Requirement And Mechanism Of Cr(Ⅵ) Removal Fromaqueous Solutions By Vetiveria Zizanioides Scrap

With the wide application of Chromium and its compounds in industry, plenty of chromium-containing waste water and industrial residue has been produced, causing serious pollution of water bodies. Vetiver, a perennial geophytic herb, has gradually been promoted in ecological environmental protection and regulation for its advantages such as wide-adaptability, resistance, multipurpose and so on. But its pruning and dry plants in the application in sewage treatment currently are still blank.In this paper it has been studied the removal efficiency and mechanism on the absorption of Cr (Ⅵ) in water by Vetiver. It's checked the effects of pH, temperature, initial concentration of Cr (Ⅵ) and particle size of Vetiver plant on the adsorption, and determined the best condition of adsorption. The results show that the lower the pH, the higher removal rate of Cr (Ⅵ) is. And when the pH is 2, the removal of Cr (Ⅵ) shows the best performance. The rate of Cr (Ⅵ) removal by vetiver is accelerated with the increasing temperature. At 75℃, it only requires 5 hours for 1g vetiver completely removing 100 mg/L of Cr (Ⅵ) and requires 84 hours at 35℃; It has different Cr (Ⅵ) removal rate with different size particles, the smaller the size is, the higher its removal rate. Also different concentrations of SO42- and NO3- affect the remove the Cr (Ⅵ). When the concentration of SO42- is small, it inhibits the degradation of Cr (Ⅵ) and with the increasing concentration of SO4-, although at the beginning it will produce a certain inhibition of the degradation, but as time changes, inhibition gradually disappear, and finally shows a promoting effect; when the concentration of NO3- is 250 mg/L, the impact on the degradation of Cr (Ⅵ) by Vetiver is still relatively negligible compared with the compared sample. But when the concentration of NO3- is 100 mg/L and 500 mg/L respectively, it shows inhibition effect on the degradation.In the Cr (Ⅵ) removal process, it is associated with the emergence of Cr (Ⅲ) and the higher pH of the solution indicating the Vetiver can not only remove Cr (Ⅵ)from the solution, but also can convert it into Cr (Ⅲ) with low toxicity. In this process, it will consume the right amount of H+.When using 0.5mol/L H2SO4 and 1mol/L NaOH respectively to make a desorption treatment on the Vetiver that reached the adsorption equilibrium,0.5mol/L H2SO4can only wash Cr (Ⅲ), but 1mol/L NaOH can wash Cr (Ⅵ) and Cr (Ⅲ) at the same time. Therefore the mechanism of the removal of Cr (Ⅵ) in solution may be a reduction reaction.