Study On Removal Of Silicic Acid By Adjacent Hydroxyl Modified Resin

Silicon is a non-toxic element,but silica scale is easily formed during industrial water use.Silicon scale adheres to the inner wall or membrane surface of the pipe and can corrode equipment or contaminate the membrane.Silicic acid exists in aqueous solution in molecular,ionic and colloidal forms.In the industrial water treatment,silicic acid is commonly removed by ion exchange resins method.However,the ion exchange method can only remove the ionized silicic acid,while the molecular state silicic acid is not good.Therefore,in this study,tiron was used to modify the ion exchange resin to achieve the purpose of removing the different forms of silicic acid.In this study,a strong alkali anion exchange resin was used to graft tiron molecules with o-hydroxy functional groups to synthesize tiron resins.The effects of the concentration,pH,and ionic strength of the tiron solution on the grafting amount were investigated by orthogonal experiments.The best conditions for the grafting of the tiron resin were found as follows:the concentration of the tiron solution was8 mmol/L,the solution at pH 10,and the ionic strength was without adding NaCl,the maximum graft yield was 1.20 mmol/g.The effects of silicic acid solution pH and coexisting ions on the adsorption of silicic acid on the tiron resin were studied by static experiments.The results showed that the amount of silicic acid adsorbed by the tiron resin was 37 times that of the OH resin,and the adsorption of silicic acid remained unchanged over a wide range of pH?4-10?,indicating that the tiron resin can adsorb different forms of silicic acid and has good adsorption properties for silicic acid.In the coexisting anions,other common anions had little effect on the adsorption of silicic acid except for B?OH?₄^-,indicating that the tiron resins have a certain selective adsorption on silicic acid.The adsorption process of silicic acid on tiron resin was analyzed by adsorption isothermal models?Freundlich,Langmuir,Temkin?and pseudo first order and pseudo second order kinetic equations.The adsorption mechanism was investigated by combining thermodynamic data.The results showed that:The Langmuir isotherm adsorption mode was most suitable for the adsorption data,which indicated a homogeneous monolayer adsorption.The maximum theoretical adsorption capacity was 8.356 mg/g?25°C??in Si?,6.576 mg/g?40°C?,and 6.045 mg/g?55°C?,respectively.The process of adsorbing silicic acid on tiron resins was more in accordance with the pseudo second kinetic model,which suggested the chemical adsorption process.From the thermodynamic point of view,the adsorption process was a spontaneous exothermic reaction and belonged to physical adsorption.According to the analysis results of adsorption isotherm models,adsorption kinetics,and adsorption thermodynamics,the adsorption of silicic acid by the tiron resin was not a single adsorption process,but a comprehensive adsorption process including physical adsorption and chemical adsorption.In order to explore the reusability of modified resins,the desorption effects of different eluents were studied.The tiron resin with adsorption saturated silicic acid after acid washing and regrafting 4 times still remained 6.41 mg/g,which was 80%of the first adsorption amount of silicic acid,indicating that the tiron resin can be regenerative recycling.In summary,the tiron resin has good adsorption properties for silicic acid,can remove different forms of silicic acid in aqueous solution,and can regenerative recycling,which is an ideal silica sorbent.