Towards zero-waste valorisation of rare-earth-containing industrial process residues: a critical review

Phosphogypsum as a construction material

The story of rare earth elements (REEs): Occurrences, global distribution, genesis, geology, mineralogy and global production

Recovery of rare earth elements from phosphate rock by hydrometallurgical processes - A critical review

Phosphogypsum (PG: CaSO4·2H2O) is a waste product generated by the phosphate industry. World production of this waste exceeds 200 million tonnes per year. PG, discharged into the sea, watercourses or in wilderness stocks, contains toxic elements harmful to ecosystems and human health, including heavy metals and radionuclides, and there is therefore a concern regarding environmental impacts. The concentrations of these elements vary between the regions and the processes used, all of which require particular and specific follow-up after the release of PG and during its use. Phosphogypsum is used in agriculture for soil amendment or as fertilizer, as well as in the brick and cement industry, and in road construction.

Phosphogypsum: potential uses and problems – a review

Phosphogypsum (PG) is a residue of the phosphate fertilizer industry that has relatively high concentrations of harmful radioactive materials. The reduction in concentration of the radionuclides from PG was investigated. The removal process is based on leaching of radionuclides using suitable organic extractants. The studied radionuclides were 226Ra, 210Pb, 238U and 40K. The factors affect the leaching process such as type of leaching materials, contact time, concentration of the desired solvent, liquid to solid ratio, and temperature were studied. Based on the experimental results, about 71.1, 76.4, 62.4, and 75.7% of 226Ra, 210Pb, 238U and 40K respectively were successfully removed from the PG. The reduction in the concentration of radionuclides was accompanied by reduction in the concentration of rare earth elements (∑REE) equals to 69.8%. Using the desired organic extractant under optimum conditions for treatment of the PG waste leads to obtain a decontaminated product that can be safely used in many industrial applications.

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Treatment of phosphogypsum waste using suitable organic extractants

Preparation of uncontaminated phosphogypsum (PG) produced by wet-process phosphoric acid plant for its safe use in industry was investigated. PG is mainly composed of calcium sulfate and contains enhanced natural radioactivity. The activity of 238U, 226Ra, 210Pb, 232Th, and 40K in PG samples was measured by γ-ray spectrometry. The values of radiation hazard indices, calculated to evaluate the environmental impacts of PG samples, were higher than the permissible safe levels. Therefore, the PG should be treated before use in agriculture and/or building materials. This involves the leaching of PG with organic extractant such as TOPO in kerosene. Reduction in the radionuclide concentration was accompanied by a decrease in the concentration of total rare earth elements (ΣREE). Extraction treatment of PG waste under optimum conditions allows preparation of a decontaminated product that can be safely used in many branches of industry.

M. M. Ali

Papers

Treatment of phosphogypsum waste using suitable organic extractants

Radiological characterization and treatment of contaminated phosphogypsum waste