Preparation And Performance Study Of Comb-shaped Cation Exchange Membrane For Electrodialysis And Recovery Of Waste Acid

During industrial processes such as electroplating,smelting,and metal surface treatment,sulfonic acids are needed for metal surface cleaning or metal composition leaching,which generates a lot of waste acid containing metal ions.If the acid-washing wastewater is directly discharged without treatment,it causes serious environmental problems,such as water and soil pollution.At the same time,it can cause a lot of waste of resources.Therefore,the rational recycling of waste acid has received more and more attention,and many methods have been derived.However,the recovery of acid by ED is a reasonable choice considering its environmentally friendly nature,no pollution,and high recovery efficiency.As the core component of electrodialysis technology,ion exchange membrane(IEM)is particularly important for the separation performance.Due to the long-term operation under acidic conditions,the mechanical properties and chemical stability of the membrane are impacted,but the biggest challenge in the waste acid recovery ED process is how to obtain a cation exchange membrane(CEM)with both high proton permeability and high permselectivity.In this work,the sulfonated poly(ether ether ketone)(SPEEK)was used as the base material.Because of its excellent mechanical properties and chemical stability,it can be relatively stable in acidic conditions.A series of comb-shaped CEMs containing different side chains were prepared by different activation reactions,and the related performance of waste recovery in ED technology were investigated.The main contents are as following:(1)Polyethylene glycol(PEG)was inserted into the sulfonated poly(ether ether ketone)(SPEEK)backbone by using the reactive activity of thionyl chloride(SOCl2).The effects of PEG long chain access on the water uptake,swelling ratio,mechanical properties,thermal stability and electrodialysis of the membranes were analyzed.Owing to the hydrophilicity and hydrogen bonding of the PEG long chain,the water uptake of the CEMs are increased from 30.8%to 36.8%,and swelling ratio of the CEMs are increasd from 12.7%to 18.6%.For electrodialysis performance,the permeation flux of H+ is improved froI the pristine 1.33×10-7 mol·cm-2·s-1 to 3.29×10-7 mol·cm-2·s-1,but at the same time,the leakage of Fe2+ is also increased,with selectivity up to 23.7.(2)In order to further reduce the swelling ratio of membranes and improve the electrodialysis performance,the hydrophobic alkyl side chain was inserted into the SPEEK backbone by CDI activation reaction,and a series of comb-shaped CEMs containing alkyl side chain were prepared.Adjusting the alkyl chain length to regulate the microphase separation structure of the membrane.With increasing length of the alkyl side chain,the hydrophilic/hydrophobic microphase separation become more obvious.The results indicate that the hydrophobic alkyl chain can effectively reduce the swelling ratio of the membrane,from the pristine 12.7%to 7.1%.And the microphase separation structure can significantly increase the H+ permeation flux from 1.33×10-7 mol·cm·2·s-1 to 2.41 ×10-7 mol·cm-2·s-1,and block the Fe2+ leakage,thus maintaining a high H+/Fe2+ permselectivity with 32.13.