Calculate HCO3 reduction by boiling

[zwiller]

Helping a friend with some water calcs but a bit short on time to research so I am reaching out here. I know we need to bump Ca to precipitate and I know the reaction is limited and leaves 60-80ppm HCO3 but we want to boil to reduce the majority of it. Plan to use gypsum as Ca salt. Best ppm for Ca to accomplish? I estimate 224ppm Ca. Also, from what I can tell the boil should be at least 30m? Sorry so short. THANK YOU IN ADVANCE!

Ward Labs report:

7.8 PH
Sodium, Na 51
Potassium, K 3
Calcium, Ca 72
Magnesium, Mg 21
Total Hardness, CaCO3 268
Nitrate, NO3-N 0.2
(SAFE) Sulfate, SO4-S 29
Chloride, Cl < 1 Carbonate, CO3 < 1.0
Bicarbonate, HCO3 334
Total Alkalinity, CaCO3 275
Total Phosphorus, P < 0.01
Total Iron, Fe 0.04

 

[ajdelange]

You have alkalinity of 5.5 mEq/L and calcium hardness of 3.6. You can only remove as much alkalinity as you remove calcium and you can generally only take it down to 1 mEq/L if you do that. Thus you need to add 5.5 - 3.6 = 1.9 mEq/L calcium. If you do that and get down to 1 mEq/L each you will have alkalinity of 50 ppm as CaCO3 and calcium at 20 mg/L. You may well want more calcium than that. Many people (I'm not one of them) think they should have 50 ppm (2.5 mEq/L). Supposing you are one of them add the extra 1.5 mEq/L before you boil. As the solubility limit if calcium carbonate is governed by [Ca++][CO3--] < Ks it is clear that increasing calcium will mean that less carbonate can remain in solution. By means of this simple trick you can sometimes decarbonate to less that 1 mEq/L. Another trick is to add some chalk to the water to provide nucleation sites for the chalk you hope to precipitate.

Precipitation reactions are always tricky to predict so it is important to experiment or at least to take alkalinity and hardness measurements on the water before and after treatment.

 

[zwiller]

Thanks AJ,
1mEq/L=20ppm > 1.9mEq/L = 38ppm Ca?

I agree with you on Ca in lagers, however, this will be for IPA and I like to bump Ca for them (along with SO4). I also like your suggestion to test and an aquarium ALK test would be a good investment.

Ward Labs SO4 needs to be multiplied by 4 right? (SO4-S) 116ppm?

 

[ajdelange]

1mEq/L=20ppm > 1.9mEq/L = 38ppm Ca?

Check

Ward Labs SO4 needs to be multiplied by 4 right? (SO4-S) 116ppm?

The multiplier is 3 so that 29 mg/L SO4-S = 87 mg/L SO4.

 

[zwiller]

Thank you aj!!!

 

[zwiller]

pH of the boiled water will remain unchanged, right?

 

[ajdelange]

No, actually it is going to shift towards 8.3 but keep in mind that the actual pH of the water isn't really that important.