Biosorption of Ag+ and Nd3+ from single- and multi-metal solutions (Ag+, Nd3+, and Au3+) 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 Nd3+ 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+, Nd3+, Au3+) was also investigated. Maximum removals were found as 174.6 +/- 4.83 mg/g for Ag+, 239.7 +/- 3.39 mg/g for Nd3+ by dried algae, and 161.6 +/- 18.2 mg/g for Ag+, 296.8 +/- 30.54 mg/g for Nd3+ 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 Nd3+ decreased when there were co-ions present in the solution. Biosorption of Au3+ was affected depending on the experimental conditions in the case of multi-metal solutions.

Automated summary

The study found that using Chlorella vulgaris for the biosorption of Ag+ and Nd3+ in e-waste has high removal efficiency. Both living and dried forms of the algae can rapidly adsorb these valuable elements, with significant amounts of biosorption completed within a short period of time.