Sequential Recovery Of Sn,Fe And Cu In A Compact Microbial Fuel Cell

Acid etching wastewater from producing printed circuit boards often contains high concentrations of mixed metals such as Sn(II),Fe(II)and Cu(II).Discharging metal containing sewage into the environment not only causes environmental pollution,but also leads to great waste of metal resources.Therefore,choosing an appropriate method to recover Sn(II),Fe(II)and Cu(II)in acid etching wastewater from producing printed circuit boards is of great significance in avoiding environmental pollution and improving the efficiency of recovering metal resources.At present,traditional recovery methods can meet the requirement of metal recovery,but they often have some disadvantages,such as expensive equipment,adding chemical agents,energy consumption,secondary pollution,slow reaction rates and low economic efficiency.Thus,a simpler,cleaner and more efficient metal recovery technology is sought.In recent years,microbial fuel cell(MFC)is a clean and effective sewage treatment technology,which could simultaneously treat organic wastewater in anode and metal containing wastewater in cathode.The recovery and separation of mixed metals in MFCs have been reported based on the difference of their redox potentials,but there are following disadvantages of these methods:(1)Redox potentials of some metals are low,so metals require an additional energy source for recovery;(2)Metals on the electrode require subsequently being scraped to recover,so it increases the cost;(3)Metals are used as electron acceptors,as a result,the system often has a low current density.In order to overcome the above shortcomings,this experiment separates and recovers Sn(II),Fe(II)and Cu(II)in acid etching wastewater based on the difference in the solubility of these metal precipitates in a compact air cathode MFC.This experiment explores the effect of hydraulic retention times(HRTs)of 6 h,12 h,18 h and 24 h on metals removal and reactor performance under continuous flow conditions.The removal of Sn(II),Fe(II)and Cu(II)is 75.8%,19.2% and 48.6% at HRT of 6 h,respectively.Under the condition of HRT of 12 h,the removal of Sn(II),Fe(II)and Cu(II)is 84.6%,46.2% and 57.9%,respectively.94.5%(Sn(II)),76.2%(Fe(II))and 68.8%(Cu(II))are obtained at HRT of 18 h,respectively.At HRT of 24 h,the removal of Sn(II),Fe(II)and Cu(II)is 97.3%,90.1% and 100.0%,respectively.These results indicate that the removal of these three metals gradually increases with an increase in HRT,and the HRT of 24 h is optimal.Then these metal precipitates obtained from cathode bottom,cathode electrode,anode bottom and anode electrode at HRT of 24 h are analyzed by XPS.Sn is mainly removed in the system by tetravalent precipitation;Fe exists in the system as trivalent,and there are more ferrous irons in anode than cathode;Cu(II)can be reduced to copper on the cathode electrode and can be removed by absorption and precipitation in other parts of this system.This experiment is more industrially practical under continuous flow conditions,and the reactor is compact which saves infrastructure or equipment costs and floor space.The compact air cathode MFC overcomes the drawbacks of conventional methods of metals recovery and successfully realizes separation and recovery of Sn(II),Fe(II)and Cu(II)in acid etching wastewater.HRTs have a significant impact on the recovery of metals and electrochemical performance of the system itself.This study provides an alternative and environmentally benign approach for separation and recovery of Sn(II),Fe(II)and Cu(II)in acid etching wastewater from producing printed circuit boards in a compact MFC with simultaneous production of renewable electrical energy.