Capacitive deionisation (CDI) has many advantages over other desalination technologies due to its low energy consumption, less environmental pollution and low fouling potential. The objectives of this study are to investigate the effect of operational conditions on the CDI electrosorption efficiency and energy consumption, to identify ion selectivity in multi-ionic solutions and to probe the effect of dissolved reactive silica on the treatment efficiency. A series of laboratory scale experiments were conducted using a CDI unit with activated carbon electrodes. The electrosorption removal efficiency was inversely related to solution temperature, initial total dissolved salts (TDS) concentration and the applied flow rate. CDI energy consumption (kWh/m(3)) is directly related to the TDS concentration and inversely related to the flow rate. The kinetics analysis indicated that the electrosorption followed pseudo-first-order kinetics model. Ion selectivity on activated carbon electrodes followed the order of Fe3+ > Ca2+ > Mg2+ > Na+ for cations and SO42- > Br- > Cl- > F- > NO3- for anions. It was found that the dissolved silica was not removed by CDI; no silica fouling was found. The deterioration of activated carbon electrodes was not observed at any time during experiment. (C) 2012 Elsevier B.V. All rights reserved.