Copper Heap Leaching Research Articles

Durability properties of concrete containing copper heap leach residue as aggregates: experimental and analytical assessments

This paper investigates durability related properties of concretes containing copper heap leach residue (CHLR) as partial replacement of natural fine and coarse aggregates. The use of CHLR as aggregates in concretes promotes the reduction of the dependance on natural aggregates, upcycling of the waste as aggregates and the reduction of carbon footprint associated with natural aggregate productions. In this study, CHLR was washed, dried, and sieved to separate fine aggregate and coarse aggregate, and concretes were prepared with a cement content of 400 kg/m3 and water-cement ratio of 0.435 by replacing 25-75% natural fine and coarse aggregates. The concrete containing 50% CHLR as a partial replacement of natural CA and FA gained compressive strength of 52.9 and 54.0 MPa; drying shrinkage of 662 and 538 με; volume of permeable voids of 6.2 and 5.7%; 1485 and 2640 coulomb of charge passed in chloride permeability; and primary sorptivity coefficients of 4.0 × 10−3 and 4.3 × 10−3 mm/sec0.5 at 180 days, respectively. In contrast, these properties for the control specimens at the same age were 59.1 MPa, 394 με, 5.19%, 1280 coulomb, and 2.5 × 10−3 mm/sec0.5, respectively. The compressive strength and durability aspects declined in concretes using 75% CHLR coarse and fine aggregates. Existing analytical models for durability related properties of concrete containing natural aggregates are compared to that of the concretes using CHLR. Finally, backscattered electron images coupled with energy dispersive x-ray spectroscopy of the CHLR concretes were analyzed to understand the pore refinement, interfacial transition zones, microcracks, and hydration products influencing the durability aspects.

Copper heap leach residue aggregates in concrete: Properties and performance

This study assesses the feasibility of using copper heap leach residue (CHLR) as a sustainable alternative to natural aggregates in concrete production. The CHLR possesses flaky-angular shape grains with rough surface texture and microcracks, crystalline silica of 51.6 %, 6.1 mg/g silt-clay with a median particle size of 4.3 mm, and it becomes suitable for the partial replacement of natural fine and coarse aggregates after removing 4.2 mg/g fines through 60-minute wash. Concrete containing 25–75 % CHLR aggregates met design slump and air content of 125±25 mm and 2±0.5 %, respectively, while also demonstrating a negligible 2.9 % reduction in fresh density and 2.8 % increase in compaction factor. Concrete containing 50 % CHLR as a partial replacement of natural coarse and fine aggregates achieved compressive strengths of 47.3 MPa and 45.1 MPa at 28 days, while the compressive strength of control mix was 46.7 MPa. The mechanical properties significantly declined at 75 % CHLR incorporated concretes. The BSE-EDS analysis highlighted improved interfacial transition zone for CHLR aggregates with minimal microcracks at early age compared to the natural aggregates but developed interfacial transition zone microcracks with prolonged curing leading to a decline in mechanical strength development.

Gangues and Clays Minerals as Rate-Limiting Factors in Copper Heap Leaching: A Review

Heap leaching is a firm extractive metallurgical technology facilitating the economical processing of different kinds of low-grade ores that are otherwise not exploited. Nevertheless, regardless of much development since it was first used, the process advantages are restricted by low recoveries and long extraction times. It is becoming progressively clear that the selection of heap leaching as an appropriate technology to process a specific mineral resource that is both environmentally sound and economically feasible very much relies on having an ample understanding of the essential underlying mechanisms of the processes and how they interrelate with the specific mineralogy of the ore body under concern. This paper provides a critical overview of the role of gangues and clays minerals as rate-limiting factors in copper heap leaching operations. We aim to assess and deliver detailed descriptions and discussions on the relations between different gangues and clays minerals and their impacts on the operational parameters and chemical dynamics in the copper heap leaching processes.

A Decision Support System for Changes in Operation Modes of the Copper Heap Leaching Process

Chilean mining is one of the main productive industries in the country. It plays a critical role in the development of Chile, so process planning is an essential task in achieving high performance. This task involves considering mineral resources and operating conditions to provide an optimal and realistic copper extraction and processing strategy. Performing planning modes of operation requires a significant effort in information generation, analysis, and design. Once the operating mode plans have been made, it is essential to select the most appropriate one. In this context, an intelligent system that supports the planning and decision-making of the operating mode has the potential to improve the copper industry’s performance. In this work, a knowledge-based decision support system for managing the operating mode of the copper heap leaching process is presented. The domain was modeled using an ontology. The interdependence between the variables was encapsulated using a set of operation rules defined by experts in the domain and the process dynamics was modeled utilizing an inference engine (adjusted with data of the mineral feeding and operation rules coded) used to predict (through phenomenological models) the possible consequences of variations in mineral feeding. The work shows an intelligent approach to integrate and process operational data in mining sites, being a novel way to contribute to the decision-making process in complex environments.

Management of Copper Heap Leach Projects: A Geologist’s Perspective

Editor’s note: The Geology and Mining series, edited by Dan Wood and Jeffrey Hedenquist, is designed to introduce early-career professionals and students to a variety of topics in mineral exploration, development, and mining, in order to provide insight into the many ways in which geoscientists contribute to the mineral industry. Abstract Copper production by heap leaching, coupled with solvent extraction and electrowinning (SX-EW), is a well-established technology, with an annual output of about 3.7 million tonnes (Mt) of copper metal. Ores presently amenable to copper heap leaching include copper oxides and secondary copper sulfides. Most copper deposits amenable to acid sulfate heap leaching result from supergene processes within porphyry copper systems, although copper heap leaching has been applied to sandstone and shale-hosted deposits, among others. Copper heap leaching is a rate-dependent process sensitive to copper mineralogy (copper oxides > secondary sulfides > hypogene sulfides), driven by the pH of the leach solution, the activity of ferric iron (Fe3+ (aq)) dissolved in the leach solution, and temperature. Acid consumption, a principal operating cost item, depends on the pH of the leach solution; the presence of reactive gangue minerals, notably carbonates, Ca plagioclase, pyroxene, Fe-rich amphibole, and olivine; and the cumulative surface area of material in the heap. There are three basic approaches to commercial copper heap leaching—run-of-mine, dedicated pad, and on-off pad leaching, with variables that include crushing, acid/ferric agglomeration, solution application rate, and leach solution pH. These approaches affect copper leach kinetics, overall copper recovery, acid consumption, and capital and operating costs. A successful copper heap leach evaluation program requires a systematic approach, beginning with geologic mapping, then drilling and hydraulic and metallurgical testing, and concluding with financial analysis, engineering, and permitting. As geologists are the unique party in the process, with a thorough understanding of the overall deposit geology, including ore and gangue mineralogy, the domains that comprise the deposit, and the geochemistry of leaching, they must remain fully involved in the project throughout the evaluation. At the outset, geologists must manage the drilling program and define the grade-mineral domains. Later, they must participate in the metallurgical and hydraulic testing programs, including the evaluation of test results; then, during financial modeling, they must collaborate with all of the other specialists.

Analysis of iron and copper speciation and activities in chloride leaching solutions of high ionic strength

In light of the recent increased use of seawater for copper heap leaching, we analyzed the speciation and activities of iron and copper in chloride media, with a focus on chalcocite leaching. Compared with other published work, the present study carried out such analysis at high solution ionic strength up to 3 M. For this purpose, the SIT (Specific ion Interaction Theory) activity model was used in the thermodynamic calculations performed by the STABCAL software. The speciation results obtained from the software were validated by the experimental measurements of solution potential, which were performed in a sealed jacketed reactor under an ultra-high purity nitrogen environment. The speciation results showed that FeCl2+ and hydrated Fe2+ were the dominant Fe(III) and Fe(II) species in the chloride concentration range 0.5 M – 3 M. In the case of copper speciation, hydrated Cu2+ and CuCl2− dominated at chloride concentrations <0.5 M. In the chloride concentration range 0.5 M – 3 M, CuCl+ and CuCl32− were the dominant copper species. Based on the speciation and activities results, we determined the actual cathodic and anodic half reactions responsible for copper leaching from chalcocite in chloride media. The proposed cathodic half reactions pinpoint ways of manipulating solution potentials, which is vital for determining the kinetics of the second stage of chalcocite leaching.

Development metallurgy guidelines for copper heap leach

This paper outlines a comprehensive, cost-effective testing program for the acid-ferric sulfate heap leaching of oxide, supergene and primary copper ores. It is based on extensive experience in copper heap leaching and uses the many technological advances in the field developed over the past several decades. The approach described requires firstly a detailed resource evaluation, then a hydrodynamic characterization of representative samples and, finally, a focused metallurgical testing program. The principles communicated here can be applied to other acid leachable minerals. The program varies considerably from conventional testing in its disciplined, orderly, step-by-step approach, its application of hydrological and chemical principles to leaching, and its reliance on fewer, more tightly controlled column tests. The purpose of the test program is to optimize the financial, time and other resources devoted to the program, while minimizing the financial risks to the development company or companies and the project funding providers.

Estimation of hydraulic parameters under unsaturated flow conditions in heap leaching

The mathematical modeling of the unsaturated flow problem requires the simultaneous resolution of two problems: the Richards equation and the estimation of the hydraulic parameters involved in hydraulic conductivity and in the retention curve. Various techniques have been applied to both problems in a wide range of situations. In this article, a novel implementation of the processing techniques involved in copper heap leaching is presented. Specifically, the impact of the used numerical method and the selection of the parametric family are evaluated. From a methodological point of view, a global algorithm is proposed that integrates the solutions of both problems. Finally, our computational experiments are compared with previous experimental results from the Chilean copper mining industry and related works.

Study on schwertmannite production from copper heap leach solutions and its efficiency in arsenic removal from acidic sulfate solutions

Schwertmannite, a ferric oxyhydroxy sulfate mineral, has gained attention in recent years due to its high sorption capacity for toxic arsenic species. In porphyry copper mines, production of schwertmannite from heap leaching solutions may be possible because the solutions contain high concentrations of ferric and sulfate ions, which are components of schwertmannite. The present study investigates the effect of Cu2+ and Fe2+, coexisting ions in heap leaching solutions, on the synthesis of schwertmannite; as well as the efficiency of As(V) removal from acidic solutions by the synthesized products. Synthesis was carried out by neutralization of 50mM Fe2(SO4)3 solutions at 65°C (final pH: 3–4), and the synthesized products were characterized by XRD. The results indicated that Cu2+ does not affect the synthesis of schwertmannite, but that Fe2+ has a significant influence on the synthesis; transformation of intermediate schwertmannite to goethite occurred in the presence of Fe2+. Schwertmannite was produced in the presence of both Cu2+ and Fe2+, suggesting that Cu2+ inhibits the transformation of schwertmannite to goethite in the presence of Fe2+. To confirm this, the transformation of schwertmannite to goethite was investigated in solutions containing Fe2+ and Cu2+ at pH3–4 and 65°C. It was shown that a complete transformation to goethite occurred in 1h in the presence of 100mM Fe2+. However, 100mM Cu2+ inhibited the transformation of schwertmannite to goethite in the presence of Fe2+. Batch sorption experiments were conducted to evaluate the As(V) sorption capacity of the synthesized products. The results showed that As(V) in acidic solutions (pH3–4) can be removed effectively by synthesized schwertmannite with the maximum As(V) sorption capacity of 94–133mgg−1. A lower As(V) sorption capacity was observed in products containing goethite synthesized in the presence of Fe2+; here, the maximum As(V) sorption capacity was 58mgg−1.

Effects of Pregnant Leach Solution Temperature on the Permeability of Gravelly Drainage Layer of Heap Leaching Structures

In copper heap leaching structures, the ore is leached by an acidic solution. After dissolving the ore mineral, the heap is drained off in the acidic solution using a drainage system (consisting of a network of perforated polyethylene pipes and gravelly drainage layers) and is, then, transferred to the leaching plant for copper extraction where the copper is extracted and the remaining solution is dripped over the ore heap for re-leaching. In this process, the reaction between the acidic solution and copper oxide ore is exothermal and the pregnant leach solution (PLS), which is drained off the leaching heap, has a higher temperature than the dripped acidic solution. The PLS temperature variations cause some changes in the viscosity and density which affect the gravelly drainage layer's permeability. In this research, a special permeability measuring system was devised for determining the effects of the PLS temperature variations on the permeability coefficient of the gravelly drainage layer of heap leaching structures. The system, consisting of a thermal acid resistant element and a thermocouple, controls the PLS temperature, which helps measure the permeability coefficient of the gravelly drainage layer. The PLS and gravelly drainage layer of Sarcheshmeh copper mine heap leaching structure No. 1 were used in this study. The permeability coefficient of the gravelly soil was measured against the PLS and pure water at temperatures varying between 3°C to 60°C. Also, the viscosity and density of the PLS and pure water were measured at these temperatures and, using existing theoretical relations, the permeability coefficient of the gravel was computed. A comparison between the experimental and theoretical results revealed a good conformity between the two sets of results. Finally, a case (Taft heap leaching structure, Yazd, Iran) was studied and its gravelly drainage layer was designed based on the results of the present research.

STABILITY ANALYSIS AND STABILIZATION OF MIDUK HEAP LEACHING STRUCTURE, IRAN

To construct copper heap leaching structures, a stepped heap of ore is placed over an isolated sloping surface and then washed with sulphuric acid. The isolated bed of such a heap consists of some natural and geosynthetic layers. Shear strength parameters between these layers are low, so they form the possible sliding surfaces of the heaps. Economic and environmental considerations call for studying such slides. In this study, firstly, results of the laboratory tests carried on the materials of the heap leaching structures bed are presented. Then, the instability mechanisms of such structures are investigated and proper approaches are summarized for their stabilization. Finally, stability of the Miduk copper heap is evaluated as a case history, and appropriate approaches and their effects are discussed for its stabilization.

A comprehensive model for copper sulphide heap leaching: Part 1 Basic formulation and validation through column test simulation

This paper covers the basic formulation of a comprehensive copper heap leach model based on computational fluid dynamics (CFD) technology together with its parameterization and validation against laboratory column test data. For the column test data used here, the model formulation covers an ore with a mixture of chalcocite and pyrite in a column under leach with a ferric raffinate and includes the reaction kinetics of the dissolution of the key minerals within the context of a shrinking core algorithm to accurately model the leach behaviour. Precipitation species, the role of bacteria and the treatment of unsaturated fluid and gas flow in porous media is also described in the context of the model. The current work demonstrates the use of small column test leach data, including particle size distribution, to characterize the ore. The model was then used with the same parameter set to produce a good fit to results from larger columns and different crush sizes.

Recovery of rhenium from copper leach solution by ion exchange

There is current interest in recovering rhenium from solutions produced as a result of copper heap and stockpile leaching. Copper-bearing leach solutions typically contain rhenium at concentrations near 1mg/L. This work has demonstrated that rhenium can be efficiently extracted from these solutions using weakly basic anion exchange resins. Breakthrough of Re occurs after approximately 5000BVs of solution flow. Rhenium is eluted from the resin using 1M NaOH, producing a rhenium-rich solution containing about 1400mg/L Re. The overall concentration ratio is about 2400:1.

Effect of compaction on binder performance in copper heap leaching

Heap leaching efficiency is reduced by poor solution flow characteristics (channeling and ponding), which result from compaction and fines migration. Agglomeration of the ore can prevent compaction and immobilize fines, but copper leaching requires an acid-resistant binder to stabilize the agglomerates. Until now, there has not been a satisfactory way to evaluate whether a binder was effective, other than squeezing a handful to see if it “feels right.” Procedures have been developed to quantitatively determine whether a binder produces agglomerates that can withstand compaction in an acidic solution, and have identified several binders that will provide sufficiently compaction-resistant agglomerates for copper heap leaching.

Polyacrylamide as an agglomeration additive for copper heap leaching

Heap leaching has significant challenges associated with permeability. Low permeability decreases recovery rates and recovery. It is believed that low heap permeability is caused by the migration of fine particles. This fines migration clogs the natural flow path of leach solutions, forcing it to flow around some regions of the heap, leaving them un-leached. Binders show significant promise in this application because they will increase agglomerate strength leading to a reduction in fines migration. However, most binders have been used without any systematic reasoning. Using a novel soak test, systematic studies have been completed on a wide range of binders. A non-ionic polyacrylamide was found to reduce fines migration as much as 93%. It is believed that this binder was successful due to electrostatic attraction, hydrogen bonding, and physical bonding.

Convergence analysis of a vertex-centered finite volume scheme for a copper heap leaching model

In this paper a two-dimensional solute transport model is considered to simulate the leaching of copper ore tailing using sulfuric acid as the leaching agent. The mathematical model consists in a system of differential equations: two diffusion–convection-reaction equations with Neumann boundary conditions, and one ordinary differential equation. The numerical scheme consists in a combination of finite volume and finite element methods. A Godunov scheme is used for the convection term and an P1-FEM for the diffusion term. The convergence analysis is based on standard compactness results in L2. Some numerical examples illustrate the effectiveness of the scheme. Copyright © 2009 John Wiley & Sons, Ltd.

Development of experimental procedures to analyze copper agglomerate stability

The efficiency of heap leaching is reduced by poor solution flow characteristics (i.e., channeling and ponding) that result from fines migration. Agglomeration of the ore can immobilize fines, but for agglomeration to be successful in copper leaching, an acid-resistant binder is needed to stabilize the agglomerates. Until now, there has not been a satisfactory method to evaluate whether a binder was effective, other than squeezing a handful to see if it “feels right.” This paper reports on several procedures that have been developed to quantitatively determine whether a binder gives good performance in an acidic solution. These procedures have been used to identify binders that would be suitable for copper heap leaching.

Use of lignosulfonate for elemental sulfur biooxidation and copper leaching

The surface-active properties of lignosulfonate, a solid by-product from the sulfite papermaking industry, were investigated in several aspects of a proposed Barrick copper heap leaching process where sulfur is added to the heap to be oxidized in-situ to produce acid. In this copper heap leaching process, lignosulfonate could affect sulfur milling, sulfur biooxidation, acid consumption, copper recovery, and solvent extraction of the copper pregnant leach solution. In milling, lignosulfonate was shown to reduce the measured Bond work index of sulfur in a batch mill, but not in a continuous mill. In biooxidation, lignosulfonate increased the growth rate of sulfur-oxidizing microorganisms, but the faster rate was not sustained during the whole biooxidation period. Lignosulfonate accelerated the kinetics of sulfur biooxidation in certain leach environments. In copper leaching, lignosulfonate did not have negative effects on copper recovery, acid consumption, or leach kinetics, but neither did it improve the kinetics of copper recovery. In solvent extraction, the separation of the organic and aqueous phases was rapid and clean if lignosulfonate was previously in contact with the copper ore or the sulfur particles. Based on these various outcomes, lignosulfonate did not have a negative impact on the copper heap leaching process tested, but does not constitute an essential additive to the process.

REVIEW OF AGGLOMERATION PRACTICE AND FUNDAMENTALS IN HEAP LEACHING

ABSTRACT This article reviews agglomeration practices for precious metal and copper heap leaching. Both industries prefer drum to conveyor agglomeration, particularly for clayey ore or ore having a high fines content. Precious metal heap leaching operations opt for cement in a dosage from 2.5 to 10 kg cement/t of ore (5–20 lb/ton) added to a cyanide solution. Copper ores are agglomerated with water and up to 40 kg sulfuric acid/t of ore (80 lb/ton) without binder. The agglomerate physical characteristics, with the exception of their strength, can be measured precisely and automatically. The impact of agglomeration on the in situ physical characteristics of the heap, other than the observable ponding and slumping, is not understood well. The most substantial benefits of agglomeration include up to 90% metal recovery from poorly permeable ores, shorter leach cycles, extra metal recovery from already-leached tailings, and better environmental heap closure.

銅ヒープリーチングの現状と将来

The present situation of copper heap leaching is reviewed in this paper. Current techniques for improving copper extraction from sulfide ore are also discussed. Morenci mine (Arizona) has expanded its cathode copper production by the leaching-SX /EW process in parallel with the conventional flotation process since mid eighties. In March 2001, Morenci mine completed Mine for Leach project including closure of the concentrators and expansion of cathode copper production with a newly equipped crush-leaching system. Technical background of the conversion is discussed with efforts to improve metallurgical performance at the Morenci concentrators during last 10 years. Extraction of copper from sulfide ore is mainly decided by copper mineralization of the ore at the leaching-SX / EW process. One of the factors that made the conversion feasible at Morenci mine was chalcocite rich mineralization of the ore. Improvement in dissolution of chalcopyrite will be one of the biggest issues for future expansion of the heap leaching-SX / EW process.