FI73403C - Process for the preparation of water purification chemicals. - Google Patents

Description

1 73403

This invention relates to a process for preparing a water purification chemical containing trivalent iron from iron.

The object of the present invention is to provide a simple and rational method for preparing a water treatment chemical containing trivalent iron from an iron starting material. More specifically, the object of the invention is to oxidize divalent iron to trivalent iron in a simple and rational manner.

Salts containing trivalent iron are now used as precipitating chemicals in water purification processes because Ferri ions have the ability to form flocs containing colloidal substances in water as well as co-precipitate the phosphates present. Trivalent iron is often added in chloride form or in the form of a double salt containing chloride and sulfate anions. Such water treatment chemicals are supplied in the form of solutions containing 12% iron and are used in large treatment plants with short flow times.

Cheap scrap iron is commercially available which should be oxidized to trivalent iron, especially in the case of chlorine, as ferric chloride is a water-soluble compound. However, dissolving metallic iron in hydrochloric acid gives only divalent iron and it is possible to obtain 2 + only a few percent of Fe in solution.

It is also desirable to be able to oxidize metallic iron to trivalent iron to obtain ferric chloride, and in particular ferrous chloride with a high Fe content, since it is Fe 2+ ions that cause flocculation when used as a water purification chemical.

73403 2

Surprisingly, it has been found possible to oxidize ferrous ions to ferric ions according to the present invention in a simple apparatus and at a cost which competes well with the oxidation methods known and used in the past, despite the use of very cheap chlorine gas in these known methods. Thus, it is a feature of the present invention to oxidize divalent iron in hydrochloric acid with chlorate iron to bring Ferri ions into solution. Other characteristic features of the invention are set out in the appended claims.

According to the present invention, it is possible to dissolve metallic iron in concentrated hydrochloric acid to give a maximum concentration of 3-4% Fe. By continuously adding chlorate-2 + ti ions to such a hydrogen chloride solution, Fe is oxidized

Fe ^ + and more iron can be dissolved and oxidized _ 3+. .

Fe: ksi.

These reactions follow the formulas 6Fe + 12 HCl -> 6FeCl2 + 6H2 6FeCl2 + NaClO3 + 6HCl -> 6FeCl3 + 3H2O + NaCl.

By means of the invention it is possible to obtain a ferric chloride solution containing at most 15% Fe. According to this method, scrap iron is dissolved in concentrated hydrochloric acid, after which the chlorate is continuously added in an amount corresponding to the amount of dissolved and oxidized iron, i.e. the o x obtained.

The amount of Fe. A smaller amount of water should be added to increase the solubility of FeCl2. FeCl2 is more soluble in water than in hydrochloric acid and provided that the solution contains large amounts of hydrochloric acid, crystallization of FeCl2 may occur.

However, it has been found that the amount of hydrochloric acid required in the reaction is less than the stoichiometric amount, while the amount of chlorate required is slightly more than the stoichiometric amount. If chlorate ions are added at a higher rate of 2+ than Fe is formed, chlorine dioxide tends to evaporate as a result of the reaction temperatures formed. The reaction Fe 2+ -> Fe 2+ is exothermic.

The invention will now be described in more detail with reference to the following working examples, some of which are included for comparative purposes.

Example 1 64 g of scrap iron was dissolved in 320 g of 32% Hei and 40 g of water. After eight hours, hydrochloric acid 2+ contained 3.5% Fe. A total of 21.5 g of sodium chlorate was then added continuously over 16 hours. The final product was 420 g of a FeCl3 solution with a 15% iron content. The density was 1.45.

Example 2

Example 1 was repeated, but with the difference that sodium chlorate was added batchwise in seven 4 g portions over 16 hours. As a result, 28 g of NaCl 2 were needed. However, it was found that significant amounts of chlorine dioxide were released with each addition. In other respects, the catch was the same.

Although sodium chlorate was used in the above embodiments, it will be apparent to anyone normally skilled in the art that any chlorate such as potassium chlorate (calcium chlorate), ammonium chlorate and barium chlorate may be used, although sodium chlorate should be preferred for cost reasons. Chlorates given in parentheses are not preferred, although they are capable of causing sulfate precipitation (CaSO 4, BaSO 4).

Hypochlorite can be used instead of chlorate, although larger amounts must be used in this case. As with chlorate, the corresponding salts can be used.