106.3.2.92 TM-92, Determination of Sulfide sulfur by oxidation of blended slag cements

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106.3.2.92.1 Scope

This method determines sulfide sulfur by oxidation of sulfide sulfur to sulfate during the Loss on Ignition (LOI) test. The LOI ignited material is tested for SO3, subtracted from the initial SO3 and divided by a factor to calculate sulfide sulfur.

106.3.2.92.2 Summary of Method

The initial SO3 is determined by the acid filtrate during the insoluble residue test. The acid filtrate is diluted to the 250-ml mark in a 400-ml beaker, heated close to boiling and 10-ml of 10% barium chloride (BaCl2) is added to the 400-ml beaker. Barium sulfate (BaSO4) precipitates out of solution and placed in a 90 degrees C oven overnight. The solution is filtered and the BaSO4 is collected using filter paper. The beaker is washed with hot deionized (DI) water and the filter is placed in a 1000 degrees C muffle furnace to ash. Once completed, the crucible is placed in a desiccator, cooled, weighed, subtracted from initial weight of the crucible and a factor is used to calculate initial SO3. LOI is determined by adding 1-gram of the blended slag cement to a crucible, placing it in a cool muffle furnace and igniting the sample for 2 hours at 1000 degrees C. LOI determines loss of carbon dioxide (CO2) and moisture (H2O) in the sample. However, blended slag cements contain sulfide sulfur. During the LOI procedure, sulfide sulfur oxidizes to a sulfate and weight gain occurs. An LOI correction is determined to identify the actual LOI. This is done by determining the SO3 on the LOI ignited material (see above), subtracting the SO3 on the LOI ignited material by the initial SO3, multiplying the result by a factor and adding to the uncorrected LOI result. Sulfide sulfur can be determined by subtracting the SO3 on the LOI ignited material by the initial SO3 divided by a factor to calculate sulfide sulfur.

106.3.2.92.3 Equipment and Reagents

  1. Glass beaker, 250 and 400-ml
  2. Hydrochloric Acid (HCl), ACS certified
  3. Filter funnel
  4. Platinum crucible, 15-ml capacity
  5. Filter paper, #40 medium and #42 retentive textured
  6. Muffle furnace, 1000 degrees C capability
  7. Barium Chloride (BaCl2), reagent grade
  8. Deionized water, generated through reverse osmosis system
  9. Glass rod
  10. Oven, maintained at 90 degrees C
  11. Hot plate
  12. Watch glass
  13. 10% BaCl2 solution, 50 grams of BaCl2/500 ml DI water
  14. Desiccator, containing calcium sulfate as drying agent

106.3.2.92.4 Procedure

Weigh 1 gram +/- 0.0005 of sample into a 250-ml beaker. Add an initial 25 ml of DI water, use stir rod to disperse sample, add 5 ml of concentrated HCl and a final 20 ml of DI water for a final volume of 50 ml. When adding acid to the sample, make sure this is done in a vented hood since hydrogen sulfide (H2S) gas evolves and it very poisonous. Place on cool side of hot plate and digest for a minimum of 15 minutes. Remove beaker from hot plate and allow to cool. Filter through a #40 medium textured filter paper and collect the acid filtrate in a 400-ml beaker. Wash beaker and filter paper with hot DI water three times until the filtrate runs clear. Take beaker and dilute to the 225-250 ml mark, place watch glass over beaker and heat on hot plate until solution is almost boiling. Carefully remove watch glass from beaker and add 10 ml of 10% BaCl2 to the solution. Barium sulfate (BaSO4) will precipitate out of solution and place in 90 degrees C oven overnight to allow BaSO4 settle to the bottom of the beaker. Remove beaker from oven and filter through a retentive #42 filter. Wash beaker and filter paper with hot DI water three times and fold a #42 filter paper in half to wipe inside of beaker for any remaining residue. Fold the filter paper in half again and wipe inside the beaker. Transfer filter paper to the filter funnel containing filter with BaSO4a and place into a pre-weighed 15-ml capacity platinum crucible. Place crucible into cool muffle furnace and raise temperature to 1000 degrees C and ignite for 2 hours. Remove, place in desiccator, cool and weigh. Calculate the weight of BaSO4 (Final weight of crucible with BasO4 – initial weight of crucible) and multiply by a factor of 34.3 = initial SO3.

Weigh 1 gram +/- 0.0005 of sample into a 15-ml capacity platinum crucible and tap crucible a few times to pack the sample at the bottom. Place crucible into cool muffle furnace and ignite for 2 hours at 1000 degrees C. The sulfide sulfur in the sample will oxidize to a sulfate during the 2 hours ignition. After 2 hours, remove the crucible, place in a desiccator, cool and weigh. Calculate the mass loss by subtracting the initial weight minus the final weight of the crucible multiply by 100 to determine %LOI. Due to the oxidation of the sulfides in the sample, an LOI correction is needed to compensate for weight gain. The LOI ignited material is transferred to a 250-ml beaker and sample is broken up with a glass rod to disperse sample at the bottom of the beaker. Follow the same procedure for determination of the initial SO3.

Note: Make sure to run a QC standard concurrently with the sample to verify validity of results

106.3.2.92.5 Calculation

As received SO3, %: weight of BaSO4 x 34.3 = initial SO3

SO3 after ignition, %: weight of BaSO4 x 34.3 = final SO3

34.3 = molecular weight of SO3/molecular weight of BaSO4 x 100

Sulfide = final SO3 – initial SO3/2.35

2.35 = molecular weight of SO3/molecular weight of H2S