Some observations on the influence of particle size and size distribution on stratification in pneumatic jigs Weslei M. Ambrós a, ⁎, Carlos H. Sampaio a , Bogdan G. Cazacliu b , Paulo N. Conceição a , Glaydson S. dos Reis a,b a Mineral Processing Laboratory, Federal University of Rio Grande do Sul, 9500 Bento Gonçalves Avenue, Zip Code: 91501-970 Porto Alegre, Brazil b LUNAM, IFSTTAR, Aggregates and Materials Processing Laboratory, Route de Bouaye – CS4, 44344 Bouguenais Cedex, Nantes, France abstract article info Article history: Received 6 June 2018 Received in revised form 17 September 2018 Accepted 14 October 2018 Available online 16 October 2018 Particle size variation plays a key role in jigging performance, and despite extensive research in the area, very lit- tle attention has been given in the case of pneumatic jigging. The aim of this study was to look into particle strat- ification 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 com- pelling 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 differ- ential 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. © 2018 Elsevier B.V. All rights reserved. Keywords: Pneumatic jig Particle size Size distribution Stratification 1. Introduction Pneumatic jigging has attracted significant interest over recent years, especially due to the inherent advantage of not using process water. Though it is strongly associated with coal beneficiation [1–3], in recent years, pneumatic jigging has been extensively studied in urban mining applications, such as recycling of construction and demolition wastes [4–6], recovery of metals from electronic wastes [7] and separation of copper wires from rubber insulators [8]. However, its separation perfor- mance remains significantly lower than that of conventional hydraulic jigs, which eventually impose severe limits on its application [9]. None- theless, the great majority of studies focused on conventional hydraulic jigs and little attention has been paid to the effect of bed properties (par- ticle density, size and shape) on stratification under dry conditions. 1.1. Overview of jigging process Jigging has been known for centuries as an ore concentration process [10]. Hydraulic jigs of different types are widely used in several applications, covering every density range from less than 1.3 g/cm 3 for some coals [11] up to 19 g/cm 3 for gold [12], whereas pneumatic jigs is still more limited to coal and solid waste processing [1,3]. The jigging process consists in the repeated expansion and contraction of a non-homogeneous particle bed, producing stratification based upon specific gravity [9,13,14]. An illustration of the jigging action is shown in Fig. 1. During the pulsation stroke, the bed initially at rest on a rigid screen is lifted as a whole when the fluid flow exceeds the final falling velocity of the bed forming a porous rigid mass. As the fluid velocity is lowered and the upward motion of the bed slows towards its maximum displacement, a loosening layer starts as particles began to settle out from the bottom upwards. This loosening wave moves upwards through the bed until it reaches its maximum void fraction, so that particles fall under conditions analogous to hindered settling [14]. The heavier, larger particles tend to reach the jigging screen first than the lighter, smaller particles due to their higher specific gravities [15]. If the fluid medium is water, then the downward motion of particles is also influenced by the descending motion of the fluid (suction stroke). Otherwise, if the medium is air, so the suction stroke is virtually absent. The cumulative effect of several jigging cycles gives rise to a stratified bed where heavier, larger particles tends to concentrate in the lower layers whereas the lighter, finer particles tends to accumulate in the upper layers. Since density (not size) is a characteristic property of Powder Technology 342 (2019) 594–606 ⁎ Corresponding author. E-mail addresses: weslei.ambros@ufrgs.br (W.M. Ambrós), sampaio@ufrgs.br (C.H. Sampaio), bogdan.cazacliu@ifsttar.fr (B.G. Cazacliu), paulo.conceicao@ufrgs.br (P.N. Conceição), glaydson.simoes@ufrgs.br (G.S. dos Reis). https://doi.org/10.1016/j.powtec.2018.10.029 0032-5910/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec