to anyone following the FLUORIDE sub-sub-sub-thread... (to everyone else, sorry)
OK, so the confusion I had when reading your article (it does remove fluoride) and what I had read years ago, obviously needed refreshing.
In Laymans terms:
Sodium Fluoride (usually quoted but never used in water fluoridation), Fluorosilicic acid (H2SiF6) (most commonly used in water), Sodium Fluorosilicate (Na2SiF6) (not as common but also used);
Can be removed from water in their inorganic state. You add the above, and then can remove (90%) of the above. Therefore you can claim that you can remove fluoride... The problem is what happens to the fluoride when we add it to water... If the fluorine/fluoride ionizes, then it cannot be removed.
NOT MINE: (respectfully quoted from a submission to Port Macquarie-Hastings by Dr John Lusk)
What happens when we add fluoride to water?
It is simply assumed by high school science teachers and supporters of fluoridation that all fluoride compounds dissociate entirely into fluoride ions, and harmless hydration compounds of silicon. Pure fluoride solutions do behave relatively predictably, both over the permissible pH range of municipal water supplies and in the extremely acidic environment of the human stomach. However, fluorosilicates dissociate in highly complex fashion in water, with an amazing range of complex derivatives forming at different pH values, none of whose toxicological properties has been adequately investigated. In other words, we don’t really know much about their effects on our health.
When fluorosilicates are added to water they dissociate to form fluorosilicate ions [SiF6 ] 2- with two negative electrical charges, accompanied by either two individual ions of hydrogen H+ (from fluorosilicic acid) or of sodium (Na+) (from sodium fluorosilicate). The individual elements, silicon (Si) and fluorine (F) in the fluorosilicate ion cannot move independently - at neutral pH they act as the complex substance fluorosilicate.
Fluorosilicates are therefore emphatically not identical to ‘fluorides’. In fact, fluorosilicates should not be referred to as ‘silicofluoride’, because this improperly implies that they are fluorides and have similar properties. This argument is often used to mislead audiences into believing that fluorosilicates are chemically interchangeable with true fluorides, and that adding fluorosilicate to drinking water is merely a ‘topping up’ process to augment fluoride concentrations below the ‘optimal’ level for preventing tooth decay.
When simple fluorides are dissolved in water, they are in the ionic form, F+. Provided that no aluminium is present, they remain so at all relevant pH levels, whether in pure water or in the acidity of the stomach.
Fluoride in the industrial sodium fluoride sometimes used in fluoridation is more bioavailable than that in calcium fluoride, whilst fluoride from water containing fluorosilicates is even more completely absorbed.
At around the normal pH of 7, approximately 97% of the fluorine in fluorosilicate added to the water is present in the form of ionised fluoride, F+ . At the very slightly acidic pH of 6, only 27% of the fluorine in fluorosilicate is present as fluoride - the rest is associated with other ions, and forms a number of complex and unstable compounds and ions that change over variable periods of time and at different pH values. At the acidity of the human stomach - pH2 to 3 - the proportion of fluorine atoms that are present as fluoride ions changes dramatically, and effectively no fluorine atoms are present in the ionic state.