Chromium ore processing residue (COPR) from roasting chromite without calcium is characterized systematically.The detoxification of COPR by SO2 reduction is investigated. The detoxification process combining mechanical activation with SO2 reduction is proposed. The results show that the main phases of the COPR are (Fe

Mg) (Cr

Fe) 2O4 and MgAlFeO4. The content of Cr2O3 in the CPR is 12.23%. The smaller the particle size of COPR

the lower the content of the total Cr(Ⅵ)

water-soluble Cr(Ⅵ) and insoluble Cr(Ⅵ). In the detoxification process of COPR by SO2 reduction

stirring can promote the process of external diffusion effectively and increasing liquid solid ratio is beneficial to the leaching of Cr(Ⅵ) in the COPR. With the increase of temperature

the leaching of Cr(Ⅵ) in COPR increases first

then decreases sharply. The pressure of reaction system has little influence on the detoxification of the COPR. Under the optimized experimental conditions:the pressure 0.1 MPa

the temperature 60℃

the stirring speed 500 r·min-1

and the reaction time 60 min

the removal rate of Cr(Ⅵ) in COPR was 90%

while the removal rate of Cr(Ⅵ) in COPR was 98.1%

and Cr(Ⅵ) content falls below 25 mg·kg-1

meeting the national discharge standard after 90 min of mechanical activation to the COPR.