Solution strategies to the stochastic design of mineral flotation plants

The aim of this study is two-fold: first, to analyze the effect of stochastic uncertainty in the design of flotation circuits and second, to analyze different strategies for the solution of a two-stage stochastic problem applied to a copper flotation circuit. The paper begins by introducing a stochastic optimization problem whose aim is to find the best configuration of superstructure, equipment design and operational conditions, such as residence time and stream flows. Variability is considered in the copper price and ore grade. This variability is represented by scenarios with their respective probability of occurrence. The resulting optimization problem is a two-stage stochastic mixed integer nonlinear program (TS-MINLP), which can be extremely challenging to solve. For this reason, several solvers for this problem are compared and two stochastic programming methodologies are applied. The combination of these techniques allows the production of high quality solutions and an analysis of their sensitivity to epistemic uncertainty. The results show that the stochastic problem gives better designs because it allows operational parameters to adapt to the uncertainty of the parameters. The results also show that the flotation circuit structure can vary with the feed grade and copper price. The sensitivity analysis shows small to moderate variability with epistemically uncertain parameters

Innovative Solutions for Seawater Use in Mining Operations

This chapter reviews the use of seawater in the mining industry in Chile, especially from the perspective of the current situation and the innovative proposals for its sustainable use. This chapter describes the current use of seawater, with and without desalting, in the mining sector in Chile, as well as its future projection. Descriptions are given for the current desalination systems, mining operations currently using seawater and new projects, current water distribution systems, seawater applications in hydrometallurgy and minerals concentration, their environmental impacts, and difficulties in adapting processes in case of use of seawater without desalination. This is complemented by a description of mining in Chile, its importance for Chile and its relationship to the global mining. Finally, problems and opportunities are identified. A second aspect considered in this chapter is the innovative solutions that are being investigated to solve some of the problems indicated above, including integrated seawater distribution systems, seawater biodesalination, partial desalination using carbon dioxide, adaptation of process to the use of seawater without desalination, and uses of discard brines from reverse osmosis plants

Feasibility of re-processing mine tailings to obtain critical raw materials using real options analysis

The re-processing of mine tailings to obtain critical raw materials (CRMs) could reduce the mining of new deposits as well as ensure the profitable use of the waste materials. Though, it requires large scale industrial installations and the development of specialized technologies to obtain CRMs. New investment in mining activities is an operation, engaging for considerable financial resources involved. The scale of such an endeavor makes a new mining activity a high-risk operation due to several uncertainties present. Therefore, there is an acute need to use new tools to assess the risk associated with the planning and development of new mining activities. This study introduces a framework to evaluate the economic risk related to the re-processing of mine tailings to obtain CRMs. The framework, based on real options analysis (ROA), and sensitivity and uncertainty analysis, was applied to analyze the profitability of using mine tailings as a source of CRMs in the Chilean mining industry. The novelty of this approach consists in enabling the investment decision making including the uncertainties related to a novel investment mining project. Results show that tailing storage facilities in Chile have some stocks of CRMs, like scandium, whose extraction could be profitable. For the data used, the results of uncertainty and sensitivity analyses show that capital expenditure has a more significant influence than the other variables. Therefore, for the case of mine tailings re-processing, it is essential to develop processes and technologies that enable lower capital expenses.Post-print / Final draf

Use of real options to enhance water-energy nexus in mine tailings management

The tailing storage facility is the largest water sink in most mines. An incorrect management of water content in mine tailings can become a threat to their stability, and consequently, their environmental safety. Also, water reuse and recycling are plausible options to mining companies for reasons pertaining to water scarcity. Dewatering technologies for tailings, desalination and water transport are energy intensive. Proper handling of mine tailings and water supply management can considerably improve the water-energy nexus. This article evaluates the water-energy nexus in copper mining companies using a water reduction model focused on mine tailing facilities and water supply to the mine site to find the trade-offs between water and energy. The originality of this work consists in the application of a real options approach, enabling to increase the flexibility of decision-making thanks to quantitative analysis. This approach deploys the Monte Carlo simulation to perform sensitivity and uncertainty analysis to evaluate every cost component of water management strategy. Results show that if seawater is the primary source of raw water to the mining plant, water transport represents the largest cost due to the use of energy. So, improving the reuse of water by using dewatering technologies will improve the water-energy nexus, by improving energy consumption. Even though the costs of these technologies are elevated because they are energy-intensive, reduction of water use requirements in the mine will reduce the cost of its treatment and transport.Publishers versio

Applying a multi-objective optimization approach in designing water supply systems for mining industries. The case of Chile

This work presents a multi-objective optimization approach to designing integrated water supply systems for the mining industry. The main goal is to estimate the total operational costs and greenhouse gas emissions from water supply systems. Chilean mining industry has been selected as a case study because of acute problem of water scarcity that it experiences. The current strategy to face the problem applied by the mining companies operating in Chile consists in building independent water supply systems that use ocean as the source of water. This solution is highly energy intensive, which is why the problem of water consumption is also a problem of energy consumption. The proposed optimization approach determines - from technical, economic and environmental perspective - the optimal topology of the system, optimal locations and sizes of water treatment plants, pumping stations, and pipelines. In addition, the analysis takes into account the eventual use of photovoltaic solar system in order to decrease greenhouse gas emissions. Our main findings have demonstrated that an integrated water supply system is always the best option from an economic and environmental point of view.Post-print / Final draf

Bioprospecting of Ureolytic Bacteria From Laguna Salada for Biomineralization Applications

The processes of biomineralization, mediated by ureolytic bacteria, possess a wide range of technological applications, such as the formation of biocements and remediation of water and soil environments. For this reason, the bioprospecting of new ureolytic bacteria is interesting for its application to these technologies, particularly for water treatment. This study demonstrates the isolation, selection, and identification of halotolerant ureolytic bacteria from Laguna Salada (inland from Atacama Desert) and the evaluation of their ability to precipitate calcium carbonate crystals in freshwater in the presence of calcium ions, as well as the ability to induce the precipitation of crystals from different ions present in seawater. Twenty-four halotolerant ureolytic bacteria whose molecular identification gives between 99 and 100% identity with species of the genus Bacillus, Porphyrobacter, Pseudomonas, Salinivibrio, and Halomonas were isolated. When cultivated in freshwater, urea, and calcium chloride, all species are able to biomineralize calcium carbonate in different concentrations. In seawater, the strains that biomineralize the highest concentration of calcium carbonate correspond to Bacillus subtilis and Halomonas sp. SEM–EDX and XRD analyses determined that both bacteria induce the formation of 9–33% halite (NaCl), 31–66% monohydrocalcite (CaCO3 × H2O), and 24–27% struvite (MgNH4PO4 × 6H2O). Additionally, B.subtilis induces the formation of 7% anhydrite (CaSO4). In seawater, B.subtilis and Halomonas sp. were able to precipitate both calcium (96–97%) and magnesium (63–67%) ions over 14 days of testing. Ion removal assays with B.subtilis immobilized in beads indicate a direct relationship between the urea concentration and a greater removal of ions with similar rates to free cells. These results demonstrate that the biomineralization mediated by bacterial urea hydrolysis is feasible in both freshwater and seawater, and we propose its application as a new technology in improving water quality for industrial uses

Development of a grinding model based on flotation performance

Usually, the concentration of minerals is carried out with a set of flotation and grinding units. Most of the modeling strategies for the flotation and grinding stages have followed separate developmental paths. This paper presents a strategy based on using flotation studies to model flotation and grinding via an integrated approach. The methodology, which is an approximate method that allows one to study of the effects of grinding on flotation circuits, is applied to a copper sulfide mineral with appropriate results. Given its nature, the application of this method will help preliminary studies on the design, improvement, and simulation of flotation circuits. The major advantages of this method are its simplicity and low cost. Thus, the main contribution of this work is a new strategy to model grinding for integration into the modeling of flotation circuits. This new strategy can be extended to other concentration technologies that include grinding.Post-print / Final draf

Impact of seawater desalination and wastewater treatment on water stress levels and greenhouse gas emissions: The case of Chile

Many regions around the world are suffering from water stress, and desalinated water and recycled water are seen asalternatives for meeting the water demand. However, high energy consumption and associated greenhouse gas emis-sions are some of the main environmental impacts. This is notable for many arid and semi-arid countries where desa-lination and water recycling are considered options for ensuring water resources availability. This research presentsthe incorporation of the quantification of greenhouse gas emissions generated during the operation of desalinationand wastewater treatment plants in the assessment of water stress levels using the water stress indicator adopted bythe 2030 Agenda for Sustainable Development. Chile was chosen as a case study, as it is a country where there is a con-siderable difference between the availability of conventional water sources and the water demand, and the electricalgrid is fed mainly by fossil fuels. The methodology proposed allows calculating the indirect greenhouse gas emissionsdue to electrical consumption for the operation of desalination and wastewater treatment plants, and the direct green-house gas emissions coming from biological processes used in wastewater treatment plants. The results showed thatChilean arid climate zones will not experience water stress in the future at the regional level, mainly because of theinstallation of several desalination plants by 2030. Meanwhile, recycled water from the urban sector will slightly con-tribute to the reduction in the level of water stress in almost all Chilean regions by 2030. Moreover, desalination andwastewater treatment plant will contribute only between 0.34% and 0.75% of total greenhouse gas emitted in Chile by2030. Therefore, the operation of these industrial systems for facing water scarcity problems in northern and centralzones of Chile is a suitable alternative because it does not generate large environmental problems.Post-print / Final draf

MICP mediated by indigenous bacteria isolated from tailings for biocementation for reduction of wind erosion

In this study, native ureolytic bacteria were isolated from copper tailings soils to perform microbial-induced carbonate precipitation (MICP) tests and evaluate their potential for biocement formation and their contribution to reduce the dispersion of particulate matter into the environment from tailings containing potentially toxic elements. It was possible to isolate a total of 46 bacteria; among them only three showed ureolytic activity: Priestia megaterium T130-1, Paenibacillus sp. T130-13 and Staphylococcus sp. T130-14. Biocement cores were made by mixing tailings with the isolated bacteria in presence of urea, resulting similar to those obtained with Sporosarcina pasteurii and Bacillus subtilis used as positive control. Indeed, XRD analysis conducted on biocement showed the presence of microcline (B. subtilis 17%; P. megaterium 11. 9%), clinochlore (S. pasteurii, 6.9%) and magnesiumhornblende (Paenibacillus sp. 17.8%; P. megaterium 14.6%); all these compounds were not initially present in the tailings soils. Moreover the presence of calcite (control 0.828%; Paenibacillus sp. 5.4%) and hematite (control 0.989%; B. subtilis 6.4%) was also significant unlike the untreated control. The development of biofilms containing abundant amount of Ca, C, and O on microscopic soil particles was evidenced by means of FE-SEM-EDX and XRD. Wind tunnel tests were carried out to investigate the resistance of biocement samples, accounted for a mass loss five holds lower than the control, i.e., the rate of wind erosion in the control corresponded to 82 g/m2h while for the biocement treated with Paenibacillus sp. it corresponded to only 16.371 g/m2h. Finally, in compression tests, the biocement samples prepared with P. megaterium (28.578 psi) and Paenibacillus sp. (28.404 psi) showed values similar to those obtained with S. pasteurii (27.102 psi), but significantly higher if compared to the control (15.427 psi), thus improving the compression resistance capacity of the samples by 85.2% and 84.1% with respect to the control. According to the results obtained, the biocement samples generated with the native strains showed improvements in the mechanical properties of the soil supporting them as potential candidates in applications for the stabilization of mining liabilities in open environments using bioaugmentation strategies with native strains isolated from the same mine tailing