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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.

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 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.