Treatment of Spent Chemical Oxygen Demand Solutions for Safe Disposal

Holm, Thomas R.

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https://hdl.handle.net/2142/2035 Copy

Description

Title

Treatment of Spent Chemical Oxygen Demand Solutions for Safe Disposal

Author(s)

Holm, Thomas R.

Contributor(s)

Illinois State Water Survey

Issue Date

1996

Keyword(s)

• Mercury wastes -- Treatment
• Sulfuric acid -- Treatment
• Chromium compounds -- Treatment
• Chemical laboratories -- Hazardous wastes -- Waste disposal

Abstract

The chemical oxidation demand (COD) test is used in numerous laboratories to characterize wastewater and effluent. The COD reagent contains high concentrations of sulfuric acid and mercury and dichomate salts. All treatment methods must first neutralize the sulfuric acid and, if necessary, reduce the dichromate to trivalent chromium. Neutralizing the acid and adjusting the pH to pH > 5 causes the precipitation of mercury oxide (HgO), which removes 96% of the mercury. This agrees very well with the amount of precipitation predicted by chemical equilibrium calculations. Adjusting the pH to a value greater than 7 causes chromium hydroxide precipitation, which reduces the soluble chromium concentration to less than 100 micrograms/liter (a reduction of greater than 99.99%), in fair agreement with chemical equilibrium calculations. A method for precipitating the mercury as mercury sulfide is reported. Excess sodium sulfide is added to precipitate mercury sulfide, then excess zinc is added to precipitate the excess sulfide. The mercury concentration in the filtrate is reduced to less than 3 micrograms/liter (a reduction of greater than 99.999%). There is no detectable odor of hydrogen sulfide. The mixed precipitate (mercuric sulfide, zinc sulfide, and chromium hydroxide) can be sent to a commercial mercury reprocessor.

Publisher

Illinois Hazardous Waste Research and Information Center

Series/Report Name or Number

Technical Research Report / Hazardous Waste Research & Information Center ; 20

Type of Resource

text

Language

en

Permalink

http://hdl.handle.net/2142/2035

Sponsor(s)/Grant Number(s)

• Illinois State Water Survey
• Prepared for Illinois Hazardous Waste Research and Information Center HWRIC Project 93-112

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