Jigging beneficiation is a process in which material is sorted according to density differences, mainly in a vertically elevated, variable speed media flow. The difference in size and shape of the material has an effect on the beneficiation results. The medium used in jigging can be either water or air. When water is used as the sorting medium, it is called hydraulic jigging; when air is used as the sorting medium, it is called wind jigging. At present, the production of hydraulic jigging is the most used, so the content only relates to hydraulic jigging.
The equipment that realizes the jigging process is called a jigger machine. The selected material is fed to the jigger screen, forming a dense layer of material, which is called the bed. While feeding the material, an up and down alternating water flow is fed periodically through the screen plate from the lower part of the jigger, and the material is sorted under the action of the water flow. First, the bed is gradually loosened and suspended under the action of the rising water flow, when the particles in the bed are stratified according to their own characteristics (density, size and shape of the particles) in relative motion to each other. After the end of the upward flow, during the resting period (stop feeding compressed air) and during the downward flow, the bed is gradually compacted and continues to stratify. After all the ore particles have settled on the screen surface, the bed is tight again, and most of the ore particles have lost the possibility of relative movement with each other, and the stratification has almost completely stopped. Only those very fine grains can continue to move down through the gap of the bed (the movement of such fine grains is called drill gap movement), and continue to stratification. After the end of the downward flow, the stratification is temporarily terminated, and the stratification process of one jigging cycle is completed. The stratification process of the material in a jigging cycle is shown in Figure 1. In each cycle, the material can only be subjected to a certain sorting effect, and after several repetitions, the stratification is gradually perfected. Finally, the low density particles are concentrated in the uppermost layer and the high density particles are concentrated in the bottom layer.
The main internal factor for the stratification of the material in the jigging process is the nature of the ore particles themselves, but the objective condition that allows the stratification to occur is the alternating water flow that rises and falls vertically.
When the material is fed into the jig feed end, a certain amount of horizontal water flow is fed along with the material. Although the horizontal water flow also has a certain influence on the sorting, it mainly plays the role of wetting and transport. The wetting is to prevent the dry material from agglomerating when it enters the water; the transportation is responsible for taking away the low density material that resides in the upper layer after stratification, so that it can be discharged from the jigger’s overflow weir.
The speed and direction of water movement in a jigger varies periodically, and such water flow is called pulsating water flow. The time taken to complete each periodic change in the pulsating water flow is called the jigging cycle. The relationship between water velocity and time within a cycle is called the jigging cycle curve. The maximum displacement of the water moving up and down in the jigging chamber is called the water stroke. The number of cycles of water flow per minute is called the stroke. The thickness of the bed in the jigging chamber, the form of the jigging cycle curve, the stroke and the number of strokes are the important parameters affecting the jigging process.
The advantages of the jig sorting method are: simple process flow, easy operation and maintenance of equipment, large processing capacity, and sufficient sorting accuracy. Therefore, it is commonly used in the production and is one of the most important sorting methods for re-sorting.
In coal sorting, coal jigging accounts for a large proportion. About 50% of the world’s coal is processed by jigging machine every year; 70% of all raw coal is processed by jigging in China. In addition, the size level of jigging coal processing is wide, in the range of 0.5-150mm; it can neither be graded into the selection, nor graded into the selection. The adaptability of jigging is strong, except for the extremely difficult coal selection, all can be given priority to jigging method.
In ore sorting, jigging is an effective method to deal with coarse and medium grain ores, and is used in large quantities to sort tungsten ore, tin ore, gold ore and certain rare metal ores; in addition, it is also used to sort iron and manganese ores and non-metallic ores. When treating metal ores, the upper limit of feed size can be 30-50mm, and the lower limit of recovered size is 0.2-0.074mm.
As can be seen from the following Table, the density of useful components of the materials treated by jigging ranges from 1.2 g/cm³ to 15.6 g/cm³, the density difference between the useful components and the vein (gangue) ranges from 0.3 g/cm³ to 1.3 g/cm³, and the feed size ranges from 0.05 mm to 250 mm.