Reclamation of Chromite Ore Processing Residue (Copr) Involving Recovery of Chromate Salt, Detoxification and Fabrication of Clay Brick

We studied on the methods involving the recovery of chromate salt from COPR, the sequential detoxification of COPR and the reclamation of the detoxified COPR. The results of leaching experiments showed that it is possible to recover Cr (VI) existed in COPR using an inexpensive method, in which ca. 84% of Cr (VI) extraction rate could be under the following condition; seawater as leaching solution, 25% of solid content, leaching period of 30min, intermittent agitation, gravitational sedimentation as solid/liquid separating mode, repetition number of up 5. Cr (VI) contained in leaching liquor was recovered as chrome yellow, followed by recirculating the Cr (VI)-depleted supernatant to the leaching process. For the detoxification of post-leach COPR (plCOPR), plCOPR was mixed with sodium sulfide as a single reductant in a mixer and was discharged from the mixer without retention time for reduction. Cr (VI) content in the mixture became lower than cleanup criteria by US EPA with the Na2S/Cr (VI) mass ratio of 6 at the reaction time of 36h. Also, the results of the experiment with the detoxified plCOPR as a substitution for sand in fabricating clay brick shows that acceptable compression strength (52N/mm2) is obtained when the detoxified COPR accounts for '30% in raw material mixture, with the Cr (VI) content of 0.5mglkg-bricks below cleanup criteria by US EPA.