Study On Hexavalent Chromium Adsorption By Red Mud Modified And Composite With Chitosan

With the rapid development of the alumina industry, during its production, the amount of its residue-red mud (RM) is increasing accordingly. In potential, the red mud can pollute the atmosphere, water and soil. Nowadays, recycling of red mud has attracted significant attention. Therefore, the red mud recycling and unharmful is an important direction in the environmental protection. In the experiment, to target the simulate Cr(VI) water, the red mud was modified through different methods, and then used to composite the adsorbent red mud/chitosan (RM/CTS). Then it studied the adsorption of Cr(VI) which is harmful for the health of human, animals and plants by the modified red mud and composite adsorbent RM/CTS. By the removal rate and adsorption capacity of Cr(VI), it studied the modified condition of red mud and composite process of RM/CTS and the adsorption ability of Cr(Ⅵ). It used XRD、SEM、TG-DSC to analyze and determine the effect on the adsorption by the change of the red mud. The adsorption equilibrium, kinetic model and mechanism for the removal of Cr(VI) by RM/CTS, which is the best adsorbent, were studied.The ability of red mud modified by calcined, and effect of reaction time, pH and dose on the adsorption of Cr(VI) were studied. The800℃modified red mud exhibited97.63%removal and adsorption capacity of0.23mg/g when the modified red mud dose was100g/L, contact time of180min and pH=9.The ability of red mud modified by HC1, and effect of reaction time, pH and dose on the adsorption of Cr(Ⅵ) were studied. When the HC1concentration was2.5mol/L, solid-liquid ratio of1:10, the reaction time of30min, HC1modified red mud dose was60g/L, the Cr(VI) removal rate was98.06%, at the same time, the adsorption capacity was0.32mg/g.The RM/CTS was composited and its adsorption ability of Cr(VI) were studied. The results indicated that RM/CTS was better than the other modified red mud on the removal of Cr(VI). The RM and CTS in the RM/CTS can work together more effectively than when they were separate on the removal of Cr(VI). When the RM and CTS compound ratio was1:2, and the dose was0.2g/L, pH=5, the adsorption capacity of RM/CTS could reach102.58mg/g, and the removal rate was93.35%. The adsorption of Cr(VI) by RM/CTS was slightly affected by the temperature. The adsorption of Cr(VI) by RM/CTS fitted with the Freundlich thermodynamic model and the kinetic process conformed to intra-particle diffusion kinetic model.By XRD, SEM and ICP analysis, great changes were taken in phase, structure and gap of red mud calcined at800℃and red mud modified by HC1. Treated by SEM, the RM are attached to the surface of the CTS in the RM/CTS. Based on TG-DSC thermal analysis of RM/CTS, interaction between RM and CTS promoted the RM/CTS to the adsorption of Cr(VI). By the desorption experiments, more than95%Cr(Ⅵ) were released. The adsorbent can be reused and the Cr(VI) can be unharmful and recycled.