Sensor-Based Ore Sorter

Overview

A sensor-based ore sorter examines crushed rock particle by particle and physically removes those that fail a grade criterion, using nothing but sensors, computation and compressed air. Placed between crushing and grinding, it rejects barren waste before that waste consumes grinding energy, water and reagents, and since grinding is typically half a concentrator's power draw, removing 20–50 % of feed mass as coarse waste changes the economics of marginal and low-grade deposits. Sorting also lets mines reprocess old waste dumps and cut ore-transport tonnage.

The dominant sensing mode in mining is X-ray transmission (XRT), which measures atomic density through the full particle and so is indifferent to dust, moisture or surface coatings. Optical (colour/texture) sorting, the older technique inherited from food processing, remains common for industrial minerals, gemstones and quartz. Many machines combine XRT, optical and laser channels. Commercial machine suppliers include TOMRA, Steinert and Redwave; diamond recovery has used XRT sorters since the 2000s, where they recover large stones that would be smashed in conventional crushing.

How it works

Feed must arrive as a screened size fraction, about 3:1 top-to-bottom size ratio, for example 30–60 mm, because jet energy is tuned to particle mass. The Feed System takes this fraction from the Feed Hopper through a Vibratory Feeder that spreads it into a monolayer across the Acceleration Belt. The belt runs at 2.4–3 m/s, fast enough that particles stop rolling and settle into ballistic predictability; an Encoder tracks belt speed so the processor knows each particle's position to the millimetre.

Particles cross the Sensor Array near the end of the belt. For XRT, the X-Ray Source above projects a collimated fan beam through the rock to the XRT Line Detector beneath, a dual-energy line array whose two spectral readings are combined to estimate effective atomic number independently of particle thickness. A dense sulphide or metal-bearing particle reads differently from silicate gangue regardless of its size. In parallel, Line-Scan Camera units under stabilised LED Illumination Bar capture colour and texture, and the Laser Profiler measures each particle's height and outline.

The Processing Unit handles the data flood: the FPGA Preprocessing Board flat-fields and segments the raw line streams into discrete particle objects in hardware, then the Classifier Computer computes per-particle features and applies the accept/reject rule, classical thresholds on atomic density, or trained classifiers on combined sensor channels. The whole sensor-to-decision chain completes in tens of milliseconds, while the particle is still flying off the head pulley.

Ejection is the mechanically violent part. The Air-Jet Ejection Bank spans the belt with up to ~320 Ejection Valve solenoids at 6–12.5 mm pitch feeding the Nozzle Bar. When a flagged particle's trajectory crosses the bar, the Valve Driver Board fires exactly the valves under it for exactly long enough, a few milliseconds of 6–10 bar air, scaled to the particle volume from the laser profile, punching it out of the natural trajectory fan. The Splitter Plate then divides deflected from undeflected streams into the Product Chute and Reject Chute. Machines run either "eject waste" or "eject product" logic depending on which stream is smaller, since air cost scales with ejection count.

Air, radiation and structure

Compressed air dominates operating cost, so the Compressed Air Supply is engineered seriously: a dedicated Screw Compressor of 5–25 m³/min, an Air Dryer (wet air gums the millisecond valves) and a close-coupled Air Receiver to source the huge instantaneous flows of mass firings. The X-ray zone is wrapped in lead Radiation Shielding with a Radiation Safety Interlock chain that drops tube high voltage if any panel opens; external dose stays below ~1 µSv/h and the machines are operated as closed radiation devices under national licensing. Everything mounts to the Main Frame, whose rigidity matters directly, millimetres of drift between scanner and nozzle bar translate into missed ejections.

Performance and limits

A well-run sorter achieves better than 90 % recovery of metal-bearing particles while rejecting 20–50 % of mass, but only on ores where grade differences exist at particle scale; finely disseminated ores defeat sorting because every particle looks the same. Capacity falls steeply with particle size, fine fractions below ~8 mm carry too many particles per second to sense and eject individually, and are bypassed to conventional treatment. Routine maintenance centres on sensor window cleaning, valve replacement (valves are rated for billions of cycles but fail individually), Chute Liner changes and periodic calibration against reference samples.