Process Intensification Mechanism And Efficiency Of High-gravity In Electrodeposition Treatment Of Cd-containing Wastewater

With the rapid development of industrialization,the pollution of heavy metal cadmium（Cd）in water has seriously threatened the sustainable development of society and human health.At the same time,Cd as a resource is also widely used in industrial production.Therefore,the efficient treatment of Cd-containing wastewater and the recovery of Cd resources are the goal pursued in the field of wastewater treatment.Electrodeposition as a clean technology can be applied for treatment of Cd-containing wastewater,which can convert Cd²⁺into Cd resources for recycling and solving the problem of permanent residue of Cd²⁺.However,the bubbles produced and the mass transfer limited in conventional electrodeposition process affect the electrodeposition efficiency in the heavy metal wastewater treatment.High-gravity technology as a new process intensification method has unique advantages in enhancing ion mass transfer and reducing the effect of bubbles.Based on this,the high-gravity electrochemical device with multi-concentric cylindrical electrodes in a rotating bed（MCCE-RB）was developed by our group in the early research and used to create high-gravity fields for the electrodeposition process intensification.The mechanism and efficiency of electrodeposition which is enhanced by high-gravity for the treatment of Cd-containing wastewater were studied in this paper.Firstly,the high-gravity enhanced electrodeposition behavior of Cd²⁺in wastewater was studied to reveal its process intensification mechanism.The effects of various factors on the reduction potential and peak current of Cd²⁺electrodeposition were investigated by cyclic voltammetry,and the high-gravity enhanced mechanism of Cd²⁺electrodeposition was investigated by linear scanning,chronoamperometry and electrochemical impedance spectroscopy.The results showed that the reduction peak current of Cd²⁺increased first and then decreased with the increase of each factor.Compared with the study results of electrodeposition of Cd²⁺in the normal gravity field,the hydrogen evolution reaction could be inhibited,the diffusion coefficient increased more than 81.08%,the polarization potential increased by 4.11%,the reduction peak current increased by 216.26%,and the solution resistance and polarization resistance decreased by 43.59%and 43.72,respectively,in the high-gravity field.It can be concluded that high-gravity can intensify Cd²⁺electrodeposition process to a certain extent by inhibiting gas evolution reaction and enhancing mass transfer,which can improve efficiency and reduce energy consumption of electrodeposition process.Secondly,based on the above research results,the Ti/Ir O₂-Ta₂O₅ was used as the anode and titanium was used as the cathode to study the efficiency and energy consumption of electrodeposition treatment of Cd-containing wastewater in high-gravity fields.The influence of high-gravity factors,current density,electrodeposition time,electrolyte,and initial p H value,circulation flowrate,initial concentration of wastewater on the removal efficiency of Cd²⁺was investigated.The results showed that the removal efficiency of Cd²⁺could reach 99.4%and the current efficiency was 44.8%under the best operating conditions.Compared with the results in the normal gravity field,the current efficiency,the removal efficiency of Cd²⁺and the quality of electrodeposits could be improved by 18.4%,15.7%and 34.5%,respectively.The mass transfer coefficient increased more than 10 times.The cell voltage,electrodeposition time and total energy consumption were reduced by 21.7%,42%and 21.2%,respectively.The reason for the improvement of efficiency was that the bubbles were forced to separate from the electrode surface,the hydrogen evolution reaction was inhibited,the mass transfer coefficient was improved,the cadmium electrodeposition reaction was enhanced,and the removal of Cd²⁺and the recovery of Cd resources was improved by high-gravity.Finally,XRD,SEM,EDS and XPS were used to analyze the phase composition and the microstructure of electrodeposits.The results showed that the electrodeposits were the Cd and Cd（OH）₂ obtained in the high-gravity and normal gravity field.The formation of electrodeposits with dendrite structure was inhibited by the process intensification of high-gravity.The electrodeposits with flaky or layer structure were formed and the crystallinity of electrodeposits was improved in the high-gravity field.It could promote the formation of Cd（increased by4.9%）,so the percent weight of elemental Cd was increased by 19.17%and the purity of Cd resources was improved.In this paper,the effect of bubbles generated in the electrodeposition treatment of Cd-containing wastewater was alleviated and the mass transfer process was enhanced by high-gravity.The high-gravity intensification mechanism was revealed,guiding the Cd²⁺treatment efficiency and Cd resources recovery to be improved.It can provide theoretical bases and technical supports for the clean and efficient treatment of Cd-containing wastewater or other heavy metals wastewater.