Precipitation transformation of rare earth sulfate into chloride with p-dodecylphenoxy carboxylic acids

Abstract

Methods for transforming rare earth (RE) sulfate into chloride mainly include extraction process with organophosphonic mono-acids or aliphatic acids and precipitation process with ammonium bicarbonate (NH4HCO3). In this paper, alkylphenoxy carboxylic acids(HAs) of p-dodecylphenoxy acetic acid (HA-I), p-dodecylphenoxypropanoic acid (HA-II) and p-dodecylphenoxybutyric acid (HA-III), which were liquid at room temperature were synthesized and characterized. The precipitation mechanisms of RE elements with the HAs were investigated and the HA/RE molar ratios of the solid complexes were determined as 3:1 by equi-molar series method which accord with the principle of charge balance. Applicability of HAs for the transformation of RE sulfate from concentrated sulfuric acid roasted RE concentrate into chloride via precipitation method was discussed. 100% HA-II was selected as the liquid organic precipitant without dilution of volatile solvent soracceleration of phase separation by phase-modifiers. The RE sulfate solution can be precipitated by HA-II after neutralization with liquid NaOH and stripped with concentrated HCl at room temperature. High concentration of RE chloride of 218.1 g/L with low residue of sulfate radical of 0.536 g/L was obtained. The residual organic precipitant in the raffinate solution was tested to be lower than 8 mg/L at 25 °C and the chemical oxygen demand (COD) in wastewater was less than 50 mg/L.