Determination of silica in boiler water - Database & Sql Blog Articles

Determination of Silica in Boiler Water

The determination of silica in boiler water is a critical process to ensure the quality and efficiency of water treatment systems. This method involves spectrophotometry, specifically using the silicon molybdenum blue technique with the UV-1200 spectrophotometer. The procedure is suitable for analyzing silica concentrations below 10 mg/L. The method relies on the reaction between soluble silica and ammonium molybdate under acidic conditions (pH 1.2–1.3), forming a yellow complex that is then reduced to a blue color. The intensity of the blue color correlates with the silica content in the sample. To eliminate interference from phosphates, oxalic acid or tartaric acid may be added, or the acidity can be adjusted accordingly. Safety precautions are essential when handling reagents such as ammonium molybdate, stannous chloride, sulfuric acid, and sodium carbonate. Proper storage and handling of all chemicals are crucial to prevent accidents and maintain accuracy in measurements. The reagents required include: - 50 g/L ammonium molybdate solution: prepared with high-purity water and stored in plastic bottles. - 1% stannous chloride solution: made by dissolving stannous chloride in hydrochloric acid and glycerin, and stored at low temperatures. - Sulfuric acid (C(1/2H2SO4) = 10 mol/L): carefully mixed by adding concentrated sulfuric acid to deionized water. - Sodium silicate (Na₂SiO₃·9H₂O) and anhydrous sodium carbonate, both of high purity. - Deionized water for dilution and preparation. Instruments used include a UV-1200 spectrophotometer, 2 cm cuvettes, platinum crucibles, and a high-temperature furnace set at 100°C. For the test, standard solutions are prepared to create a calibration curve. The silica stock solution is diluted and measured against the standard curve to determine the concentration in the water sample. The absorbance is measured at 720 nm, and the results are calculated using the formula: X (mg/L) = (a ÷ v) × 1000 where 'a' is the amount of silica found in the standard curve, and 'v' is the volume of the water sample in mL. Additional notes include: - Ensure all colorimetric tubes are thoroughly cleaned and tested with blank samples. - Maintain a consistent temperature above 20°C during the analysis to avoid errors due to temperature fluctuations. - If ammonium molybdate dissolves slowly, add a small amount of concentrated ammonia to aid dissolution. - Stannous chloride-glycerol solution can be prepared entirely with glycerin, and heating to about 50°C can improve its stability. Keywords: spectrophotometry; silica; analysis instrument; UV-1200