| Heavy metal pollution have an enormous threat to human health life. Heavy metal pollution incident is show that governance in the heavy metal pollution is urgent. Compared with other heavy metal wastewater treatments, the adsorption posses a simple process, good treatment effect, especially suitable for the treatment of large volumes of heavy metal wastewater. The key is the performance of adsorbent. In this study a series of calcium silicate were prepared by means of template synthesis method and modified it by amine and thiol group. The effects of the variety of template agent on the mesoporous silicate pore diameter, specific surface area and adsorption and desorption regeneration performance of heavy metal ions were studied systematically. Preliminary the adsorption kinetics and thermodynamics were also studied.(1) A series of calcium silicate were prepared using calcium nitrate and sodium silicate as raw materials by means of template synthesis method and the effects of the four template agent: sodium dodecyl sulfate, P123, hexadecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide and four methyl hydrogen mixed amine oxide template agent on the mesoporous silicate pore diameter, specific surface area, morphology were studied. The mesoporous calcium silicate synthesized by hexadecyl trimethyl ammonium bromide as template has mesoporous slit-pore structure, with a specific surface area of 158.13 m2·g-1, and 8-40 nm pore size; it nitrogen adsorption-desorption curve is the H3 type hysteresis loop and mesoporous show is made by the accumulation of particles, which further confirmed by scanning electron microscopy. X-ray diffraction and infrared spectra show mesoporous hydrated calcium silicate is calcium silicate, the surface contains a large amount of hydroxyl groups, which provide a modified site for modified calcium silicate.(2) Mesoporous calcium silicate as modified matrix which synthesis by hexadecyl trimethyl ammonium bromide as a template. Two kinds of functional mesoporous silicate: amino-functionalized calcium silicate(MCSC-NH2) and thiol-functionalized calcium silicate(MCSC-SH) were prepared from two silane coupling agent: 3-aminopropyl triethoxysilane and(3-mercaptopropyl) trimethoxysilane as a modifying agent by means of post-grafting. The modified mesoporous calcium silicate synthesized were characterized by the x-ray diffraction(XRD), Brunauer-emmett-teller(BET), infrared spectrum(FT-IR), scanning electron microscope(SEM), elemental analyzer(EDS) and thermogravimetric analysis(TG). The results show that, mesoporous modified calcium silicate N and S elemental contents were 1.988 % and 0.538 %, indicating that the modified mesoporous calcium silicate successfully synthesized. The modification process are stabled, because modified mesoporous calcium silicate of XRD patterns are same with unmodified mesoporous calcium silicate. The specific surface area of MCSC-NH2 and MCSC-SH were reduced by 43 m2·g-1 and 28 m2·g-1.(3) The adsorption properties of MCSC, MCSC-NH2 and MCSC-SH towords Cu2+, Pb2+, Cd2+, and Cr3+ were studied, compared with activated carbon(AC) adsorption and desorption regeneration performance were also studied. The results show that when MCSC, MCSC-NH2 and MCSC-SH dosage is 10 mg the residual concentrations of Pb2+, Cd2+, Cu2+ and Cr3+ can all achieve the best. The adsorption capacity of MCSC and MCSC-NH2 to four heavy metals ions were in order of Pb2+>Cu2+>Cd2+>Cr3+ and adsorption capacity of MCSC-SH to four heavy metals ions was in order of Pb2+> Cd2+ > Cu2+ >Cr3+. Three kinds of mesoporous adsorbents were reached adsorbent equilibrium after 3-8 h. The adsorption rate of unmodified mesoporous calcium silicate is greater than the modified mesoporous calcium silicate. The adsorption capacity of four adsorbents toward Pb2+ were in order of MCSC-NH2>MCSC-SH>MCSC>AC. The adsorption of mesoporous adsorbents were desorpted by using 0.1 mol·L-1 triethylenetetramine solution. The adsorption capacity and removal rate for Pb2+ of MCSC, MCSC-NH2 and MCSC-SH have only decreased 0.335 mg·g-1, 0.143 mg·g-1 and 0.541mg·g-1 after 5 times elution-regeneration. The result indicated that the modification, which happens on the mesoporous calcium silicate, strikingly enhanced their adsorption.(4) Preliminary, the kinetics and thermodynamics of the adsorption were studied by the method of curve fitting. The results show that, the adsorption isotherms accorded with Langmuir equation, according to the Langmuir equation to calculate the saturated adsorption heavy metal ions quantity order of are as follows: MCSC-NH2>MCSC-SH>MCSC, after modification, mesoporous calcium silicate adsorption for heavy metal ions were largely enhanced, heavy metal ions adsorption quantity order of Pb2+>Cu2+>Cd2+>Cr3+ MCSC and MCSC-NH2 as adsorbents, heavy metal ions adsorption quantity order of Pb2+>Cd2+>Cu2+>Cr3+ MCSC-SH as adsorbent. The kinetic data indicate that the adsorption process of heavy metal ions can be better described by the pseudo-sencond-order equation and theintraparticle diffusion model and the intra-particle diffusion accompanied by film diffusion is testified the rate-controlling step. The thermodynamic results show that the modification calcium silicate of adsorption process is endothermic so that the rise in temperature is helpful to the adsorption behavior, but without modification calcium silicate of adsorption process is exothermic reaction, physical adsorption.In summary, mesoporous calcium silicate which this study synthetic has excellent adsorption properties of Pb2+, Cu2+, Cd2+ and Cr3+ heavy metal ions, has a broad application prospect. |
PDF Full Text Request