Jigging method and apparatus for gravity separation in the fine and

Abstract

In jigging for purposes of gravity separation of material to be concentrated the material is sorted into a heavy fraction which is withdrawn through a screen (2) and a light fraction withdrawn above the screen (2), by periodically passing flows from the bottom to the top through the feed material. If the material is predominantly of finer character, there will be a ragging (3) on the screen (2) composed of particles which are larger and usually also specifically heavier than those of the feed material. In this manner, however, the separation of feed material will be unsatisfactory in the fine particle size range having upper particle size limits between 300 .mu.m and 1 mm, particularly so if the particle size ratio of the material is rather broad. To obtain high-grade concentrates, and high yields at the same time, also in the fine particle size range mentioned and in the finest particle size range below the same, therefore, it is provided that, below the feed bed (5) a filter layer (4) is introduced which consists of particles having a density approximately the same as that of the heavy fraction and a size which is within the limits of from 1.2 to 2.5 times the upper particles size limit of the feed material, the height of the filter layer corresponding to at least twice the mean particle size of the filter layer particles, that, for jigging, the feed bed (5) first is stratified such that the finer particles of the specifically lighter material mainly are moved into the upper part of the feed bed (5), and that, during jigging, the periodic inflowing is effected or adjusted in frequency such that the filter layer will adopt a porosity of between 60% and 70% by the upward stroke and the stroke amplitude will range between 50% and 200% of the filter layer height. A jig for carrying out the method is disclosed as well.