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 Home Brew Forums > Boiling to precipitate out bicarb

04-18-2011, 12:50 AM   #1
Yooper
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 Boiling to precipitate out bicarb

I have high bicarb- 228 ppm. If I preboiled my sparge water, is there a way to figure out (without sending in another water test) what the bicarb level would be after boiling it and racking off the precipitates?

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04-18-2011, 01:02 AM   #2
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Get a cheap TDS meter and measure TDS before and after the boiling. If the carbonate precipitates, the TDS should drop. The level of drop should give you the amount of carbonate lost.

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04-18-2011, 11:54 AM   #3
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I'm sure Martin will chime in when he sees this but IIRC his little write up in Bru'n Water says as long as there is sufficient Calcium to bond with the carbonate then by boiling you can get the Bicarb down to ~80ppm. The ending Calcium concentration is calculated using this equation:
Ending Ca (ppm) = Starting Ca (ppm) - ((starting HCO3 (ppm) - ending HCO3 (ppm))/3.05)

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04-18-2011, 04:14 PM   #4
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Quote:
 Originally Posted by SpanishCastleAle I'm sure Martin will chime in when he sees this but IIRC his little write up in Bru'n Water says as long as there is sufficient Calcium to bond with the carbonate then by boiling you can get the Bicarb down to ~80ppm. The ending Calcium concentration is calculated using this equation: Ending Ca (ppm) = Starting Ca (ppm) - ((starting HCO3 (ppm) - ending HCO3 (ppm))/3.05)
Thanks!!!! That's what I seem to remember (not the formula, but that Martin mentioned it).

What is "sufficient calcium", though? Is it a ratio?

I have 57 ppm Ca to start with, CaCO3 is 207, while the HCO3 is 228. Assuming I boil, and rack off of the precipitate, I can assume the resulting HCO3 is +/- 80 ppm?

Would a TDS meter actually work for something like this?
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04-18-2011, 04:55 PM   #5
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The overall reaction is Ca++ + 2HCO3- ---> CO2 + CaCO3 + H2O. Thus it is clear that bicarbonate can only be removed to the extent of calcium (ignoring magnesium here - it precipitates some carbonate too). LeChatelier's principal says that you can move the reaction to the right by increasing reactant concentrations (on the left) or removing products (on the right). Thus increasing calcium and/or removing CO2 will get the maximum amount of bicarb out. As calcium is removed with the precipitation it is likely that you will want to replace some or all of it with the chloride or sulfate. LeChatelier says do this before you boil. On the products side, removing CO2 is the name of the game. This can be done by sparging it with steam by actually allowing the water to come to the boil but that is not necessary as CO2 removal can be accomplished by sparging with air or spraying the heated water through a shower head or some such device. Another thing which helps is to have nucleation sites and that is acheived by suspending some chalk before heating.

The actual reaction is Ca++ + CO3-- --> CaCO3 i.e. the bicarbonate must be converted to carbonate. This can be done by raising the water's pH with lime (calcium hydroxide) which also increases the calcium but then the pH needs to be adjusted back down with acid.

As a practical matter water can be decarbonated by lime treatment or boiling to around 1 mEq/L (50 ppm as CaCO3). Using some of the tricks given above you can get a bit below this. Of course this assumes that the hardness is at least equal to, and preferably higher than the alkalinity.

Few, if any, commercial operations decarbonate this way any more because of energy costs. They use RO, microfiltration or lime treatment. With fuel as expensive as it is today I wonder if this consideration might begin to apply to home brewers as well. What really troubles me about decarbonation by boiling is the safety aspect depending on how you handle the CO2 sparge. Just letting it boil in your kettle wouldn't appear to be any more dangerous that boiling wort.

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04-18-2011, 07:44 PM   #6
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Here's a link to Martin's article.

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04-19-2011, 11:42 AM   #7
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Quote:
 Originally Posted by Yooper Would a TDS meter actually work for something like this?
I don't know, good question. After a couple of really weird/bad batches using lots of grocery store RO I finally broke down and bought an RO unit and went ahead and bought a TDS meter with it for \$25 (haven't received any of it yet). Hope it wasn't a waste.
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04-19-2011, 12:11 PM   #8
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Yes, a TDS meter will give you a rough indication of what is going on. The meter measures the conductivity of a solution and either displays that conductivity or the concentration of the sodium chloride in a solution with the same conductivity. The conductivity depends on the charge and mobility of the ions in the solution so that the mg/L number displayed for a solution of calcium bicarbonate alone would not be correct but roughly speaking would give an idea as to what's in there. With a little research you could probably find the relative conductivities of sodium chloride and calcium bicarbonate solutions and thus figure out how much calcium bicarbonate got removed. An alkalinity test (very simple) would be a better indicator. If the alkalinity is reduced from 200 ppm as CaCO3 to 50 ppm as CaCO3 (a drop of 150) then the calcium hardness must have dropped by the same amount.

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04-19-2011, 01:02 PM   #9
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Yes, there are alkalinity test kits that brewers can use to check their post boil alkalinity. There are cheaper kits that aquarium enthusiasts use and then there are more accurate and expensive kits that small water companies use.

As mentioned above, the typical post boil alkalinity ranges between 60 and 80 ppm. Since I wanted to be conservative with the effectiveness of boiling, Bru'n Water includes boiled water profiles that assume the ending alkalinity only falls to 80 ppm. That equation above, allows any brewer to estimate what their resulting calcium concentration will be if they know their starting calcium concentration and the starting and ending alkalinity. (the test kit is good for that). Since calcium carbonate is much less soluble than magnesium carbonate, virtually all the precipitate created during the boiling will be calcium carbonate and therefore, the magnesium concentration will not change. Only the calcium concentration and alkalinity change.

As AJ mentions, boiling is not the most efficient method. Lime softening is a better way to generally achieve similar results as boiling. If magnesium concentration is high along with high alkalinity, then its also possible to drop out magnesium carbonate with this process by increasing the water pH a little higher (>11). In water with temporary hardness and very little permanent hardness, the lime softening process can drop the calcium concentration to about 30 ppm and the magnesium concentration to about 10 ppm. Those values go up as the amount of permanent hardness go up. Visit Braukaiser's website for a good explanation of the lime softening process. Eventually, I'll add it to Bru'n Water.

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04-19-2011, 04:12 PM   #10
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It's actually primarily magnesium hydroxide which is precipitated in the split treatment. It is orders of magnitude (pKs 11.25 vs 5.17) less soluble than the carbonate. Compare to calcium carbonate whose pKs is about 8.47 (calcite). The saturation level of magnesium is pMg_sat = 2*pH - 16.75 so that at pH 11 we'd have pMg = 5.25 corresponding to a Mg concentration of about 0.13 mg/L. At pH 12 the saturation concentration is 2 orders of magnitude less than that.

To compare with carbonate assume that pH 11 is reached by adding 3.56 mmol/L sodium carbonate leading to a carbonate concentration of 3.56 mmol/L. Magnesium is saturated with respect to carbonate at this level of carbonate at pMg = 5.17 - p[CO3--] = 2.72. Thus the saturation magnesium concentration is 1000*24.3*10^-2.72 = 46 mg/L

The pH raising technique works even if there is no carbonate/bicarbonate content. You can easily remove magnesium from water with no temporary hardness.

In the classic split treatment you get the Mg down to 1/2 - 2/3 of what it is in the original water because you raise the pH of 1/2 to 1/3 of the volume with lime, and then use the acid (bicarbonate ion) in the remainder of the volume to neutralize the lime (after decanting off the Mg(OH)2). Of course you could eliminate virtually all the magnesium by neutralizing with carbonic, sulfuric or hydrochloric acid rather than more of the original water.

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