Fundamental Research On The Tuning Of Reactive Oxygen Species And Its Catalytic Oxidation Mechanism In The Alkaline Electrochemical Advanced Oxidation Processes

The high-efficiency,clean,and comprehensive utilization of the refractory,low grade primary metal ores and secondary resources is a major strategic demand in the hydrometallurgical field.The hydrometallurgical advanced oxidation process,focused on the tuning of reactive oxygen species(ROS),is growing to a hot topic.The cleaner oxidation technique for the amphoteric metal ores by the sub-molten salt(SMS)media was developed by Institute of Process Engineering,Chinese Academy of Sciences.The SMS technology has obtained favorable application effect,which utilizes ROS with high oxidizing capacity in the SMS media.However,the mechanism of ROS intensified amphoteric metal oxidation process and the tuning strategy for increasing the ROS production and oxidative capacity still need further investigations.As a controllable,efficient,accurate,and sensitive method,electrochemistry can control the interfacial electron transfer process for the ROS tuning at the atomic and molecular level.In this dissertation,the ROS electrochemical tuning strategy in alkaline media was proposed.The in-situ generation,quantitative determination,targeted tuning,and catalytic oxidation of ROS in the electrocatalytic process was mainly studied.On this basis,in order to achieve the targeted tuning of ROS and greatly enhance the ROS production,we proposed that the main strategies for improving electrochemical two-electron oxygen reduction reaction(ORR)performance is heteroatoms doping method and hetero(composite)structure design.The alkaline electrochemical advanced oxidation process(EAOPs)was further constructed based on the tuning of HO2-and OH species.The alkaline EAOPs have applied in the catalytic oxidation processes of chromium,vanadium,and arsenic,supporting the theoretical basis of amphoteric metal conversion.The main progresses are achieved as follows:(1)The electrochemical ROS in-situ generation system in alkaline media has been established based on the electrochemical two-electron ORR reaction.Large amount of HO2"can be produced in the cathodic region.The quantify determination method was built and the effect of work potential,current density,oxygen flow rate,and stirring speed on the electrochemical ROS in-situ generation process was discussed in order to obtain the optimization conditions.The Cr(Ⅲ)oxidation by ROS was investigated by the electron spin resonance(ESR)spectroscopy and the quenching experiments.The results indicated that OH with higher oxidative capacity was induced by Cr(Ⅲ),plays a vital role in the oxidative process,which expands the scope of knowledge of ROS in the electrochemical system.(2)Based on the heteroatoms doping and hetero(composite)structure design strategies,nitrogen-doped carbon felt(N-doped CF)and MOS2/CF composite electrodes are fabricated,respectively.The material characterization results demonstrated that the nitrogen groups are introduced onto the CF surface and the MOS2 nanosheets are self-assembly grown on the CF,which are considered as the main electrocatalytic active sites.The electrochemical experiments including cyclic voltammetry(CV),chronoamperometry,and rotating disk electrode/rotating ring disk electrode(RDE/RRDE),indicated that the improved two-electron ORR performance was obtained.In comparison to the CF,the ROS production on the N-doped CF and MoS2/CF increased by 48%and 50%,respectively.(3)High-efficiency Cr and V conversion processes by ROS catalytic oxidation effect were investigated.In the ROS catalytic oxidation process,the OH presents high oxidation capacity,which is generated from the chromium-based or vanadium-based electro-Fenton-like reaction.During the oxidation/dissolution process,·OH is induced by Cr(Ⅲ)and V(Ⅲ),causing a much higher improvement for further catalytic oxidation.Therefore,we proposed a new concept of alkaline EAOPs,achieving effective conversion of chromium and vanadium under the effect of ROS catalytic oxidation processes.In comparison with direct electrochemical oxidation process,the conversion ratio of Cr and V by ROS catalytic process increased by 71%and 63.7%,respectively.The ESR and quenching experiment results showed that the synergy of HO2-and OH can promote the oxidation process.During the conversion of Cr(Ⅲ)and V(Ⅲ),the contribution of OH is 30%and 35%,respectively.(4)The proposed alkaline EAOPs have applied in the regeneration of arsenic-poisoning spent SCR catalyst and the treatment of As(Ⅲ)wastewater.The surface adsorption and in-situ oxidation mechanism in the regeneration of spent SCR catalyst was proposed.The OH generated in the vanadium-based Fenton-like reactions plays a significant role in the arsenic removal.The arsenic remove ratio on the catalyst surface can be reached 95.2%by the presented method.The SCR performance of the regenerated catalyst is recovered to the commercial level.Highly efficient oxidation of As(Ⅲ)in the arsenic-containing wastewater is achieved by the synergetic effect of electrochemical oxidation and ROS oxidation.In comparison with electrochemical direct oxidation and oxygen oxidation processes,the conversion ratio of As(Ⅲ)by this method increased by 75%and 60%,respectively.Combing with the following precipitation step,the arsenic-containing wastewater,with almost 100%As(Ⅴ)removal ratio,can reach the demand of discharge standards.