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Papers by Pedro P S Cavalcanti

Powder Technology, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Powder Technology, 2019

Slow compression tests are routinely used both in quality control of fired iron ore pellets durin... more Slow compression tests are routinely used both in quality control of fired iron ore pellets during production and in negotiating commercial contracts. In spite of their widespread use, such tests represent stressing conditions consistent with those experienced by pellets during transportation in ships, wagons and conveyor belts, as well as when they are stored in silos and hoppers. However, operations that are most likely to damage pellets occur during transfers in chutes, screening, ship and wagon loading, stockpiling and reclaiming, where they are subjected to rapid loading. The present work compares the mechanical behavior of individual pellets subjected to slow compression and rapid loading, this later in an impact load cell device. Besides pellet strength, fracture energy and also stiffness of the pellets are analyzed, demonstrating that pellets present significantly higher stiffness when subjected to impact, with only marginally higher pellet strengths and no clear trend regarding fracture energy. These strain rates differences are then discussed and their potential effect on deformation behavior and wave propagation in the pellet are analyzed.

Minerals Engineering, 2018

Interest in understanding the response of particles to low-energy (incremental) breakage has incr... more Interest in understanding the response of particles to low-energy (incremental) breakage has increased significantly in comminution in recent years, mainly due to the recognition that a large proportion of impacts in tumbling mills is insufficient to cause breakage at the first collision event. Likewise, degradation during handling is another field in which low-energy breakage is of great relevance. The investigation of this mode of breakage, however, is very tedious when conducted in drop weight testers, so that more convenient alternatives for testing have been sought. A device, called JK Rapid Breakage Tester (JKRBT), has been proposed as a more convenient alternative to other breakage testers, mainly the Drop Weight Tester, being used in recent studies that investigate incremental breakage. The present work demonstrates, through experiments and simulations, that care should be exercised when using this device in investigating breakage by low-energy impacts, since testing of iron ore pellets resulted in significantly more breakage than expected, when compared to a drop test. This has been confirmed by simulations using the discrete element method, which demonstrated that ricocheting of a fraction of particles can happen against the rotor, resulting in overestimation of breakage for the set energy level. Such effect has been observed to be relevant not only in the case of nearly spherical shapes, such as the iron ore pellets studied, but also in the case of very irregularly-shaped particles.

Powder Technology, 2018

Degradation that results from transportation and handling can have an important economic impact i... more Degradation that results from transportation and handling can have an important economic impact in steelmaking materials, given the lower value of the finer material that is generated. In spite of their higher strength when compared to lump iron ores, fired iron ore pellets also undergo some degradation, which increases with severity of the handling operations that occur from the pelletizing plant to the end user. Such degradation can occur in the form of fine debris lost from the surface of the pellet, in a mechanism of surface breakage, or as result of complete loss of integrity of the pellet (fracture), generating a wide range of fragments in size. The work deals with this second mechanism of breakage, describing the probability of fracture of pellets under impact conditions, the amenability of pellets to break under repeated impacts, besides the size distribution of the progeny for selected iron ore pellets, proposing appropriate experimental methods and models to describe them quantitatively.

Powder Technology, 2018

The fracture load of iron ore pellets in the 12.5 to 16-mm size range is routinely measured in pe... more The fracture load of iron ore pellets in the 12.5 to 16-mm size range is routinely measured in pellet plants following the ISO 4700 standard. The analysis of such data, however, seldom goes beyond averages and standard deviations of the load required for fracturing each pellet. Iron ore pellets are produced in the range from approximately 8 to 19 mm, so the entire distribution of fracture strengths over the range of sizes produced is relevant. This study analyzed in great detail the variability and the size-scale effect on the strength of five industrial iron ore pellets. The fracture strength data of pellets contained in five size ranges were analyzed on the basis of 12 probability distributions, as well as different parameter estimation methods. Further, other measures collected from compression tests, that is, pellet stiffness and specific pellet fracture energy, were also analyzed as a function of pellet size. Results show that the Weibull distribution provided comparably good fitting to pellet strength data. Fracture energy data could be described well using the normal distribution with square root transformation, although the Gumbel distribution was identified as the best fit-for-purpose distribution describing the data. The maximum likelihood parameter estimation method was demonstrated to be marginally more capable of fitting the data than the least-squares technique. It was also shown that the fracture strength of pellets increases with a reduction in pellet size. This size effect on strength was found to be more pronounced than that predicted using Weibull theory on the basis of variability in pellet strengths.

Powder Technology, 2019

Abstract Surface breakage or attrition occurs when iron ore pellets are subjected to handling sta... more Abstract Surface breakage or attrition occurs when iron ore pellets are subjected to handling stages in which the stressing level is insufficient to cause their massive fracture. This breakage mechanism has been investigated for five types of industrial iron ore pellets from impacts against a steel target, leading to a model that accounts for the effect of pellet size, impact energy and angle. The model is then validated on the basis of two different tests. First, a tumbling test on a small drum (0.305 m diameter) is used to demonstrate the validity of the model to describe surface breakage by motion of the pellets at comparatively low velocities, such as those that are found during flow in hoppers and silos. The model is also validated on the basis of simulations of a RO-TAP® sieve shaker. It is demonstrated that it is able to predict with confidence results from the tests, proving to be a powerful tool when used in combination with simulations using the discrete element method, to predict mechanical degradation due to surface breakage during handling.

Anais dos Seminários de Redução, Minério de Ferro e Aglomeração

O pelotamento é a mais complexa etapa de aglomeração de finos de minério de ferro. Sua resposta é... more O pelotamento é a mais complexa etapa de aglomeração de finos de minério de ferro. Sua resposta é naturalmente oscilante, sendo bastante influenciada pelas características físicas obtidas nos processos de beneficiamento mineral que a precedem e tem papel crucial para a etapa de tratamento térmico de sinterização à jusante. O presente trabalho aborda o processo de classificação de pelotas verdes, sólidos singulares de aspecto deformável e pegajoso, em peneiras de rolos por modelamento por aplicação de Método dos Elementos Discretos. Esta técnica mostra-se como uma importante ferramenta pois supera as limitações impostas na modelagem física (quantificação e identificação de fluxos por ausência de instrumentação em escala industrial, amostragem sem representatividade) ao reproduzir de forma verossímil as repostas do sistema para importantes variáveis de controle: comprimento de gap, umidade, dispersão de tamanhos e resistência das pelotas.

ABM Proceedings, Sep 1, 2016

Resumo A suscetibilidade à degradação mecânica de pelotas de minério de ferro é diretamente influ... more Resumo A suscetibilidade à degradação mecânica de pelotas de minério de ferro é diretamente influenciada tanto pela composição quanto pela sua estrutura. O trabalho analisou criticamente essas relações para pelotas queimadas para a redução direta, por meio de análises detalhadas com quatro tipos distintos de pelotas, que incluíram análises químicas e mineralógicas, medidas de porosidade e distribuição de tamanhos de poros por tomografias de raios X, distribuição de poros por região da pelota por meio de microscopia, da dureza, bem como de resistência à compressão, abrasão, bem como um novo método de avaliação da resistência à fragmentação por abrasão. O trabalho mostra que há, de fato, forte correlação entre a suscetibilidade à degradação e várias dessas características analisadas. Forte correlação foi observada entre a porosidade e o tamanho máximo de poros. Boa correspondência qualitativa foi observada entre o acabamento superficial e a resistência à compressão. Resultados de um novo teste proposto de suscetibilidade à fragmentação superficial sugerem que a porosidade total e a mineralogia exercem pouca influência nesse comportamento, enquanto as características superficiais, como o acabamento e a microdureza exercem uma influência direta nesse mecanismo.

Powder Technology, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Powder Technology, 2019

Slow compression tests are routinely used both in quality control of fired iron ore pellets durin... more Slow compression tests are routinely used both in quality control of fired iron ore pellets during production and in negotiating commercial contracts. In spite of their widespread use, such tests represent stressing conditions consistent with those experienced by pellets during transportation in ships, wagons and conveyor belts, as well as when they are stored in silos and hoppers. However, operations that are most likely to damage pellets occur during transfers in chutes, screening, ship and wagon loading, stockpiling and reclaiming, where they are subjected to rapid loading. The present work compares the mechanical behavior of individual pellets subjected to slow compression and rapid loading, this later in an impact load cell device. Besides pellet strength, fracture energy and also stiffness of the pellets are analyzed, demonstrating that pellets present significantly higher stiffness when subjected to impact, with only marginally higher pellet strengths and no clear trend regarding fracture energy. These strain rates differences are then discussed and their potential effect on deformation behavior and wave propagation in the pellet are analyzed.

Minerals Engineering, 2018

Interest in understanding the response of particles to low-energy (incremental) breakage has incr... more Interest in understanding the response of particles to low-energy (incremental) breakage has increased significantly in comminution in recent years, mainly due to the recognition that a large proportion of impacts in tumbling mills is insufficient to cause breakage at the first collision event. Likewise, degradation during handling is another field in which low-energy breakage is of great relevance. The investigation of this mode of breakage, however, is very tedious when conducted in drop weight testers, so that more convenient alternatives for testing have been sought. A device, called JK Rapid Breakage Tester (JKRBT), has been proposed as a more convenient alternative to other breakage testers, mainly the Drop Weight Tester, being used in recent studies that investigate incremental breakage. The present work demonstrates, through experiments and simulations, that care should be exercised when using this device in investigating breakage by low-energy impacts, since testing of iron ore pellets resulted in significantly more breakage than expected, when compared to a drop test. This has been confirmed by simulations using the discrete element method, which demonstrated that ricocheting of a fraction of particles can happen against the rotor, resulting in overestimation of breakage for the set energy level. Such effect has been observed to be relevant not only in the case of nearly spherical shapes, such as the iron ore pellets studied, but also in the case of very irregularly-shaped particles.

Powder Technology, 2018

Degradation that results from transportation and handling can have an important economic impact i... more Degradation that results from transportation and handling can have an important economic impact in steelmaking materials, given the lower value of the finer material that is generated. In spite of their higher strength when compared to lump iron ores, fired iron ore pellets also undergo some degradation, which increases with severity of the handling operations that occur from the pelletizing plant to the end user. Such degradation can occur in the form of fine debris lost from the surface of the pellet, in a mechanism of surface breakage, or as result of complete loss of integrity of the pellet (fracture), generating a wide range of fragments in size. The work deals with this second mechanism of breakage, describing the probability of fracture of pellets under impact conditions, the amenability of pellets to break under repeated impacts, besides the size distribution of the progeny for selected iron ore pellets, proposing appropriate experimental methods and models to describe them quantitatively.

Powder Technology, 2018

The fracture load of iron ore pellets in the 12.5 to 16-mm size range is routinely measured in pe... more The fracture load of iron ore pellets in the 12.5 to 16-mm size range is routinely measured in pellet plants following the ISO 4700 standard. The analysis of such data, however, seldom goes beyond averages and standard deviations of the load required for fracturing each pellet. Iron ore pellets are produced in the range from approximately 8 to 19 mm, so the entire distribution of fracture strengths over the range of sizes produced is relevant. This study analyzed in great detail the variability and the size-scale effect on the strength of five industrial iron ore pellets. The fracture strength data of pellets contained in five size ranges were analyzed on the basis of 12 probability distributions, as well as different parameter estimation methods. Further, other measures collected from compression tests, that is, pellet stiffness and specific pellet fracture energy, were also analyzed as a function of pellet size. Results show that the Weibull distribution provided comparably good fitting to pellet strength data. Fracture energy data could be described well using the normal distribution with square root transformation, although the Gumbel distribution was identified as the best fit-for-purpose distribution describing the data. The maximum likelihood parameter estimation method was demonstrated to be marginally more capable of fitting the data than the least-squares technique. It was also shown that the fracture strength of pellets increases with a reduction in pellet size. This size effect on strength was found to be more pronounced than that predicted using Weibull theory on the basis of variability in pellet strengths.

Powder Technology, 2019

Abstract Surface breakage or attrition occurs when iron ore pellets are subjected to handling sta... more Abstract Surface breakage or attrition occurs when iron ore pellets are subjected to handling stages in which the stressing level is insufficient to cause their massive fracture. This breakage mechanism has been investigated for five types of industrial iron ore pellets from impacts against a steel target, leading to a model that accounts for the effect of pellet size, impact energy and angle. The model is then validated on the basis of two different tests. First, a tumbling test on a small drum (0.305 m diameter) is used to demonstrate the validity of the model to describe surface breakage by motion of the pellets at comparatively low velocities, such as those that are found during flow in hoppers and silos. The model is also validated on the basis of simulations of a RO-TAP® sieve shaker. It is demonstrated that it is able to predict with confidence results from the tests, proving to be a powerful tool when used in combination with simulations using the discrete element method, to predict mechanical degradation due to surface breakage during handling.

Anais dos Seminários de Redução, Minério de Ferro e Aglomeração

O pelotamento é a mais complexa etapa de aglomeração de finos de minério de ferro. Sua resposta é... more O pelotamento é a mais complexa etapa de aglomeração de finos de minério de ferro. Sua resposta é naturalmente oscilante, sendo bastante influenciada pelas características físicas obtidas nos processos de beneficiamento mineral que a precedem e tem papel crucial para a etapa de tratamento térmico de sinterização à jusante. O presente trabalho aborda o processo de classificação de pelotas verdes, sólidos singulares de aspecto deformável e pegajoso, em peneiras de rolos por modelamento por aplicação de Método dos Elementos Discretos. Esta técnica mostra-se como uma importante ferramenta pois supera as limitações impostas na modelagem física (quantificação e identificação de fluxos por ausência de instrumentação em escala industrial, amostragem sem representatividade) ao reproduzir de forma verossímil as repostas do sistema para importantes variáveis de controle: comprimento de gap, umidade, dispersão de tamanhos e resistência das pelotas.

ABM Proceedings, Sep 1, 2016

Resumo A suscetibilidade à degradação mecânica de pelotas de minério de ferro é diretamente influ... more Resumo A suscetibilidade à degradação mecânica de pelotas de minério de ferro é diretamente influenciada tanto pela composição quanto pela sua estrutura. O trabalho analisou criticamente essas relações para pelotas queimadas para a redução direta, por meio de análises detalhadas com quatro tipos distintos de pelotas, que incluíram análises químicas e mineralógicas, medidas de porosidade e distribuição de tamanhos de poros por tomografias de raios X, distribuição de poros por região da pelota por meio de microscopia, da dureza, bem como de resistência à compressão, abrasão, bem como um novo método de avaliação da resistência à fragmentação por abrasão. O trabalho mostra que há, de fato, forte correlação entre a suscetibilidade à degradação e várias dessas características analisadas. Forte correlação foi observada entre a porosidade e o tamanho máximo de poros. Boa correspondência qualitativa foi observada entre o acabamento superficial e a resistência à compressão. Resultados de um novo teste proposto de suscetibilidade à fragmentação superficial sugerem que a porosidade total e a mineralogia exercem pouca influência nesse comportamento, enquanto as características superficiais, como o acabamento e a microdureza exercem uma influência direta nesse mecanismo.