Research On Treatment Of Cadmium-containing Wastewater In CdTe Solar Cells Field By Electroreduction

The shortage of traditional fossil energy and deterioration of climate environment have promoted the rapid development of photovoltaic and other new energy industries in recent years.With the rapid growth of the scale of traditional crystalline silicon cells,the demand for distributed photovoltaic has increased.Cd Te solar cells meet the requirements of photovoltaic building integration because of high light absorption coefficient,stable temperature coefficient and large-area uniformity,showing good prospect of large-scale application.However,the control of cadmium pollution has become the main resistance restricting the development of Cd Te solar cells.In the process of Cd Te solar cell production and recovery,the realization of closed-loop treatment of cadmium in wastewater is the basic requirement of sustainable development strategy.At present,the treatment of industrial wastewater Cd-containing can’t be effectively recovered,it’s easy to cause secondary pollution.Based on the full analysis of the research status of cadmium removal by electroreduction,the technology of anion exchange membrane（AEM）and proton exchange membrane（PEM）assisted electroreduction for the treatment of cadmium wastewater was studied in this paper.In this paper,the research status of different methods for treating cadmium wastewater in recent years,especially the electroreduction method,is analyzed in detail.It is found that the acidity of high concentration cadmium wastewater is too strong and the mass transfer capacity of low concentration Cd-containing wastewater is insufficient,the technical scheme of using ion exchange membrane（IEM）to explore the highly-efficiency electroreduction treatment of Cd-containing wastewater and reduce energy consumption is proposed and then.Firstly,the electrochemical mechanism of cadmium removal by electroreduction and the ionic conductivity of AEM were studied.The changes of experimental parameters in the treatment of high concentration cadmium wastewater(33.6 g·L^-1)by membraneless and AEM assisted electroreduction were compared.The effects of K₂SO₄ and H₂SO₄ on the energy consumption and minimum cadmium concentration in the treatment of high concentration cadmium wastewater were explored respectively.Secondly,the effects of external voltage,H⁺concentration of the anode solution and foam cathode on the energy consumption and removal rate of the low concentration cadmium wastewater(200 mg·L^-1)treated by PEM assisted electro reduction were studied.In addition,by comprehensively analyzing the experimental results of AEM and PEM,the action mechanism of large cation electrolyte in AEM assisted treatment of very low concentration cadmium wastewater(5 mg·L^-1)was studied,and the effects of large cation concentration and cathodic oxygen reduction reaction on energy consumption and removal effect were explored.The results show that using 100 ml dual-chamber electrolytic cell on both sides of the anode and the cathode,when the membraneless electroreduction at 0.04 A·cm^-2 constant current density takes about 20 h to remove cadmium,Cd²⁺in 200 ml simulated wastewater can be reduced from 33.6 g·L^-1 to 23 mg·L^-1,charge efficiency is 79%,energy consumption is 115Wh·L^-1,final p H of the solution is reduced to near 0.4.Under this p H condition,it’s easy to balance the cadmium evolution rate with the acid corrosion rate of metal cadmium,and aggravate hydrogen evolution,The final cadmium content in wastewater is relatively high;Then AEM is introduced to block the diffusion of H⁺generated on the anode side and improve the effect of sharp decline of p H on cadmium removal.Firstly,when K₂SO₄ is used as the anode electrolyte,it’s carried out under the condition of 0.04 A·cm^-2 constant current density.The lowest p H value rises to 0.97,which takes about 12 h.Cd²⁺in 100 ml simulated wastewater can be reduced from 33.6 g·L^-1 to 200 mg·L^-1.Then,by circulating the method of adjusting p H and electroreduction current,when p H=2 and electroreduction current density is 0.008 A·cm^-2,Cd²⁺continues to be reduced to 1.06 mg·L^-1,with charge efficiency of 98%and total energy consumption of 230 Wh·L^-1.Secondly,when H₂SO₄ is the anode electrolyte,it’s found that when the content of H₂SO₄ is 0.1 mg·L^-1,the p H of the cathode solution still rises to about 0.87,effectively prolonging the reaction time to about 20 h.The high concentration cadmium wastewater is treated to 0.8 mg·L^-1,with charge efficiency of 80%,and total energy consumption of 310 Wh·L^-1.In view of the problems that Cd（OH）₂ precipitation is easy to form in the later stage of the process of AEM assisted electroreduction,the electric neutrality is not easy to maintain,and the low concentration of Cd²⁺is difficult to remove,PEM is used to provide a certain H⁺diffusion channel to weaken the impact of rapid p H rise on the treatment effect of cadmium.Finally,when the applied voltage is 40 V and the anode H⁺concentration is0.004 mol·L^-1,the removal rate of 99.8%can be achieved only by relying on the flat copper electrode,and the energy consumption is 90 Wh·L^-1;Combined with the previous research results,firstly,when AEM membrane was assisted by 0.1 mol·L^-1 C₄H₁₂NCl large cationic electrolyte,with synergistic effect of 0.004 A·cm^-2 constant current density and 64V constant voltage was adopted to treat 100 m L Cd²⁺concentration of 5 mg·L^-1 wastewater,which takes about 3h to reduce Cd²⁺concentration to 0.33 mg·L^-1,with removal rate of 93.4%,and energy consumption of about 21 Wh·L^-1;Secondly,after N₂ treatment,the wastewater with 100 ml Cd²⁺concentration of 200 mg·L^-1 was treated by electroreduction.It was found that after 4 h of reaction,the Cd²⁺concentration was reduced to 0.45 mg·L^-1,with removal rate of 99.78%,and energy consumption about of 90 Wh·L^-1;Considering that the distance between electrode and membrane will affect the effect of cadmium removal,a zero gap electrolytic cell device for economical treatment of Cd²⁺wastewater is designed based on the above technology,which provides a basis for the amplification of the actual cadmium removal device in industry.