Seeing Environmental Issues as a Source of Rare Earths

Abstract

Rare Earth Elements (REE) are one of the most strategical resources and have become the main interest of many developing and developed nations in the past seventy years, and its importance tend to increase further. New technologies demand these elements and some of them are critical, with high demand and limited supplies, amongst them are Y, Nd, Eu, Dy and Tb [1], [2]. In the state of Minas Gerais (Brazil), the mining industry plays a crucial role in the economy, whose main products are notably lead, zinc, gold, niobium, and copper. Furthermore, Minas Gerais has strategically important Rare Earth Element (REE) ores, whereas production is still incipient [3]. Acid Mine Drainage (AMD) is a continuous natural leaching process that may contain variable concentrations of REE, it occurs in some sites around the world [4]-[6]. One of these sites is located in a closed uranium mine in Caldas, Minas Gerais, Brazil, where the REE concentrations in AMD are about 130 mg L-1 [7], [8]. The AMD waters are treated with lime with a maximum flow rate of 300 m 3 h-1 , and the neutralization of the waters consumes about 12 t of lime per day and generates enormous amounts of precipitate [9]. The recovery of the RRE can yield in approximately 936 kg daily. Our research team is studying two ways of recovering the REE present in the AMD waters, using ionic resins and co-precipitation with iron, aluminum and manganese oxihydroxides. Results show that REE can be successfully recovered by both methods with high efficiency. Specifically, the use of a cationic resin in batch experiments can recover up to 90% of the REE present in the feed solution at pH = 1.3. The co-precipitation with aluminum and manganese oxihydroxides at pH = 8 can recover up to 95% of the REE present in a laboratory AMD, producing a solid phase with ±14% of REE oxides. Further studies focus on optimizing the processes and on concentrating the REE after the recovery, specifically the elution of the resins and the leaching of the precipitates.