By Denise Nunes
Processing plants are designed according to metallurgical tests performed on composite samples and the range of recoveries is explored by testing composites for variability. Nevertheless, the day-to-day activities of a mining operation are more dynamic than ever and every project has its range of ore variability.
Mill performance changes may be due to feed variations or deliberate design changes. The feed may change due to natural ore variability; fluctuations in ore blend may occur because of mine scheduling or unplanned changes, such as equipment shutdowns. The plant may add a new unit operation and make minor equipment modifications and, despite all optimisation efforts, the plant may not be performing as expected.
Mineral processing is complex and combines a sequence of interlocked unit operations, each affecting the performance of downstream processes, as well as impacting the overall mill performance. However, sometimes the benefit of optimising a single unit operation may be eclipsed by the losses in other circuits, as mineral processing can be counterintuitive, even for the most experienced plant operator. What should be done when this happens? How about plant benchmarking?
Benchmarking is a good practice designed to detect issues with plant performance and guide the operation in planning improvements. Plant benchmarking may comprise a full plant audit with historical review and process modelling. Systematic sampling across the mill will provide mass, constituent and water balances, and a careful look at plant survey data will help identify bottlenecks and opportunities for process optimisation. A historical review of operational and geological data will add to the understanding of site challenges and help to determine optimisation strategies.
Process modelling can facilitate the evaluation of circuit alternatives for improved overall efficiency. The use of simulation tools will enable the analyses of different scenarios more economically than plant trials, and it can also assist in developing process control strategies and team training in operations. When geological data are combined with mill performance analysis, the information generated can be used to optimise mine scheduling, blend definition, throughput and mill efficiency; thus optimising the overall project profitability.
SRK realises the challenges faced by the mining industry, including a shortage of technical personnel. Quite often, the operations team does not consider the mill as a whole, and plant optimisation efforts end up generating more frustration than positive results. SRK can assist operations in getting the best use of their knowledge and build on it, by offering site support for plant benchmarking, process optimisation, integrated planning and personalised training.