Adsorption and Fenton-like removal of chelated nickel from Zn-Ni alloy electroplating wastewater using activated biochar composite derived from Taihu blue algae

A novel biochar composite impregnated with alpha-Fe2O3 in hierarchical porous structures (Fe(III)-ABC-20) was synthesized by means of pyrolysis combining with KOH activation using the yearly bloomed Taihu blue algae as resources. It was found that the biochar activated by KOH obtained the specific surface area of 1657.8 m(2) g(-1), nearly 92.6 times larger than that of the biochar without modification (17.9 m(2) g(-1)). Meanwhile, abundant oxygen-containing functional groups such as -COOH, -OH, etc. are introduced onto the surface of algae biochar. Besides, Fe(III) was successfully loaded onto the porous structure of biochar from combined characterization of XRD, SEM, TEM, FTIR and XPS. Under the optimized operating conditions of pH at 6, Fe(III)-ABC-20 and H2O2 dosage of 0.5 g and 20 mM, adsorption equilibrium and Fenton-like reaction time at 20 and 60 min respectively, the biochar composite exhibited 98.87% removal rate of chelated nickel in electroplating wastewater. Moreover, the catalyst exerted better stability after four repeated experiments, as which still remained 93.26% of nickel removal. Meanwhile, electrochemical measurements revealed the presence of ligand to metal charge transfer (LMCT), indicating the promoting of Fenton-like reaction. Noticeably, degradation pathways of N,N,N',N'-Tetrakis(2-hydroxypropyl) ethylenediamine (EDTP), one of the main complexing agents according to the component identification using mass spectrum within electroplating wastewater are proposed. EDTP might be first degraded to 2-hydroxypropanal or 2-Aminoethyl(ethyl) amine, then further degraded to acetaldehyde or ethylene, and finally oxidized to CO2 and H2O. Therefore, the biochar composite developed here could provide a novel route for the resource utilization of blue algae and heavy metal removal in electroplating wastewater containing refractory complexing agent.