Investigation of Alkaline Roasting Effect on the Recovery of Rare Earth Elements from Apatite Concentrate by Deep Eutectic Solvents

Extraction of Rare Earth Elements from apatite concentrate (Chador Malou Plant) via alkaline roasting and leaching with binary and ternary Deep Eutectic Solvents (DESs) was investigated. First, caustic roasting of concentrate was performed using NaOH at different temperatures, times, and weight ratios of NaOH-to-apatite to determine the optimum conditions. Leaching was done afterward by DESs on both as-received and roasted samples. The results demonstrated that roasting has a positive effect on REE recovery. At the conditions 700°C, 360 minutes and weight ratio of NaOH-to-apatite 0.5, recovery was the highest. At this temperature, irregularities of the apatite lattice reach to a maximum state thus, REEs can easily react with NaOH. Similarly, increasing the reaction time proportionate positively with the recovery. Due to the differences in specifications of REEs like electronegativity, ionic radius, and content in the sample, dissolution is relatively selective, where Dy, Gd, and Y are more dissolved. FTIR on DESs demonstrated that the stronger hydrogen bonds with greater dispersion were more abundant in the binary DES.