Recovery of Phosphorus from Modified Steelmaking Slag with High P2O5 Content via Leaching and Precipitation

• Published in: ISIJ International 2018/05/15, Vol.58(5), pp.833-841
• Main Authors: Du, Chuan-ming, Gao, Xu, Ueda, Shigeru, Kitamura, Shin-ya
• Format: Article
• Language: English
• Subjects: citric acid; K2O modification; phosphorus recovery; selective leaching; steelmaking slag
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.ISIJINT-2017-454

The P contained in steelmaking slag is regarded as a potential phosphate source, especially with regard to slag with high P2O5 content, which is generated from the utilization of high P iron ores. If P can be efficiently extracted from slag, the obtained P can be used as a phosphate fertilizer. Moreover, the remaining slag can be recycled inside the steelmaking process. Compared with other phases, the P-condensed C2S–C3P solid solution in slag is more easily dissolved in water; therefore, selective leaching was applied to recover P from slag with high P2O5 content. In this study, the effect of K2O modification on P dissolution in the citric acid solution was investigated, and subsequently, a process for extracting phosphate product from the leachate, via precipitation, was explored. It was determined that K2O modification promoted dissolution of the solid solution, resulting in a higher dissolution ratio of P. By modification, the majority of the solid solution was dissolved at pH 6, and other phases remained in residue, indicating that a better selective leaching of P occurred. As the pH decreased, the dissolution ratios of both P and Fe increased. Following leaching at pH 5, a residue with a higher Fe2O3 content and lower P2O5 content was obtained. When the pH of the leachate increased, the dissolved P in the aqueous solution was precipitated. Through separation and calcination, a phosphate product with a P2O5 content of 30% was obtained, which has the potential to be used as a phosphate fertilizer.