Selective recovery of phosphorus as AlPO4 from silicon-free CFB-derived fly ash leachate
Budhathoki, R., Väisänen, A., & Lahtinen, M. (2018). Selective recovery of phosphorus as AlPO4 from silicon-free CFB-derived fly ash leachate. Hydrometallurgy, 178, 30-36. doi:10.1016/j.hydromet.2018.03.025
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© 2018 Elsevier B.V. This is a final draft version of an article whose final and definitive form has been published by Elsevier B.V Published in this repository with the kind permission of the publisher.
The prospect of phosphorus (P) recovery from siliceous fly ash was investigated. The phosphorus content in the pristine fly ash was 1.21%. Obtaining pure phosphorus products from fly ash is very challenging because of high concentration of other elements, silicon (Si) at 17.3% being the major contaminant. The fly ash was fractionated with sieve size of 125 μm to concentrate the phosphorus in the small-size fraction, which also facilitated the removal of 78% of silica (Si) in the solid phase. The fractionated fly ash was treated with 8 M HCl in order to remove 98% of Si by aging (5 h) of leachate until precipitation of Si-gel, and a phosphorus-rich solution is obtained. Iron (Fe) is also considered an impurity in the recovered P-product and its co-precipitation is prevented by the use of EDTA as Fe-masking reagent at [EDTA]/[Fe] ratio of 1. About 70% of Fe is retained in the solution during recovery of phosphorus with aluminum at pH 4. Amorphous white solid was recovered containing 18.08% P, this is 15 times high than that in the pristine fly ash used as raw material in this recovery process. ...