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-   -   let's get this straight finally - boiling the water - HCO3 (http://www.homebrewtalk.com/f128/lets-get-straight-finally-boiling-water-hco3-322952/)

400d 04-21-2012 02:30 PM

let's get this straight finally - boiling the water - HCO3
 
ok people,

I'm searching all over the internet for this info, but no luck.

If I want to boil off some bicarbonates from my hard water how long do I have to boil and how do I know how much of it precipitated?

is there a formula? something like - 5 minutes of boiling equals 100ppm precipitated HCO3?

thank you!

mabrungard 04-21-2012 02:40 PM

Boiling drives off CO2. It only takes a few minutes of rolling boil to drive the CO2 off and elicit the precipitation of calcium carbonate. Bicarbonate is not precipitated alone. The water has to have enough calcium present to foster the reaction and precipitation.

You can read more about Decarbonation by Boiling in the Water Knowledge page on the Bru'n Water website. It goes further in describing the limits of the process and what you can expect for your water quality after boiling.

ajdelange 04-22-2012 12:22 PM

You don't even have to boil it - just get it hot enough and drive the evolved CO2 off.

Ca++ + 2HCO3- --> CO2 + CaCO3

Le Chatelier's principle says that you move a reaction to the right either by removing a product (CO2) or increasing a reactant. The reason boiling works is that steam sparges off the CO2 and that is indeed one way to do it but you can also just aerate the water as by pumping it through a nozzle or pouring it back and forth between containers. This latter doesn't strike me as a very safe thing to do with hot water and boiling is certainly simpler than rigging a pump.

The general rule of thumb is that you can decarbonate to about 1 mEq/L i.e. an alkalinity of 50 or bicarbonate content of 61 mg/L. This requires that the total hardness of the water initially be higher than the alkalinity and that is a clue (plus consideration of LeChatelier) as to how to get below 1 mEq/L i.e. by supplementing calcium. It also helps to suspend a little chalk as nucleation sites. The reaction itself is quite swift. If your water is really hard and alkaline it will turn milky before boiling temperatures are reached. Only the briefest boil (enough to sparge off the CO2) is required.

Rbeckett 04-22-2012 01:00 PM

Thanks for a very informative discussion of precipitating unwanted components in the brewing water. As a brief aside, will an RODI filter achieve the same goal? Thank you for sharing youre knowlege.
Bob

ajdelange 04-22-2012 01:25 PM

RO takes out not only bicarbonate and calcium but most (95% or more) of everything else. DI water finishes the job by taking what the RO unit doesn't filter out an replacing with hydrogen or hydroxyl ions. The result is pure (or very nearly pure) water.


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