Preparation and Nitrite-nitrogen Adsorbing Properties of Chitosan Composite Resin
|School||Dalian University of Technology|
|Keywords||Chitosan Activated carbon Composite resin Adsorption Nitrite-nitrogen|
A novel composite resin of chitosan supported by active carbon was prepared using the emulsification cross-linking technique, which include first pre-crosslinking, second quasi-crosslinking and final releasing of amino adsorption sites. It was applied in the adsorption of low concentration NO2--N in drinking water. The effect of preparation conditions on granulation rate and adsorption capacity was studied so did the pretreatment of activated carbon. In order to reduce the preparation cost, recycling use of liquid paraffin was researched. In the adsorptive experiment, the effect of partical size, pH, adsorption kinetics, adsorption thermodynamics, adsorption selectivity, adsporption mechanism and saturated adsorption capacity were studied.It is found that the granulation rate is affected greatly by the partical size of activated carbon, emulsifier span 80, dispersant liquid paraffin, formaldehyde and chitosan concentration while the adsorption capacity is affected by crosslinking agent and ethyl acetate. The preparation conditions are that the partical size of activated carbon is less than 0.15mm, the concentration of chitosan is 3%, the mass ratio of activated carbon to chitosan is 0.5, emulsification is at room temperature, the volume ratio of span80 to liquid paraffin, liquid paraffin to acetate solution and ethyl acetate to acetate solution are 3‰,1.5 and 0.03 respectively.The functional groups ratio of formaldehyde and epichlorohydrin to chitosan are 38.4 and 2.8 respectively.The SEM image indicates that the surface of the resin was uneven and had many developed micropores. The infrared spectrum shows that every reaction step has happened.Adsorption capacity of composite resin increases when activated carbon was treated by HC1, while the characteristic parameters of composite resin are lower than those of the chitosan resin for the addition of activated carbon. Because of the recycling use of liquid paraffin, the productive cost and wast discharge reduce while the characterisitic change slightly. With the partical size increasing, the mass distribution improves, while adsorption capacity drops slightly. The adsorption capacity of chitosan composite resin is much greater than the simple compounding made up of activated carbon and chitosan resin. When the temperature is lower than 40℃, the adsorption is a physisorption process primarily caused by electrostatic attraction, so it can be regenerated by HC1. The adsorption selectivity of composite resin for NO2--N is affected by the concentration and negative charge number of co-existing anions. The adsorption reached equilibrium in 60 min with a calculated equilibrium capacity of 0.479 mg/g. When the temperature is higher than 40℃,the adsorption is a chemisorption process caused by chemical bond force and adsorption selectivity for NO2--N increases. The adsorption reached equilibrium in 90min with a calculated equilibrium capacity of 0.700 mg/g. Adsorption capacity increases but the velocity decreases. The saturated adsorption capacity is greater than 2.563 mg/g .Chemisorption is endothermic, spontaneous, entropy increasing process and it can not be regenerated by HC1. The chemisorption and physisorption isotherm equations are conformed to the Freundlich model, and the adsorption process accords with second-order kinetic rate mode.