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Water Purification & Filtration
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There are many ways to purify water. We thought we would discuss some of these methods here, to better understand the quality of the filters we offer.
Compositionally, zeolites are similar to clay minerals. More specifically, both are alumino-silicates. They differ, however, in their crystalline structure. Many clays have a layered crystalline structure (similar to a deck of cards) and are subject to shrinking and swelling as water is absorbed and removed between the layers. In contrast, zeolites have a rigid, 3-dimensional crystalline structure (similar to a honeycomb) consisting of a network of interconnected tunnels and cages. Water moves freely in and out of these pores but the zeolite framework remains rigid. Another special aspect of this structure is that the pore and channel sizes are nearly uniform, allowing the crystal to act as a molecular sieve. The porous zeolite is host to water molecules and ions of potassium and calcium, as well as a variety of other positively charged ions, but only those of appropriate molecular size to fit into the pores are admitted creating the "sieving" property. Another important property of zeolite is the ability to exchange cations. This is the trading of one charged ion for another on the crystal. One measure of this property is the cation exchange capacity (CEC). Zeolites have high CEC's, arising during the formation of the zeolite from the substitution of an aluminum ion for a silicon ion in a portion of the silicate framework (tetrahedral units that make up the zeolite crystal).
Water and the materials dissolved within it are made up of ions. Ions are atoms that are electrically charged and are commonly the building blocks for other molecules. The charge may be positive or negative, depending on the type of ion, with every ion having a charge which cannot change. In electrolysis, which involves the use of two oppositely charged electrodes (negative and positive) to separate out ions in a solution, the positive electrode is called the anode and the negative electrode is called the cathode. Consequently, negatively charged ions are attracted to the positively charged anode (and are therefore called anions), where as the positively charged cations are attracted to the negative cathode.
For example, if salt (sodium chloride) is put into water, it dissolves and then dissociates into two separate ions - a positive sodium ion (or cation, Na+), and a negatively charged chloride ion (or anion, Cl-). So in solution, sodium chloride no longer exists and it's ions are free to move and combine with other ions of an equal and opposite charge. Consequently, all ions can be split into two groups; the positively charged cations such as calcium, magnesium, sodium, iron (all metals) and the negatively charged anions such as bicarbonate, carbonate, chloride, sulphate, nitrate etc. Fortunately, the vast majority of impurities and inconsistencies between our tap water and that of pure water are due to an excess of specific ions. And as these ions will either have a negative or positive charge, with a little applied chemistry, we can target and remove these offending ions using water purifiers. Next: Dealing with the dissolved ions.After the initial filter media have worked on the raw tap water, there should only be a significant quantity of inorganic compounds remaining as ions which can then be removed using ion exchange technology. What is ion exchange?Ion exchange is a reversible chemical process in which the specific ion (such as sodium, Na+) are released from the insoluble solid medium (which is the ion exchange resin) and exchanged for non-desirable, or target cations, such as heavy metals. There are two types of ion exchange that can be caused to occur within a water purifier; that which removes target cations and that which removes target anions. Ion exchange was first discovered in 1845 by an Englishman called Thompson who passed an ammonia-rich solution of manure through some ordinary garden soil, only to discover that the ammonia content of the liquid manure was greatly reduced. It was later shown that the soil contained fine particles of a natural material called zeolite which would even later be shown to have ion exchange properties. The water industry has not looked back since, but developed better and more efficient media to do the job of water purification. How cation exchange works.Cation exchange resins are usually made from an inert compound called polystyrene-divinylbenzene which is heated in its manufacturing process with concentrated sulphuric acid, causing a sulphonic group (SO3-) to be permanently fixed on to the structural chemistry of the resin beads. Because these sulphonic groups have a negative charge, they can be charged with positively charged ions (cations) typically sodium (Na+), potassium (K+) or even hydrogen (H+). When tap water containing dissolved cations (such as heavy metals) pass by the resin, then these are exchanged for, and trade places with, the loosely held sodium ions on the resin. There will come a time when no more cations can be removed by a fully reacted resin which is then described as being 'exhausted', and which must then be replaced. The better a resin is protected by pre-filtration from fouling contaminants such as iron and chlorine (which can actually cause the resin polymer beads to disintegrate), the longer it's active life will be. Cation exchange resins will remove most metallic, positively charged ions such as barium, cadmium, copper, iron, manganese, zinc, calcium and magnesium.Consequently, if the flow rate has been sufficiently slow and there has been sufficient active areas for cation exchange on the resin, then the levels of contaminant cations are reduced, and retained within the resin. All this leaves is the negatively charged contaminants or anions which must then be removed. How anion exchange works.Anion exchange units use a different resin that works in the opposite way to a cation exchange resin. It is charged with either chloride (Cl-) or hydroxyl (OH-) ions, are then released into the water in exchange for the less desirable contaminant anions. Anion exchange removes nitrates, sulphates and other negatively charged ions. What is the difference between absorption and adsorption?A sponge absorbs water into the inside of it's porous structure. Ion exchange resins are not porous and so we describe the action by which they attract and retain ions on to their surface as adsorption. There are several new generation adsorptive media that seek to replace or improve upon the purifying performance of activated carbon. Some are natural media, while others boast patented technology that enables them to adsorb most heavy metals and dissolved gases. Mixed bed ion exchange.As the term suggests, these ion exchange media contain both anionic and cationic exchange media, combined in one cartridge. To ensure that there is efficient purification, mixed bed ion exchange resins are usually used in a series of multiple cartridges, preceded as ever, by at least a carbon filter and at best an additional fine micron mechanical pre-filter. In summary, water purification uses a series of complementary filtration processes that involve both mechanical and chemical means to produce 'purified' water. Our tap water can deliver quite unpredictable levels of ions and other 'contaminants' such as herbicides and pesticides, as well as chlorine and chloramine. Different purifiers boast different qualitative and quantitative performance figures; a function of the different types and configurations of media used in these purifiers. The team of different media work to target and remove these contaminants, whether they are present in our tap water or not. It never ceases to amaze me that by using the innate 'electrical' features of the dissolved contaminants themselves, the manufactured media or resins can effectively remove them from tap water, with no power or electricity required to power them. - Portion of the above excerpt provided by "The Pond Doctor" Kinetic Degradation Fluxion) - Redox (more ion exchange) KDF is a patented media that is a giant step forward in water purification. KDF media utilizes an old process in a new way - the oxidation and reduction of ions, known as redox... the principle of Oxidation-Reduction or Redox potential. Redox media remove virtually any soluble heavy metal, help prevent mineral hardness scale accumulation, a nd reduce levels of microorganisms.Redox reactions, or oxidation-reduction reactions, primarily involve the transfer of electrons between two chemical species. The compound that loses an electron is said to be oxidized, the one that gains an electron is said to be reduced. KDF process media are high-purity copper-zinc granules used in a number of pretreatment, primary treatment and wastewater treatment applications. KDF media supplement or replace existing technologies to dramatically extend life of the system, control heavy metals, toxic gases and microorganisms, lower total cost, and decrease maintenance. KDF process media work to reduce or remove chlorine, iron, hydrogen sulfide, lead, mercury, calcium carbonate, magnesium, chromium, bacteria, algae, fungi, and much more! Iron and hydrogen sulfide are oxidized into insoluable matter and attach to the surface of the media. Heavy metals such as lead, mercury, iron, cadmium and aluminum are removed from the water by the electrochemical process. They are attracted to the surface of the media, much like a magnet. In short, the redox process works by exchanging electrons with contaminants. This give and take of electrons converts many harmful contaminants into harmless components, such as chlorine to chloride. Other contaminants, including heavy metals, bond to the KDF media, which greatly reduces or virtually eliminates these substances. The media also inhibits bacteria, algae, and fungi growth. KDF process media control microorganisms in two ways. The first is a by-product of redox; the exchange of electrons sets up an electrolytic field in which most microorganisms cannot survive. Secondly, the process of forming hydroxyl radicals and peroxides from some of the water molecules interferes with the microorganisms' ability to function.
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