PROCESS FOR PREPARING SOLUTIONS FOR WATER TREATMENT, CONTAINING TRIVALENT IRON AND USE OF OBTAINED PRODUCTS

摘要

The invention relates to a process for the preparation, from ferrous iron, of solution-form water treatment chemicals which contain ferric iron, to a granulated intermediate product obtained in the process, and to the use of the end products of the process. In the process, a raw material which contains ferrous iron in the form of an aqueous solution and possibly impurities is oxidized at an elevated temperature so that a precipitating, substantially pure ferric compound and a solution phase which contains the said impurities are obtained. The essential idea of the invention is that the precipitation is conducted in such a manner that part of the ferric iron precipitates in the form of goethite FeO(OH) or, in the presence of sulfate ions, in the form of hydronium jarosite H3OFe3(OH)6(SO4)2, while part of the ferric iron remains as a water-soluble ferric compound in the solution phase. Suitable raw materials include impure ferrous sulfate and pickling solutions which contain ferrous chloride. The precipitated pure ferric compound can further be separated by filtration or, alternatively, the slurry can be granulated to form a solid intermediate product and be later reslurried in water, whereupon a pure ferric compound can be separated by filtration. The pure ferric compound is dissolved in an acid, whereupon it is suitable as a coagulant for the purification of drinking water, and the solution phase is suitable as such as coagulant for the treatment of waster water.