| Aluminosilicate-tailings are the main waste generated during aluminum production from bauxite by a combined Bayer Process and bauxite flotation method. It is reported that 0.2 tons of aluminosilicate-tailings will be generated when 1 tons of bauxite ore is treated by flotation. The enormous quantity of tailings generated every year posses a very serious and alarming environmental problem, such as dust pollution caused by fine particles, land occupation and so on. The main compositions of bauxite tailings are diaspore, kaolinlite, illite and pyrophyllite. So, on the basis of summary and analyse of many interrelated documents both at home and abroad, systematical experiments had been carried out in order to find out effective and low-cost sorbent and realize the renewable use of bauxite tailings.Various ions had been used for the study of removal behaviors of bauxite tailings under the different conditions by modifying and adsorption test. Various measurement techniques had been carried out, such as photoelectron spectroscopy analysis, Zeta potential measurement, infrared spectroscopy, micrography, account of solution chemistry, thermodynamics and kinetics to determine the reaction mechanisms between sorbents and minerals.The results of modifying tests indicate that leaching is more effective than calcinations. Hydrochloric acid and FeCl3 modified bauxite tailings are more effective than other acide, alkali, organic and other salt in the removal of Cr(Ⅵ) ion. But the dosage of HC1 is large, so FeC13 was chosen as the best modified reagent for bauxite tailings. In optimization tests, a removal rate of Cr(Ⅵ) ion (30mg/L) 68.81% was also obtained under the conditions that bauxite tailings samples (20g/L) were treated with 0.1M FeC13 shaking for 12h in speed of 170±3 stroks min-1 at 30±1℃.The results of adsorption indicate that tailings modified by FeC13 are conducive to anion adsorption, and unmodified tailings are easy for cation adsorption. Modified tailings by FeC13 and unmodified tailings both show good adsorption on methylene blue. The maximum removal rate of Cr(Ⅵ) and As(Ⅴ) are 97% and almost 100% by modified bauxite tailing, respectively. The maximum removal rate of Pb(Ⅱ) and Cd(Ⅱ) are almost 100% by unmodified bauxite tailing. After adsorption, all solutions with the second class contamination emission level can be obtained. The condition tests show that the most influence factor on adsorption of methylene blue is adsorbent dosages, and it doesn't relate with the species of sorbent and pH. The maximum removal rate of methylene blue is almost 100%, so it can be considered the process is a physical adsorption process.The broken bonds on the surface of minerals in tailings are ionic/covalent A1-O bonds and Si-O bonds, that cause absorption and electrostatic action with anion reagents. The zeta potential measurements show that the potential of tailings are increased after modified, and its isoelectric point shifts from 3.63 to 5.08, which indicates that there is much absorption of FeC13 on the surface of tailings. So the modified tailings are conducive to Cr(Ⅵ) ion adsorption, and its isoelectric point shifts from 5.08 to 3.26. After the adsorption of Pb(Ⅱ), the isoelectric point shifts from 3.63 to 5.86.The account of solution chemistry shows that after modifying tests, the surface of bauxite tailings can adsorb hydrated iron oxide as form of Fe(OH)2+, Fe(OH)2+ and Fe(OH)3. The optimal pH condition of adsorption Cr(Ⅵ) ion is 3.52 in which the main form of Cr(Ⅵ) ion is HCrO4. The optimal pH condition of adsorption Pb(Ⅱ) ion is 6.2 in which the main form of Pb(Ⅱ) ion is Pb2+, PbOH+.The results of infrared spectroscopy show that the modified tailings samples have a strong band of O—H—O at 3431 cm-1, and the band of—C—CH3 (1427 cm-1) is disappeared while the adsorption bands of Si—O and A1—O is weaken. This indicates that the modification of tailings may have taken place on these positions on the surface of theunmodified tailings and produce hydrated iron oxide. There is a new band at 672 cm-1 which is due to Cr2O72-. It suggests that Cr(Ⅵ) adsorbed on the modified tailings surface in the form of chemistry adsorption.Freundlich model fits better than Langmuir model to the adsorption of Cr(Ⅵ) by modified tailings. However, Langmuir model represents the adsorption process better than Freundlich model for the adsorption of Pb(Ⅱ) on unmodified tailings. The results of this study show that Pb(Ⅱ) can be adsorbed successfully in significant amounts of unmodified tailings.A batch of adsorption kinetic experiments reveal that the adsorption of Cr(Ⅵ) and Pb(Ⅱ) on unmodified and modified tailings is well represented by the pseudo-second-order kinetic model.
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