Associated Rare Earth Elements Extraction from Phosphogypsum by Carbonate-Alkaline Method

Problem Statement (Relevance). At least 500 million tonnes of phosphogypsum (by-product of phosphoric acid and phosphate fertilizer technology) are in Russian dumps. In most cases, it is common to store phosphogypsum by open method, which inevitably leads to environmental pollution, disturbance of the natural landscape and loss of valuable components. According to literary data, the level of phosphogypsum utilization today is approximately 1 %. Phosphogypsum consists of from 0.1 % to 0.9 % of the rare earths, consequently it is an available secondary source of these metals. Objective is an increasing of phosphogypsum processing level by carbonate-alkaline method due to obtainining an additional rare earth product. Methods Applied. Chemical composition of phosphogypsum samples and productive solutions was determined by ICP analysis, the morphology of phosphogypsum – by SEM, and the rare earth metal sediments identification – by XRF analysis. Originality. Carbonate-alkaline method approbation was carried using different originated phosphogypsum samples (formed from phosphorite and apatite; obtained by dihydrate and semi-hydrate technology; dumped and freshly obtained). Result. Conversion level of calcium sulphate into calcium carbonate was determined for technogenic phosphogypsum samples and was 96.4–98.4%; based on experimental data obtained degree of rare earth metals extraction into solution was 56.8–68.2% for sum rare earth; variants of further rare earth metals extraction from leaching solution by sedimentation with oxalic or phosphoric acid were proposed. Practical Relevance. Scientific results can be applied for development of phosphogypsum utilization technology by carbonate-alkaline method.