| Chromium, as a toxic metal, has been listed as one of the top priority toxic pollutants by the US Environmental Protection Agency (EPA). With the development of economy and industry, wastewater containing chromium produced by electroplating, leather tanning, pigment and chemical industry processes are released into surface water and cause the water pollution. Cr(â…¢) and Cr(â…¥) were two main oxidation states of chromium in aqueous systems. Chromium (â…¥) is highly soluble in water and toxic to many different aquatic organisms even at low concentrations, the toxicity Cr(â…¥) of is approximate 100 times than that of Cr(â…¢). Therefore, reduction of Cr(â…¥) into Cr(â…¢) is an important approach to treatment the pollution of Cr(â…¥).Nano zero valent iron particles (NZVI) are widely applied for treatment of pollutants in water with high removal efficiency due to the high reducibility. However, a serious technical problem for application of NZVI in water contamination control is aggregation of nanoparticles, resulting in the decrease of NZVI activity in the reaction. This study used three kinds of green polymer dispersants for surface modification of NZVI to improve its dispersion and activity. And modified NZVI were applied for removal of Cr(â…¥). The main research contents are as follows:The characterization of scanning electron microscopy(SEM) and transmission electron microscopy (TEM) indicate that, the dispersion of starch modified NZVI (SNZVI), polyethylene glycol 400 modified NZVI (PNZVI) and guar gum modified NZVI (GNZVI) had been improved compared with bare NZVI (BNZVI), and the aggregation of modified NZVI was inhibited.When the concentration of SNZVI, PNZVI and GNVI was 0.1 wt%,1.0 wt%, 0.05 wt%, respectively, the highest removal efficiency of Cr(â…¥) was achieved. The removal efficiency of Cr(â…¥) was 94.03%,92.80%, and 95.2%, respectively, while only 58.2% Cr(â…¥) was removed by the BNZVI. The removal efficiencies of Cr(â…¥) with modified and unmodified NZVI followed the order of GNZVI> SNZVI> PNZVI> BNZVI.The reaction between modified NZVI and Cr(â…¥) was influenced by initial concentration of Cr(â…¥), pH, and temperature. The removal efficiency of Cr(â…¥) decreased with increasing initial concentration and pH value, and increased with increasing reaction temperature. The reaction between modified NZVI and Cr(â…¥) followed a pseudo-first-order kinetic model.Mechanism analysis of Cr(â…¥) removal with modified NZVI indicated that Cr(â…¥) was mainly adsorbed within the first 15 min, and then the reaction was controlled by chemical reaction after 15 min. |
PDF Full Text Request