The Enhanced Removal Of Cr(â…¥) In Water By Modified Attapulgite

Along with the development of industrial technology, the heavy metals pollution of water is getting more and more serious, among them the problem of chromium pollution is more outstanding.The Cr6+ is potential Carcinogenic substance, which has a great risk to human health.So it is an urgent problem to explore the high efficiency and economical treatment technology of chromium pollution.At present, the attapulgite is abundant in our country, and the price is low. And it have large surface area and strong chemical adsorption, therefore it is widely used in the removal of heavy metals in water. In order to improve the adsorption ability of attapulgite to Cr6+, we can research the adsorption effect of attapulgite to Cr6+ in water through the modification of attapulgite in this paper. We researched the factor influencing modified attapulgite adsorbing Cr6+ in water including adsorption time,adsorption temperature,initial pH, the dosage of modified attapulgite,initial concentration, and explore preliminarily on the removal mechanism of modified attapulgite to Cr6+in water, and the study on the enhanced coagulation of the actual water was carried out.The results showed that:the removal rate of Cr6+ in water is 90% by using modified attapulgite which is modified 5h in 4mol/L HC1 and 10min of ultrasonic. The optimal operating conditions are:the adsorption time is 120min, the adsorption temperature is 25 ℃, the pH is 7, and the dosage is 0.8g. The larger surface area of modified attapulgite, improved its adsorption ability.Through the study on adsorption mechanism of modified attapulgite,we found that the secondary dynamics model could describe modified attapulgite’s adsorption capacity to Cr6+ better than the first-order dynamics model; Langmuir model could describe modified attapulgite’s adsorption capacity to Cr6+ better than Freundlich model. When Cr6+ was removed from water by the combination of polymeric aluminum chloride and modified attapulgite, the dosage of the polymeric aluminum chloride was reduced to 15mg/L and the modified attapulgite were added to the water as coagulant aids, the adding of modified attapulgite before 30s in Polymeric aluminum chloride’s adding, the turbidity, chroma, UV254, and Cr6+ removal rate is better, the removal rates are:90.21%、74.25%、44.07%、21.55%; the optimum ratio is 15mg/L polymeric aluminum chloride, and the 30mg/L modified attapulgite;the best pH is 6.5-7. Compared with 15mg/LPAC alone, adding modified attapulgite as the coagulant aid, the removal rates of Turbidity, chroma, UV254, and Cr6+ can increase 20.61%,29.28%,11.88% and 15.9%. It is because the dosage of modified attapulgite can increase the collision rate of particles in water, the colloid are more likely to form larger flocs, and modified attapulgite has larger surface area and negatively charged, thereby strengthening the removal of pollutants in water.