Ion-exchange water softening, sometimes referred to as Base-exchange water softening, is a chemical process whereby scale-forming mineral salts naturally present in the water, are replaced with alternative mineral salts which cannot lead to scale formation. Since these pre-existing mineral salts are those responsible for causing hard water, the process of replacing them is known as ‘softening’. This method is extremely effective at preventing scale for a wide range of applications, and is a straightforward process which can be carried out quietly and efficiently in most buildings.
The mineral salts that cause hard water, i.e. water than can lead to scale formation in water systems, are calcium and magnesium. These are both naturally present in water, and their quantities depend on the location and source of the water. The hardness of water is dependent on how much contact time water has had with calcium and magnesium after it has fallen to the earth as rain. For example, areas close to the east coast with very chalky terrain will produce hard water, because water falls on this land and percolates through the earth, dissolving these hardness forming minerals. The softest water is found in areas such as the Scottish highlands, where rain falls on hard rock strata, and runs off quickly, with little time to dissolve any minerals.
Once dissolved, these minerals form ‘ions’, which are particles possessing either a negative or positive charge. The fundamental component of a water softener is an ‘ion exchange resin’, whose job it is to ‘exchange’ the ions in the water. The resin is pre-charged with sodium ions, which will be released into the water upon capture of the undesirable calcium and magnesium ions. Each resin has a finite capacity of water it can soften, before needing to be recharged with sodium ions.
The process of recharging the resin with sodium is known as ‘regeneration’. This is effected by passing a high strength brine through the resin bed, forcing the resin to release the hardness ions it has captured, and re-adopt fresh sodium ions. Waste water from this process is passed to drain, thus removing the calcium and magnesium ions from the system.