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Re: CaCO3 solubility (was APD V3 #902

Hello Dave,

You are rught about the amount of CaCO3 necessary to raise hardness. The
practical problem lies in the insolubility of CaCO3. It will just sit on
the bottom and NOT dissolve, because there is insufficient CO2 in the
water to drive the equation  2 CaCO3 + H2CO3 --> 2 CaHCO3  to the right. 

To complicate matters, to keep the bicarbonate in solution, an excess of
CO2 is needed, up to 5 times stoichiometric. That takes a lot of CO2.
Unless CO2 is supplied, CaCO3 will not dissolve in water. (That's why we
have lime caves -- they do not dissolve away completely, because the
water in them is CO2 limited.)


> At 03:48 AM 3/12/99 -0500, Steve Benz asked:
> >Anybody know roughly how much crushed
> >limestone to use and why?
> Assuming your limestone is all CaCO3 (if it isn't this will likely lead to
> a slight underdose), to raise the hardness of 1000L =250 gallons of water 1
> dH =18ppm requires 18g of limestone.  That is about 2/3rds of an ounce.  If
> you have a postal scale, weigh out one ounce, that is enough for 375
> gallons to increase 18 ppm.   Prorate as needed.
> - --
> Dave Gomberg, San Francisco            mailto:gomberg at wcf_com
> http://www.wcf.com/co2iron
> - -----------------------------------------------------------------