Ore Grade Control

Ore Grade control is a critical component of all and any extraction and processing operations. 

Gatesbridge recently worked with a Jordanian minerals and mining group to improve their certainty of their feed-to-plant phosphate grade.

What: Phosphate waste stockpile re-processing. 20 million tonnes of historical discharged phosphate bearing rock, located across 15 stockpiles, each between 1 and 15km apart. 

The Issue: The variability in stockpile grades located between two historical mining areas would directly influence the economic viability and operational efficiency of a proposed Phosphate beneficiation plant, for both the short and the longer term.

We guided our client to understand that ‘Ore’ Grade Control involves managing the overall quality of Phosphate ore waste (concentration of  P2O5, gangue minerals and their variability) to ensure that ore collected meets the planned specifications of feed to plant for efficient processing and the maximisation of product yield. Whilst ‘Processing’ Grade control involves the delivery of the plant’s processing basis of design and operating strategy through tactical sampling, reconciliation and process change. Delivered in terms of 3 ‘Rs’: Rate, Recycle and Reagents.

An emphasis was placed on the consistency between planned and actual ore feed mineralisation to reduce waste, maximise resource recovery, enhance profitability, and ensure compliance with customer and regulatory requirements.

Developing grade control activities, such as stockpile ore sampling or pre-concentration helped in identifying and avoiding the plant processing of waste rock containing little or no concentration of  P2O5. 

The overarching grade control process developed integrated all operational control activities. 

The key steps.

Stockpile Grade Models:

Following a programme of ore sampling across all (or some) of the existing stockpiles located across the two sites, we prepared a stockpile-by-stockpile grade model to describe the grade variation contained across these stockpiles by concentration and by location (for example, on a 100m x 100m grid). 

Production Sampling and Ore reclamation operations:

Once in operation, a process of continuous ore sampling was propsoed to confirm that the planned feed-to-plant remained achievable and maintained – this was key. Variation could then be recorded and addressed.

Organising and synchronising all ore recovery and handling activities would ensure that variation in ore grade shall be reduced and the forecasted head grade maintained. An integrated management systems to control the ore recovery, pre-concentration activities and ore blending was proposed to be managed centrally through production planning and operational management. Once in place, the use of databasing and predictive forecasting (application of AI technologies) could be considered and developed for implementation, if deemed suitable.

Product Grade Control

Phosphate product processing grade control would ensure the quality and consistency of the final product by monitoring and managing the ore's grade throughout the processing stages. 

For the variety of ores, the process would involve real-time sampling, analysis, and adjustments to maintain the desired product specifications, such as  P2O5 content and impurity levels. Methods for phosphate grade control included:

• Sampling and Assaying: Regular sampling of ore and product streams, followed by chemical assays, to ensure accurate monitoring of phosphate grades. For real time adjustment of processing, the identified systems were:

  • X-Ray Fluorescence (XRF) Analysis: the non-destructive technique providing rapid and precise elemental analysis.

  • Laser-Induced Breakdown Spectroscopy (LIBS): offering real-time, in-situ analysis of phosphate content.

• Automated Sorting / Pre-Concentration Systems: The use of technologies applying optical or sensor-based sorting to separate ore based on grade were identified as an opportunity and were to be deployed at the stockpile, or within the plant blending stockpiles to improve feed grade and reduce waste at source.

Reconciliation

Reconciliation Analysis: is the comparison of stockpile sampled ore grades with both observed and planned grades to identify deviations and refine future grade control plans. As part of wider reconciliation activities stockpile, process streams and final products would be submitted to an independent certified laboratory, and results cross-referenced with the on-site laboratory and real-time process analysis data.  

Data Integration: returning grade control data back into the stockpile grade models to update resource estimates and improve predictability of stockpile grades.

Process Optimisation: the focus on enhancing the efficiency and sustainability of processing operations. Through the application of technologies, data analysis, and continuous improvement strategies were developed to maximise productivity and reduce waste.

A typical integrated grade control strategy.