Method D-6784

Standard Test Method for Elemental, Oxidized, Particle-Bound, and Total Mercury in Flue Gas Generated from Coal-Fired Stationary Sources (Ontario Hydro Method)

This method is for the isokinetic collection and analysis of mercury (Hg) emissions from coal-fired stationary sources.  It is a draft method and commonly known as the Ontario Hydro Method.  It was developed by a predecessor company of what is now Ontario Power Generation for utilities that are required to perform Hg stack testing for EPA's Hg Information Collection  Requirement (ICR). 

Particle-bound Hg is collected in the front half of the train.  Oxidized Hg is collected in the impinger containing chilled, aqueous potassium chloride (KCl).  Elemental Hg is collected in impingers containing chilled, aqueous acidic hydrogen peroxide (H₂O₂) and chilled, aqueous acidic potassium permanganate (KMnO₄). This method also allows for the determination of particulates following Method 5 procedures.

Samples are collected isokinetically using a modified Method 5/17 train consisting of a quartz filter containing no organic binders and a series of eight impingers.   Impingers 1-3 are filled with 100mL of a 1N KCl solution.  Impinger 4 is filled with 100mL of an aqueous 5% HNO₃ and 10% H₂O₂ solution.  Impingers 5-7 are filled with 100mL of aqueous acidified KMnO₄ and 10% H₂SO₄. Impinger 8 is filled with 200-300g of silica gel. 

If the source is known to contain high amount of moisture, the method suggests placing an oversized impinger or empty impinger between the KCl and HNO₃ impingers.

It is important that no metal be used in the probe, probe liner, filter support, or in the collection brushes used in sample recovery.  Metal parts could serve as a source of contamination of the sample.  It is also important to note safety precautions to be used when shipping the KMnO₄.  There must be a way for the glass container to vent as KMnO₄ reacts with acid present in the solution to form a gas and there must be a way for the container to vent, otherwise, it becomes an explosion hazard.

After collection, the contents of all impingers are weighed for the determination of stack moisture.  The filter is folded such that the particulate is on the inside on the filter and placed in a petri dish.  An acetone rinse of the probe, liner, and front half of the filter holder (if particulates are determined) is collected in a separate container.  A rinse with 0.1N HNO₃ is then performed on the same parts of the train and collected in a separate container.  If there is no particulate determination then only the HNO₃ rinse is performed and collected.

The contents of impingers 1-3 are combined in one container.  The filter support, back half of the filter holder, and connecting glassware is rinsed with 0.1N HNO₃ and combined with the impinger contents.  If the solution is not purple, then all a small amount of 5% KMnO₄, gently mix, until the purple color remains.  Let the solution sit for 15 minutes after each addition.  Then rinse with 10% HNO₃ to get rid of any persisting brown deposits in the impingers.

The contents of HNO₃/H₂O₂ impinger 4 are combined with a 0.1N HNO₃ rinse of the connecting glassware.  Rinse a minimum of two times.

The contents of impingers 5-7 are combined in one container.  The connecting glassware and impingers are rinsed two times with 0.1N HNO₃.  A third rinse is performed with 0.1N HNO₃ that contains several drops of 10% hydrosylamine solution.  This rinse is used to remove any brown deposits from the impingers.  Combine all rinses in the same container as the impinger contents.  If the contents of the container go clear, add a small amount of H₂SO₄/KMnO₄ solution until it's pink or slightly purple.

This sample recovery method produces five unique fractions from each sample.  Each fraction is analyzed separately and in duplicate.  Per the method, every 10th sample should be measured in triplicate.  All measurements should be within 10% of each other.  Analysis is performed using cold-vapor atomic absorption (CVAAS) or cold-vapor atomic flourescence spectroscopy (CVAFS).