Process for chrome recovery from industrial waste and the like, as from chrome-ladened tannery waste, including pollution control of the same

A process for reducing BOD loading in tannery primary treatment while increasing the efficiency of hexavalent chrome recovery therefrom, that comprises, alkaline-treating skins and the like to unhair the same;

• separating out a filtrate and a substantial portion of the resulting alkaline solids;
• applying the filtrate to an alkaline equalization tank, mixing the same with trivalent chrome acid and feeding the mix to a sedimentation tank with substantially reduced alkaline solids and associated BOD loading;
• removing the resulting sludge from the sedimentation tank and applying thereto the said alkaline solids sufficiently to raise the pH to at least 11.5 to 12 so as to provide conditions required, upon incineration, efficiently to oxidize the trivalent chrome to the hexavalent state;
• dewatering the sludge;
• and incinerating the resulting solids in the presence of hot air and carbonate to recover chrome ash in the hexavalent state.

A process in tannery primary treatment for increasing the efficiency of hexavalent chrome recovery therefrom, that comprises, alkaline-treating skins and the like to unhair the same, applying such to an alkaline equalization tank, mixing the same with trivalent chrome acid and feeding the mix to a sedimentation tank;

• removing the resulting sludge from the sedimentation tank;
• dewatering the sludge;
• incinerating the resulting solids in the presence of hot air and carbonate to recover chrome ash in the hexavalent state;
• and backwetting the ash and roasting the same to improve the hexavalent conversion.

A process for reclaiming chromium from roasted chromium ash containing chromium in substantially completely the hexavalent state, that comprises, adding the ash to a sulfuric acid-water solution to form an acid ash slurry;

• adding a reducing agent to the slurry to convert the hexavalent chromium to the trivalent state;
• filtering out an extract solution, water-washing the filtering, and recovering the residue;
• applying the water-wash to use as one of waste treatment processing as a flocculating agent, a component of a pickling agent, and a re-cycled solution;
• and utilizing the extract solution for one of pretanning and production of a chrome tanning liquor.