Isolation of rare earth element phosphate precipitate in the nitrophosphate process for manufacturing of fertilizer

Mahmood Alemrajabi, Kerstin Forsberg, Kivanc Korkmaz, Åke Rasmuson

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

In the present study, the recovery of rare earth elements (REE) in the nitrophosphate process of fertilizer production is investigated. The apatite has been recovered from iron ore tailings by flotation. After digestion of apatite in concentrated nitric acid, Ca(NO3)2.4H2O is first separated by cooling crystallization and then the REEs are recovered by precipitation. Optimum conditions in these steps have been determined in a previous study. The precipitate mainly consists of CaHPO4.2H2O and REE phosphates. In the present study, selective dissolution and re-precipitation have been studied in order to obtain a precipitate that is more concentrated in REEs. The precipitate was selectively dissolved in nitric and phosphoric acid at different acidities (pH 6 to 0) with the liquid /solid ratio of 100 mL/g. It is shown that most of the CaHPO4.2H2O and other calcium containing compounds will be dissolved at pH 2 while the REE phosphates are not dissolved above a pH of approximately 2. Thus, by partial dissolution of the REE precipitate at pH 2.5 most of the solid calcium phosphates will be dissolved and the remaining solid phase, which is more concentrated in REEs, can be filtered off as a fairly concentrated REE solid mass and the liquor can be recycled back to recover more P nutrients. Alternatively, the REE enriched precipitate was dissolved completely in nitric acid and re-precipitated again by addition of ammonium hydroxide to pH 1.2. A chemical equilibrium software, MEDUSA (Puigdomenech, 2013) has been used to evaluate the experimental results and to estimate the optimum conditions for selectively dissolving the precipitate.

Original languageEnglish
Title of host publicationIMPC 2016 - 28th International Mineral Processing Congress
PublisherCanadian Institute of Mining, Metallurgy and Petroleum
ISBN (Electronic)9781926872292
Publication statusPublished - 2016
Externally publishedYes
Event28th International Mineral Processing Congress, IMPC 2016 - Quebec City, Canada
Duration: 11 Sep 201615 Sep 2016

Publication series

NameIMPC 2016 - 28th International Mineral Processing Congress
Volume2016-September

Conference

Conference28th International Mineral Processing Congress, IMPC 2016
Country/TerritoryCanada
CityQuebec City
Period11/09/1615/09/16

Keywords

  • Apatite
  • Precipitation
  • REE
  • Selective dissolution

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