- Experimental Procedure
Because of the toxicity of barium salts and the use of acids, all work should be performed in the hood and appropriate eye protection must be worn. The use of gloves and lab apron or coats is also recommended.
Qualitative analysis of solubility
Make solutions of the following salts by dissolving 0.1 g of the following compounds in 10 mL of distilled water: Na2SO4, NaCl, Na3PO4 , Na2C2O4, and Na2CO3. To each solution add a solution of 0.1 M barium nitrate dropwise and determine whether a precipitate forms.
Quantitative analysis of solubility
Place about five grams of ACS grade BaCO3, BaC2O4, Ba3(PO4)2, in a clean, standard taper 14/20 size D Buchner type filter funnel (Ace catalog number 9439-08). Dry the funnel and sample for one hour in a 120°C oven, allow to cool to room temperature in a dessicator, and then weigh the funnel and contents on an analytical balance. Insert the funnel into a 14/20 500-mL round-bottom flask and attach to a trap that is attached to an aspirator. Fill a separatory funnel with 500 mL of distilled water. Drip the water from the funnel onto the compound in the filter (stirring gently) using vacuum filtration. The drip rate should be about 10-20 drops per second. There should be approximately a 1/4 inch of water above the compound at all times. When the separatory funnel is empty, fill it once more with 500 mL of distilled water. Drip the water through the funnel. When all the water has passed through the compound in the filter funnel, continue suctioning for a few minutes and then place the funnel with the compound in the oven for two hours. After cooling, reweigh. The loss in weight represents the solubility of the barium salt in 1000 mL of water.
Preparation of alforsite
Combine approximately 10 grams BaCl2x2H2O and 5 grams ammonium dihydrogen phosphate in a 250-mL Erlenmeyer flask. Record the weights of reagents used in order to determine the percent yield. Add 60 mL of distilled water and stir (magnetically) to dissolve. To this solution add 20 mL of 3M NH3 to bring the pH to 10-11, as determined by pH paper. Place the flask on a stir/hot plate and digest the precipitate for at least three days at 70° before drying. The pH should be checked periodically with pH paper and adjusted with NH3- as necessary to keep it at 10-11. Collect the product with vacuum filtration in a filter crucible. Wash with three 20-mL portions of hot water and three 20-mL portions of cold water. Continue the suction for about 15 minutes and then dry the product in a 120°C oven for at least 2 hours.
Qualitative analysis of product
Place a small amount of product in three small test tubes. Add one ml of 1M nitric acid, stir, and then add distilled water to dissolve the barium nitrate. To test for the presence of Ba2+, add one drop of 0.1 M sulfuric acid to one of the solutions. In another test tube, add a few drops of 0.1M ammonium molybdate to test for the presence of phosphate. To test for the presence of Cl-, add a few drops of 0.1M silver nitrate to the solution in the last test tube. In each case, the formation of a precipitate is indicative of a positive test for the ion.
Quantitative analysis of barium
Weigh out about 0.3 g of product, to 0.1 mg (using an analytical balance), in a 50 mL beaker. Dissolve the compound in 3.5 ml of 1 M HNO3 with stirring. Add about 20 mL of water to dissolve the barium nitrate. To the solution add 3 mL of 1M H2SO4 and heat gently for about 30 minutes. Allow the mixture to cool and then filter the precipitate using ashless quantitative filter paper (for example, S&S No. 589 Blue Ribbon). Wash the precipitate 3 times with 5 mL portions of cold water. Fold the filter paper carefully around the precipitate (being careful not to touch the precipitate) and place into a tared, clean porcelain crucible, which has been previously heated to constant weight. Carefully heat the crucible and its contents using a Bunsen burner at low heat and with the lid slightly displaced to allow access to a small amount of air. If the paper catches on fire, the lid should be placed over the crucible to extinguish it. After the paper is completely charred, the Bunsen burner can be adjusted to high heat with the lid removed. The crucible should be heated strongly for approximately 2 hours. After cooling to room temperature, reweigh the crucible and precipitate.
Note: This procedure can also be performed in 3% HCl, which, according to some authors, increases the particle size of the precipitate and make filtration easier.
Quantitative analysis of chloride
Dissolve one gram of product, weighed to 0.1 mg on an analytical balance, in 10 mL of 0.3M HNO3 with mild heating and stirring. Add 200 mL of distilled water and continue heating. Add 0.3M HNO3, slowly, until the mixture is no longer cloudy. [Silver chloride is slightly soluble in acid, so an attempt should be made to minimize the amount of acid in solution.] Now, add 10mL of 0.1M AgNO3. Let the solution digest with stirring (via a stir bar) for one hour. Collect the precipitate with vacuum filtration in a previously dried filter crucible. Wash with 10 mL of cold water. Dry the precipitate in a 110° oven for one hour and then weigh on an analytical balance.
Contamination of soil
Soil obtained from a nursery should be sieved to a particle size no greater than 1.7 mm. Place 25 grams of the soil nto a D-porosity Buchner-type filter funnel. Dry in a 120°C oven for at least two days. After cooling to about room temperature, wash the soil sample with 1.5 L of distilled water using the technique described under Quantitative analysis of solubility. The water must be run through quickly; if water sits in the crucible, the dirt will become a mud that water cannot penetrate. Return the funnel (with soil) to the oven for at least two days.
Now, empty the funnel into a tared aluminum pan. Weigh the pan to find the mass of soil. Add 25 mL of 0.3M barium acetate per 25 grams of soil. Stir the mixture with a stirring rod to ensure homogeneity. Rinse the stirring rod into the pan with distilled water to ensure little loss in mass of soil and barium. Let the mixture dry in the hood for one week.
Determination of barium in contaminated soil
Place about half of the contaminated soil into clean, tared D-porosity Buchner-type filter funnels. Each funnel should contain about ten grams of soil. Dry the funnel with soil in the oven for 2 hours and then cool and weigh. Then quickly run 1000 mL of water through the soil using the procedure described under Quantitative analysis of solubility. Add 10 mL of 1M H2SO4 to the filtrate. Let the mixture settle, then quantitatively filter it through ashless filter paper. Use at least two glass funnels and filter papers for each filtrate to minimize the amount of time involved. After filtering, place the papers into tared crucibles and burn off the paper using the same technique described in Quantitative analysis of barium. Weigh the crucibles to determine the amount of BaSO4 present.
Remediation of soil
Add a solution of 0.1 g NaCl and 0.6 g ammonium dihydrogen phosphate in 30 mL of distilled water to 25 grams of soil. Add about 10 mL of 6 M NH3 to bring the pH to 9. Check the pH with pH paper, and add more base if necessary to keep the pH at 9. Pour the solution over the soil, mix with a stirring rod, and rinse the stirring rod into the pan with distilled water. Let the soil dry for two weeks, adding ammonia to adjust the pH as necessary during the first week.
Determination of barium in remediated soil
Place about 10-grams of the remediated soil into clean, tared Buchner-type filter funnels and dry in a 125°C oven for 2 days. After cooling, weigh the funnel to find the mass of soil. Using the same technique described for Quantitative analysis of solubility, run 1000 mL of distilled H2O through the sample. Add 10 mL of 1M H2SO4 to the filtrate. Let the mixture settle, then quantitatively filter it through ashless filter paper. Use at least two funnels and filter papers to minimize the amount of time involved. After filtering, place the papers into tared crucibles and burn off the paper using the same technique described in Quantitative analysis of barium. Weigh the crucibles to determine the amount of BaSO4 present.
- Background Information
Throughout the past few decades, much attention has been given to environmental lead contamination. The U.S. Agency for Toxic Substances and Disease Registry, as well as the Center for Disease Control, has ranked lead as the most hazardous substance in America. Almost 10% of American preschoolers have dangerous levels of lead in their blood (1). Lead has the danger of cumulative effects from multiple exposures (2) and can be stored in the bones. It retards growth, leads to neurological impairment, stillbirth or miscarriage, and decreases fertility (2).
Industry, lead-based paint, and leaded gasoline have led to the majority of environmental lead contamination. It is estimated that a residue of 4 to 5 million metric tons of lead has been dispersed throughout the environment due to the combustion of leaded gasoline (3). Moreover, almost equal amounts of lead were added to gasoline between 1929 and 1989 and white paint between 1884 and 1989 (3). Concentrations of lead in virgin soil range from 15-200 ppm (4). At lead battery recycling sites throughout the United States, concentrations range from 60,000-100,000 ppm (5). Despite controversy over the bioavailability of lead to humans through ingestion or inhalation, the EPA set "tough" limits on allowable lead concentrations in soil. Hazardous lead levels are defined as >400 ppm in bare soil in children's play areas or >1200 ppm for all other soil (6).
Many different techniques designed to extract lead from the environment are being explored. These techniques include separation by particle size followed by acid leaching, extraction by chelating agents, the use of high temperature, electrodeposition, and conversion to lead chloride which can than be extracted (5).
In situ immobilization is a more cost efficient alternative to extraction of lead (7). Pyromorphite, Pb5(PO4)3Cl, is the least soluble environmental form of lead. Treatment of contaminated soil by hydroxyapatite, Ca5(PO4)3OH, has been shown to remove at least 98% of lead (7). Research is underway to determine if ingesting pyromorphite has toxic effects. Pigs fed pyromorphite did not have an increase in blood lead levels (5).
- Nedwed, T.; Clifford, D. A. Waste Mgt. 1997,17, 257.
- Sigma Aldrich MSDS, 2001.; Jin, A.; Teschke, K.; Copes, R. Sci. Total Env. 1997, 208, 25.
- Mielke, H. W.; Reagan, P. L. Env. Health Pers. 1998, 106, 218.
- Lanphear, B. P.; Burgoon, D. A.; Rust, S. W.; Eberly, S.; Galke, W. Env. Research 1998,76, 125.
- Nedwed, T.; Clifford, D. A Waste Mgt. 1997,17, 258.
- Public Health Reports. 2000, 115, 502..
- Chen, X.; Wright, J. V.; Conca, J. L.; Peurrung, L. M. Water, Air, Soil Poll. 1997, 98, 59.