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Gravity concentration is the process by which particles of different densities, sizes, and shapes separate from each other when under the action of gravity or centrifugal forces [...]

Wastes from old electronic devices represent a significant part of the electronic scrap generated in developing countries, being commonly sold by collectors as low-value material to recycling hubs abroad. Upgrading the quality of this waste type could drive the revenue of recyclers, and thus, boost the recycling market. On this basis, this study investigated the possibility of concentrating metals from old wasted printed circuit boards through a physical separation-based route. Preparation of samples comprised fragmentation, size classification, density, and magnetic separation steps, followed by chemical and macro composition analysis. Cu, Al, Fe, and Sn constituted the major metals encountered in the scraps, including some peak concentrations of Zn, Sb, Pb, Ba, and Mn. Four distinct concentrate products could be obtained after suitable processing: (a) a light fraction composed of plastics and resins, (b) an aluminum concentrate, (c) a magnetic material concentrate, containing mainly iron, (d) a final concentrate containing more than 50% in mass of copper and enriched with nonferrous metals. Preliminary evidence showed that further processes, like the separation of copper wires through drumming, can potentially improve the effectiveness of the proposed processing circuit and should guide future works.

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.

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, aswater is particularly scarce. Four coal layers of the Moatize coal deposit were studied, which are currentlyexploited 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. This research was funded by Instituto Tecnológico Vale (ITV) Ouro Preto, Brazil.

Green routes to prepare or manufacture sustainable building materials have been attracting much attention over the years targeting sustainability issues. In this investigation, for the first time, sludge from the inert mineral part of the construction and demolition waste (RA-S) is used as a primary raw material in the fabrication of fired bricks for building purposes. Fired bricks fabricated with different dosages of RA-S and earth material (i.e., 0%, 30%, 50%, 70%, and 100% by weight) were prepared and evaluated in terms of their physical-chemical properties. The RA-S was characterized, and the results showed that it could be classified as a clayey material and richly graded silty sand according to the French Standards. XRD analysis revealed that the addition of the RA sludge into raw earth material provoked changes slightly in the fired bricks. The compressive strength (CS) results indicated that the CS of the fired bricks increased with the addition of the RA-S from 30% to 70%. The highest CS was attained at the firing temperature of 800 °C. The density of the fired brick slightly reduced with the RA-S addition. The thermal conductivity results suggest that RA-S has better insulation properties compared to earth material. The RA-S sludge can be used in combination with earth material to fabricate fired bricks, which can meet the requirements of many Standards all over the World. In the light of these results, it is possible to say that the RA-S generated from recycling inert mineral part of construction and demolition waste plant is an excellent raw material to prepare efficient fired bricks that can be successfully employed in the real construction sector. Also, the highlighted results suggest that brickwork factories have the opportunity to improve production quality while significantly reducing manufacturing time, energy consumption, resource depletion, and environmental impact. The authors are also grateful to the Council for the Development of Higher Education at Graduate Level, Brazil (CAPES) for the postdoctoral scholarship granted through the National Postdoctoral Program (PNPD). The authors also thank Mr. Ferro, president of Esterel Terassement, for financial support and for providing the RA-S samples. Dr. Simoes dos Reis gives a special thanks to the cooperation opportunity between UFRGS and IFSTTAR through his Post-doctoral studies provided by PNPD. E.C. Lima thanks to Foundation for Research Support of the State of Rio Grande do Sul (FAPERGS), and National Council for Scientific and Technological Development (CNPq, Brazil) for financial support and sponsorship.

Sampaio, C.H. et al., Demolished concretes recycling by the use of pneumatic jigs, Waste management and research, 38 (4) pp. 392-399. Copyright © 2020. DOI: 10.1177/0734242X20902835. Large quantities of construction and demolition waste is generated annually around the world. Part of this material is processed in recycling plants. After removing metals, fines and lights, the construction and demolition waste is crushed and sized and can be used as aggregates for low resistance concrete, for road sub-base, city landfill and other low value-added applications. For their use as coarse aggregate in structural concretes, construction and demolition waste must exhibit high densities and regularity of the material. This material usually is presented in demolished concretes. About 20% of the particles from demolished concretes can be used as coarse aggregates substituting part of natural aggregates in structural concretes. This article presents studies of demolished concretes recycling by the use of a pneumatic jig. All jigging tests were carried out with three different concretes produced in three strength classes: C16/20, ordinary concrete; C50/60, high strength concrete; and C70/85, very high strength concrete. Based on density distribution of the three concretes, there are reasonable masses with densities over 2.7¿g¿cm-3, particle density considered appropriate to the used as coarse aggregate for structural concretes. The concretes present different mass recoveries of the denser particles (different liberation). Coarse aggregates can be recovered with reasonable masses by the use of air jigs: About 65% for high strength concretes and about 75% for the low strength concrete. The jigging concentration efficiency depends on the concrete liberation, density and size distribution. The authors would like to thank the Brazilian National Council for Scientific and Technological Development (CNPq) for financial support. We are also very thankful to NORIE (Núcleo Orientado para a Inovação da Edificação), LEME (Laboratório de Ensaios Estruturais) and LEAMET (Laboratório de Estudos Ambientais para Metalurgia), research groups of the Federal University of Rio Grande do Sul, Brazil, where production and characterization of the concrete samples were carried out.

Nowadays, large quantities of CDW (Construction and Demolition Waste) are produced worldwide: European Union between 310 and 700 million tons..

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.

Artisanal and small-scale processes of dyeing of agates are usually non standardized and often ineffective. In the Brazilian scenario, local arrangements need actions to improve the current processes and to minimize energy consumption and production of wastes. In this sense, the aim of this study was to investigate new standard dyeing procedures capable of producing a satisfactory color alteration using minimal quantities of inorganic dyes and heat. A so-called cold dyeing route was outlined and tested for the artificial colors black, red, blue and green. In all cases, experimental results showed a significant, and in some cases dramatic, improvement in the final color of agates dyed according to the proposed cold dyeing system in comparison to the conventional warm process. Most important, these improvements were achieved with an average reduction of heat energy and reactant consumption of 94.6% and 56.6%, respectively. Potential benefits obtained from applying the cold dyeing route include the reduction of operating costs and decrease in wastewater burden due to the use of dye solutions of low concentrations under optimized conditions.

Brazil is one of the leading suppliers of colored agates, mostly of its extraction and processing carried out by artisanal miners. Dyeing is the principal method used for color alteration, and the long heating times account for most of the energy consumption. In this context, this study aimed to evaluate the implementation of a cold dyeing procedure, dispensing any need for dye solution heating, for the cases of organic dyeing with Rhodamine B and Crystal Violet. The results obtained indicated that using cold dyeing allowed obtaining coloring levels similar to those produced commercially. Also, for some cases, satisfactory color alteration could be achieved using dye concentrations lower than that conventionally used. The proposed cold dyeing process arises as a sustainable option for saving energy, reduce greenhouse gas emissions, decrease solvent losses, and enhance the income of artisanal and small-scale producers.

© 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ This work aims to evaluate the use of the air jigging technique, a density-based separation technology commonly applied in mineral processing, to upgrade the quality of mixtures (density and geometric properties) that represents the typical composition of construction and demolition waste (CDW) produced in Brazil. In this sense, tests involving the variation of the main operational parameters of jigging (bed expansion rate, pulsation frequency and jigging time) were carried out aiming to find those which provided the best recycled aggregates quality after processing. Also, fines and dust emissions generation during jigging were measured in order to estimate their potential impacts on human health and environment. The results showed that the air jigging process is adequate to improve the quality of CDW by increasing the concrete concentration in the dense product. The use of high bed expansion rates showed to be of major importance to decrease the content of ceramic aggregates in the dense product, allowing obtaining products richer in concrete. Also, the measured properties of the obtained aggregates (size distribution, shape, etc) met the usual standards required for natural aggregates. Finally, material losses and dust emissions generated were negligible in comparison to the total mass processed, although special attention must be given to safety measures due the presence of inhalable particles (

Particle size variation plays a key role in jigging performance, and despite extensive research in the area, very little attention has been given in the case of pneumatic jigging. The aim of this study was to look into particle stratification in a pilot-scale pneumatic jig when varying the particle size and the range of the particle size distribution in ternary mixtures of aggregates. Jigging tests were especially designed to reduce contamination of jig products and a stratification index was elaborated to evaluate stratification efficiency. Experimental results provided compelling evidences that widening the particle size distribution of the system or using beds composed of particles of smaller sizes can enhance stratification by density. Similarly, smaller particles showed a remarkable tendency to concentrate in the upper zones of the stratified bed, whereas larger particles tended to concentrate more in lower zones. The obtained results suggest that particular operating features of pneumatic jigging together with differential packing effects should play a decisive role in the stratification extent of beds formed by particles of different sizes. Experimental results are of practical importance since, among other benefits, they point to the possibility to increase pneumatic jigging performance in some cases by using wider size distributions of the feed, thus reducing the need of prior stages of narrow size classification.

Recycled concrete aggregates (RCA) are composed of two different materials: natural aggregate and attached cement paste. It is generally admitted that finer the RCA greater is the quantity of adhered cement paste. In this study it is shown that for a given granular class, very large disparities may be present in the adhered cement paste content, which could generate dispersion of the results of characterization tests of RCA. The heterogeneity of a narrow granular class of coarse RCA (6.3/10 mm) was investigated by sorting samples according to their densities using a water jig. The water jig sorting was essentially a separation by density and not by size. It was shown that the average water absorption after an immersion in water during 24 h was about 5% for a representative sample of the feed RCA, before sorting tests, while for the homogenous specimens separated by density, the water absorption ranged from 2% to 9%. The distribution of the water absorption in a sample of 120 kg of RCA was well estimated by a log-normal distribution. This intrinsic heterogeneity of RCA implies being able to have representative samples with sufficient accuracy, not only concerning the size but also the mineral composition of grains in the stockpiles of RCA. So, after discussing the results of this study, water jig appeared to be an efficient tool to separate RCA and obtain representative samples for their characterization.

The use of ethanol as fuel has encouraged many countries to improve their production processes. However, costs related to its current production model have been occasionally mentioned as a disadvantage to the use of this biofuel. One of the main costs is the energy expenditure for an effective distillation of the fermented ethanol wort, to result a final product called hydrous ethanol (about 95% by volume of ethanol in water). A promising alternative is the use of ethanol fuel with high fractions of water (above 5% by volume), the so-called wet ethanol, which would reduce the energy cost of production during the distillation. Thus, this study proposes the development of a mathematical model that, along with experimental data, is able to predict the effect that the use of wet ethanol has on the performance of internal combustion engines. In order to do so, along with commercial hydrous ethanol, blends were prepared with the following volume fractions of water: 10% (E90W10), 20% (E80W20), 30% (E70W30) and 40% (E60W40). Tests were performed considering two engine operating conditions: (a) fixed ignition timing and (b) adjusted ignition timing for maximum engine torque. The model was able to successfully simulate the gradients of pressure and temperature in the cylinder and it showed good ability to predict engine performance based on the variations of power, torque, conversion efficiency, and specific fuel consumption. Except for the specific fuel consumption, where the estimated error for variations was greater than 20%, the estimates for the other performance parameter presented relative errors lower than 7%. For all tests, the relative error was lower than 13%. The gradual increase of specific fuel consumption was associated with the increasing water content. Among the fuels tested, E70W30 showed the best performance, followed by the E80W20 blend; both were more efficient than the commercial ethanol.

The use of air jigging for performing multi-component separation in the treatment of mixed construction and demolition waste was studied. Sorting tests were carried out with mixtures of equal bulk volume of concrete and brick in which fixed quantities of unwanted materials - gypsum, wood and paper - were added. Experimental results have demonstrated the possibility to use air jigging to carry out both the removal of low-density contaminants and the concrete concentration in only one process step. In relation to the removal of contaminants only, the overall performance of jigging process can be comparable with that of commercial air classifiers and automatic sorting systems. Also, the initial content of contaminants seems does not have a significant effect on the separation extent. These results are of particular importance for recycling plants processing as they represent an alternative to optimize the use of air jigs. Further investigation is needed in order to evaluate the practical feasibility of such method.

This work deals with the separation of concrete, brick and gypsum particles from a CDW recycled aggregate mixture. Construction and Demolition Waste materials can be handled as an ore treatment problem. Efficient sorting processes of low quality CDW recycled aggregate could allow the reuse of concrete, brick and gypsum particles. The processes also improve the remaining mixed aggregates for recycling in unbound sub-base materials, by increasing their self-cementing properties and by reducing the sulfate content through the removal of gypsum. All tests were carried out in the size range between 4 and 20 mm using a laboratory air jig. The aim of the work is to concentrate a high amount of gypsum (light material) and concrete (heavy material) particles. Three working parameters are relevant for the jigging processes control such as the sorting duration, the frequency and the expansion ratio. Each of them are studied. It was found that a quadratic model of the number of jig cycles, a product of the frequency and time, accurately predict well the sorting results, if the expansion is large enough. An optimal point seems achieved at about 320 jigging cycles. Concentrates with concrete contents higher than 90% and gypsum contents significantly lower than 1% were possible to be reached and can be an alternative in aggregates for the concrete market. Indeed, gypsum reduction in concrete concentrates was about 25 times. This level of reduction could be satisfactory in sorting real demolition products. On the other hand, contents of over 70% of gypsum concentrates were obtained, increasing the reuse and recycling abilities.

Catalisadores heterogêneos são comumente formados por metais ou óxidos metálicos associados a componentes estruturais. Em alguns casos, todo o catalisador pode ser estruturado do mesmo material, é o caso dos catalisadores nanoestruturados de óxido de cobalto. O cobalto é um metal crítico que apresenta risco de fornecimento primário e, portanto, o estudo de fontes de obtenção secundária e sua reciclagem são interessantes. Catalisadores exauridos de óxidos de cobalto apresentam em sua composição, além dos óxidos de cobalto, material residual do processo que catalisou, como óleos orgânicos ou fuligem. Sendo assim, esse trabalho se propôs a estudar um processo de reciclagem deste resíduo para a obtenção de cobalto metálico. Para tanto, foi feita a caracterização do resíduo e o estudo de rotas de redução para o cobalto, contemplando o estudo da cinética dessas reações. O catalisador é formado pela mistura de óxidos de cobalto (II) e misto (CoO.Co3O4) que correspondem a 98,9% da sua massa, o restante é umidade e matéria orgânica que correspondem a 0,4% e 0,7%, respectivamente. O processo de redução acontece em duas etapas, na primeira o cobalto (III), presente no óxido misto, reduz a cobalto (II) e na segunda o cobalto (II) reduz a cobalto metálico. Outros fenômenos térmicos que afetam a velocidade da redução são: a sinterização do catalisador que ocorre a partir de 700°C e a decomposição do óxido misto a óxido (II) que ocorre a partir de 900 °C. O primeiro redutor utilizado foi uma mistura de hidrogênio (5%) e argônio (95%), que foi estudado na faixa de 300 até 700°C e vazões de 2,5 até 13,5 mL/min, tendo seu melhor resultado a 500°C e 13,5 mL/min, com tempo para redução completa de 30 min. O segundo redutor foi uma mistura de monóxido de carbono (10%) e dióxido de carbono (90%), numa faixa de temperatura de 550 até 900°C e vazões de 5 até 15 mL/min. Para avaliação das reduções com monóxido de carbono, os ensaios foram divididos em dois grupos 550-650°C e 700-900°C devido à sinterização. O estudo cinético, através do método do tempo reduzido, foi feito para cada uma das reações. Tendo como mecanismo de controle para ambas, difusão na camada sólido-gás. Não foi possível realizar o estudo cinético no grupo de 700-900°C com monóxido de carbono, uma vez que a decomposição do óxido tem uma cinética totalmente diferente das reduções. Todo o material oriundo da redução foi analisado por microscopia eletrônica de varredura e difração de raios-X, não mostrando sinais de óxidos ou carbono precipitado, sendo, portanto, cobalto metálico. Heterogeneous catalysts are commonly formed by metals or metallic oxides associated with structural components. In some cases, the entire catalyst can be structured from the same material, as is the case with nanostructured cobalt oxide catalysts. Cobalt is a critical metal that poses a risk of primary supply and, therefore, the study of secondary sources and its recycling are interesting. Exhausted cobalt oxide catalysts present in their composition, in addition to cobalt oxides, residual material from the catalyzed process, such as organic oils or soot. Thus, this work proposed to study a recycling process for this waste to obtain metallic cobalt. Therefore, the characterization of the residue and the study of reduction routes for cobalt were carried out, contemplating the study of the kinetics of these reactions. The catalyst is formed by a mixture of cobalt (II) and mixed oxides (CoO.Co3O4) which correspond to 98.9% of its mass, the rest is moisture and organic matter which correspond to 0.4% and 0.7%, respectively. The reduction process takes place in two stages, in the first, cobalt (III), present in the mixed oxide, reduces to cobalt (II), and in the second, cobalt (II) reduces to metallic cobalt. Other thermal phenomena that affect the speed of reduction are: catalyst sintering that occurs from 700°C onwards and the decomposition of mixed oxide to oxide (II) that occurs from 900°C onwards. The first reducer used was a mixture of hydrogen (5%) and argon (95%), which was studied in the range of 300 to 700°C and flow rates from 2.5 to 13.5 mL/min, with its best result being 500°C and 13.5 mL/min, with time to complete reduction of 30 min. The second reducer was a mixture of carbon monoxide (10%) and carbon dioxide (90%), in a temperature range from 550 to 900°C, and flow rates from 5 to 15 mL/min. To evaluate carbon monoxide reductions, the tests were divided into two groups 550-650°C and 700-900°C due to sintering. The kinetic study, through the reduced time method, was carried out for each one of the reactions. Having as a control mechanism for both, diffusion in the solid-gas layer. It was not possible to carry out the kinetic study in the 700-900°C group with carbon monoxide, as the oxide decomposition has different kinetics from the reductions. All material from the reduction was analyzed by scanning electron microscopy and X-ray diffraction, showing no signs of oxides or precipitated carbon, being, therefore, metallic cobalt.