HXMA-8 holds the key to the successful separation. We were also interested in warranting the previous claim that NaOl is readily adsorbed on both minerals via chemisorption. Our results provided valuable insights into the application of mixed collectors and an effective depressant for flotation separation.

Adsorption of a novel reagent scheme on scheelite and calcite causing an effective flotation separation.

A molecular dynamics study of the interaction of oleate and dodecylammonium chloride surfactants with complex aluminosilicate minerals.

Froth flotation of scheelite has regained new focus since the 2010s and research regarding floatability and reagents has made great progress over the years. The main objective was and remains the selective flotation of scheelite from other calcium-bearing minerals, in particular calcite, fluorite and apatite. Due to similar properties, most attempts have limited success or only specific application (linked to a type of ore or a location). This article aims at reviewing all general physical-chemical information on froth flotation of scheelite, including electrokinetic properties, influence of pH and already existing reagents as well as ones still under examination. It appears that chelating or mixed collectors and modified versions of sodium silicate and quebracho hold great promise for scheelite flotation, while the use of said depressants and/or promoters seems inevitable.

Froth flotation of scheelite – A review

Anisotropic surface energies and adsorption behaviors of scheelite crystal

The effect of sodium alginate on the flotation separation of scheelite from calcite and fluorite

The interactions of two diphosphonic acid based surfactants, namely alkylimino-bis-methylene-diphosphonic acid (IMPA-8) and 1-hydroxy-alkylidene-1,1-diphosphonic acid (Flotol-8), with three calcium minerals, fluorite, calcite, and fluorapatite, were quanitfied on the basis of molecular modeling computations. Both force field (UFF) and semiempirical quantum mechanical (MNDO) methods were employed for this purpose. The results of theoretical calculations in terms of the prediction of the order of response of these three minerals to flotation with diphosphonic acid reagents were found to match remarkably well with the experimental microflotation test results. The utility and power of this approach in the design/screening of surfactant molecules for flotation separation are demonstrated, and its tremendous implications for the industry are discussed.

T. K. Rao

Papers

Molecular Modeling of Interactions of Diphosphonic Acid Based Surfactants with Calcium Minerals

Molecular Modeling of Interactions of Alkyl Hydroxamates with Calcium Minerals