Features of water softening in a two-chamber electrolyzer

The current state of the hydrosphere is largely determined by human anthropogenic activity. Insufficiently treated or not treated at all wastewater when discharged into surface water bodies significantly deteriorates the quality of water in them and prevents their direct consumption and use. One of the important indicators of natural waters is their hardness, the increased levels of which negatively affect both individual human organs and the possibility of safe operation of technological equipment in many technological processes. The traditional water softening technology today is considered to be the reagent soda-lime or soda-sodium technology, the essence of which is the two-stage treatment of hard water first with calcium carbonate, and then with lime or sodium hydroxide. The main disadvantage of this technology is low efficiency at ordinary temperatures and significant consumption of reagents. Today, ion exchange technology based on cation exchangers is considered more effective, but its use is accompanied by the discharge into the environment of significant volumes of concentrated sodium chloride solutions with admixtures of calcium and magnesium compounds. As a result, a closed cycle of sodium, calcium and magnesium chlorides is formed. Therefore, there has always been a need to reduce the scale of this cycle and reduce the volume of pollutants discharged into the hydrosphere. One of the possible promising processes for softening hard water today is electrochemical technology, which allows, by treating solutions with electric current under appropriate conditions, to correct the hydrogen index, transforming calcium and magnesium ions into insoluble compounds with their subsequent separation from the liquid phase. Our studies have shown that to maintain the necessary efficiency of the softening process, the value of the hydrogen index for the transformation of magnesium ions must be kept at 11.5. For calcium ions, a similar indicator requires a value of 13.0 units. Experiments with a two-chamber electrolyzer with a diaphragm have shown that the voltage applied to the electrodes, which determines the current density on the electrodes, the electrolysis time and the initial water hardness, are decisive in this process. It has been established that in order to obtain the required value of the hydrogen indicator in the cathode chamber, increased water hardness and its corresponding conductivity are necessary. Thus, for magnesium ions, acceptable results were obtained already at their content of 10 mg-eq/dm3 with the addition of 10 mg-eq/dm3 of sodium sulfate. For calcium ions, achieving the required level of the hydrogen indicator turned out to be very problematic and under the specified conditions it did not exceed 12.12, which is insufficient for effective water softening. Thus, the removal of calcium ions from a solution in the form of its hydroxide by electrochemical methods is quite problematic and can perhaps be implemented in specially designed electrolyzers or in the form of other compounds, such as calcium carbonate.