Detoxification of waste water from gold processing is under increasing discussion in recent times. Limits for the release of cyanide are set to protect waterbodies and the soil surrounding gold processing facilities from contaminations. Standards and limits are often based on varying data of the hazardousness. Notably concerning the volatilization of hydrogen cyanide and further reactions of HCN in the environment a variety of findings are published, with data, wide apart from each other, which influence the assessment of the hazard particularly for the workers in processing facilities. Likewise, the determination of the proper amount of volatilized cyanide in degradation experiments is essential for the accurate identification of the degraded part. In photoelectrocatalytic experiments, using TiO2 films, light, and moderate electrical bias, the volatilization and the degradation rate of cyanide were determined at different pH. It is shown that the volatilization rate at pH < 9 is predominant and cannot be neglected up to pH 13. Indirect vs. direct hole transfer on the semiconductor are discussed. With a new approach to the discussion of the comparability for different photocatalysts and varying experimental conditions we indicate a relationship between the rate constant of the degradation reaction and the difference of the energy of the valence band of the photocatalyst to the redox potential of oxidizable species.