Thermodynamic data for magnesium (potassium) phosphates. (December 2019)

• Record Type: Journal Article
• Authors: Lothenbach, Barbara; Xu, Biwan; Winnefeld, Frank
• Is Part Of: Applied geochemistry. Volume 111(2019)
• Publication Date: 2019-12
• Subjects: Magnesium phosphate cement -- Thermodynamic data -- Solubility -- Temperature; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2019.104450
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: Magnesium potassium phosphate (MKP) cements show fast setting and high early strength. MKP cements harden in the presence of water due to the reaction of potassium dihydrogen phosphate (KH2 PO4 ) with magnesia (MgO) resulting in the formation of mainly K-struvite (MgKPO4 ⋅6H2 O). Other hydrates, newberyite, phosphorrösslerite, cattiite and Mg2 KH(PO4 )2 ⋅15H2 O are formed as intermediate phases during hydration. This paper presents a consistent thermodynamic database for magnesium phosphate hydrates based on solubility measurements for newberyite, phosphorrösslerite, farringtonite, Mg3 (PO4 )2 ⋅4H2 O, bobierrite, cattiite, K-struvite, KMgPO4 ⋅H2 O, and Mg2 KH(PO4 )2 ⋅15H2 O carried at different temperature. It was found that the formation of the different hydrates is strongly influenced by pH. Newberyite, phosphorrösslerite and Mg2 KH(PO4 )2 ⋅15H2 O are intermediate phases, which form at low pH as typical at very early hydration times. As pH rises, bobierrite and cattiite may be stabilised, while at high pH K-struvite forms. The phases formed are also strongly influenced by the temperature. Graphical abstract: Image 1