miscellaneous productsReading time:
Potassium permanganate is mainly used to oxidise and eliminate manganese.
The product (purple flakes) is dissolved by tank mixing. It is not very soluble (5 to 30 g · L–1 at 20°C for a 15 to 60 minutes contact time). There is a danger of deposits forming when concentration rises above 15 g.L-1 and solutions will only keep for short periods. Feeding pumps are used to dispense this product.
Potassium permanganate attacks ferrous metals. Protected steel or plastic materials are used. This product must be handled with care (gloves, goggles).
Carbonate powder is used as a mineral filler in mineralisation applications.
The product is virtually insoluble (15 mg · L–1 to 20 °C). It is formed into a suspension and dispensed at a concentration of approximately 50 g · L–1, using the same devices as those used for lime slurry.
bentonite (clay) – structuralite (clay)
This product is used to weigh the floc obtained from raw water that contains few suspended solids, or little bacterial floc obtained from activated sludge.
Its suspension is prepared and distributed in the same way as calcium carbonate.
Ferrous sulphate is used to precipitate certain salts (CN–, S2–) and, more rarely, in coagulation. The crystallised product (FeSO4, 7 H2O) is supplied as a green powder. It is water soluble (391 g·L–1 at 20 °C, see chemistry and reagents). A densimeter is used to check its concentration.
The solution is prepared in concrete tanks into which product skips are discharged direct along with the dissolution water. A system of perforated pipes is used to recover the aqueous solution. These pipes are usually located in the bottom of the tanks and bedded in a layer of filter sand. As the preparation of solutions below saturation level is not easy achieved, we mainly used saturated liquors that easily re-crystallise when the temperature drops. In order to avoid the associated drawbacks (deposits, solidification in the tank, blocked pipes), several solutions are possible including maintaining a constant temperature.
As the pH of aqueous solutions of ferrous sulphate is acid, the parts in contact with the liquid must be protected or made of plastic materials.