Sintering behaviour and sinter properties of phosphorite

Phosphorite is the main raw material used in the production of phosphorus in chemical industries. Given the decrease in the supply of high-grade phosphorite lump ore, an agglomeration process must be performed for the phosphorite concentrate after beneficiation. In this study, the mineralogy, granulation and sintering of phosphorite ores from Leshan, China, were investigated. Phosphorite comprises four main phases, namely, fluorapatite, hydroxylapatite, quartz and dolomite. Results showed that an increase in the proportion of nucleation particles in the phosphorite improved the granulation test results, whereas the addition of silica was detrimental to the growth of the granule size and the permeability of the bed. The addition of 3% water to the concentrate that contained approximately 8·3% free water was optimal for the mixture without silica, whereas the addition of 4% water was optimal for the mixture with silica. The yield of strong sinter increased with the increase in carbon dosage up to 7%, but decreased with further increase in carbon dosages. The P₂O₅ content in the sinter also followed the same trend with the yield. The addition of silica was detrimental for both the sinter yield and the grade. Ca₅(PO₄)₃F was identified as the main phase in the sinter. The formation of Ca₂MgSi₂O₇ increased along with the increase in temperature and silica content. The agglomeration mechanism for phosphorite sintering should include ‘sintering’ and ‘pelletising’ processes.