Study On Preparation Of Chelating Fibers With Microwave Irradiation And Its Adsorption Performance For Cu²⁺ Ion In Water

Many industry activities such as mining, metallurgy, electroplating, discharge huge amounts of wastewater containing heavy metals. When the water flow into rivers or other aquatic environment directly would bring severely impair to organism and human health. Recently, several accidental water pollutions with heavy metal have been reported in China. The adsorption has drew abundant attraction to recover heavy metal ions from water owing to its remarkable advantages such as cost effectiveness, high efficiency, and no or minima l generation of secondary waste. Therefore, synthesizing an adsorbent with high adsorption capacity, good stability and suitable application ability in a rapid and efficient way is of great significance for developing an effective emergency disposal technology towards heavy metal pollution control.In this study, based on polyacrylonitrile fiber, fibrous absorbents with amino and carboxylic groups were prepared with microwave irradiation using diethylenetriamine and sodium chloroacetate as grafting agent s. Parameters for preparing the modified fibers were optimized by orthogonal and single factor experiments. The fiber samples before and after modification were characterized by fourier transform infrared spectroscopy(FT-IR), elemental analysis(EA), and mechanics property analysis. Results showed that the optimal conditions for amination reaction which gain 44-50% weight increase were: grafting temperature 115 °C, reaction time 30 min, the volume ration of diethylenetriamine and deionized water at 2:1. Furthermore, the optimal carboxymethylation reaction conditions with 21-25% weight gain were: grafting temperature 105 °C, reaction time 20 min. Compared to traditional heating method, modified fibers prepared with microwave irradiation was achieved in much less time while the modification effects ascended simultaneously. The damage to the structure of fibers caused by chemical modification was unobvious that implied the absorbents with good mechanical performance can meet the requirement for practical application..Using Cu2+ as treatment object, parameters which influence the sorption process such as initial concentration, temperature, p H value and adsorption time were investigated. The adsorption performance of chelating fibers of other common divalent metal ions was also examined under the optimum conditions. Studies have found that within a certain range, the adsorption ability of chelating fibers toward Cu2+ increased along with the rise of solution p H and temperature. Under the condition of 15 °C, the capacity of modified materials reached half of saturated within 15 min and the adsorption amount was nearly as thirty times as the raw fiber. At the room temperature, the chelating fibers also have a good behavior toward Hg2+, Pb2+, Cd2+, Ni2+ and Zn2+. Meanwhile, after adsorption, the fibers were regenerated by HNO3.The experimental results indicated that 0.5 mol·L-1 HNO3 can refresh the absorbents very well. After 10 circles of adsorption-desorption processes, the adsorption amount still remained more than 80% of the first time, which implied that the modified fibers have a bright application prospect. Freundlich isothermal model and pseudo-second-order kinetic equation were well fitted to describe the adsorption process, suggesting that the process was chemical adsorption.The column dynamic experiments of chelating fibers dealing with copper in water were conducted with a series of experiments under different initial solution concentrations, flow rate, and packing height of column. The influences of solution concentration and velocity to the regeneration behavior of fixed bed were carried out. The experimental data demonstrated that the column would receive a good running result when the wastewater containing 100 mg·L-1 Cu2+ flowed through 10 cm fibrous absorbents fixed bed at the rate of 10 m L·min-1. Thomas and BDST model were all suitable to describe and predict the dynamic adsorption performance of modified fibers for Cu2+. These results provide reliable design parameters for modified fibers to apply practically in the accidental water pollution with heavy metal.