Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng Experimental study of sulfuric acid effects on hydro-mechanical properties of oxide copper heap soils H. Ghasemzadeh ⁎ , M. Sanaye Pasand, M.M. Mollanouri Shamsi Civil Engineering Faculty, K. N. Toosi University of Technology, Tehran, Iran ARTICLE INFO Keywords: Sulfuric acid Column leaching Particle reduction Clogging Internal friction angle Heap stability ABSTRACT Several mechanisms contribute to changes in the performance of oxide copper heaps. These include physical, biological, chemical and thermal interactions between sulfuric acid and the formation of soil particles. A series of experimental studies was conducted by simulating the column leaching process in the laboratory. The leaching of selected gravel and crushed copper oxide ores from two copper mines was carried out to measure their permeability and strength. The influence of effective parameters on gravel clogging was studied and the clogging coefficient was estimated with time. Furthermore, the ratio of particle reduction (R PR ) caused by acid seepage was evaluated and an equation for the internal friction angle of ore particles over time was generated. The present study shows significant reductions of gravel permeability (28% after five months leaching) and friction angle of ore particles (25% after eight months leaching). The effects of sulfuric acid flow on the hydro-me- chanical properties of oxide copper heap soils could enhance the accuracy of slope stability design and drainage layers design in industrial heap leaching systems. 1. Introduction Heap leaching is one of the mineral processing techniques whereby a heap of low grade ore is leached with various solvents to extract precious and base metals. Since the 1950s, it has been practised for the extraction of copper, gold, silver, and uranium (Kappes, 2002). The ore is crushed and agglomerated before constructing a heap to achieve a uniform distribution of particles and better percolation of the solvent. Agglomerated ore particles are also used in industrial heaps (Bouffard, 2008; Dhawan et al., 2013). For the extraction of copper from oxide ores, the solvent is sulfuric acid and the leaching rate is in the range of 5–20 L/m 2 h(Petersen, 2016). The leaching process can cause physical and chemical interactions. Consequently, many characteristics of ore particles in the heap such as permeability, particle size distribution, porosity and strength parameters could change over time. In heap leaching, most of the solvent percolates as vertical flow channels due to gravity. The zones between the networks of channels are occupied by the semi-stagnant solvent due to the interplay between gravity and capillary forces. If the ratio of gravity to capillary forces will be around one, the solvent is stagnant (held up) between the par- ticles. The increase in stagnant liquid holdup could increase the clog- ging (Ilankoon and Neethling, 2013; de Andrade Lima, 2006). The solvent spreads through the heap with little horizontal spread and the homogenous solvent flow does not typically occur in the heap leaching process (Ilankoon and Neethling, 2016; McBride et al., 2017). It should be noted that after adding a new layer above the surface of heap, the solvent is introduced at the top of that layer. The main flow channels in the previous layer may be changed and/or the solvent may flow through the existing flow paths. The heap leaching process is simulated at laboratories by column leaching tests. The column dimensions in these tests have considerable ranges depending on the aim of each test. The ratio of the column diameter to the maximum soil particle size should be between 8 and 12 in order to reduce the wall effects (Fraser et al., 1993). Clogging coefficient is defined as the ratio of permeability before leaching and permeability after leaching. It consists of physical, che- mical and biological characteristics and is important for designing heap leaching systems. A good estimation of these coefficients can be ob- tained by performing tests on leached samples. Clogging takes place on the top of the heap layers due to particle size segregation. Moreover, clogging is formed in the filter layer, drainage layer and the collection pipes due to the movement of fine particles which may be formed after disintegration. The effective parameters in clogging formation are: particle size distribution, constituent elements, solvent flow rate, aeration, liquid holdup and added reagents and their parameters such as pH (Liu and Huang, 2008; Maley et al., 2009; Halinen et al., 2009; Xia et al., 2015; Torkzaban et al., 2015). The elements present in ores responsible for chemical clogging in oxide copper heaps and drainage https://doi.org/10.1016/j.mineng.2017.12.010 Received 5 April 2016; Received in revised form 20 November 2017; Accepted 10 December 2017 ⁎ Corresponding author at: P.O. Box 1996715433, Iran. E-mail address: ghasemzadeh@kntu.ac.ir (H. Ghasemzadeh). Minerals Engineering 117 (2018) 100–107 0892-6875/ © 2017 Elsevier Ltd. All rights reserved. T