Technology and theory of producing APT from tungsten concentrates by sulfuric acid conversion-ammonium salt leaching

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School of Chemical Technology | Doctoral thesis (article-based) | Defence date: 2019-05-29
Degree programme
63 + app. 59
Aalto University publication series DOCTORAL DISSERTATIONS, 96/2019
Tungsten is considered as a strategic and critical raw material, due to its remarkable physical and chemical properties, wide industrial applications and non-substitutability. Ammonium paratungstate is the main intermediate product extracted from tungsten ores with metallurgical processes, intrinsically linking to the tungsten industry across all supply chain stages. An efficient and cleaner technology for producing ammonium paratungstate is crucial to the sustainable development of the tungsten industry. This work presents a novel process by the sulfuric acid conversion-ammoniacal ammonium carbonate leaching route. The complete conversion of tungsten concentrates in H2SO4 solutions can be achieved by controlling the sulfuric acid concentration and adding an oxidizing agent. The formation mechanism of the H2WO4 layer on unreacted tungsten particles is explained by isopolytungsten ions diffusion-tungsten acid deposition in the diffusion layer. The more difficulty of wolframite conversion than scheelite in H2SO4 solutions is attributed to the thermodynamics, especially the accumulation of Fe2+ and/or Mn2+ in the solutions. The kinetics of scheelite conversion in moderate H2SO4 solutions agrees with the shrinking core model under chemical surface reaction control. Subsequently, an ammonium tungstate solution is directly obtained by leaching converted products in ammoniacal (NH4)2CO3 solutions at 30 °C, with WO3 leaching yield of >99%. The transformation of calcium sulfates to carbonates influences the WO3 leaching yield by secondary reactions, which can be suppressed by an excess (NH4)2CO3 in solutions through the formation of more stable vaterite and calcite. The leaching agent can be recovered to restore the leaching system. Additionally, thermodynamic modelling of the CaSO4–H2O system is carried out to better understand the thermodynamic property of CaSO4 solution and facilitate the solutions cycle and scaling prevention, as well as the upcoming CaSO4–H2SO4–H2O system. The critically revaluated solubility data were assessed with the NPL Pitzer model by MTDATA software to optimize the Pitzer parameters. The obtained model predicts very well the CaSO4–H2O system up to 300 °C, and agrees with most published solubility data.This work makes it possible to produce ammonium paratungstate cleanly and economically, featuring circulation of the leaching reagents and bypassing the conversion of Na2WO4 to (NH4)2WO4, which will hopefully be adopted in industrial practices.   
The research presented in this thesis was carried out in the Alkaline Metallurgy research group at Central South University for the experimental part and in the Metallurgical Thermodynamics and Modeling (TDM) research group at Aalto University for the thermodynamic part.
Supervising professor
Li, Xiaobin, Prof., Central South University, P.R. China
Lindberg, Daniel, Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland
Thesis advisor
Taskinen, Pekka, Prof., Aalto University, Finland
Li, Xiaobin, Prof., Central South University, P.R. China
Sippola, Hannu, Dr., Aalto University, Finland
scheelite, wolframite, sulfuric acid, ammoniacal ammonium carbonate, conversion, leaching, aqueous solution recycling, thermodynamic modelling
Other note
  • [Publication 1]: Xiaobin Li, Leiting Shen, Qiushen Zhou, Zhihong Peng, Guihua Liu, Tiangui Qi. Scheelite conversion in sulfuric acid together with tungsten extraction by ammonium carbonate solution. Hydrometallurgy, 2017, 171: 106-115.
    DOI: 10.1016/j.hydromet.2017.05.005 View at publisher
  • [Publication 2]: Leiting Shen, Xiaobin Li, Qiushen Zhou , Zhihong Peng, Guihua Liu, Tiangui Qi, Pekka Taskinen. Wolframite conversion in treating a mixed wolframite-scheelite concentrate by sulfuric acid. JOM, 2018, 70(2): 161-167.
  • [Publication 3]: Leiting Shen, Xiaobin Li, Qiushen Zhou, Zhihong Peng, Guihua Liu, Tiangui Qi, Pekka Taskinen. Kinetics of scheelite conversion in sulfuric acid. JOM, 2018, 70(11): 2499-2504.
    Full text in Acris/Aaltodoc:
    DOI: 10.1007/s11837-018-2787-2 View at publisher
  • [Publication 4]: Leiting Shen, Xiaobin Li, Qiushen Zhou, Zhihong Peng, Guihua Liu, Tiangui Qi, Pekka Taskinen. Sustainable and efficient leaching of tungsten in ammoniacal ammonium carbonate solution from the sulfuric acid converted product of scheelite. Journal of Cleaner Production, 2018, 197: 690-698.
    Full text in Acris/Aaltodoc:
    DOI: 10.1016/j.jclepro.2018.06.256 View at publisher
  • [Publication 5]: Leiting Shen, Hannu Sippola, Xiaobin Li, Daniel Lindberg, Pekka Taskinen. Thermodynamic modeling of calcium sulfate hydrates in CaSO4–H2O system from 273.15 K to 473.15 K with extension to 548.15 K. Journal of Chemical and Engineering Data, publishing on-line.
    DOI: 10.1021/acs.jced.9b00112 View at publisher