Solid–liquid equilibrium curve of calcium in 6 mol/L ammonium nitrate solution

• Solid–liquid equilibrium curve in 6 mol/L ammonium nitrate solution is determined.
• The equilibrium curve in 6 mol/L ammonium nitrate solution has a three-stage form.
• Sulfur and manganese are leachable in 6 mol/L ammonium nitrate solution.
• Aluminum and iron are not leachable in 6 mol/L ammonium nitrate solution.

Calcium leaching of cement-based materials is of concern for scientific and application significance. Solid–liquid equilibrium curve of calcium is crucial for understanding the calcium leaching mechanism and for calcium leaching modeling. Solid–liquid equilibrium curve of Portland cement system in 6 mol/L ammonium nitrate solution is experimentally obtained using the dissolving equilibrium between cement paste powders and simulated pore solutions. The obtained equilibrium curve in nitrate solution has a similar three-stage form to that in water, but the concentrations of dissolved calcium increase up to two orders of magnitude, which is the main acceleration mechanism for calcium leaching. Besides the solid–liquid equilibrium curve of calcium, the equilibrium curves between other solid elements (including sulfur, aluminum, manganese, iron) and dissolved calcium are presented. It is found that sulfur and manganese are also leached in three stages, but aluminum and iron are not leachable.