Search

Mineral processing plants remain nowadays infamous for their low energy efficiency. Economic model predictive control (EMPC), by directly considering the energy costs, could possibly help reduce their footprint, but its environmental benefits are yet to be clearly quantified. In an attempt to cast some light on this topic, this paper compares the response to a given ore feed size and hardness disturbance sequence of an EMPC to that of basic and advanced regulatory control systems using the profits and the specific energy (power draw/ore feed rate) as metrics. The simulated circuit comprises a high-pressure grinding rolls (HPGR), a ball mill, and a flotation circuit. It is based on population balance modeling and is an extension of previous works. The basic regulatory control (BRC) system comprises only single-input–single-output control loops with proportional–integral (PI) controllers and operates at a fixed feed rate. The advanced regulatory control (ARC) system consists of PI controllers maximizing the plant feed rate with override constraint handling. The results show that (1) ARC generates more revenue and maintains a lower circuit specific energy consumption than BRC, (2) ARC can produce the same economic performance as EMPC because the constraints of the system define the economic optimum, and (3) EMPC can trade revenues for a lower circuit specific energy with a hybrid criterion that penalizes power draw. • The work compares different control systems on an HPGR grinding circuit. • A decentralized PI control system can generate equivalent revenues to an EMPC. • EMPC can trade revenues for a lower circuit specific energy. [ABSTRACT FROM AUTHOR]

This paper proposes a development to reformulate the fundamental equations of primary drying into a linear-based representation to support control design. The model is expressed by transfer functions with variable gains that incorporate analytical relations derived from a phenomenological model. The time constants denote the dynamics of the heating/cooling and vacuum systems. Compared to fundamental equations, this approach simplifies the development and implementation of well-established control algorithms. The quality of the proposed representation is illustrated in the design of a control system using two different strategies: model predictive control and a feedback controller with proportional-integral action. The simulation case study allows assessing the performance of both designs with regard to cycle time reduction and robustness under parametric disturbances. Results evidence that the proposed model is detailed enough to provide accuracy in a simplified way, facilitating the implementation of in-line control strategies, which in turn enable significant reductions of drying time. [ABSTRACT FROM AUTHOR]

The demand for lithium-ion batteries for electric vehicles (EV) has triggered an unprecedented interest in this metal. Although there is asignificant history in the scientific literature regarding lithium mining in Quebec between 1950–1980, very few studies document the current state of the art and address the possibility of the province integrating alocal production chain oriented towards the EV battery market. This paper presents Quebec's position and analyses its needs and potential market through aliterature review focusing on the main opportunities to produce domestic spodumene concentrates, as well as the major challenges the province will have to face to make the most of its competitive advantages. Furthermore, it provides an updated list of lithium mineral resources and reserves in Quebec, in compliance with NI 43–101. The results show that Quebec holds 94.1% and 85.8% of all Canadian mineral reserves and resources, respectively. The paper also provides an overview of the lithium industry in the province and compares its status with other Canadian jurisdictions. Quebec lithium mines would benefit if their production could be directly integrated with other local or nearby partners, generating ajoint benefit throughout the manufacturing chain of lithium-ion batteries for the EV market. [ABSTRACT FROM AUTHOR]

[Display omitted] • An observer allows estimating the slip profile in an HPGR working gap. • It is based on force balance equations and the Coulomb friction criterion. • The observed ore showed slippage at the working gap level. Modelling the high-pressure grinding rolls mass flow rate from the continuity principle represents a difficult task, partly because the ore may slip against the rolls. In effort to increase the understanding of this phenomenon, this paper introduces a state observer to estimate the slip profile in the HPGR working gap from the force balance equations and Coulomb friction criterion. The observer is used off-line and a posteriori, i.e. it requires a series of HPGR tests conducted at different levels of specific force and roll speed. It allows observing the slip profile on a gold ore at the pilot scale. As the material enters the compression zone, it descends at a slower rate than the vertical component of the roll peripheral speed. As it progresses downward, its velocity increases. It exceeds the roll peripheral speed at the working gap level and peaks below. The pressure peaking above the working gap makes slipping possible. It leads to the material above the working gap to push onto the one below and thus accelerating it. [ABSTRACT FROM AUTHOR]

Batch fluidized bed drying is a common process for water removal in pharmaceutical particles. Multiple phenomenological models for this type of dryer are proposed in the literature, with many of them relying on the two-phase theory. This article elaborates on a two-phase model and extends it for the pharmaceutical case by improving the particle, batch size and heat loss descriptions. An explicit methodology with low computational cost is also developed for solving the fluidized bed equations. Then, based on a grey-box modeling strategy, parameters with known value are fixed, while the unknown parameters are calibrated with experimental data collected on a pilot scale fluidized bed dryer. Lastly, the model is dynamically validated on distinct experimentation datasets. It is shown that the simulations are able to reproduce the pilot data trends, but there is still room for improvements in the heat loss representation. [ABSTRACT FROM AUTHOR]

In flotation systems, it is generally assumed that the bubble size presents an inverse correlation with the gas hold-up. However, this hypothesis is not systematically true. The focus of this work is to study the effect of solid particles on the bubble size distribution and gas hold-up, as well as the correlation between the bubble size distribution and gas hold-up in column flotation. Experiments were conducted in two and three-phase systems using a laboratory flotation column (5.6 cm internal diameter, total height of 650 cm), and mixtures of quartz (hydrophilic gangue) and talc (naturally hydrophobic mineral), classified in four different size fractions. For the studied flotation system, experimental results are compared with literature correlations and models to reveal that hydrophobic particles affect the gas hold-up through three different mechanisms modifying the Sauter mean diameter and rise velocity, namely (1) surface interactions, and the joint antagonistic effect of (2) bubble loading and (3) coalescence. [ABSTRACT FROM AUTHOR]

Primary drying is the bottleneck of pharmaceutical lyophilization, as it represents the most time and energy-consuming stage and largely determines the quality of the final product. The common practice runs the process under pre-calculated input profiles while considering average drying dynamics for the batch. This results in conservative and underperforming cycles. In this regard, the paper proposes and experimentally validates an in-line control strategy for primary drying. It explicitly accounts for intra-lot drying heterogeneity using three models, each one calibrated for a reference vial position in the chamber. Two separate experiments evaluate the proposed framework: offline and in-line process control. Validation on a pilot-scale unit shows a cycle time reduction of the proposed approaches compared to standard drying protocol at constant operating conditions. The input profiles obtained by offline control lead to a 16% shorter cycle time; however, the lack of feedback during the cycle impedes addressing potential parametric variations and model mismatches. Conversely, in-line control yields a reduction of 13% while allowing careful monitoring of the product status, ensuring a more dependable cycle. In both cases, the visual quality inspection confirms the acceptability of the final product without visible degradation. [Display omitted] • A control strategy for multi-vial control of primary dying that can accommodate any number of vials. • Three representative vial positions considered: center, edge and corner. • Application of offline control yields a 16% cycle reduction but can be susceptible to disturbances. • Application of in-line control in a pilot unit yields the safest cycle and a time reduction of 13%. [ABSTRACT FROM AUTHOR]

Modeling of flotation has been the subject of many investigations aiming at better understanding the process behavior per se, and as well for process design, control and optimization purposes. With this regard, the importance of hydrodynamic characteristics, either as manipulated or measured variables, are paramount. The interfacial area of bubbles ( I b ) is introduced in Part 1 of this paper as a hydrodynamic variable providing more information about the size distribution than the commonly used bubble surface area flux ( S b ). Experimental evidence shows that the bubble size distribution can exhibit normal, lognormal, and even multi-modal shape. Unlike the Sauter mean diameter ( d 32 ) and S b , the interfacial area of bubbles is derived from the complete bubble size distribution, and takes into account these specific characteristics. Fundamental expressions are proposed to allow characterising I b using the population mean and standard deviation. Experimental results indicate that for lognormal bubble size distributions, I b correlates well with the gas hold-up and d 32 . Part 2 of the paper analyzes the correlation of gas dispersion characteristics with flotation rate constant. [ABSTRACT FROM AUTHOR]

The estimation of the flotation rate constant is generally considered difficult because of the number of variables – not always measurable – determining its value. Among them, the particle size distribution and hydrodynamic characteristics are considered key elements. Part 1 of this paper introduced the interfacial area of bubbles ( I b ) as a hydrodynamic variable providing more information about the size distribution than the bubble surface area flux ( S b ). Fundamental expressions were proposed to characterize I b using the population mean and standard deviation. Experimental results indicated that for lognormal bubble size distributions, I b correlates very well with the gas hold-up and d 32 . Part 2 investigates the correlation between the flotation rate constant and particle size as well as given hydrodynamic variables using a Projection to Latent Structures (PLS) analysis. The tests were conducted under ‘ideal’ conditions (i.e. shallow froth, low mineral concentration and pure mineral particles). Results suggest that for the fine particle sizes, the bubble surface area flux ( S b ) should be considered for the kinetic constant modeling. For coarser particle, the gas hold-up ( ε g ) is the determining parameter. In practice though, the particle size distribution often lies between these two extreme cases, and can either span a very large range or contains intermediate size particles. In such cases, the interfacial area of bubbles ( I b ) better correlates with the flotation kinetics. [ABSTRACT FROM AUTHOR]

• This paper presents a steady-state high-pressure grinding rolls model. • It consists of unified previously published works. • It is calibrated on 18 pilot scale data sets. This paper unifies high-pressure grinding rolls crusher (HPGR) models of the working gap, mass flow rate, power draw, and centre and edge product particle size distribution models to produce a framework that allows the simulation of the equipment for process optimization and control studies. Calculating the model parameters requires exclusively a series of HPGR tests, but the framework prediction capabilities remain confined within the range of the calibration data set. The model inputs the specific force, the roll speed, the zero-gap and the edge width setting. It makes no restricting hypothesis regarding slip or material bypass and does not necessitate prior knowledge of the flakes density. The work presents an extensive model analysis with calibrations on 18 data sets with invariable moisture content and feed particle size distribution, which includes computing the parameter uncertainties and analyzing the residuals. Seven of these data sets are new, while the rest consists of previously published values. The analysis shows that the model performs satisfactorily for all data sets. [ABSTRACT FROM AUTHOR]

Highlights: [•] The paper presents a framework for the fully dynamic simulation of column flotation. [•] The proposed framework is based on a vertical superposition of mixers-in-series. [•] It provides a macroscopic description of the pulp and gas behaviour using material balancing and specific empirical models. [•] The emphasis is placed on the simulation of water, solids and gas flows and their effect on the pulp level and output flow rates. [Copyright &y& Elsevier]

Abstract: Even after having been used for several years in mineral processing plants, the full potential of the column flotation process is still not fully exploited. There is obviously more than one reason explaining this, but one important contributing factor is certainly the under usage of available control capabilities. Researchers and practitioners have been interested in column flotation simulation and control for more than two decades. This paper provides an overview of the literature focused on these specific fields of research. It also discusses some future investigative issues and how the current industry may benefit from past developments. [Copyright &y& Elsevier]

• A dynamic model of a continuous horizontal fluidized bed dryer is developed. • A screw conveyor control the product residence time in the dryer. • The model allows for gas bubbles and product axial mixing. • Parameters are lumped and equations are solved at low computational costs. • Simulation results are consistent with theory. The bottleneck of pharmaceutical continuous wet granulation lines may often be the drying stage. The introduction of horizontal fluidized beds is currently contemplated to solve this issue, inter alia. However, it would require an appropriate process control system to reach and maintain over time the targeted residual moisture of the product. To support the endeavor of both the process and control designs, this paper develops a dynamic model with lumped parameters of a continuous horizontal fluidized bed dryer equipped with a screw conveyor. To this end, the framework makes use of a two-phase tanks-in-series configuration, thus taking into account expected gas bypasses (bubbles) and product axial mixing. Array programming and vectorized operations on each tank reactor allow solving equations explicitly at a low computational cost. Simulation results for calcium carbonate granules in a laboratory scale dryer are consistent with fluidization, drying and continuous reactor fundamentals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stability of ferrocolumbite low-index facets was investigated by DFT calculations. • Wulff construction was utilized to predict the predominantly cleaved surfaces. • O-terminated surface is more stable than metal or mixed metal O-terminated surface. • Water would improve surface stability in all directions. • The {1 1 0}, {0 0 1}, {1 1 1}, and {0 2 1} facets contribute to >85% of the Wulff shape. Ferrocolumbite, a variegated oxide mineral bearing the strategic element niobium, exhibits an array of surface chemical compositions across various cleavage orientations. The complexity of Nb-bearing ores hinders the efficiency of separation processes, necessitating fundamental research to bridge the knowledge gap regarding the surface dominance and properties of the mineral. In this regard, density functional theory (DFT) simulations were performed to determine the stability of different low Miller index surfaces of ferrocolumbite. The thermodynamic Wulff construction theory was then employed to predict the morphology of a ferrocolumbite nanoparticle, taking into account the DFT-calculated surface energies and the symmetries in the ferrocolumbite crystal. Several descriptors, such as ionic atom density and bond length distribution, were partially successful in correlating with surface energies; however, no global correlation could be captured for this complex system. Our findings suggested oxygen-terminated surfaces generally exhibit greater stability than metal or mixed-metal–oxygen-terminated surfaces within a given facet. Based on the Wulff shape prediction, the {1 1 0}, {0 0 1}, {1 1 1}, and {0 2 1} facets contribute to >85% of the surface area of the ferrocolumbite particles after comminution. Therefore, a sound conclusion about the adsorption behavior of reagents on ferrocolumbite should include all of these facets. This fundamental research highlights the complex and diverse nature of the ferrocolumbite surface and paves the way for future investigations. [ABSTRACT FROM AUTHOR]

Hydration of pyrochlore is a preponderant step during its flotation well before any other surface-reagent interaction to take place. Water adsorption on low-index pyrochlore surfaces is investigated by Density Functional Theory (DFT) simulation, with a focus on the mechanisms of water interaction with surface sites and their coordination. As far as the pyrochlore (100) and (111) surfaces favor the associative physisorption of water, the dissociative chemisorption of water on the (110) surface is by far the most energetically favorable. The affinity of pyrochlore surface to water increases from −81.4 (111), −102.7 (100) to −331.6 kJ/mol (110) leading to decreasing hydrophilic surfaces: (110) ≫ (100) > (111). Water adsorption on the Nb sites located on the (100) surface is unlikely due to the full-coordination state of the exposed Nb. Moreover, the dissociative adsorption of water, driven by a lack of coordination on the (110) surface, would be at the origin of the selective (or non-congruent) dissolution of pyrochlore calcium by weakening its innate bonds. These primary results on the relationship between water and the atomic topology of pyrochlore cleavage planes will help guide the choice of aqueous chemical reagents to be used to address the challenges of this mineral's flotation. [Display omitted] • H 2 O adsorption on low-index pyrochlore surfaces is described by DFT. • Water adsorption on pyrochlore surfaces varies with surface orientation. • H 2 O is physisorbed on pyrochlore (100) and (111) surfaces. • H 2 O chemisorption is energetically favorable on (110) surface. • H 2 O chemisorption on (110) surface promotes Ca dissolution. [ABSTRACT FROM AUTHOR]

Advanced process control can benefit to the operation efficiency and quality of tablets produced by wet granulation lines. Following the development of a new fully continuous fluidized bed reactor as a potential substitute for the current batch dryer design, this paper examines the energy and product quality performances of two predictive control strategies using an experimentally validated simulator. The first one proposes an economic model predictive controller explicitly minimizing the dryer energy consumption. The second one follows the same objective, but uses a simpler classical predictive control framework implementing targets on manipulated variables to drive them toward low energy consumption operating points. Both controllers lead to similar performances, and consume about 20% less energy than a reference feedback scheme without manipulated variable setpoints. Results also show that tracking the product quality attribute significantly benefits from a feedforward action because of the long residence time. This article addresses a subject little explored by the literature, the control of continuous fluidized bed dryers, and clearly demonstrates that a standard linear strategy can reduce the operating costs with an appropriate design. • Predictive control is applied on a simulated continuous fluidized bed dryer. • An economic model predictive controller (EMPC) minimizes the energy consumption. • A more standard predictive controller (MPC) also aims for low-energy actions. • Both EMPC and MPC results in low-energy operations. • Feedforward compensation improves the product quality in both cases. [ABSTRACT FROM AUTHOR]

The aim of this work is to studythe kinetics and required operationconditions for the formation of various manganese oxides using theSO2/O2gas mixture as the oxidant agent. Thispromising approach presents some obvious economical advantages overtraditional pyrometallurgical routes. Experimental evidence demonstratethat increasing the temperature of the reaction allows modifying theoxidation potential, thus facilitating the oxidation product synthesis.However, at 25 °C by varying the SO2/O2ratio and the gas mixture flow rate, it was not possible to modifythis potential. It was also observed that manganese dioxide (MnO2) is formed between 20 and 50 °C (activation energy (Ea) = 14.33 kJ/mol), oxy-hydroxide of manganese(MnO·OH) is obtained between 55 and 65 °C (Ea= 25.14 kJ/mol), and manganese(II, III) oxide (Mn3O4) is produced between 70 and 90 °C (Ea= 12.44 kJ/mol). The magnitude of these activationenergy values is characteristic of processes controlled by the diffusionof the gaseous reagents. [ABSTRACT FROM AUTHOR]

• Grey-box modeling is applied to a continuous horizontal fluidized bed dryer. • Product is displaced by a screw conveyor and fluidized by two gas chambers. • Data from a dynamically operated prototype validates the model. • Results highlight the shortcomings in the modeling assumptions. • Potential improvements to the prototype design are also raised. Fully continuous drying can improve the production flexibility and throughput of tablets manufactured by wet granulation lines. A recently developed prototype incorporates a screw conveyor to a horizontal fluidized bed dryer for pharmaceutical particles. Research on advanced process control strategies led to the publication of a two-phase tanks-in-series framework to describe its dynamics. This paper calibrates the model to replicate the prototype behavior. A grey-box identification methodology estimates the empirical and uncertain parameters using experimental input-output data. The underlying assumptions are cross-validated with time-domain comparisons, output root mean square errors and confidence intervals. Results show that the model reproduces the observed trends in general and the discrepancies result from mechanical issues on the equipment. [ABSTRACT FROM AUTHOR]