[Ash15]

Hi All, I am trying to determine the relative concentrations in mass percent of calcium hydroxide and calcium oxide in the solid phase of a slaked lime slurry sample. I am trying to optimise our lime slaking circuit, that is to determine how much quicklime (CaO) is converted to slaked lime ( calcium hydroxide). Would anyone know how to determine this? Many thanks, Ash.

[Arkcon]

Here's a reference to a method: http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt27.html

[Ash15]

Hi Arkcon, thanks for your reply. I am not sure I understand the relationship from the carbonate/hydroxide analysis to the hydroxide/oxide analysis? In the process of lime slaking, an excess of water is added to produce a slaked lime Ca(OH)2 slurry of approx 20% weight solids. Of course the Ca(OH)2 is sparingly soluble and so the bulk of the solids will be solid Ca(OH)2 with some I am assuming unreacted CaO. The reaction for the slaking process is: CaO(s) + H2O = Ca (OH)2(s).

What I am really trying to determine is what is the split of CaO and Ca(OH)2 in only the solid component (ie once the liquid phase is removed & solid sample dried). Most of the available lime tests are based on the sugar test in ASTM C110 which uses a titration with HCl. But I would have thought the HCl will consume both the solid Ca(OH2) and unreacted CaO?

[Arkcon]

Ah ... opps.  I misread the question.  Yes.  It will be tough to determine calcium oxide and calcium hydroxdie in aqueous solution,since CaO reacts to produce some CaOH.

[Enthalpy]

If the solid is uniform enough, take a known mass of it, dissolve in enough water, measure the pH? This would tell you how much H₂0 mass is already in the solid.
Or observe how much acid neutralizes the known mass.
Err, I fear I overlooked something.