Solidification treatment of rare earth tailings by a renewable biological cementation method

Abstract

Rare earth mineral is a kind of polymetallic co-associated mineral, in addition to containing iron, rare earth, niobium, and a certain amount of thorium and uranium. The tailings after wet leaching of rare earth are both a kind of hazardous waste and a kind of potential strategic resource. Therefore, the treatment and disposal of rare earth tailings should not only achieve the purpose of risk control, but also cannot affect the subsequent reuse. Microbially induced calcium carbonate precipitation (MICP) as an environmentally friendly biological cementation technique, it can solidify the tailings and stabilize the polluting elements. The valuable elements in the tailings can be further recovered after the sample solidified by MICP is decomposed by acid. In this study, a strain of urease-producing bacteria (K-1) with excellent performance was screened by dilution culture method from rare earth tailings. Through physiological and biochemical analysis and 16 s rDNA analysis, the strain K-1 belonged to the genus Lysinibacillus. In the mold, strain K-1 was used to induce the formation of calcium carbonate for cementing rare earth tailings, the strength of the cured body after cementation can reach 1.73 MPa after 28 d. There was a significant reduction in the leaching of heavy metals and radionuclides in the cured body. The results obtained from the scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated that strain K-1 induced a large amount of calcium carbonate, whose crystal forms are vaterite and calcite. The calcium carbonates cemented the rare earth tailings together for tighter texture and reduced porosity. The X-ray fluorescence (XRF) analysis of the rare earth tailings before and after solidification and after acid decomposition showed that the loss of rare earth elements in rare earth tailings after MICP treatment was small. Moreover, the cured body was relatively easy to dissociate, which facilitated the recovery and reuse of potential valuable elements in the tailings. This study provides technical support for the long-term storage of rare earth tailings and the sustainable development of the rare earth industry.