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

Claim 1

A process for reducing BOD loading in tannery primary treatment, while increasing the efficiency of chrome recovery therefrom and enabling substantial chrome reclamation and re-use, said process comprising, 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; incinerating the resulting solids in the presence of hot air and carbonate to recover chrome ash in the hexavalent state; increasing the efficiency of such hexavalent chrome recovery by backwetting the ash and roasting the same to improve the hexavalent conversion; and utilizing such of the ash as it is desired to reclaim for the tannery treatment operation by adding the same 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 waterwash 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 pre-tanning and production of a chrome tanning liquor.