Papers by Alessandro Navarra
Processes
Mineral and metallurgical processing are crucial within the mineral value chain. These processes ... more Mineral and metallurgical processing are crucial within the mineral value chain. These processes involve several stages wherein comminution is arguably the most important due to its high energy consumption, and its impact on subsequent extractive processes. Several geological properties of the orebody impact the efficiency of mineral processing and extractive metallurgy; scholars have therefore proposed to deal with the uncertain ore feed in terms of grades and rock types, incorporating operational modes that represent different plant configurations that provide coordinated system-wide responses. Even though these studies offer insights into how mine planning impacts the ore fed into the plant, the simultaneous optimization of mine plan and metallurgical plant design has been limited by the existing stochastic mine planning algorithms, which have only limited support for detailing operational modes. The present work offers to fill this gap for open-pit mines through a computationall...
Metals
The Alhué mining district, Chile, is an example of a high-grade Au-Ag-Zn(-Pb) deposit with minera... more The Alhué mining district, Chile, is an example of a high-grade Au-Ag-Zn(-Pb) deposit with mineralized veins that contain variable amounts of copper sulfides, which are detrimental to the cyanidation process. Similar deposits can be found in the central zone of Chile, with polymetallic veins (Au, Ag, Cu, Pb, and Zn) that are related to subvolcanic intrusive events, the development of collapse calderas, and extensive hydrothermal alteration, such as Bronces de Petorca, the Chancón mining district and Cerro Cantillana; areas of the world with similar formations include the western United States and the Henan Province in central China, for example. Mineralogical variation can be managed within the metallurgical process by alternating its operational modes. The decision to switch between modes is governed by current and forecasted stockpile levels feeding into the process, according to a discrete rate simulation (DRS) framework that has now been developed to incorporate head grade data ...
Frontiers in Environmental Science
As result of the adverse effects caused by climate change, the nations have decided to accelerate... more As result of the adverse effects caused by climate change, the nations have decided to accelerate the transition of the energy matrix through the use of non-conventional sources free of polluting emissions. One of these alternatives is green hydrogen. In this context, Chile stands out for the exceptional climate that makes it a country with a lot of renewable resources. Such availability of resources gives the nation clear advantages for hydrogen production, strong gusts of wind throughout the country, the most increased solar radiation in the world, lower cost of production of electrical supplies, among others. Due to this, the nation would be between the lowest estimated cost for hydrogen production, i.e., 1.5 USD/kg H2 approximately, scenario that would place it as one of the cheapest green hydrogen producer in the world.
Canadian Metallurgical Quarterly, 2021
ABSTRACT Trends toward the widespread use of electric vehicles and renewable energy sources all p... more ABSTRACT Trends toward the widespread use of electric vehicles and renewable energy sources all point to continued growth in copper demand. This demand will be met mainly by new primary copper production, with recycling expected to contribute significantly to copper supply. Significant quantities of copper ore are presently mined from porphyry deposits in which typically, near-surface copper oxides are recovered hydrometallurgically by leaching, solvent extraction and electrowinning, whereas the deeper copper sulphides are only amenable to milling followed by pyrometallurgical processing and electrolytic refining. The Chilean copper porphyries together are the largest group of operating copper mines and are likely to remain so into the future. However, several of these deposits are forecast to show increasing levels of arsenic-bearing minerals, such as enargite. As mature copper mining districts exhaust the near-surface oxides and higher-grade sulphides, individual mines will need to adjust their operations accordingly. However, it is considered that due to such changes, re-engineering efforts might be more economically coordinated across several mines, to collectively handle the evolving ore feeds. The present paper adapts a discrete event simulation (DES) approach to support mine-to-smelter integration within porphyry copper districts. Sample computations are presented that are loosely based on the Chilean context.
Journal of the Southern African Institute of Mining and Metallurgy, 2021
The mine production scheduling problem (MPSP) has been studied since the 1960s, and remains an ac... more The mine production scheduling problem (MPSP) has been studied since the 1960s, and remains an active area of computational research. In extending the concepts of the MPSP, the automated mine may now be regarded as a hierarchical intelligent agent in which the bottom layer consists of distributed robotic equipment, while strategic functionality occupies the higher layers. Here we present a disambiguation of artificial intelligence, machine learning, computational optimization, and automation within the mining context. Specifically, the Q-learning algorithm has been adapted to generate the initial solutions for a high-performing strategic mine planning algorithm, originally developed by Lamghari, Dimitrakopoulos and Ferland, based on the variable neighbourhood descent (VND) metaheuristic. The hierarchical intelligent agent is presented as an integrative conceptual platform, defining the interaction between our new Q-learning adaptation and Lamghari's VND, and potentially other hi...
International Journal of Mining, Reclamation and Environment, 2016
Abstract Stochastic mine planning algorithms have been extended to better represent ore selection... more Abstract Stochastic mine planning algorithms have been extended to better represent ore selection decisions. Under geological uncertainty, existing algorithms generate plans that may violate the mineral processing capacity; under such geological scenarios, the excess ore undergoes a recourse action which is not as profitable as regular processing, hence decreasing the net present value. This decrease has previously been represented as a penalty on excess ore, which may not accurately represent actual operations. The new framework considers the most typical recourse: increasing the cut-off grade into the mineral process. This approach is demonstrated by adapting the VND algorithm of Lamghari et al.
Minerals Engineering, 2021
Abstract Discrete event simulation (DES) is a computational tool capable of simulating the interp... more Abstract Discrete event simulation (DES) is a computational tool capable of simulating the interplay of important variables and processes within complex mining systems that are subject to geological uncertainty. Alternate modes of operation are fundamental to the development of effective DES frameworks to model and monitor system performance in response to unexpected changes (e.g. ore feed attributes). The decision to switch between modes is governed by operational policy and is triggered as critical thresholds are crossed. Hundreds of operating days can be simulated to identify potential deficiencies, bottlenecks, or other operational risks. DES is thus useful to support strategic decision-making in the design, development and sustained operation of any mining system. Based on current mining trends, tailings storage facilities are growing in both size and number, resulting in alarming tailings accumulations worldwide. Coupled with a large number of abandoned legacy mines and artisanal mining operations, tailings and other waste materials pose a significant threat to human health and safety, as well as the environment. Cost-effective tailings management strategies to mitigate these risks through site remediation are required. Research on potential uses for discarded tailings is divided between secondary metallurgical processing for extractive purposes, and incorporation into industrial materials. The current framework has been adapted to integrate geostatistical variability into DES in order to assess the potential operational risks related to secondary mining of tailings for a conceptual cement production operation. A case study loosely based on data from a tailings dam in Taltal, northern Chile, is presented. Sample calculations are provided that demonstrate the framework as a valuable tool to evaluate and mitigate potential risk factors in the development of tailings retreatment applications.
Strategic decisions to develop a mineral deposit are subject to geological uncertainty, due to th... more Strategic decisions to develop a mineral deposit are subject to geological uncertainty, due to the sparsity of drill core samples. The selection of metallurgical equipment is especially critical, since it restricts the processing options that are available to different ore blocks, even as the nature of the deposit is still highly uncertain. Current approaches for long-term mine planning are successful at addressing geological uncertainty, but do not adequately represent alternate modes of operation for the mineral processing plant, nor do they provide sufficient guidance for developing processing options. Nonetheless, recent developments in stochastic optimization and computer data structures have resulted in a framework that can integrate operational modes into strategic mine planning algorithms. A logical next step is to incorporate geometallurgical models that relate mineralogical features to plant performance, as described in this paper.
Minerals Engineering, 2019
Abstract In this paper, different methodologies to characterize the flotation rate distribution a... more Abstract In this paper, different methodologies to characterize the flotation rate distribution at laboratory batch scale are presented. Conventional model fitting is compared with a selectively chosen set of one-parameter models to describe the flotation rate distribution F(k). In addition, a numerical inversion of the Laplace Transform, which is applicable to first-order systems, is shown. A wide range of time-recovery curves and probability density functions (PDF) for F(k) are presented based on 85 flotation tests. The Single Rate Constant, Rectangular, Exponential, Rayleigh, Unilateral Raised Cosine and χ2 models are applied to fit the time-recovery curves. The best model per test is chosen and compared to the model fitting obtained from the Gamma distribution, showing a good agreement between these two approaches. The one-parameter PDFs are compared with F(k) estimates obtained from a regularized Inverse Laplace Transform. In this approach, no assumptions on the F(k) shape are made. The flotation rate distributions estimated from the Laplace Inversion show similar shapes to those obtained from the Gamma and the optimal one-parameter approach. In addition, the F(k) estimates present positive skews in all the evaluated tests. The use of the Laplace Transform Inversion along with conventional model fitting is a powerful tool to validate the F(k) estimates at laboratory scale.
Mining, 2022
Mining trends in the gold sector indicate a growing imbalance in global supply and demand chains,... more Mining trends in the gold sector indicate a growing imbalance in global supply and demand chains, especially in light of accelerated efforts towards industrial electrification and automation. As such, it is important that research and development continue to focus on processing options for more complex and refractory ores. Unlike conventional (i.e., free-milling) ore feeds, refractory gold is not amenable to standard cyanidation, and requires additional pretreatment prior to leaching and recovery. With recent technological advancements, such as sensor-based ore sorting, there is opportunity to advance the development of smaller untapped refractory resources with marginal economics, particularly those in proximity to processing infrastructure within major gold districts. However, it will be critical that the necessary tools are developed to capture the potential system-wide effects caused by varied ore feeds and improve related decision-making processes earlier in the value chain. Di...
Metals
Interdisciplinary barriers separating data scientists and geometallurgists have complicated syste... more Interdisciplinary barriers separating data scientists and geometallurgists have complicated systematic attempts to incorporate machine-learning into mine production management; however, experiences in excavating a vein-hosted gold deposit within the Alhué region of Chile have led to methodological advances, which is the subject of the current paper. These deposits are subject to several challenges, from increasing orebody complexity and decreasing gold grades to the significant geological uncertainty that is intrinsic to these systems. These challenges then translate to mineral processing, which is already dealing with increased environmental and technological constraints. Geological uncertainty causes stockout risks that can be mitigated by the approach that is developed within this paper, which features alternate operational modes and related control strategies. A digital twin framework based on discrete event simulation (DES) and a customized machine-learning (ML) model is propos...
Copper smelters have two central operations: smelting, following by converting. Firstly, the smel... more Copper smelters have two central operations: smelting, following by converting. Firstly, the smelting operation is continuous, and is usually over-dimensioned compared to the downstream operations. Secondly, the converting operation is performed in discrete batches that may be executed in parallel, and must share a limited set of resources, including offgas handling capacity and oxygen capacity. Converting is often a major bottleneck in conventional copper smelters. In recent decades there have been considerable technological enhancements that focus on different aspects of copper smelters, such as high pressure injection, matte granulation, sensors, and expert control systems. Nonetheless, copper smelters are reluctant to implement these technologies unless they are adequately justified, both qualitatively and quantitatively. The current paper adapts the Theory of Constraints to describe the bottlenecking phenomena that occur within copper smelters, and how they may be resolved usin...
RESUME : Le convertissage par methode Pierce-Smith (PS) est l'etape cle de la production de c... more RESUME : Le convertissage par methode Pierce-Smith (PS) est l'etape cle de la production de cuivre et du nickel. Cette operation se poursuit par des etapes sequentielles et presentent un cas ideal pour la programmation mathematique. Ce travail demontre les complexites thermochimiques et les etapes du convertissage au moyen d'un programme lineaire (PL) en nombres entiers mixtes. Ceci est la premiere fois que le convertissage PS est aborde dans un cadre de programmation mathematique et represente un avancement majeur de l'application de la recherche operationnelle aux etapes de production des fonderies de cuivre et de nickel. Les resultats demontrent que le cadre mathematique est fonctionnel, et peut etre utilise quotidiennement pour la gestion optimale des sequences d'operation de l'elaboration de cuivre et de nickel. Le cadre est flexible quant a la definition des contraintes du systeme et de la fonction objective. Cette flexibilite evoque la formulation de diver...
It summarizes the current state of Chilean copper smelters from an environmental, major nation-to... more It summarizes the current state of Chilean copper smelters from an environmental, major nation-to-global focus approach, current technologies for treating copper sulphurized minerals through pyrometallurgical treatments generate large amounts of pollutants such as sulphur dioxide, arsenic and other heavy metals that are present in smelters fumes. Due to the depletion of copper resources, Chilean copper deposits have lower laws and have higher amounts of arsenic, this is a problem for the installation of new pyrometallurgical plants in Chile and is also a challenge for foundries that were already in operation, along with increasingly stringent government laws creating a complex environment for such copper smelters.
Minerals Engineering
Strategic decisions to develop a mineral deposit are subject to geological uncertainty, due to th... more Strategic decisions to develop a mineral deposit are subject to geological uncertainty, due to the sparsity of drill core samples. The selection of metallurgical equipment is especially critical, since it restricts the processing options that are available to different ore blocks, even as the nature of the deposit is still highly uncertain. Current approaches for long-term mine planning are successful at addressing geological uncertainty, but do not adequately represent alternate modes of operation for the mineral processing plant, nor do they provide sufficient guidance for developing processing options. Nonetheless, recent developments in stochastic optimization and computer data structures have resulted in a framework that can integrate operational modes into strategic mine planning algorithms. A logical next step is to incorporate geometallurgical models that relate mineralogical features to plant performance, as described in this paper.
Minerals Engineering
Abstract This short communication presents the kinetic characterization of 85 batch flotation tes... more Abstract This short communication presents the kinetic characterization of 85 batch flotation tests based on an inversion approach, extending the work reported by Vinnett et al. (2019). For first-order systems, the mineral recovery R(t) as a function of time t can be expressed as R t = R ∞ ∫ 0 ∞ 1 - e - k t F k d k , where R∞ is the maximum recovery, k is the rate constant and F(k) is the flotation rate distribution. An arrangement of this expression allows the estimation of R∞F(k) by discretizing the integral term. A linear system is solved by a regularization approach that accounts for the fitting error of R(t) and the roughness of R∞F(k). Thus, R∞ is obtained, given ∫ 0 ∞ F k d k = 1 . The results show a good agreement with those obtained from F(k) following a Gamma distribution (non-linear regression), in terms of: Sum of Squared Residuals, cross-validated R2, F(k) shapes and range for the R∞ estimates.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Since 1958, the Mauna Loa Observatory (MLO) has continuously monitored carbon dioxide variations ... more Since 1958, the Mauna Loa Observatory (MLO) has continuously monitored carbon dioxide variations using nondispersive infrared (NDIR) sensors, with the Keeling curve as an early indicator of the anthropogenic contribution to global atmospheric carbon dioxide. The increasing CO2 levels are alarming and have led to international agreements that promote cleaner industrial activities. However, any change in global behavior would not immediately cause detectable changes in the MLO data; the extent to which global and long-term term trends are conflated with local and short-term variations remains unclear. Hence the current paper verifies the performance of the sampling and measurement systems of MLO, using existing data published within the months of October and November 2020, which comply with the temporal continuity requirements of chronostatistics. It has been determined that the components of the MLO air including carbon dioxide are well mixed due to their particular location. Beyond this, the variographic analysis distinguishes between small (<5%) and large (>10%) variability contributions due to sampling, including graphical depictions of MLO data. Coupled with the precision of the method being better than 0.2 ppm, it has been determined that the sampling and measurement protocols are highly suitable to meet the objective of representing CO2 fluctuations over time. The variographic application also manages to quantify short-term variabilities resulting from the local processes of the region where the observatory is located. The results support the furthering of multiscaled temporal analysis of atmospheric CO2, and potentially the incorporation of CO2 variographic parameters into empirical and semi-empirical climate models.
It summarizes strategic analyses regarding the future of copper concentrate exports, its problems... more It summarizes strategic analyses regarding the future of copper concentrate exports, its problems and Chile’s participation not only as a global copper producer, but as a refined copper producer. These analyses aim to develop a basis for modernization and possibly the construction of new foundries in Chile; are considered economic, competitive and strategic aspects. In Chile, an increase in the production of copper sulfide concentrates is projected, considering the depletion of oxidized minerals. This increase also includes complex or dirty concentrates with a high presence of impurities, mainly arsenic. Currently in an environmental context, Chilean smelters on average do not meet the emissions standard for copper smelters due to the age of these smelters and the high investment required to modify their infrastructure. Strategically, the increase in high impurities in concentrates results in higher treatment costs, penalties and difficulty of acceptance in the international market....
Minerals
Oil remains a major contributor to global primary energy supply and is, thus, fundamental to the ... more Oil remains a major contributor to global primary energy supply and is, thus, fundamental to the continued functioning of modern society and related industries. Conventional oil and gas reserves are finite and are being depleted at a relatively rapid pace. With alternative fuels and technologies still unable to fill the gap, research and development of unconventional petroleum resources have accelerated markedly in the past 20 years. With some of the largest bitumen deposits in the world, Canada has an active oil mining and refining industry. Bitumen deposits, also called oil sands, are formed in complex geological environments and subject to a host of syn- and post-depositional processes. As a result, some ores are heterogeneous, at both individual reservoir and regional scales, which poses significant problems in terms of extractive processing. Moreover, with increased environmental awareness and enhanced governmental regulations and industry best practices, it is critical for oil...
Minerals Engineering
Abstract Geological variation may be managed by alternating between modes of operation. These mod... more Abstract Geological variation may be managed by alternating between modes of operation. These modes provide an integrated response to changes in feed mineralogy, and other operational conditions within the mineral value chain. The decision to alternate between modes depends on current and forecasted stockpile levels. Moreover, the optimization of stockpile thresholds that would trigger a mode change is related to the classical RQ problem from inventory theory. Particularly for concentrators that are designed for blended feeds, there may be production intervals in which a particular ore class is at risk of stockout. Indeed, geological uncertainty causes stockout risk, which should be balanced with other key performance indicators, including throughput and recovery, and is a context for multiobjective optimization. Computations are presented in which a concentrator that had originally been designed for a certain ore blend, after years of successful operation, now requires alternate modes to realign its operations with geological forecasts.
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Papers by Alessandro Navarra