| Cadmium, mercury and lead have been regarded as highly hazardous heavy metals in the environment which are non-biodegradable and can readily accumulate in plants and thus endanger human and animal health. The presence of Cd2+,Hg2+,Pb2+ in water, which have been released to environment through the discharge of industrial effluent and combustion of fossil fuels etc, is extremely harmful to the aquatic environment. Up till now, the commonly used processes for removing heavy metal ions from water include chemical, physical and biological methods in general. Nevertheless, most of these processes were sometimes restricted by the cost, efficiency and/or causing seriously secondary pollution to environment in practical application. Therefore, this paper devoted to synthesize a new adsorption material which is of special advantages, such as low cost, high efficiency and eco- friendly for the treatment of Cd2+,Hg2+,Pb2+-containing effluents. Meanwhile, several characterization means were used to characterize the obtained products to show more about the physical and chemical properties of the new material.(1)Polyurethane foam plastic(PU) which bears N H-activated centers is inexpensive, stable, experimentally convenient reagent and can be easily separated from water, it was chosen as skeleton by being grafted with dithizone(H2D2) via the Mannich reaction. The optimum synthesis processes were studied, and the effects of various experimental parameters, such as pH, time, material ratio and temperature have been investigated in batch mode. FT-IR was used to analyze the molecular structure of the material, which confirmed that dithizone was grafted on PU successfully. Maximum 96.51% grafting rate have been reached upon optimum synthesis condition. Then, a new material(grafted PU) that can remove Cd2+,Hg2+,Pb2+ deeply from water was obtained.(2)The grafted PU was used as adsorbent in this paper, its performance for the static adsorption of heavy metal ions in aqueous solution was evaluated further. The influences of factors such as solution p H, solid- liquid ratio, adsorption time, temperature and some co-exiting ions were studied in batch system. The results showed that this material has a favourable adsorbing capacity for Cd2+,Hg2+,Pb2+ from water, maximum 99.95% removal of cadmium(II)(initial concentration:5mg/L), 99.99% removal of mercury(II)(initial concentration:8mg/L) and 99.96% removal of lead(II)(initial concentration:5mg/L) has been achieved under optimum adsorption condition, concentration of Cd2+,Hg2+,Pb2+ in the treated water was below 0.0025mg/L、0.0008mg/L、0.002mg/L respectively, which reached the WHO drinking water standard. Common- ions in water do not affect uptake of heavy metal ions. The property of the grafted PU for the static desorption was studied. Desorption rate of the “Cd/Pb-grafted PU” reached over 98%, much higher than that of the “Hg-grafted PU”. Meanwhile, the grafted PU was observed unsatisfactory adsorption ability after desorption.(3)Dynamic adsorption and desorption experiments were cond ucted under the same conditions as the optimum ones of static experiments. The results indicated that the dynamic saturated adsorption capacities were close to the static value, and the dynamic desorption rate of “Cd/Pb-grafted PU” were high.(4)FT-IR and EDS were used to characterize the adsorption processes, which confirmed that Cd2+,Hg2+,Pb2+ were adsorbed by grafted PU actually. Equilibrium data were described by Langmuir and Freundlich isotherm models. It was found that equilibrium data were better represented by Langmuir isotherm model, which suggests that the heavy metal ions adsorption is regarded as monolayer one. The kinetic regression results manifested that the kinetics of adsorption were well represented by a pseudo-second-order model and the ion diffusion was not the only rate controlling step. The activation energy calculated illustrated chemical adsorption. Moreover, the thermodynamic studies showed that cadmium/lead adsorption process was spontaneous, entropy decreasing and exothermic nature, while mercury adsorption was spontaneous, entropy increasing and endothermic nature within the experiment temperature range.(5)The process of removing heavy metal ions by grafted PU from industrial effluents was preliminarily designed upon the results obtained above. The feasibility of the process was confirmed ultimately.The new adsorption material synthesized in this article, which has not been reported before, has many obvious advantages such as economic, eco- friendly, high efficiency etc. The synthesis techniques is simple and,what’s more, the material shows favourable adsorbing capacity for heavy metal ions. The optimum adsorption conditions obtained in experiments were similar to the chemical environment of most industrial wastewater, and the mater ial has no secondary pollution due to the strong force between heavy metal ions and adsorption sites, upon which the grafted PU are expected to be used in practical application. This paper may be of reference value to the application of synthesizing other adsorption materials which choose PU as skeleton in the area of treating heavy metal ions-containing water. |
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