Coagulation purification of natural water with iron oxide salts

Summary

The efficiency of using ferric chloride and ferric sulphate for coagulation purification of natural and model water depending on the turbidity, color, alkalinity of the source water and flocculation duration is considered. It is shown that for the purification of turbid water, the doses of coagulants related to the iron ion do not depend on the type of coagulant and increase with rise of the turbidity of the purified water. Power dependence of the dose of ferric chloride on the turbidity of the source water was determined. Ferric chloride is the most effective coagulant for reducing turbidity and color, simultaneously providing for the standard concentration of iron ions in purified water. The higher efficiency of ferric chloride compared to ferric sulphate is determined by the presence of polyoxychloride complexes in ferric chloride solutions. It has been established that the main contribution to the reduction of turbidity of water coagulated with iron oxide salts is made by alkalinity that determines the rate and amount of insoluble products of hydrolysis of iron oxide salts. Using the example of coagulation purification of colored waters from different water sources using iron oxide salts, it has been shown that with an increase in color and alkalinity of the source water, no clear correlation dependence of the dose and purification efficiency on these parameters is observed.

Key words

settling , turbidity , chromaticity , coagulation , flocculation , natural water , ferric sulfate , alkalinity , hydrolysis , ferric chloride

Chemical aspects of decoloration of low turbidity natural water with aluminium salts

Summary

The mechanism of decoloration of natural water with aluminium sulfate aluminium polyoxychloride is considered. The complexing reactions of humus acids with aluminium salts mainly contribute to the decoloration of natural water. The parallel proceeding reaction of aluminium sulfate and polyoxychloride hydrolysis facilitates the reduction of aluminium ion concentration in treated water but does not reduce color. Empirical dependences of coagulant dosages on color and alkalinity of raw water have been determined. Higher efficiency and lower dosages of aluminium polyoxychloride compared to aluminium sulfate used for decoloration are stipulated by the polymer origin of aluminium polyoxychloride. The use of coagulants in combination with cationic Praestol 650 flocculant provides for improving the efficiency of decoloration by 10–20% at the optimal coagulant: flocculant ratio of 50:1 for aluminium polyoxychloride and 20:1 for aluminium sulfate.

Key words

chromaticity , natural water , aluminium sulphate , cationic flocculant , aluminium polyoxychloride , humus acids , alkalinity , hydrolysis , complexing