Electro-assisted adsorption of heavy metals from aqueous solutions by biochar

Electro-assisted adsorption was investigated for Pb2+, Cu2+ and Ni2+ removal using date seed biochar (DSB-Electro). Compared with pristine biochar, the results showed that DSB-Electro effectively increased the adsorption capacity of Pb2+, Cu2+ and Ni2+ by 21% to 94%. Significant differences were observed between Pb2+ and Cu2+ adsorption compared with Ni2+, which could be explained based on ion polarizing power. Under the same voltage, Ni2+ solution shows the highest electric conductivity; thereby more Ni2+ is transported to the biochar anode, giving them a greater chance to interact with the surface groups. Electro-assisted adsorption occurred rapidly as around 88% of Pb2+ and Ni2+ adsorbed within the first 3 h, while 96% of Cu2+ occurred within the first hour of contact. Reversing the polarity did not seem to cause significant desorption of the adsorbed ions as the amount released from reversing polarity was less than 38%, indicating that only a small fraction of the ions was held by the electrostatic charge introduced by the current. It was likely that the enhanced charge facilitated other adsorption mechanisms by bringing the ions in contact with the biochar initially via electrostatic force. Electro-assisted adsorption can improve the biochar economic feasibility for metals removal (particularly Ni2+) from industrial streams.