选择性吸附去除硅酸的研究

发布时间：2018-11-27 09:27

【摘要】：硅垢是水体中的硅酸发生聚合反应或与金属离子反应形成溶解度很低的沉淀。在水利用系统中,硅垢易附着在设备内壁和膜表面,堵塞管道和膜,减小流速,导致导热不均匀,严重影响设备的正常运行,给工业生产带来巨大经济损失与安全隐患。减小水体中的硅酸含量是防止硅垢形成的根本方法,工艺上常用离子交换法去除硅酸。溶解态的硅酸在水体中多以离子和分子的形式存在,离子交换法只能去除水体中的离子态硅酸,对分子态的硅酸处理效果不佳。因此,本研究用没食子酸(GA)对离子交换树脂进行接枝改性处理,以期实现对不同形态硅酸的去除目的。本研究对普通的OH型离子交换树脂接枝GA,考察了溶液pH、离子强度和GA浓度变化对接枝量的影响,确定了 GA的最佳接枝条件。为研究GA型树脂对硅酸的吸附性能,对比了改性后的GA型与普通OH型树脂对硅酸的吸附效果,初步探讨了硅酸与GA的反应机理,并研究了溶液中共存阴离子对GA型树脂吸附硅酸的影响。利用不同的吸附等温模式、吸附动力学模式和吸附热力学对实验数据进行拟合,研究GA型树脂对硅酸的吸附机理。为探讨改性树脂的重复利用性,研究了不同洗脱液对吸硅GA型树脂的脱附效果,确定最佳洗脱液,同时对GA型树脂对硅酸的循环吸附去除效果做出了综合评价。所得主要结论如下:(1)普通的OH型树脂可以接枝GA,且其最佳接枝条件为:溶液pH为6-7之间、离子强度为零、GA浓度为2.5g/L,最大接枝量为340.3 mg/g。(2)GA型树脂对溶液中可溶性的硅酸(分子态和离子态)都有一定的吸附性,溶液pH变化对GA型树脂吸附硅酸无明显影响,且不同pH条件下GA型树脂对硅酸的去除率和吸附量均远大于OH型,是OH型的30倍。(3)GA型树脂对硅酸具有较高的选择性吸附。低浓度的共存阴离子不影响GA型树脂对硅酸的吸附,阴离子浓度升高时会降低GA型树脂对硅酸吸附量,且多种阴离子共存对吸附量的影响要大于单一阴离子的存在。(4)GA型树脂对硅酸的饱和吸附量为6.471 mg/g(以Si为计),吸附量远大于OH型树脂,且受水环境要素的影响较小。吸附过程更符合Temkin吸附等温模式和准二级动力学模式,颗粒内扩散和化学反应是控制反应速率快慢的主要步骤,表明硅酸是通过化学吸附作用吸附在GA型树脂上。热力学结果表明,反应是自发、吸热的物理化学吸附过程。综合动力学和热力学研究结果得知,GA型树脂对硅酸的吸附过程是物理吸附和化学吸附共同作用的结果。(5)吸附硅酸的GA型树脂在碱性条件下脱附硅酸的效果最好,在不对树脂进行再接枝的条件下,GA型树脂对硅酸的两次循环吸附去除率均在90%以上,效果良好,可以每循环吸附两次进行一次接枝处理。
[Abstract]:Silicon scale is a precipitate in which silicic acid in water is polymerized or reacts with metal ions to form very low solubility. In the water utilization system, silicon dirt is easily attached to the inner wall and the membrane surface of the equipment, clogging the pipes and membranes, reducing the velocity of flow, causing uneven heat conduction, seriously affecting the normal operation of the equipment, and bringing huge economic losses and hidden dangers to the industrial production. Reducing the content of silicic acid in water is the basic method to prevent the formation of silicon scale. The dissolved silicic acid exists in the form of ions and molecules in the water. Ion exchange method can only remove the ionic silicic acid in the water body, but the effect of the molecular silicic acid treatment is not good. Therefore, the ion exchange resin was grafted with Gallic acid (GA) in order to achieve the removal of different forms of silicic acid. In this study, the effects of pH, ion strength and GA concentration on the grafted GA, grafted with common OH ion-exchange resin were investigated, and the optimum grafting conditions of GA were determined. In order to study the adsorption properties of GA resin for silicic acid, the adsorption effect of modified GA resin and common OH resin on silicic acid was compared, and the reaction mechanism of silicic acid with GA was preliminarily discussed. The influence of anions in solution on the adsorption of silicic acid by GA resin was studied. The adsorption mechanism of silicic acid on GA resin was studied by fitting the experimental data with different adsorption isotherm models, adsorption kinetics models and adsorption thermodynamics. In order to study the reusability of modified resin, the desorption effect of different eluents on GA resin was studied, and the optimum elution solution was determined. At the same time, a comprehensive evaluation was made on the removal of silicic acid by circulating adsorption of GA resin. The main conclusions are as follows: (1) ordinary OH resin can graft GA, and the optimum grafting conditions are as follows: solution pH is 6-7, ionic strength is zero, GA concentration is 2.5 g / L. The maximum grafted amount of 340.3 mg/g. (2) GA resin had a certain degree of adsorption on soluble silicic acid (molecular state and ionic state) in the solution, and the change of pH had no obvious effect on the adsorption of silicic acid by GA type resin. The removal rate and adsorption capacity of silicic acid by GA resin under different pH conditions are much higher than those of OH type and 30 times of that of OH type. (3) GA resin has higher selective adsorption of silicic acid. The low concentration of anions did not affect the adsorption of silicic acid on GA resin. The increase of anionic concentration would decrease the amount of silicic acid adsorbed by GA resin. The effect of coexistence of anions on the adsorption capacity of silicic acid was greater than that of a single anion. (4) the saturated adsorption capacity of silicic acid by GA resin was 6.471 mg/g (in terms of Si), and the adsorption capacity was much larger than that of OH type resin. And the influence of water environmental factors is relatively small. The adsorption process is more in line with the Temkin adsorption isotherm model and the quasi-second-order kinetic model. The diffusion in particles and chemical reaction are the main steps to control the reaction rate. It is shown that silicic acid is adsorbed on GA resin by chemical adsorption. Thermodynamic results show that the reaction is a spontaneous, endothermic physicochemical adsorption process. The results of kinetics and thermodynamics show that the adsorption process of silicic acid by GA resin is the result of both physical and chemical adsorption. (5) the desorption of silicic acid by GA resin adsorbed silicic acid is the best in alkaline condition. Under the condition that the resin is not regrafted, the removal rate of twice cyclic adsorption of silicic acid by GA resin is above 90%, and the effect is good, and the graft treatment can be carried out twice per cycle.
【学位授予单位】：内蒙古大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ425.23;O647.3

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