Spectroscopic evidence for the formation of layered Ni-Al double hydroxides in dement

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 evidenc e for the formation of Ni- and Al-containing hydrotalcite;like layered doub le hydroxides (Ni-Al LDHs) when cement material (a complex mixture of mainl y CaO, SiO2, Al2O3, Fe2O3, MgO, and SO3) was treated with Ni in artificial cement pore water under highly alkaline conditions (pH = 13.3). The study s hows that Ni-Al LDHs were formed in cement suspensions oversaturated with r espect to beta -Ni(OH)(2) and aged at room temperature for 150 days. This f inding indicates that Ni-Al LDHs and not Ni-hydroxides may determine the so lubility of Ni in cement materials.