The Study Of Adsorption And Oxidation Of Arsenate And Arsenite By Pyrolusite In Acid Wastewater

Arsenic is ubiquitous toxic element, which has been harmful to humans for its chronic toxicity and potential carcinogenicity. In order to develop high efficient adsorption materials for arsenic removal, the adsorption property and reaction mechanism of pyrolusite to As(Ⅲ) and As(Ⅴ) was investigated in acidic water. The optimum conditions and mechanisms of desorption was also determined .The results indicated that pyrolusite showed great adsoption capacity to As(Ⅲ) and As(Ⅴ) in acid condition. When the pH of solution was 2, the adsorption capacity of 1mg/L As(Ⅴ) and As(Ⅲ) were 3.77mg/g and 9.55mg/g, respectively, while that of 0.5mg/L As(Ⅴ) and 0.5mg/L As(Ⅴ) combined mixtures was 3.19mg/g. This was because of the oxidation of pyrolusite, the real adsorption capacity was 2.42mg/g. When As(Ⅲ) and As(Ⅴ) were adsorbed by pyrolusite, it begined with surface adsorption and then followed diffusion.The adsorption of pyrolusite to As(Ⅲ) and As(Ⅴ) accorded with Langmuir equation, in which r² was over 0.99, and the mechanism of adsoption was approximate chemical adsorption. The effects of temperature and particle size on adorption by pyrolusite were relatively minor. When the temperature was 298K, the adsorption capacity was maximum, whereas the adsorption capacity decreased when the temperature was above or below 298K. Similarly to the biggest adsorption capacity was achieved when particle size was 40 .The coexisting CO₃^2-, SiO₃^2-, PO₄^3-,Ac^-, F^- ions had negative effect on removal of arsenic except for Fe³⁺.The optimal conditions for desorption of pyrolusite were 500ml stripping liquid and 1mol/L NaOH solution. The desorption rate of As(Ⅲ) and As(Ⅴ) were 0.03975 and 0.04774 mg.g^-1.min^-1, respectively. And it could reach desorption equlibrium within 1 hour. The feasibility of recycle of pyrolusite was demonstrated by regenerative experiment.