Treatment of monazite by organic acids I: Solution conversion of rare earths
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Â© 2017 Elsevier B.V. In the present study, the potential for using organic acids to enhance the dissolution of monazite (nominally CePO 4 ) was examined. Oxalic acid was found to release a significant amount of phosphorus ( > 30%) at pH â‰¤ 1.3 and room temperature over periods of up to 72 h. However, only very small proportions of rare earths were present in solution. The lower than expected iron level present in solution (and thus dissolution of iron oxides) displays the selectivity of the process given the established ability of oxalic acid to complex iron. Analysis of the solids determined that the rare earths were re-precipitating as oxalate salts. This is significant as rare earth oxalates have been shown to be amenable to dissolution. Leach tests conducted over 168 h displayed slowing of the reaction to the point where little further leaching was occurring. This was confirmed to be due to oxalate consumption and not passivation via the re-precipitation of the oxalate species. While a slight increase in temperature (25 to 45 Â°C) had little impact, elevation to â‰¥ 65 Â°C greatly accelerated the reaction achieving similar results in only 10 h. However, iron dissolution also increased markedly. Further temperature elevation to 85 Â°C significantly increased the dissolution of iron to the detriment of phosphorus release. This is a significant consideration in terms of both extraction efficiency and reagent consumption. This process presents the opportunity to remove the greatest hazards, both safety and environmental, and decrease the energy and potentially reagent requirements for monazite treatment. The second paper of this series discusses the subsequent stage of processing the treated monazite for rare earth extraction.
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Lazo, D.; Dyer, Laurence; Alorro, Richard; Browner, Richard (2018)© 2018 Elsevier B.V. In the present study, the second stage of a sequential extraction method of rare earths from monazite is discussed. The high cost and environmental impact of the conventional extraction processes of ...
Silicate, phosphate and carbonate mineral dissolution behaviour in the presence of organic acids: A reviewLazo, D.; Dyer, L.; Alorro, Richard (2017)Researchers in the field of geoscience have identified several effects on the stability of the surrounding minerals caused by naturally occurring solution species. Organic acids and their conjugate salts have been shown ...
Interactions of phosphate solubilising microorganisms with natural rare-earth phosphate minerals: a study utilizing Western Australian monaziteCorbett, Melissa; Eksteen, Jacques; Niu, Xi-Zhi; Croue, Jean-Philippe; Watkin, Elizabeth (2017)Many microbial species are capable of solubilising insoluble forms of phosphate and are used in agriculture to improve plant growth. In this study, we apply the use of known phosphate solubilising microbes (PSM) to the ...