A numerical simulation and optimization tool for pulsed current electroplating processes is applied to the industrial preparation of high quality Tl-203 deposits. Reliable predictions on current efficiency and deposit quality are enabled by the construction of an adequate reaction mechanism for Tl deposition from highly basic solutions (pH > 12.5) in the presence of the EDTA complexing agent. In order to account for multi-ion mass transfer effects near the electrode, the diluted electrochemical ionic system model is to be solved without simplifications, in combination with electron transfer and homogeneous complex forming reactions as defined by the proposed reaction mechanism. Physical and chemical parameters for this model are achieved by comparing and tuning simulated steady-state polarization and efficiency curves at a rotating disc electrode (RDE) with experimental data.