AWWA M4:2004 pdf download.History, Theory, and Chemicals
Because fluorosilicic acid contains a high proportion of water, shipping large quantities can be expensive. Large users can purchase the acid directly from the manufacturer in bulk lots (tank cars or tank trucks), but small users must obtain the acid from distributors, who usually package it in drums or polyethylene carboys. Rather than attempt to adjust the acid strength to some uniform figure, producers sell the acid as it is produced and adjust the price to compensate for acid strength greater or less than the quoted figure.
Suppliers usually provide assay reports of the acid strength of each lot. Attempts to dilute the acid are subject to errors in measuring both the acid and the diluting water. The acid should be used undiluted as it comes from the shipping containers. If the acid is too concentrated for the solution feeder to handle, then a smaller sized feeder should be used or a weaker solution of other, less expensive compounds should be used, such as saturated solutions of sodium fluoride. (Very small metering pumps are available.)
Sodium fluorosilicate is sold in two commercial forms: regular and fluffy. The regular form has a density of about 85 lb/ft 3 (1,400 kg/m 3 ), the fluffy form about 65 lb/ft 3 (1,000 kg/m 3 ). A typical sieve analysis of the regular grade allows more than 99 percent through a 200-mesh sieve and more than 10 percent through a 325-mesh sieve. Depending on feeding characteristics, other size specifications can be selected. Experience shows that a low moisture content plus a relatively narrow size distribution results in a material that is handled better by dry feeders.
Considerable quantities of sodium fluorosilicate are imported. Sodium fluorosili- cate is normally packed in bags and drums similar to those used for sodium fluoride. As with sodium fluoride, sodium fluorosilicate must be made into a solution in a dissolving chamber before being fed into the water supply.AWWA M4 pdf download.