WATER SOFTENING

Soft water is a desirable prerequisite for all textile wet processes, except for bleaching with solutions of hydrogen peroxide stabilised by sodium silicate. Modern synthetic detergents do not form precipitates in hard water containing calcium and magnesium ions so a certain degree of hardness is tolerable provided that other dyes and chemicals are not seriously affected by this. In general, however, if a mill is in a region where the water is hard, a softening pretreatment is essential for at least part of the water used. The objective of this is simply to reduce the concentration of the alkaline earth metals to a level at which the water has the desired quality. In many cases, the softening process may reduce the calcium and magnesium ion concentrations to zero.