Mineral technology for coal combustion ashes from Baixo Jacuí-RS coal area

Este artigo reúne informações e dados sobre os aspectos físicos que marcam as cinzas de carvão mineral geradas na queima da matéria-prima em usinas térmicas. A abordagem se dá sob o foco da tecnologia mineral, com o objetivo de aproveitamento econômico dos resíduos e gestão ambiental sustentável. Os métodos utilizados relacionam-se com a distribuição granulométrica, colorimetria, densidade e moabilidade. Os principais resultados são: as cinzas pesadas, em geral, têm D50 < 0,6 mm e as cinzas leves < 20 μm; as alvuras em ambas as cinzas variam muito, indicando variações na presença de carvão incombusto nas amostras das três usinas; as densidades, em ambas as cinzas, variam entre 2,16 e 2,33 g/cm3, indicando homogeneidade entre elas; o Índice de Trabalho de Bond em amostra de cinza pesada tem valor de 11,9 kWh/t, indicando ser o material de fácil moagem. Com estes resultados de características físicas, conclui-se que, além das cinzas leves, as cinzas pesadas também podem ser aplicadas como aditivo à indústria do cimento, com o uso de processos de moagem de baixo custo operacional.This paper shows information and data about the physical characteristics of coal ash samples generated in power plants that burn coal. The study focuses on mineral technology and the objectives are both the economic uses and sustainable environmental management for the waste. The methods applied are related to particle size distribution, colorimetry, density and grindability. The main results are: bottom ash and fly ash generally have D50, respectively, < 0.6 mm and < 20 μm; the brightness values in both ashes vary widely, indicating variations in the presence of unburned coal in the samples of three power plants; the densities in both ashes ranging from 2.16 to 2.33 g/cm3, indicating homogeneity among them; the Bond Work Index value is 11.9 kWh/t in a sample of bottom ash, indicating that the material is easy to grinding. These results suggest that physical characteristics of the bottom ash, as the fly ash, also can be applied as an additive to the cement industry, using grinding processes with low operating cost

Construction and demolition waste recycling through conventional jig, air jig, and sensor-based sorting a comparison

The paper presents a comparison of the concentration methods conventional jig, air jig, and sensor-based sorting to treat construction and demolition waste. All tests were made with concrete, brick, and gypsum particles and the tests aim to separate these materials into different size ranges, depending on the method. The equipment tested, conventional jig, air jig, and sensor-based sorting present good results to concentrate construction and demolition waste particles, with different concentrations and mass recoveries. The results show particularly good mass recoveries and particle concentration for conventional jig, especially for concrete and gypsum particles. Sensor-based sorting should preferably use concentration circuits for best results

Production of high-quality coarse recycled aggregates through a two-stage jigging process

The use of recycled aggregates (RA) to replace natural aggregates (NA) in new concrete production has been pointed out as one of the main strategies to close the loop of construction materials. However, producing RA with properties similar to those of NA has been challenging, since current recycling methods struggle to remove contaminants like ceramics and mortar, whose presence impairs RA properties. In this study, a processing route consisting of a two-stage separation in hydraulic jig was tested, aiming to produce RA from a representative sample of Brazilian construction and demolition waste. All material streams generated in the tests were characterized in terms of composition, size distribution, density, shape index, and water absorption. The results indicated the possibility to produce a high-quality RA, containing more than 99.5% mass of concrete, with adequate properties to replace NA in new concrete production. Also, a conventional RA with suitable properties for downcycling uses (for example, base and sub-base material) could be obtained as a co-product. Finally, the results showed it was possible to recover more than 75% of the original concrete in Construction and Demolition Waste CDW, avoiding its disposal as waste

Destoning the moatize coal seam, Mozambique, by dry jigging

This paper proposes pre-beneficiation studies by air jigs of the coal layers from a Moatize coal deposit. Pre-beneficiation, also called destoning, removes tailings before the beneficiation plant. The air jigs operate in the same granulometric size range as the heavy-media cyclones (HMCs) that are installed in the preparation plant. With the destoning, the heavy-media circuit operates with a lower coal feed and higher organic matter contents, increasing its cutting efficiency and lowering operational costs. The use of air jigs reduces the total water consumption in the plant, which is especially important for the region where the plant is installed, as water is particularly scarce. Four coal layers of the Moatize coal deposit were studied, which are currently exploited in the mine. As main results of the study, it is possible to say that the concentration of lights (feed of the preparation plant) and heavies (waste fraction) in air jigs can be carried out with reasonable efficiencies for all coal layers studied, making air jigs a feasible option for coal destoning

Destoning the moatize coal seam, Mozambique, by Dry Jigging

This paper proposes pre-beneficiation studies by air jigs of the coal layers from a Moatize coal deposit. Pre-beneficiation, also called destoning, removes tailings before the beneficiation plant. The air jigs operate in the same granulometric size range as the heavy-media cyclones (HMCs) that are installed in the preparation plant. With the destoning, the heavy-media circuit operates with a lower coal feed and higher organic matter contents, increasing its cutting efficiency and lowering operational costs. The use of air jigs reduces the total water consumption in the plant, which is especially important for the region where the plant is installed, as water is particularly scarce. Four coal layers of the Moatize coal deposit were studied, which are currently exploited in the mine. As main results of the study, it is possible to say that the concentration of lights (feed of the preparation plant) and heavies (waste fraction) in air jigs can be carried out with reasonable efficiencies for all coal layers studied, making air jigs a feasible option for coal destoning

Characterization of demolished concretes with three different strengths for recycling as coarse aggregate

This paper presents a physical characterization for the recycling into new concretes of three comminuted concretes: C16/20 (“ordinary concrete”), C50/60 (“high strength concrete”), and C70/85 (“very high strength concrete”). The top size of the crushed concretes was 19.1 mm and the size range was 4.75 to 19.1 mm. The characterization was carried out with coarse aggregate liberation, to be prepared and concentrated in a gravity concentration process. The density distribution of the coarse aggregate, cement paste, and sand was carried out in different size ranges (4.75/19.1 mm; 4.75/8.0 mm; 8.0/12.5 mm; and 12.5/19.1 mm) for the three concretes studied. The form factor of the samples, as well as the porosity determination of particles in different density ranges, are presented. The obtained results indicate that the coarse aggregate liberation was more intensive for the low resistance concrete (C16/20), but a reasonable coarse aggregate recovery is possible for all concretes

Estudo sobre reutilização dos cianetos empregados no tratamento de minério aurífero por meio de soluções sintéticas e efluentes da cianetação

Compostos de cianeto são largamente utilizados em plantas de beneficiamento de minérios auríferos, com o objetivo de facilitar a extração e a posterior concentração do metal precioso. Devido as altas concentrações de cianeto utilizadas, os efluentes gerados ao final do processo de tratamento contêm altos teores de cianeto livre e de complexos metálicos de cianeto em solução, caracterizando-se assim pelo elevado potencial de toxicidade. Um processo de regeneração de cianetos, desenvolvido em escala laboratorial por meio de um aparato destilador, consiste em diminuir fortemente o pH da solução pela adição de ácido sulfúrico, visando assim converter o cianeto presente nas formas livre ou como complexo metálico em gás cianídrico, que é então volatilizado e recolhido numa solução alcalina para posterior reutilização. Este trabalho tem como objetivos: (1) testar a eficiência do dispositivo destilador para determinação de cianeto total a partir de soluções sintéticas e de soluções de cianetação; (2) reconhecer as relações químicas que se estabelecem entre o cianeto e os metais durante o procedimento de destilação; (3) constituir parâmetros de controle de processo para os testes com as soluções da cianetação dos minérios auríferos; (4) demonstrar a aplicabilidade de um processo de regeneração de cianetos para soluções resultantes da cianetação de minérios auríferos para ser utilizado em plantas hidrometalúrgicas. A destilação de soluções constituídas estequiometricamente por cianeto complexado com ferro, zinco e prata, em diferentes concentrações, apresentou altos teores de cianeto disponíveis para reciclagem; teores relativamente baixos foram obtidos a partir de complexo de cobre e muito baixos teores de cianeto foram disponibilizados a partir de complexos cianíticos de ouro e de mercúrio. A regeneração de cianetos a partir de concentrado de minério e de minério aurífero submetidos ao processo de cianetação mostrou-se um procedimento possível de ser realizado. As recuperações de cianeto obtidas indicam que a aplicação de um método que reutilize cianetos existentes em efluentes de mineração pode otimizar o processo de obtenção do metal precioso e também contribuir para a melhora das condições ambientais na área de operação.Cyanide compounds are widely used in gold ore processing plants in order to facilitate the extraction and subsequent concentration of the precious metal. Owing to the high cyanide concentrations employed in gold processing, effluents generated have high contents of free cyanide as well as metallic cyanide complexes, which lend them a high degree of toxicity. The process under study, developed in laboratory scale with the use of a distillation apparatus, consists of highly decreasing the solution pH by adding sulfuric acid. Thus, the cyanide present in either free form or as a metallic complex is made volatile and the resulting cyanide gas is absorbed in an alkaline solution for reutilization. This work aims at (1) testing the efficiency of the apparatus to determine the total cyanide from surrogate solutions, (2) recognizing the chemical relations between the cyanide and metals during distillation, (3) determining process control parameters for the tests with real cyanidation solutions of gold ores and (4) demonstrating the feasibility of a cyanide regeneration process for cyanidation solutions from gold ores to be used in industrial scale. The distillation of solutions containing cyanide complexed with iron, zinc and silver in different concentrations presented high cyanide contents available for recycling. On the other hand, relatively low cyanide contents were verified in solutions with cyanide complexed with copper and very low in solutions in which the cyanide was complexed with gold and mercury. The regeneration of cyanide from gold processing showed to be a viable procedure. Cyanide recoveries pointed to the fact that if a method for reutilization of cyanide contained in mining effluents is employed, the precious metal processing will become more efficient. Also, the environmental conditions in the area of the operation will be improved

Estudo sobre reutilização dos cianetos empregados no tratamento de minério aurífero por meio de soluções sintéticas e efluentes da cianetação

Compostos de cianeto são largamente utilizados em plantas de beneficiamento de minérios auríferos, com o objetivo de facilitar a extração e a posterior concentração do metal precioso. Devido as altas concentrações de cianeto utilizadas, os efluentes gerados ao final do processo de tratamento contêm altos teores de cianeto livre e de complexos metálicos de cianeto em solução, caracterizando-se assim pelo elevado potencial de toxicidade. Um processo de regeneração de cianetos, desenvolvido em escala laboratorial por meio de um aparato destilador, consiste em diminuir fortemente o pH da solução pela adição de ácido sulfúrico, visando assim converter o cianeto presente nas formas livre ou como complexo metálico em gás cianídrico, que é então volatilizado e recolhido numa solução alcalina para posterior reutilização. Este trabalho tem como objetivos: (1) testar a eficiência do dispositivo destilador para determinação de cianeto total a partir de soluções sintéticas e de soluções de cianetação; (2) reconhecer as relações químicas que se estabelecem entre o cianeto e os metais durante o procedimento de destilação; (3) constituir parâmetros de controle de processo para os testes com as soluções da cianetação dos minérios auríferos; (4) demonstrar a aplicabilidade de um processo de regeneração de cianetos para soluções resultantes da cianetação de minérios auríferos para ser utilizado em plantas hidrometalúrgicas. A destilação de soluções constituídas estequiometricamente por cianeto complexado com ferro, zinco e prata, em diferentes concentrações, apresentou altos teores de cianeto disponíveis para reciclagem; teores relativamente baixos foram obtidos a partir de complexo de cobre e muito baixos teores de cianeto foram disponibilizados a partir de complexos cianíticos de ouro e de mercúrio. A regeneração de cianetos a partir de concentrado de minério e de minério aurífero submetidos ao processo de cianetação mostrou-se um procedimento possível de ser realizado. As recuperações de cianeto obtidas indicam que a aplicação de um método que reutilize cianetos existentes em efluentes de mineração pode otimizar o processo de obtenção do metal precioso e também contribuir para a melhora das condições ambientais na área de operação.Cyanide compounds are widely used in gold ore processing plants in order to facilitate the extraction and subsequent concentration of the precious metal. Owing to the high cyanide concentrations employed in gold processing, effluents generated have high contents of free cyanide as well as metallic cyanide complexes, which lend them a high degree of toxicity. The process under study, developed in laboratory scale with the use of a distillation apparatus, consists of highly decreasing the solution pH by adding sulfuric acid. Thus, the cyanide present in either free form or as a metallic complex is made volatile and the resulting cyanide gas is absorbed in an alkaline solution for reutilization. This work aims at (1) testing the efficiency of the apparatus to determine the total cyanide from surrogate solutions, (2) recognizing the chemical relations between the cyanide and metals during distillation, (3) determining process control parameters for the tests with real cyanidation solutions of gold ores and (4) demonstrating the feasibility of a cyanide regeneration process for cyanidation solutions from gold ores to be used in industrial scale. The distillation of solutions containing cyanide complexed with iron, zinc and silver in different concentrations presented high cyanide contents available for recycling. On the other hand, relatively low cyanide contents were verified in solutions with cyanide complexed with copper and very low in solutions in which the cyanide was complexed with gold and mercury. The regeneration of cyanide from gold processing showed to be a viable procedure. Cyanide recoveries pointed to the fact that if a method for reutilization of cyanide contained in mining effluents is employed, the precious metal processing will become more efficient. Also, the environmental conditions in the area of the operation will be improved

Tratamento de efluentes gerados por processos de beneficiamento de minérios auríferos

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