Magnesium brucite solubility

Under some circumstances, the Mg enters sparingly soluble phases other than brucite. Roy et al. (R70) observed the formation of a hydro-talcite-type phase in a slag cement paste that had been treated with MgS04 solution. Its formation was possibly favoured by the enhanced availability of A1(0H)4 provided by the slag. Cole (C70) reported the formation of a hydrated magnesium silicate in a deteriorated concrete seawall. 

Strongly Alkaline, Confined Environments, Because Si is most soluble in the form of silicate anions, it is not surprising that smectites form most rapidly in dilute alkaline solutions of sodium silicate and magnesium chloride. The layer silicate structure evolves by the precipitation of a planar Mg(OH)2 (brucite) sheet, on which monomeric silicate ions condense. Silica polymers are unable to reorganize into layered structures. It seems that the metal hydroxide sheet must be layered to begin with, a fact that necessitates 6-coordination of the metal ion that is to form the octahedral sheet of the 2 1 layer. Smectites can be formed from hydroxide sheets of the following cations (listed in order of increasing radius) ... 

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