U AND REE RECOVERY FROM PHOSPHATES IN THE PHILIPPINES

摘要

Phosphate-bearing rocks are an important mineral resource and are utilized as raw material in the production of phosphate-based fertilizer. Phosphate-based fertilizer is the dominant form of fertilizer produced and consumed in the Philippines. The Philippines itself has no domestic phosphate ore deposits, thus, mined phosphate-bearing rock is imported from abroad as raw material for fertilizer production. In addition to being an important phosphate source for fertilizers, phosphate-bearing rock is also known to contain naturally occurring radionuclides and rare earth elements. Chemical analysis of this material has shown that it contains 66-145 μg/g uranium, 1-20 μg/g thorium, 108-1085μg/g rare earth elements and several other elements. Historical results have shown that during the wet phosphoric acid process for phosphate fertilizer production about 86% of the uranium reports to the phosphoric acid, while the majority of the rare earth elements and other elements report to the byproduct waste phosphogypsum. Studies have shown that NPK (Nitrogen-Phosphorous-Potassium) fertilizers may have concentrations of uranium at levels as high as 228 μg/g, considerably greater than the global average concentration of uranium in soil of 0.3-11μg/g. Application of uranium-bearing phosphate fertilizers to soils for agricultural purposes may result in a source term of uranium to the local biota. This is dependent on the bioavailability of the uranium in the fertilizer.With the primary objective of recovering these elements of interest (U, REEs) to reduce potential environmental and human health risks, the Philippine Nuclear Research Institute (PNRI), in collaboration with the leading phosphate fertilizer producing company in the country, Philippine Phosphate Fertilizer Corporation (PHILPHOS), is developing technology to recover uranium from phosphoric acid (UxP) and is researching innovative approaches to recover rare earth elements from phosphogypsum. In conjunction with the technical cooperation programme of the International Atomic Energy Agency and financial assistance from local funding agencies, the Philippines Council for Industry Energy and Emerging Technology Research and Development and National Research Council of the Philippines, laboratory-scale solvent extraction technology using the D2EHPA-TOPO process was developed to extract and concentrate uranium from phosphoric acid. Batch experiments on the uranium recovery process from pretreatment of raw phosphoric acid to precipitation of uranium yellow cake provided basic understanding of the extraction process and has generated and optimized the operating parameters in each process step. In 2018, PNRI has embarked in the next step of the UxP activity cycle by developing the first scaled-up continuous uranium extraction facility in the country. Along with this, PNRI has realized the great potential for recovery and extraction of rare earths and other critical elements from the accumulated 9 Million tons (Mt) of by-product phosphogypsum at the PHILPHOS site. Further research and exploration activities will be conducted to estimate the quantity and quality of phosphogypsum with high confidence in terms of its rare earth element, as well as, its radionuclide content. This presentation will present on the results achieved to date and discuss on-going collaborative work to ultimately advance the process to full industrial scale.