Removal of nitrates from copper-containing aqueous acidic leach solutions by electrodialysis

Abstract

The north of Chile is characterised by a large content of caliche minerals which represent high amounts of sodium and potassium nitrates. The presence of these nitrates, in copper-containing aqueous acid leach solutions, are responsible for serious problems in the hydrometallurgical extraction of copper-from-ore. The main problems are: extractant losses due to nitration and/or hydrolysis and negative effects upon bioleaching microorganisms such as lower growth cell and higher microbial lag times. On the basis of these problems, the objective of this work was to evaluate electrodialysis (ED) as an alternative method for removal for nitrates from copper-containing aqueous acid leach solutions. For this purpose, ED experiments in a three-compartment cell using both real and synthetic solutions at different current densities, flow rate and temperature were studied. It was found that high temperature, high flow rate and low current densities favour the ED performance, under the range investigated. Thus, optimum operating conditions were found at 40 °C, 120 Lh^-1and 150 A m⁻², where current efficiencies (CE) of 96.4% and 89.4% were obtained for synthetic and real catholyte, respectively. Likewise, the energy consumption (EC) was 25% lesser (0.75 kWh kg⁻¹) with real catholyte versus 1.01 k Wh kg⁻¹ consumed using synthetic catholyte. These results demonstrated that electrodialysis could be applied for removal of nitrates from copper-containing aqueous acid leach solutions as an alternative technology.