ISO 21741:2020 pdf download Stationary source emissions — Sampling and determination of mercury compounds in flue gas using gold amalgamation trap
6.2 Water Conforming with grade 1 specified in ISO 3696 for all sample preparation and dilutions.
6.3 Nitric acid w(HNO 3 ) = 65%, d(HNO 3 ) = 1,4 g/ml. NOTE Nitric acid is available both as d(HNO 3 ) = 1,40 g/ml [w(HNO 3 ) = 650 g/kg] and d(HNO 3 ) = 1,42 g/ml [w(HNO 3 ) = 690 g/kg].
6.4 Sulfuric acid c(H 2 SO 4 ) = 0,5 mol/l. Add slowly 28 ml of concentrated sulfuric acid [d(H 2 SO 4 ) = 1,84 g/ml] to a 1 000 ml volumetric flask containing approximately 500 ml of water while cooling and stirring, and then add water with stirring to make a volume of 1 000 ml.
6.5 Stannous chloride solution ρ(SnCl 2 ) = 100 g/l. Add 60 ml of sulfuric acid (6.4) onto 10 g of tin (II) chloride dehydrate and heat it to dissolve while stirring them. After cooling, add sulfuric acid (6.4) to make a volume of 100 ml. This solution should be purged with inert gas such as argon and nitrogen prior to use to remove traces of Hg. This solution shall be used up within one week from preparation.
6.6 Phosphate buffer solution c(KH 2 PO 4 ) = 0,025 mol/l and c(Na 2 HPO 4 ) = 0,025 mol/l, pH6, 86 at 298 K. Take 3,39 g of potassium dihydrogen phosphate and 3,54 g of disodium hydrogen phosphate in a beaker and add water to dissolve them. Transfer the solution from the beaker to a 1 000 ml volumetric flask and add water to make a volume of 1 000 ml. Store it in a fluoroplastic bottle made of PTFE, PFA or FEP.
6.7 Hydrofluoric acid
w(HF) = 40 %, d(HF) = 1,16 g/ml.
6.8 Hydrochloric acid
w(HCl) = 37 %, d(HCl) = 1,19 g/ml.
6.9 Mercury stock solution
Conforming with mercury standard solutions as specified in ISO 12846 and ISO 17852.
6.10 Rinse solution
w(HNO 3 ) = 50 g/kg.
Take 77 g of nitric acid [w(HNO 3 ) = 650 g/kg] or 72 g of nitric acid [w(HNO 3 ) = 690 g/kg] in a fluoroplastic bottle made of PTFE, PFA or FEP, and add water to make a total weight of 1 kg.
6.11 Sample gas drying agent
Self-indicating coarse grade silica gel.
6.12 Trapping agent of mercury Supporting materials, such as diatomaceous earth and silica beads, coated with gold thin layer or gold nanoparticles are used as trapping agent of mercury. Since the capacity of amalgamation is dependent on the surface area of gold, supporting materials and a gold coating method shall be selected that gives a sufficient surface area for the targeted determination range of mercury. The trapping agents are commercially available or can be prepared in the laboratory. An example of preparation of trapping agent is as follows: onto 3 g of diatomaceous earth with 420 μm to 590 μm grain size, add the solution prepared by dissolving 1 g of tetrachloroauric(III) acid in 20 ml to 30 ml of water, and mix them to make uniform. Heat it at about 353 K to dry it, put it in a furnace, and heat it at about 1 073 K for 30 min while air is being flowed. Gold nanoparticles (average diameter; ca. 10 nm) dispersed in water or ethanol are also available for preparation of trapping agent as well as tetrachloroauric(III) acid. In this case, use the solution prepared by adding 0,3 g of aqueous or ethanol solution of gold nanoparticles at 10% in 20 ml to 30 ml of water instead of tetrachloroauric(III) acid solution. In general, supporting materials coated with gold nanoparticles are able to collect larger amounts of mercury than those coated with gold thin layer prepared with tetrachloroauric(III) acid. 7 Apparatus
7.1 General Two types of sampling systems, a main-stream and a side-stream arrangement, can be employed. In the main-stream system all the sampled flue gas is passed though the gold amalgamation traps, while in the side-stream arrangement only a part of the sampled flue gas is passed through the gold amalgamation traps. The main-stream sampling is used when the flow rate and total sampling volume for the measurements of gaseous and particulate mercury are the same. The side-stream sampling is used when the flow rate or total sampling volume for the measurements of gaseous and particulate mercury is different.
It is also possible to use two sampling trains, one for particulate mercury and one for gaseous mercury, even when the flow rate or total sampling volume is different. Two sampling nozzles, for particulate mercury and gaseous mercury respectively, are placed at neighbouring points in which the physicochemical parameters such as mercury concentration and gas flow rate are considered to be equivalent. Particulate mercury is collected on the filter isokinetically. Gaseous mercury is captured on the gold amalgamation traps non-isokinetically after particles are removed. Non-isokinetic sampling of gaseous mercury is possible only when no water droplets occurs in the flue gas.ISO 21741:2020 pdf download