Wolframite Conversion in Treating a Mixed Wolframite–Scheelite Concentrate by Sulfuric Acid

Abstract

Complete wolframite conversion in sulfuric acid is significant for expanding the applicability of the sulfuric acid method for producing ammonium paratungstate. In this paper, the conversion of wolframite in treating a mixed wolframite-scheelite concentrate by sulfuric acid was studied systematically. The results show that the conversion of wolframite in sulfuric acid is more difficult than that of scheelite, requiring rigorous reaction conditions. A solid H2WO4 layer forms on the surfaces of the wolframite particles and becomes denser with increasing H2SO4 concentration, thus hindering the conversion. Furthermore, the difficulty in wolframite conversion can be mainly attributed to the accumulation of Fe 2+ (and/or Mn 2+) in the H2SO4 solution, which can be solved by reducing Fe 2+ (and/or Mn 2+) concentration through oxidization and/or a two-stage process. Additionally, the solid converted product of the mixed wolframite-scheelite concentrate has an excellent leachability of tungsten in an aqueous ammonium carbonate solution at ambient temperature, with approximately 99% WO3 recovery. This work presents a route for manufacturing ammonium paratungstate by treating the mixed concentrate in sulfuric acid followed by leaching in ammonium carbonate solution.

Thermodynamics of Tungsten Ores Decomposition Process Options

“…We favor the higher values because thermodynamic calculation result show an accordant trend with the experimental results[26], while the more negative values seem more suited to pyrometallurgical calculations. So we accept, respectively, -1154.8 and -1053.91 kJ• mol -1 for ∆ 298 and ∆ 298 of ferberite in this paper, which was also accepted in the recent research of Martins[28] and Lange's Handbook of Chemistry[32].…”

“…Our previous research [26] showed that increasing Fe 2+ in the solution hinders the FeWO4 decomposition, while oxidization of Fe 2+ to Fe 3+ or/and renewing the acid solution by a two-stage decomposition favors FeWO4 reaction. This explains the impact of oxidization by HNO3 in Fig.…”

“…When tungsten ore is decomposed in acid solutions, a solid H2WO4 product layer will form on the surfaces of unreacted tungsten mineral particles. It can be dissolved incorporating actions, such as controlling the acid concentration and adding an oxidizing agent [25,26,45]. Due to the absence of thermodynamic data, unfortunately, this paper does not carry out a detailed thermodynamic analysis on tungsten ore decomposition to H2[WO3(C2O4)H2O] and H3PW12O40.…”

“…Hydrochloric, nitric or sulfuric acid in the presence of phosphorus was found to decompose scheelite and form a water-soluble phosphotungstic acid chelate compound (12-tungstophosphoric heteropoly acid, H3PW12O40) [21][22][23][24]. In previous work, we systematically studied the conversion of scheelite and mixed scheelite-wolframite concentrate in sulfuric acid, and found that the tungsten concentrates can be completely converted in H2SO4 solutions by adding an oxidizing agent and controlling the H2WO4 formation in moderate acid concentrations [25,26].…”

Sustainable and efficient leaching of tungsten in ammoniacal ammonium carbonate solution from the sulfuric acid converted product of scheelite

“…Considering discharge of high-salinity wastewater, volatility, and cost, sulfuric acid is an appropriate candidate to decompose scheelite concentrate (Forward and Vizsolyi, 1965), forming solid H2WO4 and CaSO4. In our previous work, the conversion of tungsten concentrate in H2SO4 solutions was systematically studied, including the mechanism of H2WO4 layer formation on unreacted tungsten minerals (Li et al, 2017b;Shen et al, 2018a) and the kinetics of scheelite conversion in sulfuric acid (Shen et al, 2018b). It has been approved that tungsten concentrates can be completely converted in H2SO4 solution under appropriate conditions .…”