Recovery of silver and neodymium from aqueous solutions by using microalgae

Electronic waste is one of the fastest growing streams of waste due to the increase in electronics production. Electronic waste consists of valuable elements that many governments and companies wish to extract from the waste. Although the increase in the usage of electronic devices is inevitable, eco-friendly and easily operated recovery methods for the valuable elements can be developed. In this study, characterization of electronic waste were carried out by using three different digestion methods; USEPA 3051, USEPA 3050B and Modified Microwave Digestion Method to define focus elements. The recovery of selected elements was carried out by using green microalgae, Chlorella vulgaris. Results showed that silver and neodymium were found as major precious metal and rare earth element, respectively. Biosorption capacities were found as 151.7 mg/g for silver, and 296.8 mg/g for neodymium. Bioaccumulation capacities refer to 161.6 mg/g for silver and 239.7 mg/g for neodymium. When there were multi-elements in the solution, the uptake capacities decreased and uptake of selected element can be limited via changing the process parameters. Variations in functional groups were observed that suggests binding of elements to the microalgae. Silver and neodymium were seen on algal surfaces as particles and scattered, respectively. Pseudo-second order kinetics fitted better both to biosorption and bioaccumulation for silver and neodymium. Freundlich isotherm model and linear model was found suitable for biosorption and bioaccumulation, respectively. In the context of sustainability, this study supports the achievement of United Nations Sustainable Development Goals by following Goals: 3, 9, 11, and 12.