Rare earth elements in raw materials and products of the phosphate fertilizer industry in South America: content, signature, and crystalline phases

Abstract

Phosphate ores are well-known for containing rare earth elements (REE) in a wide range of contents. The presence of REE in phosphate (P) products may enhance plant and animal development. Yet, our current understanding of the role of different P products as carriers of REE to soils is still incipient, especially regarding the extent to which the original REE content in raw materials remains in their respective products and the changes in crystalline phases associated with the phosphate ore processing. This study evaluated phosphate concentrates used as raw materials in major phosphate industries in South America as well as final products – including P fertilizers, di-calcium phosphate, and phosphogypsum – in order to characterize their REE contents, signatures, and REE-carrying crystalline phases. The results showed that the REE content in raw materials and products from the phosphate industry in South America is highly variable. Phosphorites from Bayóvar Phosphate Mine showed the lowest REE content among the studied raw materials (~ 70 mg kg− 1). Considering materials of igneous origin, the phosphate concentrate from the Catalão Minerochemical Complex presented the highest total REE content (∑ REE up to 16,650 mg kg− 1) and the highest concentrations of light REE (∑ LREE/∑REE ~ 98%), whereas those from the Araxá Minerochemical Complex, especially materials from the F4 Mine, presented the highest contents of heavy REE (∑ HREE ~ 1200 mg kg− 1). A great variety of mineral phases was found not only in phosphate concentrates but also in final products, with the apatite-group appearing as the main REE-carrying crystalline phase. The REE contents and composition in the final products were generally strongly influenced by their respective raw materials, resulting in a strong match of REE signatures, which reinforces the usefulness of REE signatures as accurate tools for tracing the origin and provenance of final products of the P fertilizer industry