The high level of heterogeneity present in some deposits, either in grade distribution and/or composition, cannot be measured to the bench level. As such, many concentrators face a highly variable feedstock, sometimes on an hourly basis. Material above the cut-off grade may routinely be sent to waste. Conversely, the feed stockpile can too easily drift below the specified cut-off grade.
Bulk ore sensing and sorting enables the preconcentration of the concentrator feed while simultaneously improving its consistency. It sets a foundation for better performance in all subsequent operations delivering dividends by:
- Increasing resource utilization
- Adding throughput with no plant expansion
- Reducing water consumption per ton of product
- Reducing energy consumption per ton of product
- Increasing recovery
For a new greenfield mine, effective ore sorting could mean a smaller milling circuit and overall concentrator layout resulting in lower CAPEX. It could also mean accessing satellite deposits of lower grade more effectively.
Bulk ore sorting is reliant on analytical technology that can rapidly differentiate material that is at or below cut-off grade. Analyzer precision and accuracy are equally critical with high penalties for both false acceptance and false rejection. False acceptance negatively impacts the average grade of the feed stockpile or plant feed. False rejection sends recoverable copper to the waste pile resulting in losses. A high spec analyzer solution will minimize the loss of valuable material sent to waste, while routing only economically viable ore into the process.
Learn more about the solutions we have to offer to the copper industry from our ebook.
Advantages of PGNAA analysis on stockpile feed
Stockpile feed can be highly variable, with some material being highly desirable while other material is below an acceptable grade. With PGNAA online analysis, data about the feed can be obtained before the material reaches the mill. This information can be fed back to the mine or the truck dispatch, allowing corrective action to be taken if necessary. When used in mine-to-mill accounting, PGNAA provides a point of reconciliation that can more easily be related back to a given situation with mine ore feed grades, without the issues of lag time or stockpile dilution that can come with mill flotation feed grade evaluation. It illuminates the variability of the ore grade from mine to mill, allowing action to be taken to reduce variability and thereby ensure a more stable feed supply to the plant. PGNAA analysis introduces several distinct advantages:
- Use of PGNAA provides finer resolution than truck or shovel sensors
- Rapid feedback to the mine helps to optimize operations by allowing quick response to mis-routings or grade control sampling errors
- Production economics can benefit from data provided on potentially mishandled waste and ore that might be inadvertently routed into the stockpile—such undesirable material could either be recovered or, at the very least, not sent to the plant
- PGNAA makes possible tracking of gangue minerals through light element analysis
By providing an understanding of the variability of the ore grade from mine to mill, and allowing action to be taken to reduce variability, PGNAA analysis can optimize a plant’s performance. Such refinements can impact the performance of the concentrator and influence the production costs of the final product, improving the business model for the life of the mine.
Advantages of PGNAA analysis on mill feed
While stockpile feed analysis by PGNAA reveals variations in material prior to that material reaching the mill feed, once material reaches the mill feed, further analysis can be performed to determine the optimum particle range size for a given mill feed grade. The grinding that happens in the mill is an essential first step in mineral liberation, but often there is no clear understanding of what the target particle size should be. With more than 50% of energy consumption coming at the crushing and grinding state, overgrinding beyond the ideal particle size rang has definite economic implications. PGNAA analysis on mill feed helps determine what the optimum particle size range should be, thus helping operators set up process control strategies to achieve optimal grind size and maximize the metal yield.
- PGNAA analysis provides mill feed data to the plant for process control purposes, allowing operating setpoints to be adjusted prior to the Flotation feed
- Tracking of gangue minerals through light element analysis is made possible, thus allowing decisions/actions on gangue control strategies
- For end-of-month mine/mill reconciliation purposes, having PGNAA analysis on the mill feed provides a much more "provable" point of issue as compared to attempts at reconciling mine to flotation feed. (In the latter situation, the issue is often difficult to identify and often the flotation feed sampler or weightometers are "blamed," requiring expenditures of time and resource to either prove or disprove the accusation)
Having the data to find the balance between particle size and circuit throughput, thus limiting consumption of grinding medica and maximizing metal yields, is crucial to limiting energy costs and optimizing plant output. PGNAA analysis of the mill feed can provide this highly advantageous information.
Why should PGNAA / PFTNA be used in copper mining?
Neutron activation analysis techniques such as Prompt Gamma Neutron Activation Analysis (PGNAA) or Pulsed Fast Thermal Neutral Activation (PFTNA) are well-suited to bulk ore sorting. Irradiating materials with neutrons cause the elements to emit secondary, prompt gamma rays, creating an identifying ‘fingerprint’. PGNAA and PFTNA analyzers penetrate the entire incoming ore stream, ensuring that the whole material stream is analyzed equally and accurately.
Find out more about the Thermo Scientific CB Omni Agile Online Elemental Analyzer which offers market-leading performance for efficient ore sorting.
