Electroosmotic drainage, a pilot application for extracting trapped capillary liquid in copper leaching J. Valenzuela a , L. Romero a,b, ⁎, C. Acuña c , M. Cánovas d a Centro de Investigación Tecnológica del Agua en el Desierto-CEITSAZA, Universidad Católica del Norte, Antofagasta, Chile b Chemical Engineering Department, Universidad Católica del Norte, Antofagasta, Chile c Chemical and Environmental Engineering Department, Universidad Técnica Federico Santa María, Valparaíso, Chile d Metallurgical and Mining Department, Universidad Católica del Norte, Antofagasta, Chile abstract article info Article history: Received 12 August 2015 Received in revised form 18 March 2016 Accepted 12 April 2016 Available online 13 April 2016 Electroosmotic drainage tests were carried out using one-cubic-meter tanks filled with solid residues from leaching copper. The main objective was to evaluate the efficiency of this technique for the removal of capillary-entrapped solution as a function of the following parameters or operational variables: electrode config- uration, voltage applied, distance between electrodes, polarity reversal and intermittency of the applied voltage. The efficiency of this technique was compared to that of drainage by gravity, based on three indicators: moisture reduction, energy consumption per cubic meter of drained solution and drainage time factor, which allows a vi- sualization of the reduction of drainage time in relation to natural drainage time by applying electroosmotic drainage. Of the three tested electrode configurations, hexagonal, linear and alternate linear, the last configura- tion with intermittency in applied voltage (12 V) and a distance of 0.6 m between electrodes gave the best results, with a moisture reduction of 2.02, an energy consumption of 6.7 kWh/m 3 and a drainage time factor of 6.45. Considering these results, it is demonstrated that the technology increases the spatial capacity of copper leaching and reduces the weight of the material to be transported. © 2016 Elsevier B.V. All rights reserved. Keywords: Electroosmotic drainage Copper leaching Electrode configuration Moisture reduction 1. Introduction The Atacama Desert in northern Chile is one of the most important copper mining regions in the world. Copper ore, previously agglomerat- ed by adding concentrated sulfuric acid, is heaped on an impermeable plastic and/or clay lined leach pad where it can be irrigated with a sul- furic acid solution to leach the ore. The solution then percolates through the heap and leaches out the copper contained in the solid phase into the aqueous phase, thereby generating an acid solution rich in copper as copper sulfate. The copper-rich solution is then collected and pumped to next step of solvent extraction and electrowinning to pro- duce copper cathodes. Ore heaps are typically 3 to 8 m high, with a base area of several thousand square meters, and are made up of 100,000 to 500,000 tons of ore (Domic, 2001). Depending on the ore, leaching can take several months to dissolve and extract 75–80% of the leachable copper com- pounds. Leaching generates large amounts of solid waste that contains mainly gangue (inert material) that is discarded and then accumulated. These wastes are stored above ground where they may constitute a po- tential risk of groundwater contamination (Dold and Fontboté, 2001). After having removed much of the soluble copper, the heap is left standing to drain the solution trapped in the pores of the remaining solid. Two drying processes occur during the natural drainage of the heap: (i) gravitational drainage at the base; and (ii) evaporation through solar radiation and convective drying at the surface. After 25– 35 days of natural drainage, the final moisture content reached by the solid is approximately 13–16% on a wet basis. The remaining lixiviant is trapped in the capillary interstices of the solid matrix and its extrac- tion by conventional drainage techniques may be difficult. Drainage is particularly difficult in low permeability materials such as clay soils and where fine-grained material has accumulated due to the breakup of agglomerated particles that have interacted with the lixiviant. Therefore, to reduce the remaining moisture content of the solid material after extracting most of the soluble copper and accelerate the drainage process, electroosmotic drainage technique is proposed. Electroosmotic drainage consists of applying a low electric potential to dewater a porous medium. Casagrande (1947, 1949, 1952) first employed this technique to consolidated clay soils as a simple and efficient way to accelerate dewatering in soils with low hydraulic conductivity. Since then, electroosmotic drainage has been successfully applied to wastewater treatment, remediation of contaminated soils, and industrial and drying processes, among other uses (Runnells and Hydrometallurgy 163 (2016) 148–155 ⁎ Corresponding author at: Centro de Investigación Tecnológica del Agua en el Desierto- CEITSAZA, Universidad Católica del Norte, Antofagasta, Chile. E-mail address: leon@ucn.cl (L. Romero). http://dx.doi.org/10.1016/j.hydromet.2016.04.005 0304-386X/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet