106.3.2.91 TM-91, Determination of Total Sulfur in Fly Ash by Sodium Carbonate fusion
106.3.2.91.1 Scope
This method determines total sulfur in fly ash by sodium carbonate fusion (Na2CO3). A sample of fly ash is fused with Na2CO3, dissolved in acid, converted to a base, filtered, converted back to an acid, heated near boiling on a hot plate, barium chloride (BaCl2) is added and sulfur precipitates out as barium sulfate (BaSO4). Filter the solution and the filter paper is ignited in a muffle furnace. The weight of BaSO4 is determined and calculated as total sulfur.
106.3.2.91.2 Summary of Method
A small sample of fly ash is mixed with Na2CO3 in a platinum crucible, covered and fused in a muffle furnace. The crucible is taken out of the muffle furnace, allowed to cool, placed in a 400-ml beaker and dissolved in 1-2 Hydrochloric acid (HCl). The cover and crucible are quantitatively transferred out of the beaker. Add litmus paper to the beaker, stir and add Ammonium hydroxide (NH4OH) dropwise until litmus paper turns blue. The ammonium hydroxides will precipitate out of solution, place watch glass on top of beaker, boil on hot plate and allow to cool. Filter through a #41 filter pad and collect the filtered solution in a 400-ml beaker. Wash the beaker and filter paper 3 times with hot DI water and make acidic using methyl red as the indicator. Place covered beaker on hot plate to nearly boiling and add 10 ml of 10% BaCl2 solution. BaSO4 will precipitate out of solution and place covered beaker in hood overnight. Filter the solution, wash beaker and filter paper with hot DI water. Place filter paper in pre-weighed crucible and ignite in a muffle furnace. Remove, allow to cool, weigh and calculate the weight of BaSO4. The weight of BaSO4 is converted to SO3 by a factor, which is total sulfur.
106.3.2.91.3 Equipment and Reagents
Glass beaker, 400-ml Hydrochloric acid, ACS grade Filter funnel Platinum crucible, 15-ml capacity Filter paper, #41 and #42 Muffle furnace, 1000 degrees C capability Barium chloride (BaCl2), reagent grade Deionized (DI) water, generated through reverse osmosis Litmus paper Glass rod Hot plate/stirrer Watch glass 10% BaCl2 solution, 50 grams of BaCl2/500 ml of DI water Desiccator, containing calcium sulfate (CaSO4) as drying agent Stir bar and retriever
106.3.2.91.4 Procedure
Weigh 0.5 grams +/- 0.0005 and mix with 2 grams of Na2CO3 in a platinum crucible. Place cover on top of crucible, place in a cool muffle furnace and fuse sample at 1000 degrees C. Take out of muffle furnace and allow to cool. Place crucible and cover in a 400-ml beaker, add 1-3 HCl to the beaker and allow to dissolve. After sample has dissolved, quantitively transfer crucible and cover out of the beaker, add stir bar, litmus paper, NH4OH dropwise, stir until litmus paper turns blue and ammonium hydroxide group precipitates out of solution. Place watch glass on top of beaker, boil on hot plate and allow to cool. Filter solution through a #41 filter and collect the filtered solution in a 400-ml beaker. Wash the beaker and filter paper 3 times with hot DI water. Remove filter paper and wash empty filter funnel with hot DI water into the filtered solution. Turn the solution acidic using methyl red as an indicator and place on hot plate until solution is near boiling. Carefully remove watch glass and add 10% BaCl2 solution to the beaker. BaSO4 will precipitate out of solution and place in hood overnight to cool. Filter through a #42 filter pad, wash beaker and filter paper 3 times with hot DI water. Using a #42 filter paper, fold in half and wipe the inside of the beaker to collect residuals remaining. Fold in half again, repeat wiping, remove filter paper from the funnel and place in pre-weighed crucible. Place crucible in cool muffle furnace and ignite to 1000 degrees C for 2 hours. Remove, cool and calculate the weight of BaSO4. The weight of BaSO4 is converted to SO3 by a factor, which is total sulfur.
106.3.2.91.5 Calculation
Total sulfur as SO3, %: weight of BaSO4 x 34.3
34.3 = molecular weight of SO3/molecular weight of BaSO4 x 100
