Utilization of Sodium Hexametaphosphate for Separating Scheelite from Calcite and Fluorite Using an Anionic–Nonionic Collector

Abstract

This study presents a highly selective reagent system that utilizes sodium hexametaphosphate (SHMP) to improve the separation of scheelite from calcite and fluorite using an anionic–nonionic collector. The recoveries of calcite and fluorite decreased to 20% as the SHMP dose exceeded 6 × 10−6 mol/L, whereas that of scheelite remained at 85%. The interaction mechanisms of minerals with SHMP were investigated through equilibrium speciation, Zeta potential, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy analyses. SHMP exists as hydrogen phosphate anion in the aqueous solution with a pH of 7–12. Moreover, it may be adsorbed intensively on the positively charged surfaces of calcite and fluorite via electrostatic force or chelation with calcium ion to impede further adsorption of the assembled collector. By comparison, the adsorption of SHMP is feeble on the scheelite surface because of its negative charge. The roughing grade of low-grade scheelite ore is substantially improved from 0.74% to 1.65% compared with that in the contrast test in the absence of SHMP.

Laboratory Testing of Scheelite Flotation from Raw Ore in Sangdong Mine for Process Development

“…Tungsten has been one of the important metals, which is widely used in various industries such as alloys, electron, chemical engineering, etc. [1][2][3][4][5][6][7]. Not only does it have the highest melting point among metals, but it also shows particularly high physical properties including moduli of compression and elasticity, thermal creep resistance and electrical conductivity [1,3,4,8].…”

“…Due to its significant economic importance and high supply risks, it has been classified as a strategic metal. According to a recent report, more than 80% of tungsten is produced in China, though a large amount of tungsten has been produced in Korea [1,6,9]. The Sangdong mine in South Korea was the powerhouse of the economy in the 1940s, contributing more than 50% of the export revenue in Korea [10].…”

“…There are various types of tungsten minerals. Among them, scheelite (CaWO 4 ) is considered as an economically important mineral [2,[4][5][6][7]9,[11][12][13][14][15][16][17]. To be specific, scheelite is easily ground to fine particles during crushing and grinding processes due to its brittleness [1,18,19].…”

“…A fatty acid collector is extensively used in scheelite flotation from the raw ore during the process of separation [2,8,13,15,21]. Scheelite is often associated with other Ca-bearing salt-type minerals such as calcite and fluorite, which has similar characteristics [5][6][7]22,23]. Their dissolved mineral species in the pulp might be some reactions such as hydrolysis, precipitation and adsorption which can affect the interaction between reagents and minerals [5,24].…”

“…Their dissolved mineral species in the pulp might be some reactions such as hydrolysis, precipitation and adsorption which can affect the interaction between reagents and minerals [5,24]. Therefore, it is desirable to select suitable modifiers and depressants for selective separation which is available through the flotation method [5][6][7][8]12,16,21,24]. In particular, the studies on various kinds of flotation reagents have been carried out, and most of them have focused on the development of new collectors and depressants [8,11,14,15,21,25].…”