Metals produced as by-products of the electroplating process pose threats to both human and environmental health, so it is important that they are removed from electroplating effluents. In this study, first, an innovative pH-independent anionic hydrogel composite (nFeMAH), synthesized via a facile method, was developed to remove cationic metals from aqueous solutions. The nFeMAH had a permanently negative surface with a ζ-potential between –35 and –45 mV, giving the nFeMAH a pH-independent property. With a high metal removal efficiency (90+% after 20 cycles of adsorption-desorption) and high magnetic separation efficiency (99%), the nFeMAH showed promise for cationic metal removal from electroplating effluents.

This study then paired the nFeMAH with a cationic hydrogel composite (nFeMCH...[ Read more ]

Metals produced as by-products of the electroplating process pose threats to both human and environmental health, so it is important that they are removed from electroplating effluents. In this study, first, an innovative pH-independent anionic hydrogel composite (nFeMAH), synthesized via a facile method, was developed to remove cationic metals from aqueous solutions. The nFeMAH had a permanently negative surface with a ζ-potential between –35 and –45 mV, giving the nFeMAH a pH-independent property. With a high metal removal efficiency (90+% after 20 cycles of adsorption-desorption) and high magnetic separation efficiency (99%), the nFeMAH showed promise for cationic metal removal from electroplating effluents.

This study then paired the nFeMAH with a cationic hydrogel composite (nFeMCH) via a facile method to develop a dual-function composite, and tested its ability to treat a simulated electroplating effluent, first in batch, then in a fluidized-bed column. For the batch treatment, both adsorption and desorption reached equilibrium within 30 minutes, showing the dual-function composite’s fast adsorption capacity. Its removal efficiency was also found to be pH-independent, and insignificant effect was found in the co-presence of monovalent ions (up to 10 meq/L). The composite was tested for reusability over six cycles, during which the treated effluent consistently met discharge standards and the reused adsorbent was confirmed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy to be highly stable.

The fast settling by gravity of the dual-function composite in batch motivated further studies of the material in a fluidized-bed column. Process variables such as feed flow, airflow, and adsorbent’s bed depth, which significantly control the metal removal efficiency of a fluidized-bed column, were optimized using response surface methodology (RSM), a statistical tool for process optimization. Under RSM optimized operation conditions, a maximum bed volume of 2.39 BV (597.5 mL) was treated and the discharge met China’s national standards. Therefore, in terms of practicality (fast removal, pH-independence, and high stability), the application of the dual-function composite in a fluidized-bed reactor has shown much promise for simultaneous post-electroplating removal of cationic and anionic metals.