Hexavalent Cr(VI) exists primarily as HCrO42- (bichromate) or CrO42- (chromate), which is relatively soluble over much of the environmental pH range.
Hello Mohammed, you could try ferrous sulphate. It serves as a reductant for Cr(VI) and forms a mixed Fe/Cr hydroxide which is sparingly soluble. Do not add too much to avoid acidification and release of co-contaminants (if there are any). Alternatively you may go for microbial reduction by adding a readily available carbon source. Regards, Harald
I agree with Harald and would also add that you could try mixing with metallic iron (finely divided scrap). This would tend to prevent re-oxidation and not be leached out fast as the ferrous salt.
Alan is right, Fe(0) works, too. We have successfully tried it with nano-Fe. What I do not get is the reoxidation. This should only be possible in the presence of available Mn-oxides. Mohammed, could you specify your strategy of adding the reductant. Are you thinking of an injection as a liquid phase or of an in-situ/ex-situ mixing? Harald
In soil you an crop plants that absorb and concentrate high amounts of Silicon [ Si (OH)4] as silico-phytoliths ( SiO2. nH2O). These silico-phytoliths will trap Cr an imobilize it inside teh structure of these particles that are silt sized ( Back to the soil these silica particles do not decompose thus do not release Cr back to the soil ( the precess is called phytoremediation)
Besides the reduction of Cr(VI) by ferrous sulphate, you may follow our recent publication on remediation of Cr to know answers to your questions relating to immobilisation of Cr(VI): Dhal et al., J. Hazard. Mater., 250-251, 2013, pp. 272-291.
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