Response surface methodology (RSM) for optimization of silver biorecovery process from simulated silver electroplating wastewater using oil palm (elaeis guineensis) leaves extract as the reducing and stabilizing agents

Abstract

Oil palm (Elaeis guineensis) leaves extract is capable of acting as reducing and stabilizing agents to reduce and recover silver from simulated silver electroplating wastewater by chemical reduction method. First, Plackett-Burman design (PBD) was used to evaluate six factors that affecting silver biorecovery process. From the PBD analysis, only four factors were found to be significant. In order to maximize the biorecovery process, the significant factors were further optimized using response surface methodology (RSM). The optimum conditions were found to be 50% (v/v) of palm leaves extract, 1975 mg/L of initial silver ions concentration in wastewater, pH 7.5 of reaction medium and 70 °C of reaction temperature yielding 93.30% of silver being recovered. Characterization of the biorecovered solid particles revealed that elemental silver was successfully reduced and recovered from the wastewater with sizes ranging from 20 to 60 nm. On the other hand, characterization of the palm leaves extract revealed that hydroxyl and carboxyl groups compounds act as reducing agents to reduce silver ions into zero-valence silver atoms while polysaccharides, carboxylic acids and proteins act as stabilizing agents to cap and stabilize the silver solid particles formed.