Extraction of phosphorus from steelmaking slag by selective leaching using citric acid

Takayuki Iwama, Chuan ming Du, Xu Gao, Sun joong Kim, Shigeru Ueda, Shin ya Kitamura

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


An approach to leach phosphorus from slag was applied to commercial fertilizers made from steelmaking slag, which has relatively coarse grains. After leaching at pH 3 with citric acid, about 60% of the P2O5 had been dissolved, but the dissolution ratio of MnO was less than 30%. The separation index, calculated from the dissolution ratio of P2O5 divided by that of MnO, was 2.1. In addition, the dissolution ratio of the solid solution was 90% or greater. However, 25% or more of the matrix was also dissolved. To improve the selectivity of leaching, the mineralogical phases comprising the matrix were synthesized, and their leaching behaviors were investigated. The results indicate that it is important to eliminate the glassy phases and to change the valence state of iron in its oxides to 3+ to suppress the dissolution of the matrix. Finally, a synthesized slag, containing only Fe2O3 as the only iron oxide, was prepared by slow cooling, and leaching tests were conducted. About 99% of the P was dissolved, but the dissolution ratio of Mn was less than 10%. In addition, the separation index increased to 14.1. In this case, the dissolution of the matrix was suppressed, and almost all the solid solution phase was dissolved.

Original languageEnglish
Pages (from-to)1351-1360
Number of pages10
JournalISIJ International
Issue number7
Publication statusPublished - 2018 Jul 15


  • Citric acid
  • Fertilizer
  • Leaching
  • Phosphorus
  • Steelmaking slag


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