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The Advanced Stratification Rate and Transport (ASTRAD) Jig Model

Jig Models: Bringing Operation and Theory Closer Together

The ASTRAD jig model is a mathematical model for predicting both the rate and ultimate separation of ore by density (and size) in a jig. It provides a convenient framework for interpreting, mass balancing, and scaling jig test work data from small laboratory batch jigs through to pilot plants and full scale industrial jigs.

Using Astrad with Jig Tests

 An entire series of stratification tests for a known feed washability can usually be summarized by two main parameters: a mobility coefficient, and a diffusion coefficient. Once these parameters have been determined, either by test work or from historically similar washability data, it is possible to calculate the following data:

  • Partition curves (split to product as a function of density),
  • Grade/Recovery curves (provided the density grade relationship is known),
  • Jig capacity as a function of the above curves, jig dimensions, and feed rate,
  • What-if scenarios (what if the feed rate increases by 10%?; What if the ore quality degrades by 5% etc.).

One of the main features of ASTRAD is the ability to determine improvements in jig yield as a function of jig size and feed rate which permits an economically optimum jig size to be selected. It can also determine the range of yields achievable over an ore body which has a variable but known washability (density distribution).

Example Seperation Performance vs Jig Size


In a jig bed, whether it be batch or continuous, the particles are subjected to a jigging action for a given residence time (the batch and continuous residence times being related by the transport velocity profile in the continuous jig).

The particles start in a mixed state and the denser particles progressively drop to the bottom of the bed, and the less dense ones to the top of the bed. The rate at which this happens depends on the density of the particle relative to the surrounding material, and the fluid dynamics of the jig pulse. Typically finer particles separate more slowly and less well than coarser particles.

Eventually the material separates to an equilibrium state where the material is in balance between the tendency to separate and the tendency to remix due to fluid turbulence forces and stochastic particle interactions. For this reason the final equilibrium only approaches that achievable by a heavy liquid result.  

The key factors in determining the jig capacity for an ore are therefore:

  • Residence time of particles in the jig (a function of feed rate and jig dimensions),
  • The density (and size) range of the product and reject components of the feed,
  • The separation and remixing rate determined by the jig pulse.  

The design size is chosen to best match the residence time in the jig with that required for the material in the bed to approach equilibrium (maximum separation). The operation point of the jig pulse is set to maximize the separation rate while minimizing the turbulent remixing effects.

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© Copyright 2008 Andrew Jonkers