Study On Treatment Of Tannery Wastewater And Chromium Sludge Forcr(Ⅲ) Recovery

With the rapid development of the leather industry, it has led to an increased discharged wastewater containing heavy metals (Cr(III)), which have detrimental effects on the environment and human health. Chromium sludge was inevitable outcome along with chromium–containing wastewater treatment process, it also brings the environmental pollution seriously. In order to solve effectively the problem of secondary effluent discharge and chromium sludge treatment and disposal in China’s leather industry, the development of chromium removal and recovery technology efficiently become a serious issue.This paper studied the scientific issues systematically about the preparation, characterization and application of Fe3O4@SiO2–GO and Fe3O4@SiO2–GO–IIP and the leaching and depth of reuse technology of chromium on chromium sludge, and clarified that the mechanism of synthesis and adsorption about graphene oxide nanocomposites, and the affecting factors in actual application process and process optimization strategies and other issues, and established the depth of chromium resource reuse combined process on chromium sludge, and developed efficient and economical chromium removal and recovery technology, and also laid a theoretical foundation about the sustainable development of the leather industry and further broadening the graphene oxide–based products and the application of molecular imprinting technology.Fe3O4@SiO2–GO was developed by covalently immobilizing magnetic core/shell Fe3O4@SiO2on GO surfaces. Fe3O4@SiO2magnetic microspheres grafted successfully onto the shell of the graphene oxide surface, and the load was about54.45wt%. Adsorption studies showed that Fe3O4@SiO2–GO had a strong accumulate ability for Cr(III) about pH6.0; dynamic adsorption process was a chemical processes controlled by membrane diffusion and particle diffusion; in good agreement with Freundlich isotherm model, namely uneven surface adsorption process, and adsorption capacity was about4.7mg/g; electrostatic adsorption and ion exchange process were the two principal mechanisms in Cr(III) removal.Fe3O4@SiO2–GO–IIP was prepared successfully with magnetic graphene oxide as the carrier by the surface ion imprinting technique. Adsorption studies showed that dynamic adsorption process was a chemical processes controlled by particle diffusion; in good agreement with Langmuir isotherm model just as the monolayer adsorption, and adsorption capacity was about0.25mg/g; Fe3O4@SiO2–GO–IIP has a strong identified ability for the target ion; the selectivity of Fe3O4@SiO2–GO–IIP was more than twice than that of Fe3O4@SiO2–GO–NIP; at the same time, Fe3O4@SiO2–GO–IIP had good reusability and stability under the multi–ion interference. Elution completely was achieved only through five times consecutive elution using4mL0.1mol/L HCl.The effects of four pollutants such as proteins, oils (glycerol), carbohydrates and inorganic salts on chromium removal on Fe3O4@SiO2–GO–IIP were investigated. The results showed that the presence of the protein in favor for chromium removal, while oils, salts and carbohydrates, played a negative impact, the orders of the impact were: protein>oils>inorganic salt>carbohydrate. With pollutant loads increased, the efficiency of chromium removal showed a decreasing trend. Guiding basis for wastewater pre–assessment were glycerol concentration≤60mg/L, salt concentration≤80mg/L and carbohydrates≤750mg/L. The concentrations of oils, carbohydrates and inorganic salts in secondary effluent did not reach the level of significant impact adsorption properties of ion imprinted materials.The treatment results of secondary effluent showed that when the dosage of Fe3O4@SiO2–GO–IIP reached4g/L at a contact time of2h, chromium removal was up to90%, chromium content in the treated water was less than0.3mg/L meeting fully the GB30486–2013emission standard. Fe3O4@SiO2–GO–IIP reached adsorption saturation can be regenerated using4mL0.1mol/L HCl, and adsorption efficiency had not changed in six repeated experiments, indicating that reuse of imprinted material is better.The leaching results of Cr–sludge showed that the feasible condition for chromium recovery from wet Cr–sludge was as follows:4%H2SO4as the leaching acid, Cr–sludge (dry weight) load23.55g/L, extraction time60min, and reaction temperature30°C. A chromium recovery of20.86mg/g was obtained under the feasible condition with a recovery rate of91.8%. The experimental results of ion exchange about acid–dissolution water showed that the optimum adsorbent concentration about acid–dissolution water was6g/L, and adsorption efficiency was up to80%. The IRN77resin can be eluted effectively up to95%using10%sulfuric acid as eluent, and further realizing IRN77reuse.2.5%NaCLO(v/v) could improve effectively adsorption efficiency and reusability significantly. The dynamic adsorption process was a chemical processes controlled by film diffusion; in good agreement with Langmuir isotherm model; adsorption mechanism was endothermic, entropy–driven ion exchange.Through this research, the technology of chromium recovery from secondary effluent using Fe3O4@SiO2–GO–IIP was established; and a complete Cr–sludge resource reuse system was established, which could make the continuous reuse of chromium from Cr–sludge become a reality.