Studies On Leaching Property Of Cr(Ⅵ) In Chromium Residue And Acid-Dissolved Wet Detoxication Of Chromium Residue

Chromium residue was the slag from smelting of chromium ore, which was hazard waste listed in China Hazardous Waste List, and its pollution to environmental was mainly due to the Cr(Ⅵ) in it. In this paper, focused on historic chromium residue in Hanqingba District of Baotou city, the leaching property, leaching kinetics and detoxication process was studied, so the following results can be concluded:1. pH of leaching agent was the significant fact for Cr(Ⅵ) leaching from chromium residue, in Acidic Condition, Cr(Ⅵ) was leaching more easily, pH of leachate was important for leaching of Cr(Ⅵ), the Alkalinity of chromium residue, type of leaching agent, initial pH of leaching agent. Compared to there was no great difference on the capacity of nitrate-sulfate mixed acid and de ionized water leaching Cr from chromium residue, the capacity of acetic acid leaching Cr(Ⅵ) from chromium residue.2. As liquid to solid ratio increasing, gross quantity of Cr(Ⅵ) in leachate was increasing. For the diluting effect of liquid to solid ratio increasing, the Cr(Ⅵ) concentration in leachate was increasing.3. Along with the leaching time, the Cr(Ⅵ) concentration in leachate was increasing. Leaching equilibrium of Cr(Ⅵ) from chromium residue was reached rapidly. Weather acetic acid or nitrate-sulfate mixed acid and de ionized water, the leaching equilibrium time was 8~10 hour.4. Na2CO3 and Na2SO4 could significantly enhanc the leaching rate of Cr(Ⅵ), and the leaching rate were 56%,77% respectively when the concentration of salt solutions were 1mol/L. With the concentration of anion increasing, the leaching rate of Cr(Ⅵ) was increasing, moreover, the leaching curves followed Langmuir adsorption isotherm, that suggested the leaching principle of Cr(Ⅵ) is ion-exchange. Simulation results of adsorption equilibrium constants showed the leaching ability of Na2CO3 was higher than that of Na2SO4.5. The leaching of water-soluble Cr(Ⅵ) in water was pure dissolution, however, the leaching of acid-soluble Cr(Ⅵ) in sulfuric acid was reaction, the leaching was controlled by internal diffusion, and the apparent activation energy was 9.32 KJ/mol. Leaching rate was growing, due to sulfate concentration increasing and particle size decreasing. An experimental formula about the apparent reaction rate constant k was stimulated, which was6. For solid-liquid mixed reduction detoxication process, the amount of sulfuric acid added and particle size of chromium residue was important facts for detoxication performance of chromium residue. The detoxication chromium residue attained the Standards for Pollution Control on the Landfill Sites for Domestic Waste and Industrial Wastes, when sulfuric acid added amount reached 0.245 ml/g, particle size was -160 mesh, FeSO4·7H2O added amount was 1.2 times of theory value, ratio of liquid to solid was 3:1, and leaching time lasted 5 hours.