| Composite adsorbents (SG-1, SG-2) modified with double-bonded carbonic acid had been prepared using glyoxal, glutaricdialdehyde and silica gel (SG) as raw materials. The structures were characterized by infrared spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscope (SEM) and porous analysis. The adsorption properties of adsorbents for Cr (Ⅵ), Cu (Ⅱ), Pb (Ⅱ) and Ni (Ⅱ) chosen as representatives have been investigated. The single factor tests were carried out to investigate the influence of oscillation time, concentration of metal ions, temperature, pH value on the adsorption capacity. The research results are showed as follow:(1) The FTIR results indicated that double-bonded carbonic acid has been successfully bonded onto silica gel surface for the —C=N— bond stretching was detected at 1640cm-1. The TGA curves showed that t he mass loss for SG-1, SG-2 was 17.35% and 19.21% respectively while the mass loss of silica gel was 1.83%. The pore strucuture anaysis revealed that the pore size and BET surface area become small gradually with the proceeding of the reaction. Besides, SEM results showed that the silica gel modified with double-bonded carbonic acid obtains higher roughness concentration and porosity, and more microspore structure than silica gel, which is very favorable to absorb much metal ions.(2) The results of static adsorption indicated the adsorption capacities of metal ions were Cu (Ⅱ)>Ni (Ⅱ)>Pb (Ⅱ)>Cr (Ⅵ). The most adsorption capacity of SG-1, SG-2 to Cu (Ⅱ) was 9.401,9.738 mg/g, respectively. The adsorption efficiency of SG-1, SG-2 to Cu (Ⅱ) was 93.82%,97.09%, respectively. All single factor tests results revealed the most adsorption capacities were obtained at pH 4.8, t=6. The reusability results for SG-1, SG-2 showed that the system of 6 ml 5% thiourea +0.1 mol/L HCl is very efficient since the elution rate has been both up to 85%.(3) The adsorption kinetics experiments indicated that the adsorption process of SG-1, SG-2 to heavy metal ions both conformed to Pseudo second-order kinetic, which could be explained that the whole adsorption process was up to chemical adsorption. The adsorption thermodynamics experiments indicated that the adsorption process of SG-1, SG-2 to heavy metal ions both conformed to Langmuir model within the experimental concentration range.(4) The silica-g-suppoted adsorbents SG-1, SG-2 modified by double-bonded carbonic acid could absorb heavy metals in aqueous effectively so it is both technically and economically feasible for removing heavy metal ions from waste water to reach standard. Besides, the high adsorption capacity and chemical stability make it a promising candidate adsorbent for precious metal ions uptake during sudden events. |
