Selective electrodialysis for copper removal from brackish water and coal seam gas water

This study investigates the removal rate of divalent ions during partial desalination of brackish water using electrodialysis (ED). An experiment was conducted with a benchtop PCCell electrodialysis instrument in batch mode with a non-ion selective membrane. The removal rate of total copper, a valuable plant micronutrient, was analysed. Both copper chloride and copper sulphate removal compared to sodium chloride removal were studied. The copper and the sulphate content in the diluate declined logarithmically with a removal rate of around 98 % for copper in both experiments, and 100 % for sulphate over three hours at a starting temperature of 23 °C. Copper and sulphate were removed faster than sodium chloride at 72 %. The temperature of the diluate increased by 15 % during the three-hour run. The loss of water from the diluate was approximately 10 %, limiting brine production. Modelling indicated that the Mass/Charge ratio of ions could be an indicator of the removal rate of anions, especially if they have, like sulphur, a large effective radius, whereas the Effective Ionic Radius can be an indicator for the removal of cations. The smaller the ionic radius, the faster the removal rate of the cation. This model can be used to customise nutrient concentration in the water end product. The customised water has a potential to be used for fertigation, saving the farmer money by retaining beneficial plant nutrients in the water