🌡️ Total mercury in waste gases — manual method according to PN-EN 13211

Environment PN-EN 13211

Overview

WHAT THIS STANDARD IS. PN-EN 13211:2006 is a REFERENCE method (SRM) for the determination of the mass concentration of total mercury in gases discharged through ducts and stacks. "Total mercury" means here the sum of mercury in the gas phase and mercury bound to dust — both fractions go into one result, although they are collected separately: dust on the filter, gaseous mercury in the impingers. PKN card: the standard is CURRENT, Polish version of 2006, it implements EN 13211:2001; the earlier edition PN-EN 13211:2002 (English version) was replaced by it. In accreditation scopes it is cited by 25 laboratories in 63 entries.

SCOPE OF APPLICATION. The method is validated for total mercury concentrations from 0.001 to 0.5 mg/m³, i.e. from 1 to 500 µg/m³. The lower limit has practical significance: the emission limit values for waste incineration plants lie in the same order of magnitude, so the method works close to its lower end and the quality of sampling decides the result more than the analysis itself.

TWO ABSORPTION SOLUTIONS — A CHOICE THAT MUST BE RECORDED. The standard permits two solutions: permanganate (2 % KMnO₄ in 10 % H₂SO₄) or dichromate (4 % K₂Cr₂O₇ in 20 % HNO₃). Both oxidise mercury and bind it in the solution, but they differ in how the sample is prepared for analysis and in their susceptibility to interferences. This is the point at which two laboratories carrying out "the same test according to PN-EN 13211" may work differently — and that is why it is worth indicating in the report and in the accreditation scope which solution was used. The standard number alone does not settle this.

CONDITIONS THAT DECIDE THE VALIDITY OF THE MEASUREMENT. Sampling must be ISOKINETIC — the suction velocity in the nozzle equal to the gas velocity in the duct — and the permissible range of isokineticity given for this method is 95–115 %. Outside this range the sample is not representative of the dust, and therefore not of the mercury bound to the dust either. The second criterion is an ABSORPTION EFFICIENCY above 95 %, checked by comparing the mercury content in successive impingers (the procedure described in the secondary sources we used; we did not have the text of the standard): if the last impinger contains significantly more than a trace, this means breakthrough and the result is underestimated. Both numbers are conditions of validity, not parameters of the result — a measurement that meets them gives a result, a measurement that does not meet them gives none.

FINAL DETERMINATION. The mercury content of the solutions from the impingers and of the rinsings, as well as the mercury from the filter, is determined by the COLD VAPOUR technique — atomic absorption spectrometry (CVAAS) or atomic fluorescence spectrometry (CVAFS). In the process, mercury is reduced to the atomic form and carried into the measuring cell in a stream of carrier gas; hence the name "cold vapour" — atomisation requires neither a flame nor a furnace.

TOTAL MERCURY VERSUS SPECIATION. The standard gives the sum and does not separate the forms of mercury. In measurement practice, elemental and bound (oxidised) mercury are distinguished, and their proportions depend on the fuel and on the flue gas cleaning system — but both enter the result according to PN-EN 13211. A laboratory from which separation of the forms is expected needs a different solution than this standard alone.

WHAT WE DO NOT GIVE. We did not have the text of PN-EN 13211:2006 or EN 13211:2001 — the standard is sold for a fee. The description comes from SECONDARY sources: standard cards of standardisation bodies, a report on emission measurements carried out with this method, and a publication on an interlaboratory comparison conducted according to EN 13211 and EN 14385. We therefore do not give: the volume and number of impingers, the filtration temperature, the minimum volume of the gas sample, the sampling time or the way of calculating the limit of quantification for a particular set-up. The concentrations of the absorption solutions and the criteria (isokineticity, absorption efficiency) come from the same secondary sources, not from the text of the standard — and should be treated as such.

Method principle

The gas sample is taken isokinetically through a heated probe and a filter that retains dust. Mercury in the gas phase is absorbed in a series of impingers containing an oxidising solution — permanganate or dichromate — which converts mercury into a form bound in the solution. Mercury retained on the filter is brought into solution separately. The mercury content of all fractions is determined by the cold vapour technique (CVAAS or CVAFS), and the result is given as the sum: the concentration of total mercury in the gas, related to the sample volume under standard conditions.

Applications

• Measurements of mercury emissions from waste incineration and co-incineration plants as the reference method
• Checking compliance with mercury emission limit values in integrated permits
• Calibration and checking of automated measuring systems for mercury (AMS) with the reference method
• Participation in interlaboratory comparisons conducted according to EN 13211 and EN 14385
• Indicating in the report which of the two permitted absorption solutions was used

Key parameters

Standard

Standard number

PN-EN 13211:2006 (wersja polska; wprowadza EN 13211:2001 [IDT] i EN 13211:2001/AC:2005 [IDT])

Title (PL)

Jakość powietrza — Emisja ze źródeł stacjonarnych — Manualna metoda oznaczania stężenia rtęci ogólnej

Title (EN)

Air quality — Stationary source emissions — Manual method of determination of the concentration of total mercury

Step-by-step procedure

1. Survey of the conditions at the emission source

   Establish the velocity and temperature of the gas, the dust content and the moisture, and select the nozzle for the sampling conditions. Check whether the expected concentration is within the validated range of the method.

2. Choosing the absorption solution and recording it

   Decide whether the permanganate or the dichromate solution will be used. Record the choice in the measurement sheet — two laboratories working according to the same standard may use different solutions, and the standard number alone does not settle this.

3. Isokinetic sampling

   Take the sample keeping the isokineticity within the permissible range (95–115 %). A deviation outside this range invalidates the measurement as regards the mercury bound to dust.

   ⏱ Time: depending on the concentration and the required sample volume

4. Securing the dust fraction

   Bring the filter with the retained dust into solution by a separate route — mercury bound to dust enters the result together with gaseous mercury, but is not collected together with it.

5. Checking the absorption efficiency

   Compare the mercury content in successive impingers. The absorption efficiency should exceed 95 %; a significant content in the last impinger means breakthrough and an underestimated result.

6. Determination by the cold vapour technique

   Reduce mercury to the atomic form and determine it in the stream of carrier gas by CVAAS or CVAFS — separately in the solutions from the impingers, in the rinsings and in the solution from the filter.

7. Calculation and report

   Add up the fractions, relate them to the sample volume under standard conditions and give the result as the concentration of total mercury. In the report, indicate the absorption solution used, the isokineticity achieved and the check of the absorption efficiency — without them the number cannot be verified.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• PROHIBITION OF MIXING: the permanganate solution in sulphuric acid must not be combined with the absorption solutions for other gaseous metals (nitric acid) — contact of the two acids causes gas evolution and a rise in pressure that risks bursting the vessel. This applies to measurements in which mercury is determined in parallel with metals according to PN-EN 14385, i.e. a typical situation
• Mercury and its vapours are toxic — the solutions after the measurement contain mercury in bound form and are hazardous waste, handed over for disposal
• The permanganate solution in sulphuric acid is strongly oxidising and corrosive; preparation requires adding the acid to water, never the other way round
• Potassium dichromate is a carcinogenic and mutagenic substance, and its solutions in nitric acid are corrosive — work only in a fume cupboard, in chemically resistant gloves
• Sampling at the emission source takes place on the measurement platform with hot gases — the rules for working at height and protection against burns from the probe apply
• A result without the stated isokineticity and without the check of the absorption efficiency cannot be verified — both quantities are conditions of validity of the measurement, not an addition to the report

Frequently asked questions