Research On Electrosynthesis Of Persulfate And Cyclic Regeneration Of Persulfate Microetching Solution

Persulfate has been widely used in the chemical,light industry,f ood,petroleum and printed circuit board industries.The demand for persulfate is increasing year by year.The synthesis of conventional persulfate using a Pt electrode as an anode has low current efficiency and requires the addition o f an oxygen evolution depressor.On the other hand,with the increasing demand for electronic products,the amount of micro-etching waste liquid containing high concentration of acid,copper ion,sulfate,and persulfate is increasing,which cannot be effectively recycled,causing considerable environmental problems and waste of resources.This project will solve the drawbacks of traditional persulfate production and realize the reuse of micro-etching waste liquid.In this paper,the boron-doped diamond film?BDD?electrode was used as the anode,and the electrochemical performance of the BDD electrode was investigated by cyclic voltammetry and AC impedance method.The BDD electrode has a wide potential window of about 3.5 V?-1.5 V² V vs Ag/AgCl?;it has a higher oxygen evolution potential and a lower background current than the Pt electrode;the reversibility of BDD electrode was analyzed by using the electroactive substance Fe?CN?₆^?3-/4-?;the effect of pH and temperature on the performance of BDD electrode were studied.The impedance characteristics of BDD electrode were studied by AC impedance method.A reasonable equivalent circuit was established and the kinetic parameters of the related electrochemical process were obtained.The process conditions for the synthesis of persulfate were determined.The BDD electrode was selected as the anode material for the synthesis of persulfate.The stainless steel was employed as the cathode material.DuPont 117 membrane was selected as the cation exchange membrane.The sulfate concentration kept above 3 mol/L and no depressor,the current efficiency can be maintained above80%;the current density has little effect on the synthesis of persulfate.Electrolysis time 150 minutes and the current density of 240 mA/cm²,the persulfate concentration can reach 343.93 g/L;Sodium persulfate and potassium persulfate with higher product quality,no containing ammonium salts,are produced by direct electrolysis.A current-efficient?115%?,zero-chemical dosing and zero-emission strategy for complete regeneration of spent sodium persulfate/sulfuric acid etching solution?SPS?and recovery Cu by anodizing sulfate coupled cathode reducing copper has been proposed.A laboratory scale closed-loop cycle system for complete regeneration of SPS was developed.The etching performance of the regenerated SPS has no significant difference comparing with the fresh SPS.In this developed process,spent SPS is forbidden to discharge as it is a threat to the ecosystem and human health,for containing high concentration of acid,oxidants?Na₂S₂O₈?and amounts of metal Cu.Recycling of 1 cubic meter of waste etchant can generate economic benefits of?370.This significantly reduces the cost of etching for printed circuit boards industries by savings the purchase cost of fresh SPS and treatment cost of waste SPS,which converts waste to wealth in true sense.The recycling system is a techno-economically feasible,environmentally friendly,occupationally safe,clean and green process for the sustainable SPS reuse and recovery of valuable metal Cu by anodizing sulfate coupled cathode reducing copper.