Real-time bulk-density monitoring for rotary air concentration used in alluvial gold mining

Alluvial gold mining entails extracting gold from sedimentary deposits in current and ancient riverbeds. It is widely regarded as the most eco-friendly approach to gold mining due to its minimised environmental footprint compared to underground and open-pit mining. Rotary air concentration (RAC), a novel classification method seen in this field, physically separates dense gold-bearing particles from low-density gangue materials, where particle density is the dominant factor distinguishing concentrates from tails, rather than particle size. However, the dry-processing nature of air classification and high-intensity feature of the concentrates discharge impose significant challenges in gauging particle density in real-time and there is a lack of cost-effective commercial equipment in this regard, specifically for optimal closed-loop feedback control. This study resolves the problem with a new technique on the basis of vibration measurement. A prototype consisting of a mechanical probe and an accelerometer has been designed and built for inline installation along the RAC concentrates stream. Procedures to process vibration data in frequency domain are proposed. Laboratory experiments using samples from an Australian alluvial gold deposit have proven the proposed approach effective in monitoring bulk-density variation of RAC-classified concentrates stream in real-time. • Bulk density of high-intensity dry particulate flow is linked to impact vibration. • A prototype is developed to monitor the discharge density of rotary air concentration. • Influence of mass flow rate is de-coupled from bulk-density measurement. • Bulk density is given by a representative indicator updated online every 0.1 s.