Extraction of rare earths from ion-adsorption type rare earths ore by indigenous microbial community

Indigenous microbial community were employed after subculture in stirred and column bioleaching experiments involving ion-adsorption type rare earths ore (IAREO). The diversity and structure of microbial eukaryotic communities varied dramatically across culture compositions. Compared with czapek and sucrose medium, the community cultured by nutrient broth medium had a higher diversity, which was mainly composed of Zygosaccharomyces, Ustilago, Kodamaea, Malassezia, and Aspergillus. These microorganisms secrete organic acids such as citric acid, malic acid, gluconic acid, and itaconic acid, thereby providing effective coordination electrons through hydroxyl and carboxyl groups, among others. Stirred bioleaching experiments were conducted to investigate the impact of community, inoculum dosage, liquid-solid ratio, and time on the leaching efficiency. A concentration limitation phenomenon occurred during stirred bioleaching. When the inoculum dosage of the community cultured by nutrient broth medium was 90vol%, the liquid-solid ratio was 5.0, and the time was 60 min, the leaching rate of rare earths basically reached its maximum value. Specifically, the leaching rates of detectable La, Ce, and Y were about 94%, 94%, and 95%, respectively. The leaching efficiency and the three influencing factors all conformed to the Poly5 polynomial function, with variances above 0.99. Column bioleaching experiments were performed at a scale of 1 kg. The self-propelled low pH environment improved the leaching efficiency, resulting in a leaching rate of 98.88% for rare earths after 117 hours. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that the samples were mainly composed of quartz, kaolinite, orthoclase, muscovite, and zeolite, which were predominantly present in the form of lumps, flakes, rods, and small particles. After bioleaching, the wave intensity of quartz, kaolinite, orthoclase, and muscovite increased, while that of zeolite decreased significantly. A diminution in the number of fine particles indicates the dissolution of small quantities of clay minerals. Ultimately, the differentiated bioleaching mechanism of different forms of rare earths is discussed based on experimental phenomena.