20.08.2015   Handbook Nuclear Terms

Hardness

(a) Definition. Dissolved salts of calcium and magne­sium impart the property of “hardness” to water. Hardness is characterized by the formation of insoluble precipitates, or curds, with soaps. Temporary hardness, caused by calcium and magnesium bicarbonate, is removed by boiling, which causes these salts to decompose, liberating C02 and

image215
image216

precipitating carbonates. Permanent hardness is due to the sulfates, chlorides, and all the soluble calcium and magne­sium salts other than the bicarbonates. Permanent hardness is not removed by boiling.

(b) Measurement Techniques. Total hardness is deter­mined by adding a standard soap solution to a measured amount of sample and shaking the mixture vigorously between additions of the soap solution until an unbroken lather is maintained for 5 mm on the water surface. The volume of soap used is referred to a chart or multiplied by a factor. The result is expressed in parts per million.

Chloride concentration is determined by titrating a measured volume of sample with standard AgNC>3 solution, using potassium chromate as an indicator The end point is red coloration.

Equivalent sodium sulfate determination is made by titrating with sodium hydroxide solution, with phenol — phthalein as indicator, after adding an excess of benzidine sulfate to a measured sample. The benzidine sulfate precipitates the sulfate in the sample. After standing, filtering, and washing, the precipitate is titrated with NaOH. Turbidity-measuring instruments, described in Sec. 4-7.6, can be used for sulfate determination Barium

image142

9 1 9 3

pH AT 25°C

Fig. 4.50—Theoretical relationship between pH and conduc­tivity for ammonia (From J. H. Hicks, Babcock and Wilcox Nuclear Power Generation Division Water Chemistry Manual, Part 13, Curves, 1969.)

Подпись: Fig. 4 51—Relationship between conductivity and pH for ammonia solutions. (From J H. Hicks, Babcock and Wilcox Nuclear Power Generation Division Water Chemistry Manual, Part 13, Curves, 1969 )
Подпись: SAMPLE TEMPERATURE °F 50 60 70 80 90 100 110 120 Fig 4.49—Temperature correction to 25°C for pH (ammonia solutions). (From J H Hicks, Babcock and Wilcox Nuclear Power Generation Division Water Chemistry Manual, Part 13, Curves, 1969 )

chloride and hydrochloric acid added to the measured sample cause a white precipitate of barium sulfate to form. The resulting turbidity is measured and is an indication of sulfate concentration.

4- 7.6 Turbidity

A turbidity transmitter depends upon the principle that suspended solids in a liquid absorb and scatter part of any light passing through the liquid. The transmitter is ar integral assembly of a light source, a flow tube, and a light-intensity detector (Fig. 4.52). The change in radiant energy reaching the detector varies the resistance in one arm of a Wheatstone bridge A compensating filament m the second arm of the bridge corrects for ambient tempera­ture.