Synergistic recovery of Pr, Eu, and Ce from gold mine tailings using bioleaching and oxalic acid pretreatment

Mining activities produce a significant amount of gold mine tailings (GMT) rich in rare earth elements. Despite this, little information is available regarding the effective extraction of these precious elements from GMT. We describe a novel strategy for removing Pr, Ce, and Eu from GMT using Acidithiobacillus thiooxidans combined with a pretreatment step. For the pretreatment, GMT was exposed to 2 M oxalic acid for 6 h at 90 °C and 500 rpm at a liquid-to-solid ratio of 60 mL/g, which selectively removed iron and enhanced rare earth element bioavailability. As a result, GMT powder was introduced during the logarithmic growth phase of A. thiooxidans to maximize the bacterial activity and acid production during bioleaching. Surface modifications revealed by structural analysis validated the progress of the bioleaching procedure. Based on kinetic modeling, it was determined that chemical reactions determined the rate-limiting stage. The results showed a notable improvement in the recovery of rare earth elements after iron removal, with recovery of Pr, Ce, and Eu increasing by 24.4%, 14.4%, and 9.1%, respectively. A promising approach to resource recovery in mining operations could be achieved by integrating pretreatment and bioleaching for enhancing the recovery of rare earth elements from GMT.