The dependence of the efficiency of the ion exchange of manganese ions from water on the type and form of the ionite and its hardness

Abstract

Drinking water must comply physical, chemical, bacteriological and radiochemical guidelines therefore its quality should be continuously monitored before being introduced into the distribution system. Water used for human consumption may come from various sources: groundwater, spring water; water from rivers, streams, lakes, among other. A large part of the population of Ukraine uses drinking water that does not meet hygienic requirements according to various indicators. Manganese compounds are quite often present in natural waters. Their quantitative content can vary in a wide range, depending on the region, it can be 0,5-10 mg/dm3. It is worth noting that with a high content of manganese compounds in water, their removal is a rather difficult task. Removal of manganese compounds from water can be implemented using the ion exchange method, which consists of filtering water through loading in salt or acidic form. At the same time, softening and desalination of water can occur simultaneously. Therefore, the ion exchange method should be used for comprehensive water purification, softening, and removal of manganese compounds.
 The article presents the results of obtained during the extraction of manganese ions from distilled and tap water using the strongly acidic cationite KU-2-8 and the weakly acidic cationite Dowex MAC-3. Cationites were used in Na+ and Ca2+ form. The concentration of manganese ions (Mn2+) was varied from 5 to 500 mg/dm3. It was shown that the sorption capacity of the cationite KU-2-8 depended on the concentration of manganese ions, the form of the ionite, the presence of hardness ions in water and was little dependent on the pH of the medium. The sorption capacity of the weakly acidic cationite increased with the increase in the concentration of manganese ions and with the increase in the pH of the medium, which changed with the change in the concentration of magnesium sulfate in distilled water. Sorption of manganese ions from tap water decreases for strongly acidic and weakly acidic cations, compared to solutions in distilled water, which is associated with competitive sorption of hardness ions. This is especially noticeable when using ionites in Ca2+ form in solutions in tap water. The use of ionites in Ca2+ form reduces their sorption capacity for Mn2+ and in distilled water to a certain extent. But this effect is smaller compared to tap water. The Thomas model was used in the work to estimate the full exchange capacity of weakly acidic cationite at low concentrations of MnSO4 solution in distilled water.