Pollution Prevention Resources for Industries

Mercuric Nitrate Case Study

A 24-hour composite sample collected at an MCES-permitted printed circuit board manufacturer in August of 1999 contained a mercury concentration of 4µg/L, which was above the newly implemented MCES Local Pretreatment Standard of 2µg/L. The company was immediately notified of the violation and told to investigate. Only laboratory and process wastewater passes through the monitoring point. The company determined that the mercury contamination was the result of the 15mLs of 0.01N mercuric nitrate used in the analysis for chlorides. This corresponds to 15mg of mercury discharged per analysis. Other possible sources of the contamination, such as mercury cell caustic soda, were explored but not found.

The company immediately discontinued use of the mercuric nitrate and returned the remaining solution to the supplier. Currently samples are being sent out for analysis, at $15 each, and an alternative method for chloride analysis will soon be selected.

Note to circuit board manufacturers:

With the reduction of the Metropolitan Council Environmental Services' mercury Local Limit from 100µg/L to 2µg/L in December 1998, it has become especially important for industrial users to eliminate all possible sources of mercury contamination. If you currently use the mercuric nitrate procedure to measure chloride in your acid copper baths, consider switching to one of the alternative measurement procedures listed below.

Existing mercuric nitrate procedure:

Also called mercury nitrate Hg(NO3)2 or mercury pernitrate. Mercuric nitrate is titrated with chloride to measure chloride concentrations.

Alternative procedures for chloride analysis:

Ion specific probe. This method of analysis requires an initial investment in equipment of several hundred dollars, but with proper care, the equipment has a long lifetime.

Procedures from Standard Methods for the Examination of Water and Wastewater, 19th edition, 1995:

Argentometric method. This is a titration of chloride with silver nitrate using potassium chromate as a color indicator solution. The endpoint is a little more difficult to see, since it's a pinkish yellow.

Potentiometric method. This is another titration of chloride with silver nitrate, but the endpoint is indicated by a change in voltage instead of color. A silver-silver chloride electrode and an electronic voltmeter are needed.

For comments or questions regarding the following pollution prevention pages please contact Maggie Lundell via email at maggie.lundell@metc.state.mn.us or via telephone at 651-602-4769.

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