Application of Ion Exchange Membrane Integrated Technology in the Treatment of Waste Nitric Acid from Aluminum Foil Production
Formed foil is the primary raw material for aluminum electrolytic capacitors.During the forming process of aluminum foil,a large amount of etching wastewater containing nitric acid and Al3+is generated.This wastewater discharge results in,the release of nitrate into sewage disposal systems,leading to serious environmental pollution.To address the challenges posed by low recovery rates and large volumes of etching wastewater,a project was undertaken to achieve zero discharge and cyclic utilization of nitrates from aluminum foil etching wastewater,employing a combination of multiple diffusion dialysis and electrodialysis.The project investigated the effects of flow rate and reaction time on the recovered acid concentration,acid recovery ratio,and Al3+rejection ratio.The results revealed that in the process of diffusion dialysis,the recovered acid concentration and acid recovery ratio decreased with an increase in flow rate,while the Al3+concentration increased.Conversely,in the process of electrodialysis,an increase in reaction time led to higher acid recovery ratios,reduced Al3+rejection coefficients,and improved average current efficiency.As a result of these processes,99.2％of the HNO3 was reused in the production of aluminum foil,while 83.6％of Al(NO3)3 was obtained as a by-product.Moreover,desalinated water from electrodialysis was recycled as cleaning water and receiving water in the purification process.This innovative approach not only offers a solution for achieving zero discharge of aluminum foil etching wastewater but also pave the way for the widespread implementation of membrane-integrated processes in the treatment of such wastewater on a large scale.
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