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20 Name: CALCIUM OXIDE (LIME, QUICKLIME) CAS No.: 1305-78-8 Chemical Formula CaO — Description: NAS/CWTC 007-82 Formula Weight: 56.0 Hard, white or grayish-white porous pebble or powder, odorless, and quick slaking. Solubility in water: 1 g/840 ml at 25°C, 1 g/1,740 ml at 100°C. Soluble in glycerin, but insoluble in alcohol. Used primarily as a softening agent and for pH adjust- ments. Purity Requirements: The RMIC values are based on a maximum dosage of 500 mg of calcium oxide/liter of water and are to be compared to impurity concentrations obtained by using sample proce- dures described in this monograph. If the actual dosage is other than 500 mg/liter, the user is cautioned to consult Table 2 for appropriate RMIC values. Impurity Arsenic Cadmium Chromium Fluoride Lead Selenium Silver RMIC mg Impurity/kg Calcium Oxide 10 2 10 * 10 10 *A RMIC has not been established for fluoride. All producers of calcium oxide must analyze and state the concentration of fluoride in the calcium oxide produced.
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21 Bulk Sample Collection: Sample in accordance with Standard for Lime, AWWA B202-77, American Water Works Association, Denver, Colorado (1977), except store final 2-lb sample in moistureproof glass. Analytical Sample Preparation: Crush about half of the 2-lb sample so that it passes a No. 6 U.S. standard sieve, preferably using a nonmetallic crusher or a glass mortar and pestle. Mix crushed sample thoroughly and place in an airtight moistureproof glass container. Take a 50-g portion of the crushed sample and pulverize using a nonmetallic pulverizer or a glass mortar and pestle until sample passes a No. 100 U.S. standard sieve. Mix pulverized sample thoroughly and place in an airtight moistureproof glass container. Initial Slaking: Pipette 4 ml of deionized distilled water in a 150-ml beaker. Place on a hot plate at a low heat and bring water to approximately 60°C. Place stirring rod in beaker and add 1 g pulverized calcium oxide slowly while stirring. If necessary, remove beaker from hot plate momentarily to control spattering. Mix slurry thoroughly to include all the pulverized lime. When a smooth paste is obtained, remove beaker from hot plate and slowly add 50 ml of 80°C deionized distilled water while stirring. Cool to room temperature. Filter through GF/C filter under vacuum into a 150-ml beaker. Using a 25-ml burette, add 1+4 HNO3 until the pH remains between 1.8 and 2.0 for 5 minutes. Transfer quantitatively into a 1,000-ml volumetric flask and dilute to volume with nitric acid dilution solution. Analytical Sample PreParation--Fluoride: Weigh 10 g of sample (to the nearest milligram) into a 400-ml beaker. Rehydrate the lime by slowly and care- fully adding up to 250 ml of deionized water. Place 400 ml of deionized distilled water into a 1-liter side-arm distilling flask. Carefully add 200 ml of concentrated sulfuric acid. Swirl until contents are homogeneous
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22 (essential for safety during distillation). Add 25-35 glass boiling beads. Begin heating, slowly at first, until the temperature of the flask contents reaches 180°C. Discard the distillate. Cool the acid mixture. Quantita- tively transfer the lime suspension (carefully) to the distilling flask until all the slurry has been transferred along with 300 + 5 ml of water (i.e., sample contained in 300 ml of water). If there is reason to suspect presence of chlorides in sample, add 5 mg of silver sulfate for every milligram of chloride. Distill until flask tempera- ture again reaches 180°C. Determine fluoride in the distillate. Sample Analyses: The analyses are to be performed on the calcium oxide solution in accordance with: Standard Methods for the Examination of Water and Waste- water, 15th Edition, American Public Health Association, Washington, D.C. (1981). Arsenic Cadmium Chromium Fluoride Lead Selenium Silver 304 304 304 413B 304 304 304
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