OBTAINING FERRATES OF ALKALINE METALS AND THEIR USE IN THE PROCESSES OF WATER TREATMENT AND WATER PURIFICATION

Abstract

This paper highlights the promising methods of water treatment and water purification using ferrates (VI) of alkali metals as an alternative to existing reagents in the processes of water purification and water treatment. The publication also discusses the basic methods of obtaining ferrates of alkaline and alkaline-earth metals.Ferrate technologies are more effective and less harmful than existing traditional oxidation treatment methods such as chlorination, chloramination and oxidation by permanganate; and can be compared to advanced technologies, such as ozonation or oxidation with chlorine dioxide, that are more expensive and dangerous or require special expertise to work.Oxidation with ferrate can change the surface properties of suspended solids and organic pollutants, that facilitates their removal through coagulation and sedimentation. The product of ferrates decomposition in the solution is iron hydroxide in the form of colloidal aggregates with a highly developed surface, which adsorb heavy metal ions, particles of suspended solids and organic residues, providing additional water purification by coagulation of the pollutants.Ferrate, alone and in combination with additional coagulants, can reduce the total amount of suspended solids, chemical oxygen demand, biological oxygen demand and organic matters. Ferrate also oxidizes cyanides, sulfides, arsenic, phenols, pharmaceuticals, pesticides, and destroys various viruses and bacteria.Significant efficiency of ferrate is due to high oxidation potential and various functions. In acidic conditions, the oxidation potential of ferrites is the strongest (E0 = +2,20 V) among all the oxidizers / disinfectants used up-to-date to clean water and wastewater (in neutral conditions E0= +0,72 V).The achievement of high productivity with the use of smaller doses of the reagent should attract attention of water industries, because, firstly, it will reduce chemicals cost, and secondly, decrease the production of sludge and, ultimately, save operating costs.Regarding methods of obtaining ferrates of alkali metals, there are three main groups: chemical oxidation of iron (II) and (III) compounds in alkaline solutions; electrochemical oxidation of iron in alkaline solutions; high temperature oxidation of iron and iron (III) compounds in solid form. Ferrates of alkaline-earth metals are synthesized by the interaction of aqueous solutions of Na2FeO4 or K2FeO4 with chlorides or hydroxides of calcium and barium. The issue of reduction of producing costs of ferrates by using secondary iron-containing raw materials is still poorly explored and requires more detailed research.Key words: ferrous (VI), water treatment, water purification, oxidation, coagulation.