Adsorption of Cr(VI) on Mill Scale

Abstract: Mill scale is a by-product from hot rolling of steel. It has a high content of iron oxide which has the ability to adsorb ions. Hexavalent chromium is a pollutant which could be adsorbed to mill scale. Different pre-treatment of the mill scale was tested to optimize the adsorption of hexavalent chromium. For an efficient adsorption of hexavalent chromium the pH had to be below 6 in the aqueous phase. Optimal adsorption was obtained on mill scale treated at a low temperature, as sintering at higher temperatures decreased the surface area, with the optimal pre-treatment being heating at 200 °C followed by a rapid cooling of the mill scale. This study also showed that the mill scale used for adsorption can be reused after desorption with only a slight decrease in capacity. A large heterogeneity of the material was noticed during the adsorption tests and the capacity fluctuated significantly between 50 % and 85 % for the different samples. The content of organic matter in the material and its removal was also studied. Chemical treatment with NH3 and NaOH showed no increase in removal of organic matter only heating at different temperatures showed success. This indicates that the present organic matter most likely is stable long chained hydrocarbons e.g. lube oil.