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

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(-1) copper (Cu) and 10.34 mg g(-1) 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(-1)) 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 Pseudomonas balearica SAE1, pretreatment of e-waste was done using cost-effective ferric chloride (FeCl3) chemical lixiviant. The concentration of FeCl3 lixiviant was optimized to recover Cu metal prior to bioleaching process. Bioleaching of Ag was done under optimized conditions by Pseudomonas balearica SAE1 using 100 mL Luria Broth (LB) medium, 5 g L-1 glycine, pH 9, temperature 30 degrees C and 150 rpm. 95% Cu was recovered with 1% FeCl3 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 Pseudomonas balearica SAE1 with economic and ecofriendly redox lixiviant even from low-grade e-scrap.

Automated summary

Shredded dust from dismantling waste electrical and electronic equipments is a rich source of valuable metals, such as copper and silver. Through a hybrid method involving bioleaching and chemical lixiviant, precious metals like silver can be efficiently recovered, especially when copper is pre-recovered to enhance the bioleaching of silver.