"Hard" water contains minerals, usually Calcium and Magnesium, that form scale and soap scum. In most cases, soft water is preferred to hard water in industrial cleaning. In some cases it can mean the difference between success and disaster.
Since its been a while since we last talked about water, you may want to review a couple of previous blogs before we go into more depth on this subject.
Water - Hard Water vs. Soft Water
Water - What are ions and ion exchange all about?
The first thing most of us think about at the mention of "soft" water is that thingy in the basement or laundry room that you have to add salt to every once in a while. Yep, that's the thing! BUT, there are other ways to either soften or counteract the hardness of water. Many cleaning chemistry formulations contain ingredients called zeolites that adsorb ions that cause hard water. These ingredients are common in household laundry and bath products and, depending on the degree of hardness and the criticality of cleaning, may be all that is needed to counteract hard water. Chelating agents are also frequently used to bond with hard water ions and metals to de-activate them during the cleaning process. In either of these cases, the "bad actors" are not eliminated but, rather, are "held at bay" by chemical or physical bonding. This type of water "softening" is not, to my knowledge, effective in preventing water spots in rinses etc.
Ion Exchange Water Softening
Fortunately, removing the minerals responsible for hard water is relatively easy and inexpensive using an ion exchange "water softener" much like the ones found in homes. Even if, as many times is the case, water that is simply "soft" is not adequate for a given process, an ion exchange water softener is usually the first step of an industrial water purification process preceded only by simple filtration. Since the hard water ions are actually removed by the ion exchange process, they reduce the burden on subsequent more costly purification processes as will be demonstrated in upcoming blogs.
A water softener is a pressure vessel or "tank" filled with small resin beads. The beads are treated to have an affinity for ions including those of Calcium and Magnesium which are the most prevalent hard water minerals. The water being treated circulates around these resin beads which "exchange" Sodium ions for the Calcium and Magnesium ions. This happens because the resin prefers to bond with Calcium and Magnesium ions over those of Sodium. When the resin has accumulated all of the Magnesium ions it can, it is said to be "depleted" and requires "regeneration." Regeneration is accomplished using a concentrated brine solution (NaCl or "salt") which due to its high concentration forces the resin to release the Calcium and Magnesium ions it has collected replacing them with Sodium ions. Regeneration can be accomplished on-site by periodic "back flushing" or can be done by a service which exchanges depleted resin beds for ones that have been regenerated off-site for a fee. Many facilities opt for off-site regeneration as it is simple and eliminates maintaining and replenishing the required chemistry in the regenerating equipment.
In general, making hard water soft is not all that complex and is usually a case of "better safe than sorry." However, water softening is only the beginning when it comes to most operations requiring extremely high purity water. The next blog will discuss some of the other, sometimes surprising, things found in water that may cause cleaning or other problems.
- FJF -