Biosorption of Ag and Nd from single- and multi-metal solutions (Ag, Nd, and Au) by using living and dried microalgae

There is an increasing need for the investigation of recovery techniques for valuable elements, especially for the growing waste streams. This study focuses on the biosorption of commonly found valuable elements in e-waste: Ag and Nd from aqueous solutions by using living and dried forms of Chlorella vulgaris. Optimization of the processes was conducted by changing the process parameters. In addition, biosorption from multi-metal solution (with Ag, Nd, Au) was also investigated. Maximum removals were found as 174.6 ± 4.83 mg/g for Ag, 239.7 ± 3.39 mg/g for Nd by dried algae, and 161.6 ± 18.2 mg/g for Ag, 296.8 ± 30.54 mg/g for Nd by living algae. Both processes were very fast, representing 60 and 5–10 min during which a significant amount of the biosorption was completed for dried and living algae, respectively. FTIR and SEM–EDS showed that the algae were able to sorb the elements. Pseudo-second-order kinetics fit better to all processes. Freundlich model suited to the dried algae process, while the linear model fit to living algae process. The biosorption efficiency of Ag and Nd decreased when there were co-ions present in the solution. Biosorption of Au was affected depending on the experimental conditions in the case of multi-metal solutions.