X-ray-transmission based ore sorting at the San Rafael tin mine

San Rafael is the largest underground tin mining operation in the world. The main methods for processing the ore are gravity separation and flotation. In 2016 a new addition to the plant was an X-ray transmission (XRT)based ore sorting island. The objective was to reject waste from a marginal development waste dump, and it is now also treating low grade material from the underground mine. XRT sorting discriminates particles on a planar projection of the density of matter attenuating X-ray radiation. Physical separation is achieved by means of an array of high speed air jets. The feed grade of approximately 0.6% tin is concentrated to 2.8% tin in the product at recovery of 90% in about 19% mass yield to product. This enriched product fraction from the sensor-based ore sorting plant feeds into the main plant. The plant, which is designed for 3600 tonnes per day, went into operation in 2016. The total capital expenditures of 24 M$ US were paid back within 4 months. The projected contribution to the production of refined tin for the year 2017 was 6000 tonnes. In summary, the positive impacts were: - Value added from previously sub-economic waste that can be mined with lower costs. - Increase of productivity in the main wet sections of the plant. - Reduction in cut-off grade and increase in reserves. - Reduction of environmental impacts. The paper describes the project from concept, through the development phase, including test work confirming feasibility, to a discussion of operational data and includes shared experiences from operation and maintenance.