Zeolite regeneration methods and applications

After saturation, the selective adsorption capacity or exchange capacity of zeolite will disappear, therefore, zeolite must be regenerated to restore its adsorption and exchange capacity so that zeolite can be recycled again, which not only saves cost, but also has no pollution to the environment. The regeneration of saturated adsorption zeolites is now a hot topic of research. Currently, physical, chemical, electrochemical and biological methods are the main methods of zeolite regeneration.

First, after zeolite adsorption of organic substances, it is regenerated by combustion and reverse purging with inert gas. Using the physical regeneration method, firstly, the adsorbed materials in the pores can be removed due to the rise in temperature; secondly, the voids can be unblocked, the specific surface area can be restored, and certain cations on the zeolite surface can be activated so that many exchangeable ions are displayed on the zeolite surface, and therefore the zeolite is recirculated. 

Ma Wanshan et al. physically regenerated the zeolite by drying the treated zeolite particles and burning them at 650°C for 20 min to remove the adsorbed organic dyes, so that the zeolite could be regenerated; for the environment, such methods do not cause secondary pollution of the environment and have a better regeneration effect.

Second, after the zeolite is saturated by adsorption, it is immersed in a chemical reagent or solution, then washed and dried to regenerate the zeolite. The regeneration process usually starts with washing and filtering, followed by rinsing with regeneration solution, then rinsing with pure water, and finally drying. 

Solutions such as KCl, NaCl, HCl or NaOH or a combination of both are generally used. Feng Lingzhi et al. studied the regeneration experiments on saturated zeolite, and the results showed that temperature had the greatest effect on the regeneration effect of zeolite, followed by pH, and the degree of zeolite regeneration was also influenced by soaking time and regeneration salt concentration. 

With the increase of soaking time, the regeneration effect increased. Zhang Lu et al. used 0.1 mol/L HCl solution to desorb saturated natural zeolite under high temperature conditions, which could recover ammonia nitrogen resources well. Under the studied experimental conditions, the higher the temperature of the regeneration solution, the more favorable the regeneration of zeolite, and the recovery of ammonia nitrogen can reach up to 82%, and the zeolite regeneration rate can be as high as 69%.

Thirdly, the zeolite was regenerated by electrolysis of NaCl solution after adsorption, and the mechanism includes:① when the NaCl solution is electrolyzed, the NH4+ in the zeolite is replaced by higher concentration of Na+, which in turn accelerates the absorption;② due to the direct oxidation through the electrode and the electrolysis of NaCl, HClO, Cl2, ClO- are produced, and they have an indirect effect on the ammonia nitrogen oxidation, which makes the ammonia nitrogen converted to N2, and thus accelerates desorption.

Fourth, at present, the regeneration method of ammonium adsorption zeolite is the main research of zeolite bio-regeneration method, and zeolite is often a carrier attached to microorganisms to grow, and under the action of microorganisms, zeolite can adsorb a large amount of ammonium and thus get bio-regeneration.