Research On Detoxificationsolidification/Stabilization Of Chromite Ore Processing Residue Along With Comprehensive Properties And Environmental Risk Of Products

Chromite ore processing residue(COPR)is one kind of toxic and harmful waste produced in the production of chromium salts,and the existence of leachable Cr(?)in COPR makes it hazardous waste.Therefore,necessary treatment and disposal should be taken.In this study,the COPR from a chemical factory of Chongqing was used as the research object,and the detoxification and immobilization of COPR was carried out through introduction of ascorbic acid(AA)in alkali-activated cementitious materials(AACM)based on a systematic analysis of the basic characteristics of COPR.In addition,the environmental stability performance of the COPR solidified bodies has been systematically studied,which has certain practical significance for the harmless treatment of COPR and the application of COPR solidified products.COPR is a hard powdery black particle with the particle size mainly concentrated in10?100?m.COPR is alkaline,with the water content of 18.63%.The micro morphology of COPR is irregular particles of different sizes.The main elements in COPR are Fe,O,Al,Cr,Mg,accounting for 94.08%in total.COPR has a high degree of crystallinity and contains various crystalline phases including magnesiochromite,ferroan,magnesium alumilium iron oxide and magnesium chromium oxide.COPR is a kind of hazardous waste with leaching toxicity.Preparation of AACM was by using composite alkali activator to activate blast furnace slag.The result of single-factor and orthogonal experiments indicated that the highest compressive strength of 154.28 MPa(28 d)was achieved after curing the solidified samples at 25?for first 24 h which were synthesized by utilizing the modulus of 1.6 and liquid to solid ratio of 0.24.The optimal combination level of AACM was utilized in the solidification/stabilization(S/S)of COPR.The compressive strength(28 d)of the COPR solidified bodies decreased with the increase of the content of COPR(10%?50%).Moreover,the compressive strength of the solidified bodies was over 100MPa when the content of COPR?30%.While the compressive strength of the solidified bodies was reduced to 49.47 with 50%COPR addition,which still had good mechanical properties.Additionally,the leaching concentration of Cr(?)in the COPR solidified bodies showed a gradual increase trend with the increase of the amount of COPR.AACM effectively immobilized the COPR through physical and chemical means.AA combined with AACM was used in the detoxification-solidification/stabilization of COPR.The detoxification experiments of COPR showed that the reduction efficiency of Cr(?)was 97%with 0.3%addition of AA in the indirect mixing mode;the reduction efficiency of Cr(?)was 96%with 0.7%addition of AA in the direct mixing mode.In the study of detoxification and immobilization of COPR by using the AACM mixed with AA,the compressive strength(28 d)of the solidified bodies was higher than 100 MPa when the D-COPR addition was within 30%;the compressive strength of the solidified bodies was dropped to 54.67 MPa when the D-COPR addition was 50%.Besides,the leaching concentration of Cr(?)in solidified bodies showed an upward trend with the increase of the amount of D-COPR(10%?50%).However,it had a significant decrease compared with that in COPR solidified bodies.The environmental stability of the solidified production was investigated from four aspects:the edge length loss,mass loss,compressive strength change,and Cr(?)leaching toxicity change.The temperature environmental stability study showed that the compressive strength varied greatly at different temperatures.The compressive strength loss was over 60%at a calcination temperature of 900?,and it can maintain nearly 70%strength at the temperature of 1200?;Cr(?)concentration in the other temperature groups increased in varying degrees compared that in the control group except for 1200?.The freeze-thaw environmental stability research indicated that the solidified bodies had a good freeze-thaw resistance.The study of corrosive environmental stability showed that the performance of the solidified bodies was different in different media:the acid resistance is average;the alkali resistance and seawater resistance are excellent.The solidified product can maintain good integrity after 90 d of leaching:the mass loss and edge length loss were at a very low level,the higher compressive strength and lower Cr(?)leaching concentration were achieved;the release law of Cr(?)in the COPR solidified product was mainly diffusion and surface wash-off,and the release rate was in low speed;the results of human health risk assessment based on the solidified bodies polluted water indicated that the non-carcinogenic risk of Cr(?)was acceptable(<1),but its carcinogenic risk value was slightly higher than the acceptable reference range of 10^-6?10^-4.