Comparison Of Adsorption Media And Arsenic Removal By TiO₂ Filter Column Adsorption From Metallurgical Wastewater

Mining and smelting are major industrial processes for multiple Arsenic（As） and Cadmium（Cd） coexisting wastewater emissions, which caused great water environment deterioration and human health risks. Adsorption has widely used in metal wastewater treatment for its high efficiency and significance regeneration performance. However, it is a great challenge to choose suitable adsorbent for metal remediation from wastewater due to the complicated compositions. The objectives of this study were to evaluate the performances of four commonly used adsorption media for As（V） and Cd removing from metallurgical wastewater to select an ideal adsorbent; and then propose a technology to use granular TiO₂ for arsenic adsorptive removal, to examine granular TiO₂ regeneration, and recovery of the metal elements. The research conclusions are as follows:（1） Comparisons of different adsorption media efficiency on As（V） and Cd in metallurgical wastewater demonstrated that, TiO₂ and GFO had higher adsorption capacity on As（V） and Cd than AA and n ZVI at a constant dosage. This suggests that TiO₂ and GFO are ideal candidates for the remediation of As（V） and Cd contaminated wastewater. The removal of As（V） and Cd on each of four adsorbents followed pseudosecond order kinetics. Ti O₂ and GFO exhibited a wider pH application range than AA and nZVI in the pH edge experiment, and the results can be well described using the CD-MUSIC model. Extended X-ray absorption fine structure（EXAFS） spectrum chart indicated that both arsenic and cadmium forms a bidentate binuclear configuration shared on the adsorbents. TiO₂ exhibited high adsorption efficiency after 5 regenerationreuse cycles in four adsorbents, and high chemical stability was further evidenced by in- situ XRD characterization after adsorption for all adsorbents. Our systematic compare-sons of the four different media for As（V） and Cd adsorption demonstrate that TiO₂ is an ideal adsorbent, which paves the way for further wastewater treatment.（2） A system using three granular TiO₂ columns in series for arsenite adsorptive removal was set up for As wastewater remediation. After a series of experiments, we concluded that arsenite could be reduced to below the wastewater discharge limit（< 0.5 mg/L）. Empty bed contact time（EBCT） was optimized and suggested that 20 min EBCT was sufficient for arsenite removal. Used TiO₂ could be regenerated using 0.5mol/L H2SO4 and 5mol/L NaOH, and NaOH can desorpted more arsenite from TiO₂. The XRD patterns of pristine and spent TiO₂ exhibited no change in crystalline structure, which ensure its high effectiveness after regeneration and enable its reuse in the following cycle. Synchrotron-radiation-based micro-beam X-ray fluorescence（μ-XRF） technology was used to analyze in-situ elemental composition of solid residue after regeneration and the results indicated that many heavy metals were coexisted. Arsenic K-edge micro-focus X-ray absorption near edge structure（μ-XANES） analysis suggested the existence of As（V） in solid residue, indicating that the strong alkali condition during the regeneration process may facilitate the oxidation of As（III）. Small amount of solid residue produced in the adsorbent regeneration process may use as a raw material for the production of arsenic chemicals. The waste solution can be further treated after mixing with raw water to adjust the raw pH from 1.4 to 7. This adsorption, regeneration, and reuse process provides an innovative technology for metallurgical industry wastewater remediation that is promising for practical application.