The Synthesis Of Novel Magnetic Weak Acid Resin And Its Application To Advanced Treatment Of Electroplating Wastewater

Electroplating, chemical engineering, metallurgy and other industries discharged a large amount of heavy metal wastewater into the environment. Heavy metals migrate and transfer in different valence state in nature. Unlike organic contaminants, heavy metals are non-biodegradable, and have the characteristics of bioaccumulation, they tend to accumulate and concentrates in living organisms by food chain and finally have a negative effect on ecosystem and humanity. Considering the high toxicity of heavy metals, the emission standard is improving continuously. Various treatments such as chemical precipitation, membrane filtration, electrochemical treatment and ion-exchange have been employed to remove heavy metals from contaminated wastewater, but they all have their inherent advantages and limitations. Among these methods, ion-exchange is suitable for advanced wastewater treatment, especially for those laden with heavy metals of low concentration. However, the diameter of conventional resin is about 0.3-1.2mm, leading to the high investment of fix-bed equipment and complex operation. MEEX(?), a magnetic anion exchange resin developed by Orica, is the only commercial magnetic resin so far. It has the characteristics of small size, fast kinetic and easy separation, resulting in its application in completely-mixed contactor. Recently, MIEX-Na, a magnetic weak acid resin has been reported by literatures.Based on the above background, this thesis focused on the preparation of new magnetic cation exchange resin NDMC and its application to heavy metals removal.Methyl acrylate, divinylbenzene, titanate coupling agent were chosen as the ingredient for preparation, for which process comprising of co-polymerization and hydrolysis.The prepared NDMC is between 80～150μm with a good performance of magnetic separation. By changing the ratio of ingredients, three series of NDMC were prepared, including crosslinking-degree, γ-Fe2O3 content and porogen content. Chemical analysis indicates that lager crosslinking degree and γ-Fe2O3 content will decrease resin capacity, on the contrary, the increased amount of porogen content could enlarge resin capacity. Three factors are all related to the resin’s performance of adsorption kinetics and thermodynamics. The investigation on adsorption of Cu2+and Ni2+reveal that the importance follows the order:porogen content, crosslinking degree andγ-Fe2O3 content. The increase of crosslinking degree reduces NDMC’s saturation capacity, and enlarges the restriction of film diffusion process. As the γ-Fe2O3 content increases, the saturation capacity decreases, and the restriction of particle diffusion rises. The increase amount of porogen could significantly reduce restriction of particle diffusion and enlarge resin capacity, meanwhile make the functional group work at relatively low temperature. However, too much porogen content will be harmful to the resin strength. After comprehensive consideration, NDMC prepared with 30% porogen content was employed in the following experiments. NDMC has the character of good acid resistance at pH 2, and the desorption efficiency regenerated by acid solution at pH 2 is near 100%, while the result of regeneration by NaCl solution is unsatisfactory. After 10 cycles of reusability experiment, no appreciable loss of adsorption capacity was observed. The NDMC was employed for advanced treatment of electroplating wastewater. After biological treatment, SMP-like substance degraded significantly, while more humic-like substances appeared. The average molecular weight of organic matters in electroplating wastewater decreased. The main factors affecting NDMC treatment efficiency include Ca2+concentration, organic matter concentration and species of organic matter, among which Ca2+ concentration is the most important. To simulate the actual biological effluent with the highest heavy metal concentration, Cu2+ and Ni2+ were replenished and the simulated concentration of them were 0.5mg/L, 0.3mg/L, respectively. Fresh resin could treat 400BV simulated wastewater and the effluent quality meets the demand of table 3 in GB21900-2008. After 5 cycles of adsorption-desorption experiments, no appreciable loss of resin capacity was observed, which suggests NDMC could be employed for advanced treatment of electroplating wastewater.