Detoxification treatment method for extracting and recycling chromium from hexavalent chromium-containing residues

A detoxification treatment method for extracting and recycling chromium from hexavalent chromium-containing residues, a main component of the residues is particles of calcium sulfate dihydrate which adsorb sodium chromate, characterized in that, the detoxification treatment method comprises steps as follows:

• 1) adding water to the hexavalent chromium-containing residues and mixing uniformly;
• 2) adding mineralizers to a seriflux obtained in step 1) and stirring sufficiently to obtain a mixed liquid;
• and the mineralizers are sodium sulfate, sodium chlorate and sulfuric acid;
• 3) treating the mixed liquid obtained in step 2) by a hydrothermal method or direct heating;
• 4) naturally cooling a solid-liquid mixture obtained in step 3) to room temperature for holding, with crystalline grains of calcium sulfate in the residues growing;
• 5) separating solid residues and a chromium-containing supernatant, and washing filtered residues with water and then drying;
• 6) precipitating the supernatant and the water used for washing the filtered residues with a precipitant CaCl2, then centrifugally washing, dewatering and drying the precipitates;
• and
• 7) recycling a chromium-containing solution obtained in step 6) for a treatment of recycling chromium;
• the treatment of recycling chromium has specific steps as follows:
• adding a reductant to the chromium-containing solution, with hexavalent chromium in the solution being reduced to trivalent chromium, then adding a precipitant NaOH to into Cr2O3;
• and the reductant is sodium sulfide or sodium bisulfite.