Spectroscopic Evidence for the Formation of Layered Ni−Al Double Hydroxides in Cement

X-ray absorption fine structure (XAFS) spectroscopy and diffuse reflectance spectroscopy (DRS) were applied to assess the solubility-limiting phase of Ni in cement systems. The study provides first direct spectroscopic evidence for the formation of Ni- and Al-containing hydrotalcite-like layered double hydroxides (Ni−Al LDHs) when cement material (a complex mixture of mainly CaO, SiO 2, Al 2 O 3, Fe 2 O 3, MgO, and SO 3 ) was treated with Ni in artificial cement pore water under highly alkaline conditions (pH = 13.3). The study shows that Ni−Al LDHs were formed in cement suspensions oversaturated with respect to β-Ni(OH) 2 and aged at room temperature for 150 days. This finding indicates that Ni−Al LDHs and not Ni-hydroxides may determine the solubility of Ni in cement materials.