Study on the selective leaching of low-grade phosphate ore for beneficiation of phosphorus and rare earths using citric acid as leaching agent

Abstract

In the study the organic/inorganic chemical leaching and enrichment technology were used for selective extraction of the dolomite which co-existed in the Zhijin low-grade phosphate ore for beneficiation phosphorous and rare earths (RE) by using citric acid as leaching agent. The effects of acid concentration, reaction time, reaction temperature, liquid/solid ratio, and particle size on P₂O₅ and rare earths grade and the recovery ratio of them were investigated. The results show that under the optimized experimental conditions (acid concentration 9%, reaction time 240 min, reaction temperature 40°C, liquid/solid ratio 50: 1, and ore particle size 0.18–0.125 mm) the P₂O₅ grade can be increased from 15.47 to 34.82%, and P₂O₅ recovery rate comes up to 88.02%. The rare earths are mainly enriched in the leaching residues. Meanwhile, the recovery rate of rare earths is 72.08%. ΣREO grade can be increased from 978.06 × 10^–4 to 1998 × 10^–4%. In addition, the reaction kinetics of the chemical reaction between citric acid and dolomite are also discussed, the results show that the leaching process is controlled by chemical reaction. The activation energy for leaching was found to be 36.6337 KJ mol^–1 and k₀ was 3.67×104 s^–1, and the rate of the leaching based on the chemical reaction-controlled process could be expressed as 1–(1–a)^1/3 = 3.67 × 10⁴e^–36.63/RTt. Compare to the conventional process, the method provided in this study not only has advantages including higher phosphate concentration and rare earth grade, and higher recovery rate, but also using less amount of chemicals. Meanwhile, the citric acid can be recycled, avoiding discharge wastewater.