The Removal Mechanism Of Tannic Acid In Source Water By MIEX Resin

Tannic acid is a typical representative of natural organic matter(NOM). The main body of the traditional water treatment technology which contains coagulation, sedimentation, filtration and disinfection has a poor removal effect on NOM, and it is a direct threat to the safety of drinking water. Tannic acid has a clear tructure and well-defined physicochemical properties, which can be used as a substitute of NOM. It can reflect the NOM in water treatment process transformation rules of migration.In this study, the magnetic ion exchange resin(MIEX) as adsorbent, tannic acid as adsorbate, based on characterization of tannic acid and MIEX resin, using the static adsorption method, through the single factor test, orthogonal experiment, response surface experiments, isothermal adsorption equilibrium test, dynamic test, test, test of regeneration of thermodynamics, adsorption characteristics and mechanism of tannic acid in MIEX resin are studied.The single factor test showed that adsorption of tannic acid on MIEX resin increased with the increaseing of initial concentration of tannic acid, tannic acid removal rate decreased with the increasing of concentration; resin dosage increase, tannic acid on the removal rate is increased; the stirring intensity of 150 rpm can be fully mixed with tannic acid resin; The adsorption amount of tannic acid on the resin stability kept at a high level when 4<pH<8; HCO3- which appeared in water can promote tannic acid adsorbing on resin, while Cl- and SO42- in water had inhibitory effect, and the strength was SO42- surpassed Cl-. According to the orthogonal experiment, the influencing order of MIEX resin for the removal of tannic acid: resin dosage > stirring time > initial pH > initial concentration of tannic acid > anions > stirring intensity; optimum parameters of tannic acid removal: resin 0.8mL/L, 120 min of adsorption time, initial pH was 11, initial concentration of tannic acid was 10mg/L, anions was HCO3-, and stirring intensity was 150 rpm. According to the response surface test results to establish the regression model of tannic acid removal of two order polynomial models, analysis of variance showed good accuracy, high reliability, can effectively predict the removal of tannic acid on MIEX resin. The interaction between the influencing factors analysis showed that the interaction between resin with pH and stirring time with pH value on the removal effect of tannic acid.The adsorption equilibrium experiment showed that adsorption amount of tannic acid on MIEX resin increased with increasing solution temperature; Freundlich can be a well description of 283 K, 293 K, 303 K and 313 K of adsorption equilibrium temperature place an order law tannic acid on MIEX resin. The kinetic results showed that Elovich model can well describe the adsorption process of tannic acid on MIEX resin, liquid membrane diffusion was the rate controlling step. Thermodynamic study suggested that the adsorption is spontaneous endothermic process of increased entropy in thermodynamics.The traditional salt(sodium chloride) regeneration method of ion adsorbed on the resin of the tannic acid had a better regeneration effect; and the regeneration method which contained ethanol and salt composition can be effectively regenerated tannic acid adsorbed resin.Tannic acid pH and coexisting anions of single factor analysis showed that solution involved two forms of tannic acid which were ionic and molecular; Equilibrium and kinetics model fitting showed that MIEX resin in the process of adsorption of tannic acid in surface had energy heterogeneities; Study on thermodynamics and regeneration showed that the MIEX resin adsorption of tannic acid was a ion exchange and physical adsorption of the composite adsorption process. Characterization analysis proved the existence of Van der Waals force, hydrogen bond adsorption force in the process of MIEX resin adsorption of tannic acid.