text: Friedel's salt could be first tentatively represented as an AFm phase in which two chloride ions would have simply replaced one sulfate ion. This conceptual representation based on the intuition of a simple stoichiometric exchange is very convenient to remind but such a simple mechanism likely does not directly occur and must be considered with caution:
  Indeed, the reality appears to be more complex than such a simple stoichiometric exchange between chloride and sulfate ions in the AFm crystal structure. In fact, it seems that chloride ions are electrostatically sorbed onto the positively charged [CaAl(OH) · 2HO] layer of AFm hydrate, or could also exchange with hydroxide ions (OH) also present in the interlayer. So, the simple and "apparent" exchange reaction first presented here above for the sake of ease does not correspond to the reality and is an oversimplified representation. 
  Similarly, Kuzel’s salt could seem to be formed when only 1 Cl ion exchanges with   in AFm (half substitution of sulfate ions):
  Glasser et al. (1999) proposed to name this half-substituted salt in honor of his discoverer: Hans-Jürgen Kuzel.
  However, Mesbah et al. (2011) have identified two different types of interlayers in the crystallographic structure they have determined and it precludes the common anion exchange reaction presented here above as stated by the authors themselves in their conclusions:
  So, if the global chemical composition of Friedels salt and Kuzels salt corresponds well respectively with the stoichiometry of a complete substitution, or a half substitution, of sulfate ions by chloride ions in the crystal structure of AFm, it does not tell directly anything on the exact mechanism of anion substitution in this complicated system. Only detailed and well controlled chloride sorption, or anion exchange, experiments with a complete analysis of all the dissolved species present in aqueous solution (also including OH, Na and Ca ions) can decipher the system.