The electrolysis of carbonate solutions using conductive-diamond anodes in single and divided electrochemical cells is studied in this work. This process leads to the formation of significant oxidant concentrations in the reaction media within the current density range used (65-150 mA cm(-2)). However, the efficiency is highest at low current densities. Carbonate concentration has a major effect on oxidant production; oxidant concentration increases with carbonate concentration in the raw material. Two techniques were used to quantify the oxidant concentration: titration using iodine/thiosulphate and spectrophotometric measurements. The results clearly indicate that in addition to hydrogen peroxide, other stable oxidants were formed in the reaction medium, namely, peroxocarbonates. Divided cells, low current densities and high carbonate concentrations in the raw matter are optimal for oxidant production. (C) 2013 Elsevier B.V. All rights reserved.