Estonian Paleozoic shelly phosphorites: a continent-scale resource for phosphorus and potential for rare earth elements

Global phosphate demand is rising due to growing population and associated food demand. World consumption of P₂O₅ is forecasted to increase to 46 million tonnes in 2020. Phosphate deposits and occurrences are widely distributed in Europe. However, very little phosphorus is produced in the EU to satisfy the growing demand for fertilizers. As a consequence, the European countries are net importers of phosphate, with an average of 4 M tonnes of natural phosphate-rich material imported per year. The European Commission has listed phosphates among critical raw materials with a significant supply risk. Other elements pertaining to this list can also be recovered from the phosphate deposits, as the rare earth elements (REE) and fluorspar (Goodenough et al., 2016). Estonia holds, the largest in Europe, unused sedimentary phosphate rock reserves, about 3 Billion metric tons (ca 819 Million metric tons of P₂O₅; Bauert & Soesoo, 2015). The Estonian shelly phosphate rocks are friable or weakly cemented bioclastic quartz sandstones deposited in shallow marine shoreface environment with a variable content of phosphatic brachiopod shells detritus. These sediments formed approximately 488 million years ago. The content of fossil shells ranges from 5–10% to 80–90 vol%. Brachiopod shells and enriched detritus contain up to 35–37% P₂O₅. Recent studies have revealed relatively enriched but variable content of REEs in these phosphate shells. For example, La in single shells ranges 50 to 550 ppm, Ce – 40–1200 ppm, Pr - 4–170 ppm, Nd – 20–800 ppm, Sm – 3–180 ppm, Gd – 4–135 ppm. The total REEs can reach 3000 ppm, however, in average they are ranging between 1000 and 2000 ppm.  At the moment the Estonian phosphorites cannot regarded as an economic REE source, but considering REEs as a co-product of phosphorous production, it may economically be feasible. Large variability in REE concentrations results probably from post-depositional diagenetic processes but its geological controls need further study. Although the raw ore enrichment (separating shells from sandstone) and phosphorous extraction are technologically easy, the technology for REE extraction in parallel with the phosphorous acid production needs further developments. Relying on the vast phosphorite reserves in Estonia, the critical nature of both the phosphorus and REEs for the European economy and security, it may be a worthwhile opportunity to develop these resources into production at the European scale. 

REFERENCES

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2. Bauert, A. Soesoo. Shelly phosphate rocks of Estonia, in Strategic raw materials of Estonia, Rakvere Conference, Rakvere, Estonia, (2015).