Hi New listers, This may interest some of you in light of the distilled water thread.
Bless you Bob Lee -- oozing on the muggy shore of the gulf coast [email protected]
--- Begin Message ---Hi Ivan and listers, Still thinking about your posting of 19 Apr 99,02:04:50, where you gave the definition of *deionization* of water. What you gave was a description of a process and I`ve stayed up two nights until 3am looking into it, and I found it. Knew that I had seen it somewhere but kept looking in the wrong places. Its how to make high purity water for lab use. Chemical Principles,Masterson,1977 ION EXCHANGE Get a paper and pencil, now draw two vertical tanks side by side. Draw a pipe going into the bottom of the left tank (inlet). Draw a pipe from the top of the left tank to the bottom of the right tank. Draw a pipe from the top of the right tank (outlet). Label the left tank *HR* and label the right tank *R`OH*. Label the inlet pipe *N2+,Cl-,H2O*. Label the pipe between the tanks *H+,Cl,H2O*. Label the outlet pipe *H2O*. Now we start the discussion. Water of very high purity can be obtained by the ion exchange process. The column (tank) at the left contains a synthetic CATION exchange resin that contains the exchangable cation H+. The right column (tank) is packed with an ANION exchange resin in which replacable OH- ions are imbedded in a cationic network. Referring to the two resins as HR (cation exchanger) and R`OH (anion exchanger), we can write the following equations to describe what happens when water containing a desolved salt (MX) is deionized by passing through the two columns (tanks). 1st column: M+(ag) + HR(s) to MR(s) + H+(ag) 2nd column: X-(ag) + R`OH(s) to R`X(s) + OH-(ag) The H+ and OH- ions produced react with each other to form water: H+(ag) + OH-(ag) to H2O Adding the three equations just written, we arrive at the overall reaction for the removal of MX: M+(ag) + X-(ag) + HR(s) + R`OH(s) to MR(s) + R`X(s) + H2O We see from these equations that there are no ions in solution at the end of the process, which is referred to as *deionization*. No ions in solution = deionization. In principle at least, any salt present in the water will be removed; M+ can be any cation (e.g.,Na+) and X- any anion (e.g.,Cl-). To regenerate the first column, it can be flushed with a strong solution of hydrochloric acid, which acts as a source of H+ ions. The second column is returned to its original state by flushing with sodium hydroxide. A source of OH- ions. Deionization of water by means of two ion exchange resins occurs as water passes through the cation (HR) exchange column, H+ ions replace other metalic cations. In the anion (R`OH) exchange column, OH- ions take the place of other anions. The H+ and OH- ions react to form water, and so the water leaving the system is essentially free of all ions. The major drawback to the ion-exchange method is the cost of the chemicals used to regenerate the resins. They are expensive enough to rule out this method for desalination except for brackish waters in which the concentration of salt is 300 parts per million or less (concentration in seawater is 35,000 ppm). On the other hand , this method is widely used to purify water in the laboratory. Water which has been passed through deionizing columns has an electrical conductivity less than one tenth that of ordinary distilled water. Distilled water has the advantage that it is pathogen free. Deionized water is not pathogen free. So we see that ultra pure water can be made with ion exchange resin beds, but its not safe to drink until sterilized. Thanks Ivan for the brain exercise, its fun. Even if it did take a long time to find it. :-) Bless you Bob Lee -- oozing on the muggy shore of the gulf coast [email protected] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
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