Reactions involving ferric sulfate are...
Ferric sulfate is shipped in car and truck load lots of 50 lb and 100 lb moisture-proof paper bags and 200 lb and 400 lb fiber drums.
General precautions should be observed when handling ferric sulfate, such as wearing goggles and dust masks, and areas of the body that come in contact with the dust or vapor should be washed promptly.
Aeration of ferric sulfate should be held to a minimum because of the hygroscopic nature of the material, particularly in damp atmospheres. Mixing of ferric sulfate and quicklime in conveying and dust vent systems should be avoided as caking and excessive heating can result. The presence of ferric sulfate and lime in combination has been known to destroy cloth bags in pneumatic unloading devices. Because ferric sulfate in the presence of moisture will stain, precautions similar to those discussed for ferric chloride should be observed. Ferric sulfate is usually stored in the dry state either in the shipping bags or in bulk in concrete or steel bins. Bulk storage bins should be as fight as possible to avoid moisture absorption, but dust collector vents are permissible and desirable. Hoppers on bulk storage bins should have a minimum slope of 36°; however, a greater angle is preferred.
Bins may be located inside or outside and the material transferred by bucket elevator, screw, or air conveyors. Ferric sulfate stored in bins usually absorbs some moisture and forms a thin protective crust which retards further absorption until the crust is broken.
Feed solutions are usually made up at a water to chemical ratio of 2:1 to 8:1 (on a weight basis) with the usual ratio being 4:1 with a 20-minute detention time. Care must be taken not to dilute ferric sulfate solutions to less than 1 percent to prevent hydrolysis and deposition of ferric hydroxide. Ferric sulfate is actively corrosive in solution, and dissolving and transporting equipment should be fabricated of type 316 stainless steel, rubber, plastics, ceramics, or lead,
Dry feeding requirements are similar to those for dry alum except that belt-type feeders are rarely used because of their open type of construction. Closed construction, as found in the volumetric and loss-in-weight-type feeders, generally exposes a minimum of operating components to the vapor, and thereby minimizes maintenance. A water jet vapor remover should be provided at the dissolver to
Ferrous sulfate or copperas is a by-product of pickling steel and is produced as granules, crystals, powder, and lumps. The most common commercial form of ferrous sulfate is FeS04-7H20,with a molecular weight of 278, and containing 55 percent to 58 percent FeS04 and 20 percent to 21 percent Fe. The product has a bulk density of 62 to 66 lb/cu ft. When dissolved, ferrous sulfate is acidic. The composition of ferrous sulfate may be quite variable and should be established by consulting the nearest manufacturers. Ferrous sulfate is also available in a wet state in bulk form from some plants. This form is likely to be difficult to handle and the manufacturer should be consulted for specific information and instructions.
Dry ferrous sulfate cakes at storage temperatures above 68° F, is efflorescent in dry air, and oxidizes and hydrates further in moist air. General precautions similar to those for ferric sulfate, with respect to dust and handling acidic solutions, should be observed when working with ferrous sulfate. Mixing quicklime and ferrous sulfate produces high temperatures and the possibility of fire. The optimum chemical-to-water ratio for continuous dissolving is 0.5 lb/ gal. of 6 percent with a detention time of 5 minutes in the dissolver. Mechanical agitation should be provided in the dissolver to assure complete solution. Lead, rubber, iron, plastics, and type 304 stainless steel can be used as construction materials for handling solutions of ferrous sulfate.
Ferric sulfate and ferric chloride react with the alkalinity of wastewater or with the added alkaline materials such as lime or soda ash. The reactions may be written to show precipitation of ferric hydroxide, although in practice, as with alum, the reactions are more complicated than this.
Ferrous hydroxide is rather soluble and oxidation to the more insoluble ferric hydroxide is necessary if high iron residuals in effluents are to be avoided. Flocculation with ferrous iron is improved by addition of lime or caustic soda at a rate of 1 to 2 mg/mg Fe to serve as a floe-conditioning agent. Polymers are also generally required to produce a clear effluent.
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