Understanding Jigs: Core Equipment for Gravity Separation

Jigs are long-standing and widely used separation equipment in gravity concentration. They separate ores based on the specific gravity difference between minerals with vertically pulsating water flow, without chemical reagents. They play an important role in coal washing, rough concentration of metallic ores, and solid waste resource recovery.

The core of jig separation is to generate periodically up-and-down pulsating water flow. Ore is fed onto the jig screen deck to form a material bed. When water pulses upward, the entire bed loosens and suspends, creating space for relative movement of particles. As the water flow falls back, valuable minerals with higher density settle faster and sink toward the screen deck, while gangue minerals of lower density settle slowly and remain in the upper layer of the bed.

After hundreds of repeated pulsation cycles, stable stratification is achieved: heavy minerals accumulate at the bottom and light gangue stays on top. Dedicated discharge mechanisms then discharge the two fractions separately to realize mineral separation. Jig separation is suitable for coarse and medium-sized particles; separation performance degrades significantly for fine materials.

Common jig types include diaphragm jigs, piston jigs, and air-pulsated jigs (Baum jigs). Air-pulsated jigs allow flexible adjustment of pulsation curves and are widely adopted in large concentrators. Diaphragm jigs deliver uniform pulsation and are mostly used for rough concentration of tungsten, tin, alluvial gold and other metallic ores in small and medium-scale mines.

1.Coal Washing

This is the most traditional application of jigs. They are commonly used in small and medium coal preparation plants for gangue rejection of thermal coal, separating raw coal from gangue. Compared with dense medium separation, jigging features lower capital investment and a simpler flowsheet, making it suitable for easy-to-wash coal.

2.Rough Concentration and Gangue Rejection of Metallic Ores

For wolframite, cassiterite, hematite, magnetite and alluvial gold, jigs are generally placed after crushing and screening for pre-discharge of large volumes of low-density gangue. The rough concentrate is then sent to shaking tables for cleaning. This greatly reduces the load on downstream cleaning equipment and raises the throughput of the whole processing line.

3.Solid Waste Treatment and Resource Recovery

In recent years, jigs have been increasingly applied to solid waste valorization: recovering pyrite from coal gangue, reclaiming residual iron minerals from iron tailings, and recovering metallic particles from electronic scrap and smelting slag. As a purely physical separation method, jigging cuts reagent consumption and aligns with green mining requirements. A coal gangue project in Guizhou adopts high-density jigs with a throughput of 200–260 t/h, producing sulfur concentrate with stable grade above 40% and overall sulfur recovery exceeding 90%.

Separation results are not determined by the equipment alone; feed conditions and operating parameters exert decisive influences.

1.Feed Particle Size

Jigs are sensitive to the size range of feed. The particle size span should not be excessively wide. Ideally, the ratio of maximum to minimum particle size is controlled at 3–5:1. A broad size range disturbs particle settling behaviour and impairs stratification, leading to loss of valuable minerals or contamination of concentrate by gangue. In production, pre-screening is normally arranged to classify ore into different size fractions for separate jigging.

2.Feed Rate and Bed Thickness

Excessive feed rate carries materials away before sufficient loosening and stratification. Insufficient feed destabilizes the bed and also deteriorates separation. Bed thickness should match the maximum ore particle size. An overly thick bed prevents water from fully lifting materials; an excessively thin bed causes direct sieve penetration and metal loss. Sensors are widely used in practice for automatic bed thickness control.

3.Water Pulsation Parameters

Water volume and air pressure determine the lifting height of the bed, while pulsation frequency governs the loosening cycle. Coarse particles suit large amplitude and low frequency; relatively fine particles suit small amplitude and high frequency. Parameters must be tuned repeatedly according to ore properties. Improper matching of air pressure and water flow directly causes gangue entrainment in concentrate or valuable mineral loss in tailings.

Jig selection should not be based merely on throughput; comprehensive evaluation of site conditions is required.

1.Ore Properties

Confirm the specific gravity difference between target minerals and gangue, feed size range and ore hardness to assess jigging suitability. Minerals with small specific gravity differences are difficult to separate by jigging and tend to yield poor indicators, so jigging is not recommended.

2.Production Scale and Site Conditions

Diaphragm jigs fit small and medium metallic ore operations; air-pulsated jigs are preferred for coal processing and large-scale solid waste projects. Floor space and water circulation facilities also need to be taken into account.

3.Process Positioning

Clarify whether the duty is rough gangue rejection or cleaning. Jigs excel at rough rejection. If high-grade concentrate is required, jig rough concentrate should be followed by cleaning equipment such as shaking tables.

4.Comprehensive Cost Evaluation

Apart from equipment procurement cost, evaluate expenses on water supply, energy consumption and wear part maintenance, as well as investment in tailings handling and water recycling systems.

Thanks to high throughput, low operating cost and reagent-free operation, jigs remain the primary workhorse for coarse-grain gravity separation. Driven by green mining policies, their application in mine solid waste recycling keeps expanding. Nevertheless, jig separation is limited by ore characteristics. Equipment is only one part of the solution. Stable pre-screening, rational process configuration and refined parameter control are essential to achieve satisfactory separation indicators