By John F. Allen

Being able to explain the details of the water softening process to a prospective buyer can be a decided asset in a sales presentation. But it take s a special skill to do this effectively – a skill few water conditioning dealers have. This article was prepared for Water Conditioning Sales to help hurdle this obstacle. It was written by John F. Allen, former Science editor of the San Francisco Chronicle, on assignment by the Western Division of Diamond Alkali Company, as a service to the Industry. The Company is a supplier of ion exchange resins. (Featured October, 1962, Editor).

You’ve seen it happen a hundred times on television: The “bad guys,” hard, destructive and mean, have it pretty much their own way during the early part of the “horse opera,” running rough-shod through the town. Just when things seem hopeless, along comes the straight-shooting sheriff. He jails the “bad guys” and then turns loose the “good guys” – always soft-hearted and good to their mothers – to clean things up.

That, if you need one, is quite a good analogy to describe the intricate and fascinating chemical reactions that go on inside a typical water conditioning unit.

Like most analogies, it’s a bit too simple. But then, for the average man, even long in the business of water conditioning sales, the explanations of the chemists are much too complex. Let’s try to strike a middle ground.

The story starts simply: with John Lyly’s “soft droppes of rain” falling from a cloud. But even as they drop, these supposedly pure and uncontaminated spheres of water – that grandma once collected in a barrel to wash her hair – are beginning to change.

Long before each drop strikes the ground it will have dissolved into itself gases from the atmosphere and minerals from air-borne dust. Already the soft rain has begun to turn hard, before it even touches the ground; already the “bad guys” have started to gather.

But they arrive in force only after the rain soaks into the earth. As the water seeps down through underground beds of various sorts of soil it takes into solution more and more of the minerals that make it hard. Chief among the villains are calcium and magnesium, found largely in beds of limestone. (Lyly, the 16th Century poet, spoke truer than he knew when he said his “soft droppes of water pierce the hard marble” – for marble is a form of limestone.)

While calcium and magnesium contribute most to the hardness of water, there are other minor “bad guys” too: metals like iron, manganese and aluminum. All are picked up by the water in the form of ions.

The Nature of Ions

An ion is a strange sort of misfit in the usually neat and ordered sub-microscopic world of the chemist and physicist. The elemental building block of that world is the atom, a fantastically tiny sort of planetary system, where electrons orbit around a central nucleus, much as the earth and the other planets of our solar system orbit around the sun.

The ordinary atom owes its stability to the fact that the positive electric charge of hits nucleus is equal to the sum of the negative charges of its orbiting electrons. The net result is a stable, electrically neutral system.

An ion lacks this stability, this neat electric neutrality. It is an atom with too few or too many electrons. If it lacks one or more electrons, the scale tips in favor of the positively-charged nucleus. This positive sort of atom or ion is called a cation (pronounced “cat-eye-on”). Where extra electrons throw the balance toward a total negative charge, the ion is called an anion (pronounced “an-eye-on”). Ions become active or mobile only when their mineral constituents are dissolved in water.

The metals which concern us here – which contribute most to the hardness of water – are cations. They are molecular fragments consisting of calcium, magnesium and other metals, fragments made up of electrically lop-sided atoms, with fewer than the normal number of electrons.

No one in the water conditioning business needs to be told about the damage these tough cations can create. Everything from the ring around the bathtub and a pretty girl’s dull hair to the water heater that springs a leak a week after its guarantee runs out can serve as testimony to the depredations of these “bad guys.”

The Battle Against Hardness

Altogether it’s little wonder that man’s search for a means of extracting the harness from water has been long and intense. In modern times this search has centered around a substance that would take advantage of the electric instability of the hard ions, to trap them and then to release in their stead soft ions. In other words, what was wanted was a sharp-shooting sheriff to round up the “bad guys” and turn loose the “good guys” to clean up the town.

Strangely enough, there is some suggestive evidence that this principle of ion exchange was used – without, of course, being understood – as early as 100 years before Christ, as a medical treatment for ailments ranging from alcoholic over-indulgence to dysentery.

This strange medicine came in the form of small discs of clay called terra sigillata (sealed earth), which were swallowed by the patients and were said to soak up the poisons in their bodies and release healing substances. Some of these discs exist to this day, and a group of New York University research physicians who have studied them suggest they may have acted as internal ion exchanges and may really have been effective.

Historians of science credit the discovery of the chemical principle of ion exchange to two British Scientists, J. Thomas Way and H. S. Thompson, who in the 1850’s reported that certain soils would remove from solution the alkaline half of a dissolved salt. Like all too many discoveries, this one sat on a shelf for many years before it found a job to do. It was not until 1910 that Richard Gans, a German chemist, put the principle to work as a water softener. He trickled hard water through a tank of crystalline aluminum silicate, and found that most of the hardness was removed. Aluminum silicate is one of a group of granular minerals called zeolites (named after the Greek word for “boiling water” because they give off their heavy content of water easily at low temperatures). These natural silicate minerals – zeolites or greensands – were the first commercial ion exchange materials use din water conditioners.

Good as they were, the natural zeolites did not fully satisfy the water conditioning industry, nor the many other industries which were finding uses for the ion exchange principle. It was the very rapid advancement in plastics technology that led in the mid-30’s to the tailor-making of resins for conditioning water.

Ion Exchange Materials

Today some ion exchange substances for water softening and other uses are composed of tiny plastic particles. The beads are made in the same chemical building blocks that end up as, among other things, children’s toys and refrigerator doors.

Let’s look first at how these beads are made. The starting ingredients are tow relatively simple liquid chemicals called styrene and divinylbenzene, both products of petroleum or coal. The first trick is to suspend the two in water and to combine or copolymerize them. In plain English, this means making one enormous molecule out of two smaller ones.

If you’ve ever stirred up a suspension of water and oil – which won’t mix, as you know – you wil have noticed that the oil in the roiled-up water tends to form into spherical droplets. This is, put very simply, how the resin beads form during the mixing process. And during the process these tiny beads change from liquid to solid.

They emerge completely inert, and the next step, known as sulfonating, is designed to convert the beads into active ion ex hangers. They are heated in a liquid sulfonating agent under carefully controlled conditions, a process that activates the previously inert beads so that they become capable of exchanging one ion for another, of distinguishing “good guys” from “bad guys”.

The final steps consist of washing out sulfonating agent, scrubbing the beads thoroughly so they will be rid of all tendency to give off color, and then converting them to the sodium state so they will be ready to soften water. Now the beads are ion exchangers and nothing more. They serve only as a medium of exchange and can give nothing of themselves into the water under operating conditions.

The Exchange Process

Now let’s look in more detail at how they work. Each tiny bead – no bigger than a coarse grain of sand – is a mass of tiny tunnels and caves, despite its solid, jewel-like look. Thus, its active surface is many times greater than that of a solid sphere, providing many more active ion exchange sites.

In another analogy, suggested by Dr. Irving Abrams, technical director at Diamond Alkali, you might think of each of these exchange sites as an almost infinitely small chemical cup hook. Attached to the surface of each average size bead and lining the internal channels and cavities are something like two hundred million billion cup hooks. This is a figure almost beyond comprehension. Spelled out, it looks like this, according to Dr. Abrams’ slide rule: 200,000,000,000,000,000. That’s a lot of hooks, particularly when you consider they’re all contained without and within a bead no bigger than a fairly large grain of sand.

When the bed of these beads in a water softener is charged and ready to go, there hangs from each of these hooks a cation of sodium, its slightly positive electric charge (due to its missing electron) providing it with just the right hold to hang from the chemical hook.

No comes the rush of water through the bed of beads, making its way into every intricate channel and cavern within each bead. As each cation of calcium or magnesium or other hard mineral passes a cup hook it knocks the sodium ion loose and grabs onto the hook itself. The reason: the hard cations, with more than one missing electron, have a higher positive charge than the sodium cations (with only one missing electron) and hence have a greater affinity for the exchange sites – a better hooking facility.

The net result is that by the time the water has passed through the bed of beads all of the hard ions are left behind, hanging on the hooks, and the water no contains only the soft ions of sodium. When finally every hook is stripped of sodium ions and occupied by their hard replacements, the whole system must be regenerated. The hooks are cleared by flushing of the hard cations and draining them away, and then each hook is rehung with a sodium cation by infusing the beads with a brine solution made from ordinary salt.

Throughout this chemical swap, the flushing and regeneration, the beads remain unharmed and chemically unaltered – the close-mouthed, unchanging sheriff who directs the ever-recurring victories of the “good guys” over the “bad guys.”

Aside from water softening, the field of ion exchange resins is vast and growing. All sorts of things can be removed from fluids or added to them simply by tailor-making the exchanger.

As one fascinating instance, take a medical use for ion exchange, harking back to those centuries-old clay discs mentioned earlier. A number of different medical groups are now using a form of ion exchange for patients with congestive heart disease and with cirrhosis of liver. In both diseases salt traps water in the body; the tissues become water-logged and swollen (in the condition familiar as dropsy) and often the patient’s life is imperiled. Now many such patients are being successfully dosed with a special ion exchange resin that picks up the excess sodium (salt) ions and replaces them with harmless substances.

Literally thousands of other uses in scores of other fields have been found for ion exchange resins. A brief sampling of the list will indicate the wide variety:

  • To improve the flavor of wines, beers and other beverages
  • In the separation of amino acids, as part of the basic biochemical research which seeks to decipher the genetic codes that spell out the differences, for instance, between mouse and man.
  • To purify a number of chemicals
  • In the manufacture of longer-lasting television tubes
  • In the manufacture of plastics
  • In the prevention of stream pollution
  • In making dietary milk and other dairy products
  • In manufacturing sugar from cane, beets and corn, and even forest products
  • For the removal of unwanted portions of petroleum products

What the future holds for ion exchange is anybody’s guess, but one of the more exciting prospects has a very direct and dramatic relationship to the Space Age. This is the use of ion exchange to drastically reduce the cost of isolating rare and valuable metals from their ores – metals like tantalum, columbium, molybdenum, vanadium and many others. All are valuable for their strength when alloyed with other metals and for their ability to withstand intense heats – the sort of heats produced when the nose cone of an atomic weapon or a satellite re-enters the earth-s atmosphere.

It’s a long way from soft water to hardened nose cones, but the principle of ion exchange covers just that remarkable spectrum.



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