Fixation and stabilization of chromium in contaminated materials
AssigneeSevenson Environmental Services, Inc.
InventorsDhiraj Pal, Karl W. Yost
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Abstract
A highly flexible multi-step treatment technology for chemical fixation and stabilization of leachable chromium, particularly hexavalent chrome, in contaminated soils, solid wastes, concrete, sludge, sand and gravel and waste waters is disclosed. The process comprises reducing hexavalent chromium to chromous (Cr.sup.2+) and chromic (Cr.sup.3+) forms in the presence of water under alkaline conditions and fixing the reduced chromium forms with phosphate. The process reduces Toxicity Characteristic Leaching Procedure chromium levels below the regulatory threshold of 5 mg/l as required by the USEPA.
Claims15
A process for the fixation and stabilization of hexavalent chromium contained in a waste material consisting essentially of the steps of:
- (a) contacting said waste material in an alkaline aqueous media with a water soluble reducing agent capable of donating electrons in an amount and for a time sufficient to convert a substantial amount of the hexavalent chromium to divalent and trivalent chromium compounds, wherein an alkalizing agent is added to the aqueous media in step (a) in an amount sufficient to maintain a pH of at least 7,
- (b) contacting the thus treated waste material with a water soluble phosphate source capable of reacting with the divalent and trivalent chromium compounds formed in step (a) in an amount and for a time sufficient to fix a substantial amount of said compounds in a non-leachable and stable phosphate mineral species, and (c) curing said phosphate mineral species until the leachable chromium levels are below 5 mg/l as determined by the Toxicity Characteristic Leaching Procedure (TCLP) (USEPA) Method 1311.
A process for the fixation and stabilization of hexavalent chromium contained in a waste material consisting essentially of the steps of:
- (a) contacting said waste material in an alkaline aqueous media with sodium dithionite in an amount and for a time sufficient to convert a substantial amount of the hexavalent chromium to divalent and trivalent chromium compounds, wherein an alkalizing agent is added to the aqueous media in step (a) in an amount sufficient to maintain a pH of at least 7,
- (b) contacting the thus treated waste material with phosphoric acid in an amount and for a time sufficient to fix a substantial amount of said divalent and trivalent chromium compounds in a non-leachable phosphate mineral species, and (c) curing said phosphate mineral species until the leachable chromium levels are below 5 mg/l as determined by the Toxicity Characteristic Leaching Procedure (TCLP) (USEPA) Method 1311.
Dependencies are inferred from the claim text.