Pretreatment of low-grade shredded dust e-waste to enhance silver recovery through biocyanidation by SAE1.

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Shredded dust originated during mechanical dismantling of waste electrical and electronic equipments (WEEEs) is enriched source of some valuable metals which might be lost as unworthy waste. Composition analysis of shredded dust printed circuit boards (PCBs) revealed the presence of 12.75 mg g  copper (Cu) and 10.34 mg g silver (Ag) along with some other metals (Fe, Ni, and Au). Low concentration of precious metal, such as gold (Au i.e., 0.04 mg g) classified this shredded dust as low-grade scrap. Despite low concentration of Au this e-waste can be considered as potential "secondary ore" to recover other valuable metals like Ag. To improve the efficiency of Ag bioleaching using SAE1, pretreatment of e-waste was done using cost-effective ferric chloride (FeCl) chemical lixiviant. The concentration of FeCl lixiviant was optimized to recover Cu metal prior to bioleaching process. Bioleaching of Ag was done under optimized conditions by SAE1 using 100 mL Luria Broth (LB) medium, 5 g L glycine, pH 9, temperature 30 °C and 150 rpm. 95% Cu was recovered with 1% FeCl prior to bioleaching. Ag solubilization was increased for treated e-waste (36%) as compared to untreated e-waste PCBs (25%). Prerecovery of Cu enhanced Ag bioleaching, as available cyanide was utilized by Ag metal. Therefore, this study provides an economical hybrid method to enhance retrieval of precious metal (Ag) by SAE1 with economic and ecofriendly redox lixiviant even from low-grade e-scrap.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02977-4.