Study On The Permselective Mechanism Of Ion Exchange Membrane And Membrane Research On Surface Coating And Modification Of Particle-Mosaic Membrane

First application of ion-exchange membrane in electrodialysis desalination process can be traced back to 1956,after more than 50 years of development of ion-exchange membrane has been widely used in various industrial fields,such as: water reuse and advanced treatment,environmental protection,recovery of acids from waste acid and metal electrowinning.Among them,the ion exchange membrane is attracting more and more attention for the application of metal electrowinning.The emissions of huge amounts of waste gas and waste water in traditional metal smelting are becoming an important factor restricting the development of the industry.The emergence of new metal electrowinning method solves the problem commendably.Ion exchange membrane,whose performance and service life determines the effect of this new technology,is the core component of the new metal electrowinning method.This process use in the homemade heterogeneous which is in poor selective permeability needs improving its performance in the way of modification.By properly designed experiment,determine the appropriate modification method and then modify the domestic membrane to get ion-exchange membrane with high permselectivity.At present,the Donnan equilibrium theory and double electrode layer theory are commonly used to explain the permselectivity of ion-exchange membrane.But recent studies have shown that the two theories have some defects that they can not explain the permselectivity of ion exchange membrane under the condition of electricity.The cavity transfer-double electrode layer theory and channel closed theory can well explain the permselectivity of ion exchange membrane under the condition of electricity.The movement of ions in solution in ion-exchange membrane consists two ways: the first way is through the pores in the membrane migrate that the ion directly through the membrane pores reaches the membrane to the other side,which is similar to the movement of ions in solution.The second way is through membrane ion-exchange groups that membrane pore is only assisted delivery channels that link ion-exchange groups,namely ion through the membrane must be repeatedly exchanged with ion exchange membrane of commutative groups.In order to determine how the migration path of ion in the film the electrodialysis test is taken: take the cation-exchange membrane in dialysis device,inject NaCl solution of 1000mg/L on both sides of the membrane,powered on for 10 minutes,keep current 0.05 A,and then measure in 10 times in a row.Measure the increases of Mg²⁺ and Na⁺ in the left compartment.When powered on for the first time,the mobility of Mg²⁺ is 95.2%,and the mobility of Na⁺ is 4.8%,increased as the number of power,the mobility of Mg²⁺ decreases and the mobility of Na⁺ increases,to the 10 th power,the mobility of Mg²⁺ is 6.6%,the mobility of Na⁺ is 93.4%.This suggests that the ions in the solution get across the membrane in the way of exchanging with the countra-ion in the membrane.By the way of reducing the pore modifies the ion exchange membrane.By sol-gel method for surface coating and inlaid in the holes of nano-silicon dioxide modified method to improve performance of ion-exchange membrane.In the Sol-gel method,Ratio of water and ethyl silicate,Ratio of ethyl alcohol and ethyl silicate,pH will have an impact on the nature of the surface coating.In the best conditions?nwater:n TEOS:nethanol=6:1:3,pH=4?,the catalyst for the hydrochloric acid and dilute ammonia,110? for 2 hours,the moisture content of 38.1%,ion-exchange capacity of 2.35 meq/g,membrane potential of 2.99 mV respectively increased by 1.6%,0.9% and 0.2% compared with the original membrane,and membrane resistance of 5.2?·cm2 and leak rate of chloride ions of 4.5% decrease by 5.5% and 56.3% compared with the original membrane.Embedded in the experiment of nanometer silicon dioxide,70 ? in a vacuum oven for 2 hours,different quantities of nano-silica doped in PVDF,compare their modifying effect: with the increase of doped Nano-silicon dioxide the ion-exchange capacity,moisture content of the modified membrane also increase but the chloride ion leakage rate decreases.When the amount is higher than 1.5% parameter changes little.For reasons of practicability and economy of dough considering,nanometer silicon dioxide doping amount at 1.5% can achieve good modification effect.