This study investigates the influence of wall effects on particle separation in an air jigging device. Tests were conducted with a ternary mixture of concrete, brick and gypsum particles in the size range from 12 to 20 mm for three different jigging times. It is shown that an unusual, remarkable segregation occurred in the direction perpendicular to the lateral walls, giving rise to a horizontal segregation pattern. In all cases, heavier particles concentrated more in the center of the particle bed while lighter particles concentrated along the side walls. Composition measurements of the stratified bed revealed that wall effects can significantly influence the composition of jig products. Linear predictions of jigging evolution suggest that stratification progress linearly after the first initial stages. Also, time evolution and analysis of local compacities indicate that stratification starts from the bottom to the upper layers of particle bed. Based on the experimental results, a mechanism for the pattern formation was proposed, which was enhanced by a geometry model of bed rearrangement. Prediction results for bed composition correlated well with experimental data and endorsed the role of lateral walls on the segregation pattern formed. The results obtained also show practical significance for the use of air jigging in the sorting of recycled aggregates. (C) 2016 Elsevier B.V. All rights reserved.