| Gallic acid(GA) is a typical hydrophilic small molecule organic matter in surface water. The excess gallic acid will lead to a large amount of dissolved oxygen in water used to oxidative decomposition reaction of gallic acid, which cause the death of aquatic organisms and the deterioration of water quality. And then in the conventional process of drinking water disinfection, halogenated disinfection byproducts generated by the reaction of gallid acid and chlorine have serious toxic effect on human body. The safety of drinking water has been seriously threatened in some degree. Hence, it is a hot spot to seek an efficient removal method of GA to solve the safety problem of drinking water.In this study, MIEX resin as adsorbent for removing gallic acid by static adsorption methods is investigated. Through the detailed experimental studies, such as the environmental factors impact experiments, orthogonal design experiments, response surface experiments, adsorption kinetics experiments, adsorption equilibrium experiments, adsorption thermodynamics, the characterization of MIEX resin and MIEX resin regeneration experiments, all used to study the adsorption characteristics and removal mechanism of MIEX resin for gallic acid.The environmental factors impact experiments show that the adsorption capacity of gallic acid on MIEX resin increases with the increase of agitation speed and p H value, but the adsorption quantities will tend to be stable at the 150 r min-1 and p H 5, respectively. The increase of temperature will accelerate the adsorption of gallic acid on MIEX resin, but the higher temperature will promote the desorption reaction. The coexisting anions, such as CO32-?HCO3-?PO43-?Cl-?NO3- and SO42-, can inhibit the removal of gallic acid, and SO42- is the greatest impact, but the addition of CO32- and HCO3- can promote the adsorption of gallic acid on MIEX resin. Interestingly, the coexisting cations of Fe3+?Ca2+?Mg2+?Na+?K+ and NH4+ also have inhibiting effect with different degrees, and the Fe3+ has the least effect. The orthogonal design experiments show the influence degree of six environmental factors on the removal of gallic acid is that initial p H of solution > initial concentration of gallic acid > MIEX resin dosage > adsorption time > coexisting anions > stirring intensity. The optimum parameter for gallic acid adsorption is found to be initial p H of solution(11), initial concentration of GA(20mg L-1), MIEX resin dosage(0.5m L), adsorption time(90min), coexisting anion(PO43-), stirring intensity(200r min-1) and then the removal rate of gallic acid is 95.80%. Based on the response surface theory, we establish a quadratic polynomial regression model of the removal of gallic acid, which has high accuracy and reliability. The equation can be used to effectively predict the removal of gallic acid on MIEX resin. Response surface and contour show that the strong interaction between p H and adsorption time has significantly affect the removal of gallic acid on MIEX resin.The adsorption mechanism of gallic acid on the MIEX resin shows that the removal process is an ion exchange adsorption of chemical adsorption. At different temperatures and initial concentrations of gallic acid, the adsorption kinetics processes of gallic acid both can be well described by the pseudo second-order kinetic model, and the liquid film diffusion is the main rate limiting step. The calculation of activation energy is further proved that the adsorption is chemical adsorption. At different temperatures, the adsorption equilibrium of gallic acid on MIEX resin can be well described by Redlich-Peterson model. With the increase of the initial concentration of gallic acid, the adsorption potential first increases and then decreases. The calculation of thermodynamic parameters indicates that the adsorption of gallic acid on MIEX resin is a spontaneous endothermic reaction.The characterization of MIEX resin before/after the adsorption of gallic acid shows that gallic acid adsorption on MIEX resin is mainly a uniform adsorption process and the aperture is mainly composed of mesopore. The characteristics of loose layer structure and abundant pore and channel are conducive to the adsorption reaction. Benzene ring as the skeleton, the structure of MIEX resin also includes hydroxyl, diethyl benzene, acrylic resin, amino, methylene, methyl and other functional groups. In addition to ion exchange, the ?-? conjugated action, hydrophobic interaction, charge attraction and hydrogen bond also play a role in gallic acid adsorption on MIEX resin.The regeneration of MIEX resin saturated by gallic acid can be accomplished by 0.5 % Na Cl solution, and after multiple regeneration, the resin still has better removal effect. Compared with other adsorbents, MIEX resin had a good removal effect on gallic acid in a short period of time, and the adsorption capacity was 192.19 mg g-1.The competitive adsorption experiments between gallic acid and hexavalent chromium show that when the concentration of hexavalent chromium and gallic acid are equal in the solution, the competitive adsorption hexavalent chromium will reduce the removal effect of gallic acid on MIEX resin and the competitive adsorption effect will be weakened with the increase of MIEX resin dosage. The coexisting anions, such as CO32-?HCO3-?PO43-?Cl-?NO3- and SO42-, will reduce the gallic acid adsorption on MIEX resin in the two-component solution. In two-component system, the adsorption equilibrium of gallic acid on MIEX resin at 303 K can be well described by Langmuir and Redlich-Peterson models. The adsorption kinetics process of gallic acid on MIEX resin can be well described by Elovich model and chemical adsorption is the main control factor of gallic acid adsorption on MIEX resin. |
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