Abstract
Electroplating and metalworking industries produce enormous amounts of waste containing heavy metals in their effluents, leading to potential threats to biotic and abiotic life. According to regulation, heavy metal contamination must be kept within the regulated standard of a few parts per million, which has led to a recent pique in interest in the utilization of nanofiltration technology for metal recovery. The effect of feed pH, pressure, metal concentration, and oxidation of metal on the rejection of heavy metal ions using three commercial nanofiltration membranes (NF, NF90, and NF270) were explored. To begin, studies of electrolyte salts, contact angle, and water permeability were employed to characterize the nanofiltration membranes. A dead-end module was used to test the permeation and retention capacities of the nanofiltration membranes. The results showed an increase in salt rejection for all metals examined irrespective of the membrane, at a pH below the isoelectric point. For divalent cations, the NF90 membrane achieved recovery capacities of 97% and 85% at 200 ppm and 20 ppm respectively, as compared to the recovery observed for Ni2+, Cu2+, and Pd2+ ions by NF and NF270. At a pH 2, 20 ppm and 5 bar, the NF90 membrane had the highest percent recovery, but at a pH 3, the recovery was at 95%. Mono and divalent stable Ag+ and Ni2+ ions showed a comparatively high percent recovery as compared to Pd2+ and Cu2+, which have high molecular weight and charge effect. In the presence of chelating agents, the membrane surface area is increased, resulting in high divalent ion recovery capacities due to favourable interaction with the polyamide functional group of the membranes. This study establishes the significance of oxidation in high removal efficiency cation in varying experimental conditions.
Highlights
Metal pollution is becoming increasingly problematic to the environment due to metallurgical and mining processes
The aim of this study was to examine the performance of three commercial nanofiltration membranes under a variety of experimental conditions and oxidation states in order to better understand the relationship between solute rejection, pressure, and feed pH to guide in the selection of an ideal membrane for a specific process
NF90s’ pore radius is smaller than that of NF270, and again, their structures are slightly different despite having the polyamide thin film composite (TFC) [21,22]
Summary
Metal pollution is becoming increasingly problematic to the environment due to metallurgical and mining processes. Such industrial processes generate a large quantity of wastewater contaminated with a variety of heavy metals. Several processes, such as solvent extraction, distillation, evaporation, ion-exchange, chemical oxidation, chemical precipitation, and flotation have been developed and employed for the recovery and separation of metal in the industry [2]. Nanofiltration membranes are synthetic polymers with charged groups that may be used to separate charged metals from water. In terms of separation properties, nanofiltration is a pressure-driven membrane separation technology that sits in between reverse osmosis (RO) and ultrafiltration (UF).
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