Features of Application of Aluminum–Iron Composite Coagulants in Purification of Water with High Content of Natural Organic Substances

Disposal of red mud from aluminum production is a worldwide problem and is of great importance in protecting the environment. In previous studies, the authors determined the possibility of obtaining a composite coagulant for the treatment of natural water and wastewaters. The effectiveness of purification of colored Dnieper water by such a reagent due to the presence of iron and aluminum compounds in its composition was shown. On the other hand, there were difficulties associated with an increase in the content of residual iron in purified water. Obviously, for this reason, iron coagulants (in “pure” form and mixed with aluminum sulfate) have not been used in the purification of Dnieper water. In continuation of these works, we have studied the use of composite coagulants and mixtures obtained from red mud using hydrochloric and sulfuric acids, sulfates of iron and aluminum in different proportions. The article presents the results of seasonal studies on the treatment of Dnieper water using jar tests, simulating the real parameters of the existing water treatment plant. It has been found that the best effect of purifying Dnieper water is achieved by using composite mixtures with a ratio of Fe2O3/Al2O3 not exceeding 1/1. A significant effect of pH on the residual concentrations of iron and aluminum in water has been noted. The results of the work are in good agreement with modern ideas about the coagulation of such waters, explain the failures in the use of iron-containing coagulants, and determine the possible ways of this application in the purification of Dnieper colored water containing a significant amount of natural organic compounds.