Phosphoric Acid and Calcium precipitation (as Calcium Apatite)

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Larry Sayre, Developer of 'Mash Made Easy'
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I perused the Palmer/Kaminski "Water" book's charts found in Appendix C for acidification with Phosphoric Acid with respect to how many mg/L (ppm) of Ca++ ions you can keep in solution before your waters Calcium will precipitate out as Calcium Apatite. This perusal was undertaken in consideration of the oft mentioned concern that the use of Phosphoric Acid can cause one to lose calcium. And indeed the concern appears very real for certain circumstances (presuming that I'm reading the charts correctly). The charts scale for the solubility of Ca++ is logarithmic, so be careful when reading it.

For the specific case of source water with an initial pH of 8.0 and a targeted pH of 5.5 via acidification with Phophoric Acid, and presuming that I'm reading the charts correctly, here is how much Ca++ you can maintain in solution for various initial mg/L Alkalinities (as CaCO3):

Example for targeting 5.5 pH:
1) For water with 50 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~420 mg/L, leaving 420 mg/L as the upper limit for Ca++ in solution
2) For water with 100 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~180 mg/L, leaving 180 mg/L as the upper limit for Ca++ in solution
3) For water with 150 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~110 mg/L, leaving 110 mg/L as the upper limit for Ca++ in solution
4) For water with 200 mg/L initial Alkalinity, Calcium Apatite precipitates out at and above ~78 mg/L, leaving 78 mg/L as the upper limit for Ca++ in solution


Water with an initial pH lower than 8.0 will hold a bit more calcium in solution, and water with an initial pH above 8.0 will hold somewhat less in solution. But not significantly.

If you target a lower pH than 5.5 the calcium you can keep in solution when acidifying with Phosphoric Acid increases rapidly and dramatically. The flip side is that if you target a pH above 5.5 things get way worse in a hurry. But by 5.2 pH as the target the values improve dramatically, and look like this (again for the specific case of source water at pH 8.0 initial):

Example for targeting 5.2 pH:
1) For water with 50 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~1,260 mg/L, leaving 1,260 mg/L as the upper limit for Ca++ in solution
2) For water with 100 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~1,100 mg/L, leaving 1,100 mg/L as the upper limit for Ca++ in solution
3) For water with 150 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~780 mg/L, leaving 780 mg/L as the upper limit for Ca++ in solution
4) For water with 200 mg/L Alkalinity, Calcium Apatite precipitates out at and above ~500 mg/L, leaving 500 mg/L as the upper limit for Ca++ in solution


Moral of the story: If you are going to acidify your water with Phosphoric Acid, and your water has high alkalinity, and you are intending to have loads of calcium in solution, target a water pH adjustment of ~5.2 and you should be fine. If however you are merely trying to reduce Alkalinity to an Alkalinity target that does not drive the source waters pH down to below 5.5 (such as for the preparation of desired higher alkalinity mash water to counter the acidic grist of a Stout, whereby leaving alkalinity behind is essential) you may indeed lose appreciable amounts of calcium unintentionally if you choose to acidify with Phosphoric Acid, with much of this dependent upon your waters initial Alkalinity level.

Everything rests upon my having interpreted the charts correctly. Please verify if I have done so. Don't shoot the messenger. All of the above can be corrected if needed upon verification of accuracy.
 
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mabrungard

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Yes, the whole calcium precipitation issue is overblown. The water would have to have a very high calcium content before an appreciable amount of calcium would be precipitated. In addition, loosing some of that already high calcium content is INCONSEQUENTIAL since elevated calcium provides no benefits.
 
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Silver_Is_Money

Larry Sayre, Developer of 'Mash Made Easy'
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I don't necessarily see it that way. As an example: To say the least, there is a lot of negativity in the UK toward using Phosphoric Acid, and there are ugly pictures on some of their forums of calcium dropping out of solution when using it for water acidification (with comments that this only happens with Phosphoric Acid). In general they desire to brew with noticeably higher levels of calcium, and they generally have relatively high alkalinity water, even when it comes from a local water authority, plus they seem to be highly averse to purchasing and installing RO units (and they often laugh at us for using them, even believing that we must use them because water is filthy and contaminated here vs. water in the UK). And on top of that, they seem to favor targeting remaining alkalinity (to style) rather than pH when they acidify their water, and the alkalinity they target is often higher than the accepted norms here in the USA. A better answer might be: 'It depends'.
 
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Larry Sayre, Developer of 'Mash Made Easy'
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Since the UK favors AMS (CRS) over Phosphoric Acid for alkalinity reduction, does anyone know why this product (or a knockoff) is not available anywhere within the USA?
 

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