Experimental And Mechanism Study On Electrochemical Regeneration Of Exhausted Activated Carbon

As a high-quality adsorption material,activated carbon is widely used in the adsorption treatment of wastewater.However,the treatment of exhausted activated carbon has become an urgent problem to be solved.Considering the secondary pollution and uneconomical of landfill,incineration,and the limitations of traditional regeneration methods,in this work,we explored a new type of activated carbon regeneration technology,namely electrochemical regeneration exhausted activated carbon.Firstly,we chose regeneration efficiency as the objective function and explored the effects of electrolyte concentration,regeneration time,regeneration current,regeneration area,and p H values of electrolyte solution on regeneration efficiency.The influence mechanism was deeply analysed,and a relatively optimized set of regeneration condition was established:the concentration of Na₂SO₄ was 0.1 mol?L^-1,a regeneration time of 6 h,a regeneration current of 0.8 A,regenerating on the cathode and the p H value of 11.5,under which,the regeneration efficiency of activated carbon could reach a maximum of 81.7%.Secondly,this work explored the changes of activated carbon before and after electrochemical regeneration and the adsorption effect after repeated regeneration.Experimental results show:1)For activated carbon electrochemically regenerated once,its surface became rough,specific surface area and pore volume（especially mesopores）reduced,surface zero charge point shifted from near neutral to alkaline,adsorption rate became slowly,and its adsorption capacity became relatively low.The maximum adsorption capacity was reduced,and the adsorption mechanism changed from the reaction controlled to diffusion controlled.2)For activated carbon electrochemically regenerated multiple times,as the number of regeneration increases,the surface of activated carbon became rougher and the specific surface area and pore volume decreased.However,the mesopore volume had a tendency to expand.For its adsorption properties,activated carbon electrochemically regenerated once varied little from the activated carbon sample after regenerated four times.Moreover,for activated carbon electrochemically regenerated multiple times,the adsorption process was controlled by the diffusion step and the particle internal diffusion model could fit the process well.Finally,this work explored the degradation mechanism of organic pollutants generated during electrochemical regeneration,and the pathway of breakdown products formed in the system under a relatively optimized regeneration condition was studied.Real-time detection and analysis of degradation products in the regeneration system were proceed by means of ultraviolet adsorption spectroscopy（UV-Vis）,high performance liquid chromatography（HPLC）,infrared spectroscopy（FTIR）,and gas chromatography-mass spectrometry（GC/MS）.A possible pathway of breakdown products formed in the system was finally obtained.Especially,the experiment verified the presence of hydroxyl radicals（·OH）when the molecules of organic pollutants were degraded by oxidation.The experiment has guiding significance for the current controversies about electrochemical regeneration mechanism.