Jigs are widely utilized not only for the purification of coal but also in the separation of heavy minerals, including alluvial gold.
1. Introduction
When dealing with coal, the concentrate is represented by the light fraction, while in the mineral industry, it is the heavy fraction that serves as the concentrate. Consequently, the products of gravity separation are denoted as either light or heavy, departing from the traditional terms of concentrate or tailing.
The typical jig is an open water-filled tank featuring a horizontal screen positioned near its upper part. Early jig designs involved a screen surface, resembling a basket that moved vertically within a water-filled barrel or tank, thereby creating a vertical flow of fluid through the particle bed. In contemporary times, some prospectors may still employ this straightforward manual device in water drums or streams. While movable screen jigs are still in use, the majority of modern jigs incorporate a stationary screen and utilize pulsed water flow.
The distinctions among various jig types is related to the methods employed for generating pulsation and the manner in which the heavy fraction is extracted from the jig. The screen’s role is to provide support to the particle bed, and the space beneath it is referred to as the hutch. Typically, the tank is divided into two primary sections: one housing the support screen with the ore bed and another responsible for generating the fluid flow.
The heavy discharge from the jig can exit in two ways: either passing through the screen or flowing over the screen. When employing jigging through the screen, every particle in the input is smaller than the screen openings, allowing them to potentially fall through the screen and gather in the hutch.
2. Operation of Jigs
The efficiency of a jig separation relies on various factors, including the amount of water added, the frequency and extent of the jig’s movements, the rate of material feeding, and the presence of the ragging layer.
Water can be introduced into the jig from above the screen (top water) or beneath the screen (back water or hutch water). The total water flowing over the top of the jig bed is termed cross water, and it governs the horizontal movement of particles across the bed. Back water lessens the impact of the suction phase of the cycle, influencing the speed of falling water relative to rising water during the pulsation part of the stroke.
Maintaining a steady operation requires aligning the feed rate with the discharge rate of the heavy fraction. If the discharge rate of heavy particles lags behind the arrival of heavy particles at the separation layer, the layer will accumulate, potentially leading to the loss of heavy minerals to the lighter fraction. Conversely, if the discharge rate of heavies, either through the ragging or discharge gate, surpasses the rate at which heavy particles move into the separation layer, some light particles may end up in the heavy fraction, reducing its quality.
Several factors related to the ragging are crucial in influencing the separation process. These factors include the size, size distribution, shape, and density of the ragging material. The effectiveness of separation is impacted by the interplay of these characteristics.
The depth and weight of the ragging layer, coupled with a shorter pulsation stroke, create conditions where it becomes more challenging for particles to infiltrate the ragging. Consequently, the discharge of the heavy fraction slows down. It is essential to note that the size of the ragging material is typically maintained at about 3-4 times the maximum particle size present in the feed. This specific sizing ensures optimal performance in facilitating the separation of particles.
Novelty Structures supplies Mining Jigs for various mineral processing plants.
