Synthesis of scheelite from sodium tungstate solution by calcium hydroxide addition

Wan, Linsheng; Huang, Xiaojing; Deng, Dengfei; Li, Hongchao; Chen, Yongming

doi:10.1016/j.hydromet.2015.03.010

Cited by 22 publications

(2 citation statements)

References 9 publications

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“…These results differ from the above calculation according to equation(6). Wan et al[39] synthesized scheelite by adding Ca(OH)2 into Na2WO4 solution in a temperature range of 20-110 o C. However, Zhao et al[40] studied the kinetics of sodium hydroxide leaching of scheelite at 60-100 o C. The results seem to be in disagreement.…”

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confidence: 81%

Thermodynamics of Tungsten Ores Decomposition Process Options

Shen

Taskinen

2018

The Minerals, Metals &Amp; Materials Series

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The thermodynamics of tungsten ore decomposition in mineral acid and alkaline solutions were studied. The published thermodynamic data of tungsten minerals were collected and assessed. The Gibbs energies of CaWO4 (-1538.43 kJ/mol), FeWO4 (-1053.91 kJ/mol), MnWO4 (-1206.08 kJ/mol), H2WO4 (-1003.92 kJ/mol), and Na2WO4 (-1455.58 kJ/mol, aq) at 25 o C were adopted in the calculation using HSC software. The results show that CaWO4 is decomposed more readily in Na2CO3 solution than in NaOH, while FeWO4 and MnWO4 are more reactive in NaOH solutions. From a thermodynamic point of view, tungsten ore decomposes easily in acid solutions despite most ∆ increasing slightly with temperature. Oxidizing Fe 2+ to Fe 3+ in acidic solutions facilitates decomposition of FeWO4, and the reaction of CaWO4 in H2SO4 solution occurs more easily than in other mineral acids, due to the formation of sparsely soluble CaSO4. The results fit well with the experimental data and industrial experience previously reported in the literature.

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confidence: 81%

Thermodynamics of Tungsten Ores Decomposition Process Options

Shen

Taskinen

2018

The Minerals, Metals &Amp; Materials Series

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“…The obtained sodium tungstate solution is then converted to ammonium tungstate in the purification operation by solvent extraction or ion exchange, simultaneously generating sodium chloride or sodium sulfate solution and thus consuming massive soda or caustic soda (Lassner, 1995). Additionally, vast volume of water is required in solvent extraction or ion exchange process (Yih and Wang, 1979), resulting in discharge of ~20 or 100 tons (Wan et al, 2012) of high-salinity wastewater for per ton APT production, where the later value was even reported as ~126 tons for ion exchange process (Wan et al, 2015a;Wan et al, 2015b). Furthermore, Leal-Ayala et al (2015) pointed out that 4% of tungsten would be loss in APT production by these processes.…”

Section: Introductionmentioning

confidence: 99%

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

Shen

Zhou

Peng

et al. 2018

Journal of Cleaner Production

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To directly obtain solution of (NH4)2WO4 instead of Na2WO4 is the key for developing a cleaner technology of ammonium paratungstate production. In this paper, ammoniacal ammon iu m carbonate solution was adopted for leaching tungsten from the converted product, a mixture of H2WO4 and CaSO4 obtained by treating scheelite with sulfuric acid. The research indicates that tungsten can be efficiently extracted in form of ammonium tungstate solution with WO3 leaching yield of > 99.5% under moderate leaching conditions. The WO3 leaching yield is influenced by the transformation of calciu m sulfate to calcium carbonate due to forming CaWO4 through the secondary reaction between CaSO4 and (NH4)2WO4, whereas an excess (NH4)2CO3 (≥ 0.64 mol/L) can suppress the secondary reaction by facilitating the transformation. Additionally, the consumed ammonium carbonate can be recovered by treating the leaching residue with ammonium sulfate solution at above 70 o C. This work presents a cleaner and sustainable technique for producing ammonium paratungstate, with circulating the leaching reagents and bypassing the conversion of Na2WO4 to (NH4)2WO4.

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