The Reduction Mechanism Of Chromium Cr(?) In Polluted Wastewater Under The Microwave-assisted Ball Milling

With the development of industry and agriculture, the pollution of the environment is more and more serious, so people pay more attention to the problem of heavy metal.This paper mainly study on the reduction of hexavelent chrominum by microwave-assisted aqueous solution ball milling, foucing on the coupling effect between microwave and ball milling for the reduction of hexavalent chromium.In the reaction process of hexavalent chromium reduced by microwave-assisted aqueous solution ball milling,some influencing factors including The rotating speed of ball mill, microwave power, quality of nodular iron, the solution pH, the quality of iron powder and gas medium were changed. The concentration of samples is tested by ultraviolet and visible spectrophotometer.The final productwas characterized by X-ray fiffraction and X-ray photoelectron spectroscopy. Themechanism of the reaction process is analyzed deeply and the different influencing factors were also discussed so that we can choose the appropriate process parameters.1.Concentration, fluorescence intensity and X-ray diffraction were compared under the effection of microwave, ball milling, microwave-assisted ball milling for the solution of hexavalent chromium. The result show that the reduction rate of hexavalent chromium is the most quickly by microwave-assisted ball milling, the reduction rate of hexavalent chromium is the second place by ball milling, the last place is microwave. In the beginning stages the quantities of hydroxyl radical generated by microwave-assisted ball milling are larger than those generated by microwave or ball milling. The final product is FeCr2O4 by X-ray diffraction with x-ray photoelectron spectroscopy.2. The aqueous solution of hexavalent chromium are four kinds of different situations under the microwave-assisted ball milling:(1) The speed of ball mill is 200 r/min,250 r/min and 300 r/min;(2) The microwave power is 400W.500W and 600W;(3) The quality of steel ball is 1.25kg, 1kg and 0.75kg:(4)The qualityof iron powder is 100g,75g,50g. The concertration of aqueous solution and reduction rate of hexavalent chromium were compared with four kinds of different situation respectively. The results show that the aqueous solution of hexavalent chromium will react quickly and cost low. What is more, the materials use ratio highly with an optimal in the speed of ball mill, microwave power, the quality of steel ball and the quality of iron powder.3. Adjust the hexavalent chromium aqueous solution pH value to 2,3,4,5 and 6. It is concluded that the aqueous solution pH= 2, the reduction ate of hexavalent chromiumis the fastest with microwave-assisted ball milling.4. In the microwave-assisted aqueous solution ball milling process, the argon gas,carbon dioxide, nitrogen and oxygen are flowed into solution respectively,the removal rate of Cr(VI) follows the order:CO2>Ar>N2> O2.5.Base on the above experiments and analyses, the author chose the speed of the ball milling in 250 r/min, and set the microwave power up to 600 w. Between 15 min-20 min, the author adjusted microwave power o 500 w, then between 35 min-45 min, adjusted to 400 w.The quality of the iron ball is 1.25kg and the quality of the iron powder is 75g; When the pH of solution was 2, the reduction speed of hexavalent chromium was fast. What is more, the expense was low.