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 beta -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.