Study On Preparation And Performance Of Potassium Ionic Composite Membrane

From the perspective of sustainable development, the extraction of potash fromseawater has bright prospects. At present, China has developed a extracting potassiumwater technology which used zeolite as the exchanger showing a good prospect.Butthis technology has some defects,such as discontinuity, long cycle and large groundoccupation of the granular potassium ion. The potassium ionic composite membranewhich is suitable for continuous separation can overcome these defects,so studyingon the potassium ionic composite membrane has important application value forimproving the market competitiveness for extraction of potash from seawater.One kind of ionic sieve with a specific memory function of potassium isprepared by hydrothermal method, and its saturated exchange capacity to potassium inseawater is56.96mg/g. The potassium ionic sieve is modified using silane couplingagent KH-550. Effects of reaction conditions such as content of coupling agent andreaction time on the surface modification are discussed. The potassium ionic sievebefore and after modification are characterized respectively by XRD, SEM, FT-IR,and thermogravimetric analysis. The results show that KH-550can graft onto thesurface of potassium ionic sieve successfully, and the grafting ratio is3.5%. Theoptimal modification conditions of potassium ionic sieve are: the concent of couplingagent is60%and the coupling reaction time is5h.Polysulfone hollow fiber is used as basement membrane. Frist,put the basementmembrane into solution of potassium sieve,the potassium sieve is adsorptioned in thebasement membrane by circulation pump.Second,put the the basement membrane intopiperazine solution and chloride solution, Through the oil-water two-phase interfacialpolymerization reaction in the outer surface of the basement membrane to form acomposite surface membrane,then the potassium ionic composite membrane iscompleted.Separation factor of K+/Na+is used to test membrane potential which can be got through by Potassium ion-sieve composite membrane reactor. Effects of reactionconditions such as concentration of potassium ionic sieve, concentration of TMC,concentration of piperazine and reaction time in chloride solution are discussed.At thesame time,post-processing temperature, post-processing time, PH ofpiperazine solution and factors of negative pressure are also discussed. Finally, theoptimal conditions of preparing membrane are: concentration of potassium ionic sieveis0.15%，concentration of piperazine is0.5%，concentration of TMC is0.15%,reaction time is90s, PH of piperazine solution is12, negative pressur is0.05Pa,timeof negative pressure is80s, post-processing temperature is50℃, post-processing timeis20min.Scanning electron microscopy （SEM） is used for membrane surface and sectionmorphology characterization. The results show that: potassium ionic sieve are welldispersed on the surface of modified membrane, and part of them embedded into thesurface pores of basement membrane. The modified layer can roughly cover thesurface and pores of basement membrane. The separation selectivity of the ion sievemembranes to K⁺, Na⁺, Ca²⁺and Mg²⁺were measured by ion exchangeexperiments.The composite member’s separation factors of K⁺/Ca²⁺, K⁺/Mg²⁺,K⁺/Na⁺are equal to60.84,93.61and4.25, modified membrane shows priorityselectivity to K+in every solution apparently. The results of the above studies showthat combining potassium ionic sieve with basement membrane to prepare potassiumionic exchange membrane is feasible.