| Reclamation of wastes is a present hot topic. According to the concept of sustainable development, developing a resource-saving and environment-friendly adsorbing material could not only make waste profitable, but also relieve the environmental pressure caused by waste material, it has subsistent significance. Water treatment wastewater sludge (shortened form waterworks sludge) is a byproduct of the water purification process. Studies have shown that waterworks sludge has a certain ability to adsorb contaminant, however this ability was not too high and difficult recovery after application. In response to these deficiencies, This study selected representative waterworks sludge as an adsorbent material matrix, the sludge was obtained from waterworks at cold area, the water source of waterworks was a reservoir. A modified method which combined with heat-acid was applied on the sludge for preparing high efficient modified powder sludge adsorbent. In addition, According to the special nature of the sludge, a novel process for preparing ceramsite was established with the sludge as the main material. The adsorptive property of sludge power and sludge ceramsite was discussed by removing Cr(VI). The adsorption mechanism was explored by establishing adsorption models of sludge adsorbent and Cr(VI), the theoretical guidance and scientific basis could be provided for practical application of waterworks sludge as adsorption material.The physical and chemical properties of before and after modification of water treatmen residual sludge and sludge ceramsite were characterized by elemental analyzer, surface area analyzer, scanning electron microscopy-energy spectrum spectrometry, X-ray diffraction, infrared spectroscopy and so on. According to the results of static experiments and dynamic experiments, the removal efficiency of Cr(VI) on the power adsorbent and ceramsite were investigated, and influence factors were analysed, adsorption models were built, reaction parameters were optimized by response surface methodology and the reaction mechanism were discussed.The optimal modification conditions for power adsorbent was calcination3h at400℃, then mixed with2.5mol/L HCl3h in accordance with the solid-liquid ratio1:1. The removal efficiency of Cr(VI) on brfore and after modification power adsorbent was studied, all influence factors were investigated. The results showed that the adsorption capacity of modification adsorbent was increased, there was a best results at pH2.0-3.0. In the acidic environment, the humic substances were dissolved out and beneficial for adsorption. The adsorption capability of brfore and after modification power adsorbent was increased by improving initial concentration and temperature and was restrained by interfering ions existence.Experiment datas of Cr(VI) adsorption on power adsorbent were fited with the pseudo-second-order. The adsorption process of modification power were described by Freundlich model and the adsorption process of non-modification power were described by Langmuir model. Adsorption process was endothermic but randomness would be increased. The mechanism was electrostatic attraction, the complexes were formed by HCrO4-and positive charge on the sludge.The optimal preparation conditions for sludge ceramsite was the pretreatment temperature of raw material500℃and pretreatment time20min, the optimum calcination temperature was1050℃and calcination time was10min. The optimum ratio of raw materials was60%：40%(60%of sludge and40%of bentonite). The removal performance of Cr(VI) was investigated by static experiments and dynamic experiments. The results showed that best results was pH4.5, it was broaden1.5units in pH scopes for removal of Cr(VI). The adsorption capability of ceramsite was increased by improving initial concentration and temperature. The adsorption capability of ceramsite was restrained by co-existing ions existence.Experiment datas of Cr(VI) adsorption on ceramsite were fited with the pseudo-second-order. The adsorption process of ceramsite was described by Freundlich model and Langmuir model. The mechanism was ligand exchange. In the acidic environment, protonation on ceramsite was occurred, positive charges were distributed on ceramsite surface and attracted with HCrO4-by electrostatic attraction, ligand exchange interaction were occurred between–OH and HCrO4-. The results of dynamic experiments showed that the adsorption process was influenced by adsorption column packing height, velocity, initial concentration and pH. Under the experimental conditions, the optimum parameters of dynamic experiments were adsorption column packing height10cm, ceramsite quality16.5g, velocity10mL/min, initial concentration50mg/L and pH4.5. The dynamic adsorption process of ceramsite was described by Thomas model and Yoon-Nelson model. The simulation parameters were offered reference for practical application.The optimization equation of modified sludge powder and sludge ceramsite for Cr(VI) adsorption was constructed by response surface methodology. The interactions between pH and initial concentration as well as temperature were analysed, there were significant effects between pH and initial concentration, pH and temperature, initial concentration and temperature. The optimization equation of modified sludge powder and sludge ceramsite were reliable and had a certain significance.In summary, the absorption efficiency of water treatment residual sludge adsorbent for Cr(VI) was very prominent, the sludge would be applied in heavy metal wastewater treatment. It has actual significance for not only reclamation of wastes but also reducing the pressure of economy and environment. |
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