Ahstraet-The uv-visible absorption of aqueous Ti'" and Ti"' was measured in the aqueous H,SO, and HCl supporting electrolytes used in subsequent batch recycle electrolyses for the electrosynthesis of Ti"'. Thermodynamic predictions of the speciation were calculated from published stability constants for the weak sulfate and chloride complexes. However, when Ti'" and Ti"' sulfate solutions were mixed, the resulting species absorbed more strongly at visible wavelengths than the Ti"' species alone, possibly indicating the formation of a Ti'"-Ti"'-sulfate charge transfer complex; no such behaviour was evident in chloride media. The visible absorption behaviour was modelled as a function of Ti"', Ti'", proton, and sulfate concentrations to obtain an estimate of the equilibrium constant for the formation of Ti'"-Ti"'sulfate complex and its molar absorptivity.
As Ti"' species are oxidised by oxygen/air, resulting in possible losses in their generation and utilisation efficiencies, the reaction kinetics were determined spectrophotometrically;
again the formation of a Tit"-Ti'a-sulfate complex was implied. The voltammetric behaviour of Ti'" and Ti'a species at a hanging mercury drop electrode in sulfate and chloride media was highly irreversible and indicated the formation of an adsorbed intermediate during Ti'" reduction, which precluded relating the voltammetric behaviour to bulk solution speciation.