How Critical a Stream in Overall Metallurgical Process Control Strategy

As we have discussed in previous articles, online slurry analysis systems provide accurate, real-time elemental analysis for process control of slurry in Minerals Processing operations. These analysis systems help improve product quality and recovery, lower production costs when used as a tool to optimize reagent addition as well as detect and react to process upset more quickly.

But just how critical is a given stream, and do all elements in a stream need to be analyzed?

The elements in the streams to be analyzed are determined by the objectives of the process control strategy and the particular metallurgical challenges which are anticipated from prior metallurgical test work. The frequency of analysis required, often referred to as the assay update time, depends on the following criteria:

The fluctuation in assays in a given process stream considering the residence times of the processes immediately upstream.
The stability of the circuit.
As a minimum the assay update times of the analyzers for the critical streams should be less than half of the retention time of the preceding process stage.

Therefore, in the tailings stream from a scavenger bank of cells with a retention time of 5 minutes, the grade can be expected to vary considerably in 2 minutes during upset conditions or reactions to process control actions so on-line analysis should be made at an interval less than this to provide the best visibility of real-time plant performance. To obtain these sorts of assay update times requires dedicated analyzers as the preferred technical solution or if lower assay availability and higher maintenance can be tolerated a centralized analyzer located nearby a cluster of process sample points.

If the critical streams are monitored frequently according to the above criteria, plant operators should be able to control the process to improve overall stability and metallurgical results. The less critical intermediate streams with longer residence times can then be monitored at a lower frequency for the fine tuning of the circuit.

The degree of confidence required in the assay-based control decisions must be known. Streams that are more critical for control of the plant need to be monitored more frequently and the chosen on-stream analyzer should deliver accurate reliable assay data with high availability with minimum OPEX to achieve the required availability. Trends in plant performance will then be shown in more detail, showing the effect of control actions on grade in real-time and giving greater confidence in control decisions.

In a base metal concentrator, the main objective might be to stabilize rougher mass pull and minimize pay-metal losses in the primary flotation circuit while meeting a minimum pay-metal concentrate grade in the cleaners while keeping Insolubles below a desired target. Continuous analysis of feed, rougher concentrate and tailings grades provides a critical tool in the operation of rougher flotation to achieve these control objectives.

On-line analysis of critical process streams in the Cleaners circuit provides a tool to manage grade-recovery in the cleaners and better control impurities to meet the downstream customer requirements.

You’ll find additional information about online slurry analysis systems in our Frequently Asked Questions page Process Control Considerations for Online Slurry Analysis in Metallurgical Plants FAQs