Hydraulic jig

In a hydraulic jig, a mixture of two solids is separated into its components by subjecting an aqueous slurry of the material to a pulsating motion, and allowing the particles to settle for a series of short time intervals such that their terminal falling velocities are not attained. Materials of densities 1800 and 2500 kg/m3 whose particle size ranges from 0.3 mm to 3 mm diameter are to be separated. It may be assumed that the particles are approximately spherical and that Stokes Law is applicable. Calculate approximately the maximum time interval for which the particles may be allowed to settle so that no particle of the less dense material falls a greater distance than any particle of the denser material. The viscosity of water is 1 mN s/m2. 

Size separation equipment in which particles move in a fluid stream is now considered, noting that most of the plant utilises the difference in the terminal falling velocities of the particles In the hydraulic jig, however, the particles are allowed to settle for only very brief periods at a time, and this equipment may therefore be used when the size range of the material is large. 

Figure 1.32. The Denver hydraulic jig (a) Downward stroke (b) Upward stroke...

The hulk liquid flow considered so far has heen at steady state. The liquid was flowing either up or down the device at a constant rate. Further, the particles or drops were assumed to he falling with a steady terminal velocity the initial transient acceleration period was not considered relevant. Correspondingly, the d z/df term in equation (3.1.61) was neglected. In the industrial operation of a hydraulic jig, the initial transient is quite important. The principle of operation of such a device (shown in Figure 6.3.3) is as follows. 

The hydraulic jig is used to fractionate mineral/par-dculate suspensions (especiaUy coal suspensions) larger than 10-20 mesh (0.165-0.083 cm), where the particle/ mineral density is substantiaUy larger than that of water. The jig described above is of the fixed-screen type with water forced up through the screen (Perry and Green, 1984) hydraulic jigs can also be of the moving-screen type. The bulk liquid velocity, paraUel to the direction of the force, is then introduced into the system by the moving screen. 

Hydraulic separation depends on a process called jigging, which creates a panicle siratifiealion from an alternate expansion and compaction of a bed of panicles by a pulsating fluid How. As originally developed, a baskel tilled with material was moved up and down in a lank filled with water. The more modem Baum jig process utilizes an air impulse concept in which the water is moved hy air pressure front an adjacent sealed chamber There are several refinements of the process, including the McNally Norton standard washer. 

Flake or Scrap Mica. In the early to mid-1900s. Hake or scrap mica was mainly processed hy a jigging procedure which consists ol hydraulically washing a pile of bulldozed ore across a series of roll crnsliers and Trommel screens gaped at iliffercnl size openings. 

Jigs to which perhaps 20 or 30 formers are fixed are moved sequentially on guide rails from station to station. Operations such as dipping into a liquid bath are achieved using hydraulic equipment. Within limits, the time spent at each station can be independently varied, so more control is possible than with the continuous... 

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