Fenton-like Treatment Of Electroplating Wastewater Using Biochar Composite Derived From Taihu Blue Algae

The unprecedented development of the automobile,jewelry,aerospace market requirements intensively promoted the rapid development of the electroplating industry.Meanwhile,considering the massive discharge of electroplating wastewater much more attention and efforts should be put on the in-depth treatment so as to meet the national discharge standard for electroplating wastewater（GB201900-2008）.In this study,a novel biochar composite（Fe（Ⅲ）-ABC-20）was prepared by pyrolysis and modification of blue algae derived from Taihu Lake,featuring for the coupling of adsorption and heterogeneous Fenton-like reactions.Moreover,the synergistic effect could effectively remove heavy metals in electroplating wastewater added with complexing agent.Besides,the reusable composites would not only avoids the large-scale production of iron-containing sludge,but also broadens the resource utilization way out for Taihu blue algae.Compared with the homogeneous Fenton reaction,Fe（Ⅲ）-ABC-20 appears more economically feasible and environmentally friendly.The main conclusions of this study are as follows:（1）The specific surface area of Fe（Ⅲ）-ABC-20 prepared by KOH activation andα-Fe₂O₃loading using blue algae from Taihu Lake is as high as 1256.5 m²/g,with the pore volume as0.566 m3/g.Detected by titration and FTIR,the composites was rich in oxygen-containing functional groups,indicating that Fe（Ⅲ）-ABC-20 has a better ability to adsorb pollutants;while XRD,TEM,EDS,FTIR,XPS and other characterization methods jointly confirmed the successful loading ofα-Fe₂O_3.Finally,the reduction current of Fe（Ⅲ）was detected by electrochemical tests,and the existence of charge transfer（LMCT）between the ligand and the supported metal was verified,indicating that composite has the ability to be a Fenton-like catalyst.（2）Under the optimized operating conditions of initial pH at 2,H₂O₂ and Fe²⁺dosage of50 and 2.8 mM,reaction time at 90 min,removal effect of heavy metals using homogeneous Fenton reaction in zinc-nickel alloy electroplating wastewater was proved to be the best.Especially,removal rates of Zn and Ni in the wastewater were 99.64%and 94.42%,respectively.However,the remaining concentration of Ni is still 0.16 mg/L,which does not meet the national emission standards.Taking into account and has disadvantages of homogeneous Fenton as large amounts of chemicals,high actual operating costs,and large amounts of iron-containing sludge,further in-depth steps should be implemented.（3）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 99.38%and 98.97%removal rate of Zn and Ni in electroplating wastewater.Moreover,the catalyst exerted better stability after four repeated experiments,as which still remained 99.15%and 93.26%of zinc and nickel removal respectively.（4）The adsorption process of Zn and Ni in electroplating wastewater by Fe（Ⅲ）-ABC-20fits the Langmuir adsorption isotherm model better,and the theoretical maximal adsorption amounts of Ni and Zn are 2.09 mg/g and 5.65 mg/g,respectively.In order to explore the Fenton-like reaction mechanism,ESR was used to capture and detect the radical species?OH and?O₂^-,and then detected and analyzed the intermediate products by GC-MS.It was speculated that the complexing agent EDTP might be first degraded to 2-hydroxypropanal or2-Aminoethyl（ethyl）amine,then further degraded to acetaldehyde or ethylene,and finally oxidized to CO₂ and H₂O.Finally,based on the theoretical basis of DFT,the frontline orbits of EDTP and the free radical attack sites were calculated,and the reliability and rationality of the EDTP degradation pathways proposed in this paper were confirmed by theoretically.