Comminution Process Research Articles

Technological transfers in the Mediterranean on the verge of Romanization: Insights from the waterproofing renders of Nora (Sardinia, Italy)

Abstract The paper reports the results of a multi-analytical characterization study on the renders constituting the waterproofing coatings of 11 cisterns located in the Punic-Roman archaeological site of Nora (Southern Sardinia, Italy). The multi-layer layout of the coatings is related both to the practice of putting several strata of render in a synchronic plastering phase, and to frequent restoration activities related to the prolonged use of the cisterns. The aims of this study are (a) to determine the compositional and textural properties of the binding materials, (b) to define the coating systems employed in diachronic plastering phases, and (c) to identify the role of diverse cultural influences in the modification of the render recipes along time. The combined interpretation of the results obtained through petrographic, mineralogical, microstructural and microchemical analyses allowed discriminating different render types employing various pozzolanic additives, whose utilization is related both to Punic and Roman technological practices. Furthermore, the cementation processes of the renders were studied through an in-detail mineralogical and spectroscopic characterization of their binder fractions. The results demonstrated that hydraulic reactions were often enhanced through specific treatments of the binding mixtures, such as the combined use of different pozzolanic additives, the adoption of comminution processes to increase their reactive specific surface and the use of saltwater to enhance silica and alumina activity in solution through pH increase. Such technological practices promoted in some cases not only the precipitation of Ca-based pozzolanic reaction products (C-S-H and AFm phases), but also the formation of nanostructured anthropogenic magnesium-silicate-hydrate (M-S-H) phyllosilicate gels, leading to a further increase of the cohesive properties of the binding mixtures. A combined interpretation of the results with the cistern construction chronologies confirmed that cistern coating techniques in Nora were still largely influenced by Punic traditions even two centuries after the Roman conquest of Sardinia.

A New Model for Environmental Assessment of the Comminution Process in the Chain of Biomass Energy Processing †

Acquiring energy contained in biomass requires its prior appropriate preparation. These treatments require some energy inputs, which significantly affect the reduction of the energy and the environmental balance in the entire life cycle of the biomass energy processing chain. In connection with the above, the aim of this work is to develop a methodology for the environmental assessment of biomass grinding in the processing chain for energy purposes. The research problem is formulated as follows: Is it possible to provide an assessment model that takes into account the environmental inputs and benefits of the grinding process of biomass intended for further energy use (for example, combustion)? How do the control variables of the grinding machine affect the environmental process evaluation? In response to these research problems, an original, carbon dioxide emission assessment index of the biomass grinding process was developed. The model was verified by assessing the process of rice and maize grinding on a real object—a five-disc mill—with various speed settings of the grinding disc. It was found that the carbon dioxide emission assessment model developed provides the possibility of comparing grinding processes and identifying the grinding process with a better CO2 emission balance, where its values depend on the control parameters of the mill.

Scientific substantiation and practical realization of selective comminution process of polymetallic mineral raw materials

The results of various methods of studying structural and texture characteristics, physical and mechanical properties determining the liberation of ore minerals are presented in the article. They allow to estimate the content of ore minerals in them, to analyze particle size distribution and spatial distribution of their grains, etc. These data provide more detailed information on the strength properties of ore and the possibility of selective comminution at the stage of study and design of beneficiation schemes. The analysis of mineralogical and geochemical composition as well as the results of technological research have shown that investigated copper-nickel ores satisfy the criteria of selective comminution.

Cyber-Physical Systems formalization in de- and remanufacturing and application to size reduction stage

Circular economy aims to shift from traditional linear approach of “take, make, dispose” to a closed loop scenario with the final goals of waste reduction and improvement of environmental friendly processes, creating new adaptable and resilient systems. Recycling processes, fundamental in circular economy, are facing issues related to the variability both in input and in output, showing mechanical treatments as the most promising in terms of environmental impacts and costs. First step in every recycling line is shredding. The objective is to obtain liberated particles (composed only by target materials) at a desired dimensional distribution. Cyber-Physical Systems are the most promising technology in recycling due to their capability to enable working always with optimized parameters, with a continuous exchange of information and actuations between hardware and software parts. The scope of this work is to present an architecture to optimize comminution processes, divided in two different steps, also based on Cyber-Physical Systems. First one aims to achieve the target optimal distribution, while the second one to minimize operational costs.

Energy consumption assessment and modeling of a comminution process: The glass fibers reinforced composites case-study

Abstract The implementation of circular economy concept is necessary to obtain sustainable processes. Meanwhile, End-of-Life composite products is one of the most rapidly increasing waste flow. Mechanical recycling, due to low cost and reduced environmental impact, is one of the most promising solutions for composite waste treatment, in which shredding plays a fundamental role. To compete with low cost of virgin fibers, an energy assessment and modeling of the process is mandatory. This work aims to evaluate the energy consumption of a shredding process of End-of-Life composite materials, aiming to its optimization, to enable a competitive and attractive value chain.

Control and monitoring of multi-disc comminution process

The article deals with the issues of intelligent, based on genetic algorithms, systems for grinding of grainy biomass to be used for further energy production processes. The aim of the study is to develop the basis for processing, active monitoring and subsequently, adaptive control of the process functional characteristics on the basis of solutions provided by artificial intelligence and identification of input variables of mathematical models and indexes, their mutual relations as well as their impact on the output variables such as: degree of fineness, production yield, power demand and unit energy consumption as well as CO2 emissions. A research methodology for practical control of the grinding potentials to improve the parameters of the multi disc grinding process parameters including: energy and power consumption, the product granulometry and the process efficiency improvement; CO2 emission index being a determinant of environmental efficiency has been developed. Parameters providing the grinding process with best possible conditions in terms of energy efficiency and emissivity, depending on the kind of the feed material, have been determined

New model for ecological assessment of comminution process in energy biomass processing chain

Acquiring energy contained in the biomass structure requires its prior appropriate preparation. These treatments require some energy inputs, which significantly affects the reduction of the energy and environmental balance in the entire life cycle of energy biomass processing chain. In connection with the above, the aim of the work was to develop a methodology for ecological assessment of biomass grinding in the processing chain for energy purposes. The research problem was formulated as follows: is it possible to create an assessment model that takes into account the environmental inputs and benefits of the grinding process of biomass intended for further energy use (combustion); how the control variables of the grinding machine affect the ecological evaluation of the process. In response to the research problem, the original index of ecological assessment of the biomass grinding process was developed. The model was verified by assessing the process of rice and maize grinding on a real object - a five-disc mill, for various settings of grinding discs speed. It was found that the developed ecological assessment model allows comparison of grinding processes and indication of the process with a more favorable CO2 emission balance and its values depend on the control parameters of the mill.

Use of drilling performance to improve rock-breakage efficiencies: A part of mine-to-mill optimization studies in a hard-rock mine

In a hard-rock mine, blasting is an important rock-breakage process that impacts energy consumption both in downstream comminution processes and mine productivity. Optimizing the blast fragmentation to improve rock-breakage efficiencies during crushing and grinding is key to mine-to-mill (MTM) optimization. This study explores the use of monitoring while drilling (MWD) data to achieve this goal. Representative penetration rates (PRs) were extracted from blastholes to estimate intact rock properties and predict the breakage efficiencies that directly affect comminution energy consumption. Two intact rock properties, tensile strength (TS) and Bond work index (BWI), were correlated with the PR data to predict these efficiencies in crushing and grinding, respectively. Because of the complexity of the raw MWD data and effects of various disturbances, the MWD data was preprocessed and normalized to achieve a representative PR value at each blasthole. This preprocessing entailed defining valid PR ranges from the MWD data that could eliminate the noise related to discontinuity features in the rock mass structure as well as errors in operator behaviors. The PR data was also normalized using the adjusted penetration rate (APR) to minimize the effects of mechanical factors such as drill feed force, torque, and rotational speed. To correlate the representative APR value with intact rock properties, TS and BWI, various laboratory experiments were conducted: drilling tests using a high-precision coring machine, Brazilian disc tests, and Bond grindability tests. Based on the results of these experiments, models were developed to predict rock-breakage efficiencies during crushing and grinding based on APR. The result of this study can be used to obtain blast energy designs that consider comminution energy consumption and efficiency in the downstream rock-breakage processes.

P.577 Elements of desire questionnaire assessment of bremelanotide efficacy for hypoactive sexual desire disorder in the reconnect studies

Sustainable circular economy is introducing new industrial challenges, including recycling, to move from the cradle-to-grave paradigm to the innovative cradle-to-cradle concept. The core of several recycling systems consists of mechanical comminution, which aims at producing homogeneous mixtures of highly liberated particles. However, the complexity of comminution processes requires adequate models to control and optimize their behavior within the entire recycling system. In the literature, the so-called Population Balance Model has been proposed, which is however limited to the mining industry. In this paper, we examine the applicability of the Population Balance Models in the Waste Electrical and Electronic Equipment recycling industry. In particular, we include the homogeneity and multiplication assumptions, and analyze the impact of the comminution chamber saturation. These simplifications reduce the number of model parameters to be estimated, as the set of parameters remains the same over a wide range of working conditions. We tested our assumptions on a real system for recycling Printed Circuit Boards. Results showed the validity of the multiplication assumption and a marginal effect of saturation (p values for rotor velocity and saturation were always above 25% in an ANOVA with the Bonferroni correction). The homogeneity assumption is also tenable, with the exception of the initial transient, as the null hypothesis of constant output mass distribution under equivalent shredding times was never rejected at the 5% significance level. Outcomes of an out-of-sample validation confirmed the effectiveness of our simplified Population Balance Model (values of the Kolmogorov-Smirnov metric lower than 0.1).

Non-destructive characterization of mechanically processed waste printed circuit boards - particle liberation analysis

This work aimed to develop and propose methods for evaluating the metal degree of liberation to characterize the metal deportment/concentration and liberation/association of mechanically processed waste Printed Circuit Boards (PCBs) that hold the complex and heterogeneity structure and metal distribution/association. Waste PCBs passed through a series of mechanical processing (i.e. comminution, sieving) for the metal recovery were characterized to understand and to evaluate the metal distribution and degree of liberation of the metals in order to optimize the comminution process, avoiding excessive fine particle production. The characterizations were performed at laboratory scale, as well as utilizing large scale experimental facilities, i.e. a portable X-Ray Fluorescence (XRF), micro-XRF and Synchrotron X-Ray Tomography. The proposed methods confirmed that metal liberation was very high in the fine size fraction (0.125–0.350 mm) while many locked particles were identified in the coarse size fraction (0.350–0.500 mm). Such results were analyzed and were discussed in order to better understand metal deportment/concentration behaviors. The advantages and disadvantages related to the different characterization approaches were identified and discussed in this paper, as well as their methodological developments in a waste PCBs’ mechanical processing perspective.

Selective weakening of mineralised synthetic particles by high voltage pulses

The phenomena of high voltage pulse (HVP) selective breakage and HVP weakening have been reported separately in the literature, but the relation between the two HVP applications has previously not been investigated. Synthetic particles made of Epirez high strength grout were cast with and without embedded metalliferous minerals of chalcopyrite and pyrite and used in a study of HVP selective breakage and weakening. When metalliferous grains were embedded in the grout, there were added either as a single grain occurrence or as a fine disseminated texture. The HVP products were assessed using the JKRBT breakage characterisation method for the mineralised particles and the barren particles (with no metalliferous minerals contained), respectively. It has been found that the HVP weakening effect mainly occurs in the mineralised particles, with a reduction in particle competence (indicated by the relative change in A × b value) between 172% and 200% for the pyrite fines dispersed synthetic particles, and 70% relative reduction for the single chalcopyrite grain embedded synthetic particles. The barren synthetic particles do not exhibit a statistically significant weakening effect and appear much more competent than the mineralised particles after HVP treatment. This finding suggests that in mineral processing circuit design utilising the HVP technology, benefits associated with HVP weakening on the downstream comminution process would be maximised by combining the HVP pre-concentration and weakening applications, in doing so removing the barren unweakened rocks from the process.

Exploring the effect of the geological texture at meso and micro scale on grinding performance

Comminution indices are used to represent the grindability of a combination of minerals treated by specific processes. If two rock samples with similar values for an index are treated in the same comminution process, they are expected to have a similar behavior during grinding. However, indices are obtained assuming the breakage of homogeneous and continuous materials without considering minor scale mineral and geological textural characteristics. Eventual differences in the process could be related to those properties and may not be explained by comminution indices by itself. In the present study, two different copper ores samples with similar Bond Work index were used to evaluate the influence of mineralogy and geological texture at meso and micro scale in a ball grinding process at laboratory scale. Samples were characterized through geological texture analysis at micro-scale using petrographic microscopy, hyperspectral characterization, X-ray diffraction, and X-ray fluorescence. The effect of mineral properties on grinding was assessed through controlled grinding kinetics performed in a Magotteaux Mill®. Results show that the BWi allows to describe the transition between initial and final states at long grinding times, but it cannot reproduce the entire grinding kinetic, while textural properties, such as grain size and matrix-grain mineralogical composition, may be linked to P80 variation over time and the variation of cumulative particle size distributions at different grinding times. Results suggest that geological texture may be considered as a complement to traditional grindability indices to evaluate the grinding performance.

Developing a stepwise approach to simulate a hammer mill through the Whiten model - the adherence for a gold ore

Abstract Comminution represents a large portion of the capital and operating cost of a mineral processing plant. In 1983, Cohen estimated that comminution processes could account for 30% to 50% of the power consumption of the mill, and typically represents 50% of the operating costs of a mine. Therefore, its optimization is directly related to reduction of these operating costs. Among the crushing equipment, the hammer mill is one which is dedicated to operations that aim for a high reduction ratio with the controlled generation of fines. This crusher is recommended for friable and low abrasive ores presenting a high productive capacity. This study aims to develop a stepwise approach that allows the use of the classical crusher model (Whiten-Andersen) in modeling and simulation of circuits containing a hammer mill, simulating the resulting product according to variation of rotation speed within the equipment. The existing model for crushers developed by Whiten-Andersen considers the Perfect Mixing Model, which represents crushing through equations related to selection and breakage functions, that provide an equilibrium condition. This study aims to develop a stepwise approach that allows the use of the classical crusher model in modeling and simulation of circuits containing a hammer mill, by simulating the effect that the variation of rotation speed within the equipment implies in the generated product. The comparisons between the experimental and simulated data indicated that the model fits the data for both, P80 values and percentage passing in 19.1 mm sieve. The model created was validated based on specific experimental campaign.

Aproveitamento do rejeito de lavra de ardósia para a produção de carga mineral

A exploração da ardósia gera uma grande quantidade de resíduos, principalmente nas suas fases de extração e de beneficiamento, dando origem a passivos ambientais. No intuito de minimizar esse impacto, este trabalho teve como objetivo aproveitar o rejeito de ardósia para produzir cargas minerais, que são amplamente utilizadas na fabricação de materiais compósitos. Com este propósito, o resíduo de ardósia foi coletado da pilha de rejeito de uma mineradora próxima a cidade de Pompéu/MG, sendo caracterizado tecnologicamente e também por processos de cominuição para adequação de granulometria. Analisando os resultados, constatou-se que este rejeito satisfaz as especificações para ser utilizado como potencial carga mineral, devido à alta porcentagem de sílica e alumina e enquadramento abaixo de 0,045mm após moagem, características estas semelhantes à de cargas já utilizadas no mercado. Desta maneira, essa possível reutilização pode contribuir de forma significativa para a gestão dos resíduos sólidos na mineração e minimização dos impactos ambientais.

Effects of ultrafine comminution treatment on gelling properties of myofibrillar proteins from chicken breast

Effects of ultrafine comminution treatment on gelling properties of myofibrillar proteins (MPs) from chicken breast were investigated. The MPs were extracted and treated by four comminution processes (mortar P0, planetary ball P6, rotation P14, and oscillatory ball P23). Particle size, texture, secondary structure, water distribution, and microstructure of MP powders and MP gels were measured via dynamic light scattering, texture analyzer, Fourier transform infrared spectroscopy, Raman spectroscopy, low field-nuclear magnetic resonance, and scanning electron microscopy. Results showed that, compared with conventional mortar grinding P0 (non-ultrafine comminution), the particle size of MPs was significantly reduced from 2396.28 ± 1.95 nm to 1036.35 ± 0.71 nm after P6 milling. The hardness and elasticity of MP gels were likewise remarkably enhanced by ultrafine comminution processes (P6, P14, and P23). Comparing P6 with P0, the content of α-helix decreased from 45.23 ± 0.07% to 34.08 ± 0.06%, while that of β-fold increased from 27.79 ± 0.41% to 37.52 ± 0.03%, free water increased from 0.30 ± 0.05% to 5.44 ± 0.02%, and immobilized water decreased from 98.71 ± 1.55% to 93.27 ± 0.77%. Furthermore, the microstructure of MP gels was compact and smooth due to enhanced hydrophobicity of MPs. In conclusion, P6 milling was more effective than P14 and P23 milling in protein gelation on the basis of particle size, protein secondary structure and water distribution, as well as exposure of hydrophobic groups.

A distributed PCA-TSS based soft sensor for raw meal fineness in VRM system

Vertical roller mill (VRM) is an increasingly popular comminution equipment in cement plants. Raw meal fineness at the outlet of VRM is one of the most important indicators to measure product quality. A soft sensing model developed for powder fineness in real-time could assist operators to monitor the comminution process online. However, due to frequent fluctuation of raw material properties, intrinsic nonlinearity of the process and changeable operation conditions, the data present a multimodal characteristic. Therefore, this paper proposes an indicator to measure the similarity between variables, that is, the shortest distance between nodes in the constructed weighted network. By combining the Girvan Newman (GN) algorithm, the nodes in the variable network are divided into multiple groups, and based on this, the distributed PCA (DPCA) similarity is adopted for time series segmentation (TSS). Compared with traditional similarities between samples (distance, density, etc.), the similarity between time series focuses more on the dynamic characteristics of variables. And the implementation of DPCA similarity is equivalent to increasing the sparse characteristics of principal components, which is beneficial for enhancing the generalization of the model. Support vector regression (SVR) models along with a support vector machine (SVM) based classifier are built to obtain final predictions of the powder fineness. Effectiveness of the proposed method is verified by actual industrial data. It has a root mean square error (RMSE) index of 0.3451 on the test set, which is much smaller than that of the multi-modal soft sensor based on either clustering approaches (0.6524) or PCA similarity based TSS method (0.4282).

Espresso coffee design based on non-monotonic granulometric distribution of aromatic profile.

Coffee beverages may be obtained using several extraction methods, among which espresso coffee (EC) represents now a worldwide adopted system. Recent advances in coffee grinding equipment allow today to achieve a detailed control of granulometric distribution, and the grinding process is an essential step of coffee production cycle both for the aromatic profile composition and for the chemical properties of the beverage (Severini, 2015). The comminution process consists of the breaking down particles into smaller fragments; as well-known, its main objective is to increase the overall particle surface area exposed to water leading to a more efficient extraction of soluble substances (Illy, 2005a). Basically, the coffee brewing process includes two steps: a washing phase concerning the snapshot dissolution of free solubles at the particle surface followed by diffusion phase of solubles within the porous particles (Spiro 1992, Baggenstoss 2008). The variability in particle size distribution on the quality of EC has been studied by various authors. Severini et al. has tackled the influence of the grinding level on the aromatic profiles and chemical attributes (percolation time, caffeine content, pH and titratable acidity) as a consequence of changes in the microstructural properties of the coffee cake. Generally speaking such results would imply that the final effect in terms of aromatic compounds extraction follows a monotonic law respect to granulometric size. This result is true in an average sense but it cannot be given for granted for any aromatic compounds if we refine the resolution of granulometric class. The reasons for which some aromatic compounds do not follow the supposed trend (the lower the grain size, the higher the aromatic compound content) can be most probably related to the internal distribution of precursors and to the different non-isotropic roasting grade of the bean, where the external part undergoes to an increased thermal load. This will change at the same time the kinetics and formation of aromatic compounds, and the mechanical properties as well, strictly correlated to the way the bean is crashed during the grinding phase and consequently to the granulometric distribution of different parts of the coffee bean. Results presented in this work allow to correlate choices in terms of granulometric distribution to characteristics aromatic compounds, in order to enhance specific flavors in espresso coffee.

An approach to solving complex decision-making problems based on IVIFNs: A case of comminution circuit design selection

The comminution process is very important in the mineral processing industry. Some characteristics of ore particles which occur as a product of this process have a significant impact on the effects of further ore processing and the separation of valuable minerals in froth flotation. At the same time, this process requires a significant amount of energy, which significantly affects the overall processing costs, and a significant amount of heavy equipment and corresponding installations, which affects investment costs. In addition, it is not so easy to accurately determine the correlation between energy consumption, the consumption of the grinding media, the utilization of valuable materials and the comminution circuit throughput. Therefore, the selection of an adequate comminution circuit design is recognized as a complex decision-making problem and a new multiple-criteria decision-making approach based on the use of interval-valued intuitionistic fuzzy sets is proposed for its efficient selection. In contrast to the use of a number of more precisely defined criteria, the use of a smaller number of the more complex criteria evaluated on the basis of the satisfaction and dissatisfaction levels is also proposed in this approach. In order to enable its use for solving various complex decision-making problems, the proposed approach is adapted so as to be used in a group environment. In addition, a new procedure for ranking interval-valued intuitionistic fuzzy numbers based on the Hamming distance to a complex interval-valued intuitionistic fuzzy reference point is also proposed. The efficiency and usability of the proposed approach are considered on the illustrative example of the preliminary selection of three generic comminution circuit designs. The results obtained by applying the proposed approach are verified by the experts involved in the evaluation. The new procedure proposed for ranking interval-valued intuitionistic fuzzy numbers is also verified by comparing the results obtained by that procedure with those obtained by the proven procedure for ranking interval-valued intuitionistic fuzzy numbers based on an extension of the TOPSIS method.

Determination of the optimal replacement content of Portland cement by stone powder using particle packing methods and analysis of the influence of the excess water on the consistency of pastes

Abstract Cement is considered the basic component with the highest environmental impact in construction, in terms of CO2 emissions. As for the aggregates, the process of comminution of rocks, in addition to artificial sand, generates stone powder that ends up being stored outdoors, generating environmental damages. Thus, the replacement of cement by stone powder appears as an attractive alternative towards the sustainable concretes. In this context, the objective of this paper is to determine the maximum packing density in Portland cement, silica fume and stone dust pastes, to determine the optimal cement substitution content for the stone powder. In addition, it is intended to verify the influence of excess water on the consistency of the mixtures produced. The substitution was done in contents equal to 0%, 7%, 14% and 21% by volume and, for each content, the packing density was determined analytically by CPM model and combinations were reproduced experimentally. Excess water was checked by the mini Kantro cone test. The results showed that the higher cement substitution content of the stone powder obtained the higher packing density, experimental and analytical, and the higher workability, allowing economic and environmental advantages. Analyzing each material, the stone powder resulted in the highest packing density and silica fume is the lowest one. Therefore, finer particles resulted in lower packaging densities, due to the greater specific surface area, which demands more water. The agglomeration resulted in more empty gaps between the grains. In addition, mixtures flowability increased with the increase of the stone powder content. As the excess water is responsible for mixture lubrication, a higher packing density for a given volume of water improves the flowability.

Experimental evaluation of the conjugate anvil hammer mill – Comparison of semi-confined to confined particle breakage

The Conjugate Anvil Hammer Mill (CAHM) was identified as a novel energy efficient technology by the Canadian Mining Innovation Council that has the potential to replace conventional crushers and Semi-Autogenous Grinding (SAG) mills. Discrete Element Method (DEM) modelling showed that the CAHM requires significantly less energy in comparison to existing comminution technologies including High Pressure Grinding Rolls (HPGR). However, experimental evidence was required to validate this potential and to address operational questions.In order to evaluate the CAHM, piston-die testing was conducted to represent the comminution conditions in the CAHM for comparison to the HPGR. Three piston-die conditions were tested including low pressure semi-confined compression as generated in the CAHM, low pressure confined compression, and high pressure confined compressions as generated in the HPGR. The particle breakage was investigated and compared in terms of applied force, energy consumption, product particle size reduction and particles’ surface area generation. Results showed that the CAHM test apparatus required a much lower force and produced a finer product particle size distribution and higher surface area when compared to low pressure confined compression. When compared to high pressure confined compression (HPGR), up to 37% and 22% energy savings were achieved by the CAHM for a soft gold ore and a harder copper ore, respectively. The results demonstrated that the CAHM technology has potential to improve energy efficiency in the comminution process.