Sequential Extraction of Valuable Trace Elements from Bayer Process-Derived Waste Red Mud Samples

Bayer Process-derived red mud produced in China can be classified into three types according to chemical composition: high-iron diaspore red mud, low-iron diaspore red mud, and gibbsite red mud. The specific chemical and mineral compositions of three such typical Bayer-derived red mud samples have been characterized by XRF, ICP-MS, XRD, and SEM. These results, for example, indicate that GX (a high-iron diaspore red mud) contains more than 1015 μg/g lanthanides, 313 μg/g yttrium, 115 μg/g scandium, and 252 μg/g niobium and that HN (a low-iron diaspore red mud) has a high content of lithium (224 μg/g), whereas SD (a gibbsite red mud) possesses a very low valuable trace element content, except for gallium (59.4 μg/g). A sequential extraction procedure was carried out to assess the leachability of valuable trace elements in these three red mud samples. Applying the extraction procedure, 60% of the yttrium in GX and 65% of the lithium in HN could be extracted which would be of interest for trace metal recovery.