Comparison between Batch and Continuous Reactor Systems for Biosorption of Neodymium (Nd) using Microalgae
Rare earth metals (REMs) are a series of 17 elements, for instance, neodymium is much less common than lanthanum or cerium and a very large amount of mining is needed for small amounts of neodymium. On the other hand, recovery of REMs is interesting due to its high market prices along with various industrial applications. Waste of electric and electronic equipment (WEEE), or electronic waste (e-waste) is a potential and important secondary source of base metal, precious metal and REMs. In the last decade, recovery of metals using bioprocess technology has been one of the most promising technologies. Biosorption represents a biotechnological innovation as well as a cost effective excellent tool for the recovery of REMs from aqueous solutions. In this study, Nd was removed from a mixed leachate solution derived from neodymium magnets in batch and continuous sorption systems by using dried green microalgae (Chlorella vulgaris). The maximum Nd uptake (q=157.21 mg/g) was determined at pH 5 with a biosorbent dosage of 0.5 g/L and an initial neodymium concentration in the mixed leachate solution was 250 mg/L at 35 °C in the batch test. Therefore Chlorella vulgaris was found to have a good potential in its role as a biosorbent for neodymium out of a mixed leachate solution derived from neodymium magnets. The use of the studied biosorbent in the removal of Nd in continuous mode was successful. Due to the slow kinetics of Nd sorption onto Chlorella vulgaris, the sorption capacity in batch assays was higher than that in continuous assays.