A low energy rock fragmentation technique for in-situ leaching

Abstract Because over 60% of the total energy consumed in conventional mining consists of excavating, hauling, and liberating processes, the energy consumption in conventional methods of mining has increased exponentially with the decline in global ore-grades. In-situ leaching (ISL) is an alternative mining technology, which eliminates these processes. However, ISL is currently limited to porous rock. Expansion of ISL to impervious mineral bearing rocks requires controlled, artificial fracture stimulation and the current practice of hydraulic fracturing is not compatible due to the associated environmental impacts and uncontrolled fracture propagation. Therefore, to extend the application of ISL to impervious rocks, an alternative fracturing method using Soundless Cracking Demolition Agents (SCDAs), which is capable of producing controlled fractures in a rock mass, is proposed in this study. With the aim of understanding the fracturing performance of SCDA under in-situ stress conditions prevalent in ISL environments, a 3D numerical model for SCDA charging was produced using Particle Flow Code (PFC3D 5.0) and validated with experimentally obtained data. The model was then extended to investigate the fracture mechanism of SCDA charging at various confining pressures of 5, 10, 15, and 20 MPa. Simulation results suggest that during SCDA charging, the number of radial fracture propagations and the total fracture damage in the rock mass increase with the confinement and the fracture pattern is dependent on the confining stress of the surrounding rock. In comparison to a hydraulically fractured specimen with identical dimensions, the fracture density of SCDA charged specimen showed a ten-fold increase at high confining pressures (20 MPa). Furthermore, as opposed to an uncontrolled, unidirectional diametrical fracture generated by hydraulic fracturing, SCDA charging produces multiple radial fractures around the injection well facilitating better spatial distribution of fluid flow for ISL. The results of this study imply that SCDA charging produces a denser and a controllable fracture network compared to hydraulic fracturing, which could potentially expand ISL applications to impervious rocks.

[1]  Xiaohua Xia,et al.  Optimal energy control of a crushing process based on vertical shaft impactor , 2016 .

[2]  P. Ranjith,et al.  Micro-mechanics based numerical simulation of NaCl brine induced mechanical strength deterioration of sedimentary host-rock formations , 2018, Engineering Geology.

[3]  A. E. Azarkovich,et al.  Effect of non-explosive splitting compounds and rational work parameters , 2006 .

[4]  Gavin M. Mudd,et al.  Critical review of acid in situ leach uranium mining: 1. USA and Australia , 2000 .

[5]  Tianyou Chai,et al.  Intelligent Optimal-Setting Control for Grinding Circuits of Mineral Processing Process , 2009, IEEE Transactions on Automation Science and Engineering.

[6]  H. Mitri,et al.  Laboratory investigation into rock fracturing with expansive cement , 2009 .

[7]  Maxim Seredkin,et al.  In situ recovery, an alternative to conventional methods of mining: Exploration, resource estimation, environmental issues, project evaluation and economics , 2016 .

[8]  Benjamin Sovacool.  Cornucopia or Curse? Reviewing the Costs and Benefits of Shale Gas Hydraulic Fracturing (Fracking) , 2014 .

[9]  Shanyong Wang,et al.  Study of the fracture process in heterogeneous materials around boreholes filled with expansion cement , 2017 .

[10]  Kamran Goshtasbi,et al.  A model to determine hole spacing in the rock fracture process by non-explosive expansion material , 2011 .

[11]  Omar J. Guerra,et al.  Advances and challenges in water management within energy systems , 2018 .

[12]  N. Warpinski,et al.  Hydraulic fracture height limits and fault interactions in tight oil and gas formations , 2013 .

[13]  Gregory J. Olson,et al.  NOVEL IN-SITU METAL AND MINERAL EXTRACTION TECHNOLOGY , 2004 .

[14]  Emmanuel Gaucher,et al.  Induced seismicity in geothermal reservoirs: A review of forecasting approaches , 2015 .

[15]  Ranjith Pathegama Gamage,et al.  An Alternative to Conventional Rock Fragmentation Methods Using SCDA: A Review , 2016 .

[16]  M. R. Saharan,et al.  Rock fracturing by explosive energy: review of state-of-the-art , 2006 .

[17]  S. R. Hencher,et al.  Forensic Excavation of Rock Masses: A Technique to Investigate Discontinuity Persistence , 2017, Rock Mechanics and Rock Engineering.

[18]  Shicheng Zhang,et al.  A new method for evaluation of fracture network formation capacity of rock , 2015 .

[19]  Z. Li.  A methodology for the optimum control of shovel and truck operations in open-pit mining , 1990 .

[20]  P. Ranjith,et al.  A modified, hydrophobic soundless cracking demolition agent for non-explosive demolition and fracturing applications , 2018, Process Safety and Environmental Protection.

[21]  Numerical Study of Stresses around Holes Drilled and Filled by Expansive Cement: Case of Isotropic Linear Elastic Block of Rock , 2018 .

[22]  G. Mudd,et al.  Using sustainability reporting to assess the environmental footprint of copper mining , 2013 .

[23]  M. M. Aliyu,et al.  Stresses induced by a demolition agent in non-explosive rock fracturing , 2018, International Journal of Rock Mechanics and Mining Sciences.

[24]  J. F. Thompson,et al.  In situ leaching of copper: Challenges and future prospects , 2015 .

[25]  Paul W. Cleary,et al.  Analysis of stirred mill performance using DEM simulation: Part 1 -Media motion, energy consumption and collisional environment , 2006 .

[26]  L. Whitmarsh,et al.  UK public perceptions of shale gas hydraulic fracturing: The role of audience, message and contextual factors on risk perceptions and policy support , 2015 .

[27]  Mohammed S. Hashem M. Mehany,et al.  A Literature Survey of the Fracking Economic and Environmental Implications in the United States , 2015 .

[28]  Debra F. Laefer,et al.  Expansive fracture agent behaviour for concrete cracking , 2010 .

[29]  Nawshad Haque,et al.  Energy and greenhouse gas impacts of mining and mineral processing operations , 2010 .

[30]  Joseph F Labuz,et al.  Fracturing of Rock with Expansive Cement , 1982 .

[31]  Daniel M. Kammen,et al.  Sustainability lessons from shale development in the United States for Mexico and other emerging unconventional oil and gas developers , 2018 .

[32]  Saeid R. Dindarloo,et al.  Prediction of fuel consumption of mining dump trucks: A neural networks approach , 2015 .

[33]  Sharif Jahanshahi,et al.  Low grade ores – Smelt, leach or concentrate? , 2010 .

[34]  Frederick M. Chester,et al.  Hybrid fracture and the transition from extension fracture to shear fracture , 2004, Nature.

[35]  Shicheng Zhang,et al.  A Novel “Soundless Cracking Agent Fracturing” for Shale Gas Reservoir Stimulation , 2015 .

[36]  P. Ranjith,et al.  Investigation of the mechanical, microstructural and mineralogical morphology of soundless cracking demolition agents during the hydration process , 2017 .

[37]  John A. Gambatese,et al.  Controlled Concrete Demolition Using Expansive Cracking Agents , 2003 .

[38]  S. Yin,et al.  Effect of hydraulic fracturing on long-term storage of CO2 in stimulated saline aquifers , 2013 .