Study Of Fluoride Ion Removal Using Lanthanum-loaded Polyacrylonitrile Fiber

Fluorine is one of the essential trace elements in the human body, high fluoride intakes from the outside world can affect human health. A large number of studies have shown that fluoride contamination of drinking water is closely related to human health. Common methods of fluoride removal are chemical precipitation, coagulation and sedimentation, electro-coagulation, electro-dialysis, membrane separation, ion-exchange and adsorption method. Easy operation, low cost, particularly suitable for processing low concentration of fluoride in water by adsorption method, its key technology is the development of efficient, cost-effective and safe adsorbent.In this dissertation, raw material based on polyacrylonitrile fiber, through cross-linked with triethylene tetramine, and then reacted with hydroxylamine hydrochloride, finally, got amidoxime fiber. And used polyacrylonitrile fiber cross-linked with hydrazine hydrate, then reacted with ethylenediamine, got amino fiber. Two fibers in lanthanum nitrate solution soaked for a period of time, distilled water washed to neutral, dried, prepared of adsorbents. Lanthanum-loaded amino fiber for optimum preparation conditions were:lanthanum nitrate concentration was5mmol/L, liquid-solid ratio was0.5L/g fiber and oscillation time was2h. At the same time, two types of adsorbents were characterized with tensile testing machine, infrared spectroscopy (FT-IR) and thermogravimetric (TG).Used ion-selective electrode analysis concentration of fluoride solution. Studied the performance of adsorbents by adsorption time, solution pH, temperature and other factors. Adsorption experiments showed that load of La could substantially improve the adsorption property of two fibers for fluoride. With pseudo-second-order kinetic equation calculated the two equilibrium adsorption capacity of the adsorbents, results and experimental determinations of the adsorption balance were closely, described the adsorption process dominated by chemical adsorption. The fitting coefficients were0.9985(lanthanum-loaded amidoxime fiber) and0.9998(lanthanum-loaded amino fiber). The two adsorbent adsorption isotherms under25℃could be well described by the Langmuir equation, this suggested that monolayer adsorption of fluoride was the primary mechanism, the saturation adsorption capacity of lanthanum-loaded amidoxime fiber was4.60mg/g and lanthanum-loaded amino fiber was6.74mg/g. Solution pH had an obvious impact on the fluoride removal of the two adsorbents, and the optimal adsorption occurred in acidic solution. When raised the temperature, adsorption capacity of lanthanum-loaded amidoxime fiber increased rapidly, but adsorption capacity of lanthanum-loaded amino fiber was less impact on the temperature. After saturation, the adsorbed fluoride could be desorbed by NaOH solution, thus provided a theoretical basis for regeneration of this novel defluoridation material.