Ironbased Compounds

Iron compounds have pH coagulation ranges and floe characteristics similar to aluminum sulfate. The cost of iron compounds may often be less than the cost of alum. However, the iron compounds are generally corrosive and often present difficulties in dissolving, and their use may result in high soluble iron concentrations in process effluents. Among the most commonly used iron compounds used in wastewater treatment applications are ferric chloride, ferrous

Liquid ferric chloride is a corrosive, dark brown oily-appearing solution having a weight as shipped and stored of 11.2 to 12.4 lb/gal (35 percent to 45 percent FeClj). The ferric chloride content of these solutions, as FeCl3, is 3.95 to 5.58 lb/gal. Shipping concentrations vary from summer to winter due to the relatively high crystallization temperature of the more concentrated solutions. The pH of a 1

The molecular weight of ferric chloride is 162.22. Viscosities of ferric chloride solutions at various temperatures are can be found in reference 13. Ferric chloride solutions are corrosive to many common materials and cause stains which are difficult to remove. Areas which are subject to staining should be

Normal precautions should be employed when cleaning ferric chloride handling equipment. Workers should wear rubber gloves, rubber apron, and goggles or a face shield. If ferric chloride comes in contact with the eyes or skin, flush with copious quantities of running water and call a physician. If ferric chloride is

Ferric chloride solution can be stored as shipped. Storage tanks should have a free vent or vacuum relief valve. Tanks may be constructed of FRP, rubber-lined steel, or plastic-lined steel. Resin-impregnated carbon or graphite are also suitable

It may be necessary in most instances to house liquid ferric chloride tanks in heated areas or provide tank heaters or insulation to prevent crystallization. Ferric chloride can be stored for long periods of time without deterioration. The total storage capacity should be 1.5 times the largest anticipated shipment, and should provide at least a ten-day to two-week supply of the chemical at the design average dosage. It may not be desirable to dilute the ferric chloride solution from its shipping concentration to a weaker feed solution because of possible hydrolysis. Ferric chloride solutions may be transferred from underground storage to day tanks with impervious graphite or rubber-lined self-priming centrifugal pumps having Teflon rotary and stationary seals. Because of the tendency for liquid ferric chloride to stain or deposit, glass-tube rotameters; should not be used for metering this solution. Rotodip feeders and diaphragm metering pumps are often used for ferric chloride, and should be constructed of materials such as rubber-lined steel and plastics.

Materials for piping and transporting ferric chloride should be rubber or Saran-lined steel, hard rubber, FRP, or plastics. Valving should consist of rubber or resin-lined diaphragm valves. Saran-lined valves with Teflon diaphragms, rubber-sleeved pinch-type valves, or plastic ball valves. Gasket material for large openings such as manholes in storage tanks should be soft rubber; all other gaskets should be graphite-impregnated blue asbestos, Teflon, or vinyl. System pacing and control requirements are similar to those discussed previously for liquid alum. Ferrous chloride, FeCl2, as a liquid is available in the form of waste pickle liquor from steel processing. The liquor weighs between 9.9 and 10.4 lb/gal and contains 20 percent to 25 percent FeCl2 or about 10 percent available Fe2+ . A 22 percent solution of FeCl2 will crystallize at a temperature of - 4 °F. The molecular weight of FeCl2 is 126.76. Free acid in waste pickle liquor can vary from 1 percent to 10 percent and usually averages about 1.5 percent to 2.0 percent. Ferrous chloride is slightly less corrosive than ferric chloride.

Waste pickle liquor is available in 4,000 gal truckload lots and a variety of carload lots. In most instances the availability of waste pickle liquor will depend on the proximity to steel processing plants.

Since ferrous chloride or waste pickle liquor may not be available on a continuous basis, storage and feeding equipment should be suitable for handling ferric chloride. Therefore, the ferric chloride section should be referred to for storage and handling details.

Ferric sulfate is marketed as dry, partially-hydrated granules with the formula Fe2(S04)3-X H20,where X is approximately 7. Typical properties of a commercial product are given in Table 3.

Table 3. Typical Properties of Ferric Sulfate




Molecular Weight

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