water softening with CaO addition

Hi guys,

I found an older book written by Wolfgang Vogel. It mentions an easy way to water softening by adding a certain amount of CaO to hard water. It precipitates the the "hard part" of the water at the bottom of the bucket. After that you only need to siphon the soft water off the hard residue.

Have you already heard about this method? I'm asking because I haven't found it in the hombrew books in English anywhere. It's a lot cheaper than anythig, I've found so far.

Thanks.

It's a method of raising the pH so that the CaCl will precipitate out of solution and lowering the carbonate hardness. There's a difference between carbonate hardness and overall hardness, so be sure of what is actually causing your tap water to be hard in the first place. In our area, we have a lot of silicates and other dissolved solids which keeps our overall hardness high, but our carbonate hardness is low. I guess it really just depends on what's in your local waters as to whether or not this method should work for you.

Our water definitely has carbonate hardness:


Ca: 80,5 mg/l
Mg: 22,2 mg/l
CaCo3:281 mg/l
SO4: 72,2 mg/l
Na:18,4 mg/l
Cl:26,9 mg/l

But I'm not sure what I get by this treatment. Are you saying that Mg, SO4 and Na levels will be the same after this treatment? What do you think, can I brew a Pilsner with with the water treated this way?

Quick Lime (CaO) and its hydrated form, Slaked Lime (Ca(OH)2 are both strong bases that are used in lime softening. This is a common water treatment method and is quite effective in softening waters with high amount of temporary hardness. The OP's water has fairly high amount of temporary hardness, but there is a lesser amount of permanent hardness. The lime softening process raises the pH of the water to at least 10 to cause calcium carbonate to precipitate from solution. If the pH is raised to at least 11, then magnesium hydroxide can also be precipitated.

If the water contained only temporary hardness (meaning that it doesn't contain sulfate or chloride), then the lime softening process can reduce calcium to as low as 12 ppm and magnesium to as low as 3 ppm. Those ending concentrations increase as the percentage of permanent hardness increases.

If you have the large vessels needed to hold the water and conduct the treatment, then lime softening can be quite effective. A pH meter is needed to verify the lime dosing and to monitor the recarbonation and acidification prior to use. Both quick lime and slaked lime are relatively inexpensive and no external power is required. So it is suited for all parts of the world.

PS: Calcium chloride will not precipitate out of typical water. Its too soluble.

CaO is 'quick' lime. It is quite reactive when exposed to water. The reaction gives off a lot of heat to the point where fires have been started when bags of quick lime have gotten wet. The reaction with water is

CaO + H2O ---> Ca(OH)2

The product is called 'slaked' lime. It is much safer to handle and is used to make pickles crisper so that it is often found in food stores (in the US).

Slaked lime reacts with bicarbonate in water to precipitate calcium carbonate:

Ca++ + 2 HCO3- + Ca(OH)2 ---> 2CaCO3 + 2H2O

Thus we see that for each equivalent of bicarbonate removed one equivalent of calcium is removed. In your water you have 80/20 = 4 mEq/L calcium hardness and 281/50 = 5.6 mEq/L but something is wrong with this set of numbers as the cation and anion concentrations mismatch by 1.3 mEq/L. Nevertheless, let's keep going. You should be able to reduce the hardness to 1 mEq/L by lime softening i.e. you should be able to drop out 3 mEq/L. In so doing you would take out 3 mEq/L alkalinity equal to 150 mg/L as CaCO3 so that your alkalinity would be 281 - 150 = 131. That's not too impressive. You can get more alkalinity out by putting more chloride in first. If you added 1,6 mEq/L calcium as the chloride then you would have 5,6 mEq/L calcium equal to the alkalinity and you should be able to drop the alkalinity and hardness both to 1 mEq/L (50 mg/L as CaCO3) for a final calcium concentraion of 20 mg/L. Your chloride would also go up by 3,2 mEq/L (114 mg/L) if you used calcium chloride and that's getting into pretty high chloride levels. Or you could use calcium sulfate but that would up the sulfate appreciably. There are other alternatives such as using acid to convert the bicarbonate to CO2. All this gets pretty complicated. There are spreadsheets that can help you with some of the calculations.:

HCO3- + HA ----> CO2 + H2O + A-

but this adds one mEq of A- (the anion of the acid) for each mEq of bicarbonate removed. Many brewers use phosphoric acid as its anion is pretty flavor neutral.

There is one easy way out if you have a source of low ion (reverse osmosis, for example) water. Just dilute 1 part of your water with 9 parts RO water. This gets the alkalinity down to 28 which is acceptable but you will have to add back some calcium chloride to get chloride (which would dilute to 2,69) and calcium (which would dilute to 80,5) back to reasonable levels. The Primer at the top of the Brew Science page tells you how to do this.

If Pils is the target this is the best way to go as Pils wants soft water (at least Pils like Pilsner Urquel or Budvar) and low sulfate. There are other routes as discussed here to some extent but they are pretty complicated for someone just starting out. Of course the RO/DI water technique is effectively throwing your water away and replacing it. You probably could brew a Pils with lime softened water. You'd have to stay away from noble hops because of the sulfate though.

For details of the lime softening process you can go to hbd.org/ajdelange and download the Alkalinity Part II pdf. It is also described in several English language brewing textbooks (e.g. DeClerck - translated into English).

OK, I’m confused. What about the magnesium? Isn’t that .9 mEq/L of your missing 1.3 mEq/L?

I agree about the Pils. With water like that, 100% RO.

The 1.3 deficit includes the magnesium. Magnesium will be precipitated to some extent but calcium carbonate is much less soluble than magnesium carbonate and so will drop out first. If you want to get rid of magnesium then you use split treatment. To do this all the calculated (and we didn't get into how to do that) lime is added to a portion of the water. This runs the pH way up to the point where magnesium hydroxide and calcium carbonate form and precipitates. You then rack off the water and add the rest of the water volume to it. Obviously at most you get 1/2 of the magnesium but that may be enough.

Thank you for the detailed answer. I think I'll read the recommended papers first and only ask later.

I was hoping that I can avoid investing into a RO filter. Unfortunately it seems that I can't...