| Heavy metal ions have great influence on the health of the living on the earth. Small amounts of lead, mercury, cadmium and other heavy metal ions can cause great damage to human beings. Therefore, the research on removal and recovery of heavy metal ions is focused.SA/PVA/HAp composite fibers are prepared via wet spinning using main heavy metal adsorbent of HAp and substrate of SA and PVA. The preparation process of SA/PVA/HAp composite fibers is studied. The effects of concentration of spinning dope, mass ratio of SA and PVA, concentration of coagulation bath, temperature of coagulation bath, spinneret draw ratio and the content of HAp on tensile strength and cadmium adsorption amount of SAPVA/HAp composite fibers are discussed using orthogonal and single factor analysis method. When mass fraction of spinning dope is6%, mass ratio of SA and PVA mass is4:1, mass fraction of CaCl2coagulation bath is2%, and temperature of coagulation bath is60℃, and spinning draw ratio is2times, the maximum adsorption amount of198mg/g at the concentration of cadmium solution of614mg/L is obtained. The structure and properties of SA/PVA/HAp composite fibers are characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), measurement of breaking strength and density, and etc. HAp and SA in composite fiber exert adsorption effect. HAp is well distributed in composite fiber. The breaking strength of SA/PVA/HAp composite fiber with maximum cadmium adsorption amount is4.32cN/dtex.SA/PVA/HAp composite adsorption fiber adsorbs cadmium ions quickly and reaches half of equilibrium at about7.5minutes. The result of adsorption dynamics simulation shows that the adsorption conforms to the pseudo-second-order model. Freundlich isotherm model better describes the adsorption behavior of composite fibers. The process of adsorption of cadmium onto SA/PVA/HAp composite adsorption fibers is found to be physical and endothermic. With the temperature increasing, the adsorption capacity increases.Inorganic hydrochloric acid (HCl) and diethylene triamine pentaacetic acid (DTPA) are good desorption agents. Good desorption can be achieved at100mmol/L of HCl and10mmol/L of DTPA. In repeated adsorption and desorption process, the amounts of adsorption and desorption gradually decrease, and ultimately approach50%of the original amount using HCl. As for DTPA, the third adsorption and desorption amount decreases to50%and gradually decreases afterwards. The tensile strength of composite fibers is enhanced after adsorption and desorption.On the basis of preparation process for composite fibers with maximum adsorption amount, crosslinking composite fiber and porous composite fiber are prepared via the addition of crosslinking agent of glutaraldehyde and pore-foaming agent of polyethylene glycol into spinning dope respectively to improve breaking strength and adsorption capacity. When glutaraldehyde mass fraction is1%, breaking strength and breaking elongation increase1times and3times respectively, and the adsorption amount reduces to75%of the original. At the concentration of polyethylene glycol of10%,2times of adsorption amount, rapid adsorption rate and shortened half equilibrium time are found. |
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