Many mineral processing operations are taking a hard look at ore sorting to improve their bottom line. Even the slightest sorting inefficiencies can lead to huge financial loss, not to mention easily preventable downstream and environmental impacts. Since our industry operates with such slim profit margins and under high government restrictions, companies need to take every opportunity to optimize these circuits. By eliminating waste material early on in the comminution process, energy is directed where it’s needed most—the valuable material. 

Ore Sorting Basics

Typical ore sorting methods use high-tech sensors that analyze every rock particle for unique physical and chemical properties. High-pressure air jets are then used to remove the waste material from the circuit. Successful ore sorting of this nature relies on feed prep and ore heterogeneity. While you can’t control the mineral makeup of the feed, you do have significant control over particle size. 

Control Particle Size for Improved Mine Economics

Effective ore sorting is dependent on the heterogeneity of the feed. The ore and waste rocks need to be liberated from one another so that the sensors can properly identify each particle for sorting. In general, ore sorters can process particles ranging from 30-120mm in size. As a general rule, the largest particle should be no more than three times the size of the smallest particle for sorting. 

Oversized particles can cause damage to the equipment and increase the likelihood of incorrect sorting. Fines also need to be controlled, as they can decrease separation efficiency, hinder recovery rates, and create dust issues. To ensure correct particle sizing, a proper crushing circuit needs to be designed. 

Comminution Circuit for Optimal Ore Sorting

A system of rock crushers and screens are used to generate the ideal particle size for ore sorting. Using the correct equipment here is vital.

Choosing Rock Crushers

When choosing a rock crusher you’ll need to decide between an impact crusher, a jaw crusher, a cone crusher, or a combination of these. The goal is to create particles in the correct size range, and in an ideal shape, while minimizing fines. 

Impact crushers are known for high reduction ratios and producing cubed-shaped rock particles. However, they typically generate the largest amounts of fines and are ill-suited for ore sorting.

Jaw crushers are usually used in tandem with cone crushers. The jaw crusher is the primary crusher in a comminution circuit for ore sorting and mineral processing. The particles produced by a jaw crusher may be flat and elongated, so a cone crusher is essential for ore sorting. 

Grizzly King Jaw Crusher
Sepro Grizzly-King Jaw Crusher

A cone crusher, like the Blackhawk 100 Cone Crusher, produces particles that are more spherical or cubic, typically in the correct size range for effective ore sorting.

Blackhawk 100 Cone Crusher
Sepro Blackhawk 100 Cone Crusher

Slowing a cone crusher down and using a coarse liner help minimize the production of fines. The Blackhawk 100 Cone Crusher has a variable speed drive for this particular application. It’s driven directly via a flexible coupling to the electric drive motor. This arrangement eliminates the need for sheaves and v-belts, resulting in a simple operation which produces particles in an ideal size and shape for ore sorting. 

Choosing Screens

Vibrating screens help improve ore sorting by removing fines from the circuit while also sending large particles back to the cone crusher. This makes a double-deck vibrating screen an ideal choice for ore sorting as this single piece of mineral processing equipment can accomplish both of these tasks. The main consideration here is to ensure that the screen size is large enough for effective fines removal. 

Incline Minerals Vibrating Screen
Sepro Screens come in a single, double, or triple deck version.

Crushing Circuit Design

Having the correct number of crushing stages helps to minimize fines is critical. For maximum efficiency, a crushing circuit will generate a reduction ratio between 5:1 and 7:1. Using a two-stage crushing circuit with a reduction ratio between 3:1 and 4:1 at each stage reduces fines and also decreases the number of particles filtered back to the crusher. 

Benefits of Ore Sorting Prep

Sorting particles early in the process removes waste material from the circuit. This removed material allows more throughput of valuable feed for downstream processes like leaching, flotation or gravity concentration. It also allows companies to choose to decrease their plant size for significant CAPEX and OPEX savings. Removing waste from circuits can also remove bottlenecks further down the mineral processing circuit. Higher head grades also result in improved leaching and flotation recoveries. 

This preconcentration also lowers the environmental footprint of the mineral processing operation as waste material can be stored in rock piles rather than ending up in a wet tailings impoundment.
Preconcentration is simple to implement and an effective way to improve downstream mineral processing operations. To get the most out of your current mineral processing system, or to design the optimal crushing circuit for future projects, contact the experts at Sepro.