Study on Strengthen of Zeolite Molecular Sieve Ion Exchange Mass Transfer Process under Ultrasound Effects
Based on previous research, absorption issues such as little adsorption capacity, lower adsorption efficiency and so on are main challenges in the application of ion exchange technology. Herein, taking full account of”channel nano-size effect”with porous adsorbent, choosing zeolite molecular sieve as ion exchanger, calcium for the exchange of object, ultrasonic means to strengthen, effect of ultrasound on process intensification of ion exchange are further studied.Static adsorption experimental results show that, Langmuir equation linear fit form can not describe calcium ion adsorption on zeolite molecular sieve properly and it is found that the equilibrium adsorption poins in the examined range are most accurately predicted by using Redlich-Peterson curve fit. But mechanism of calcium ion adsorption on zeolite molecular sieve can not be explained by Redlich-Peterson curve fit, since it can only as a method of date processing, and can not fully explain the adsorption mechanism during complex system. According to thermodynamics theory, enthalpy, Gibbs free energy and entropy are figured out. Thermodynamic analysis demonstrate that the feasibility of the ion exchange reaction because the value ofΔG m0 is negative, which shows that absorption process can be spontaneous, and the endothermic reaction because the value ofΔH 0 is positive, which support the experiment fact that high temperature is advantageous to the calcium ion absorption. Besides adsorption activation energy is 7.20 kJ . mol-1, which also proves that absorption process easier.Dynamics research results show that, the cation exchange capacity of zeolite molecular sieve is determined as 78.65 mg/g. The calcium ion diffusion on zeolite molecular sieve is controlled by film diffusion control at lower calcium ion concentration （50 mg/L） and by particle diffusion control at higher calcium ion concentration （such as 1200 mg/L） and by film and particle diffusion control jointly at middle calcium ion concentration （such as 300 mg/L）. Ultrasound can change the exchange control mechanism that is converted into particle diffusion control, no matter under the condition of lower calcium ion concentration or higher calcium ion concentration. Besides, ultrasound can not only improve adsorption rate, but also adsorption ratio, and the adsorption ratio increases with ultrasound intensity. Ultrasound frequency has little effect on adsorption ratio. Temperature parallel experimental results indicates that the increase of adsorption capacity with ultrasound not only due to thermal effect but also to non-thermal effect.X-ray diffraction and electron microscope scan results show that the the purity of zeolite molecular sieve samples is high and is the standard X-type zeolite. X-ray diffraction analyses of semi-quantitative and qualitative results show that ion exchange adsorption is the main adsorption mechanism.The mechanism of ultrasonic strengthen ion exchange adsorption mass transfer of zeolite molecular sieve mainly attribute to the additional effect which caused by ultrasonic cavitations, make the boundary layer film thinner, providing calcium ions with high energy to overcome the ” channel nano-size effect,” decreases the mass transfer resistance. Besides, ultrasound may make hydrated calcium hydrate layer thinner, easy to diffuse through channels, which may also be the strengthen mechanism. Ultrasound strengthen ion exchange adsorption mass transfer process belongs to fluid-force chemistry effects areas.