Q: Why is the grade/recovery below target?
A: Because the ore has changed.
This conversation takes place hundreds of time per week. Both the question and answer are usually valid and, other than some irritation, that is where it stops.
The Question: “What has changed in the ore?” is seldom asked, because no-one has the data to give the answer.
We are entering a phase in the treatment of ores when the metallurgist is able to exploit tools that have, until recently, only been available to fundamental researchers.
Scanning electron microscopy has been used for elemental analysis in mineralogy since the 1970’s. “On” and “In” Stream analytical techniques are frequently used in concentrators to monitor metallurgical performance. Several mining houses have units monitoring performance for precious metals research. There has been limited use by engineering companies in process and plant design. The development of software to incorporate the elemental analysis into liberation and mineral analysis has now reached the stage where the equipment can be used for operational problem solving.
Betachem (Pty) Ltd and Nasaco International Limited have pioneered the use of Mineral Liberation Analysis in their laboratory in South Africa as a process tool; initially working together with a group of like-minded metallurgists in universities and mining companies, the technique is applied to refine the process choices. This has often resulted in the use of more specific collectors, more targeted frothers and mineral-specific depressants.
As ever, sampling and sample preparation are of paramount important. The scanning unit uses a polished section of a process sample and then usually takes a scan of 20000 particles. It is not only important that the sample taken is representative of the process, but also that the sample preparation is rigorous, to eliminate particle size segregation for example.
One of the key factors in the project has been the development of software to accurately define the mineral matrix of a particular orebody. It is only by successfully doing this that testing turnaround time can be reduced to get swift feedback to make decisions quickly. This takes the process from the research, to the operational level.
Being able to identify the value element loss in the final tail, and the gangue components in the final concentrate, is important to being able to keep a plant operating efficiently. This data is also invaluable in matching the reagent suite to the needs of the plant. How the data is used is crucial to helping in the drive for continuous improvement. The process mineralogy team should make sure that they use the data firstly to identify the problem, secondly to form an opinion of why the problem has occurred and lastly and most importantly to offer a solution.
As Riaan Grobler, Manager of Nasaco and Betachem’s process mineralogy laboratory says: “Our mantra is – What, Why, Remedy.”
The process mineralogy team uses the following method to help their clients maintain an efficient flotation operation:
On final flotation tail – use the MLA data to identify the main mineral lost to tails. Then use the liberation function and the size filter function of the MLA Dataview* software to form an opinion as to why the valuable mineral is lost. This is normally due to one of the following reasons:
- Too small to float
- Too large to float
- Locked in non-floating gangue
- Incorrect process or reagent suite to float the value mineral
- Other reasons which may include process efficiency
On the final concentrate -use the MLA data to identify the main gangue mineral in the concentrate. Then use the liberation function and the grouping function of the MLA Dataview software to form an opinion as to why the gangue mineral is present. This is normally due to one of the following reasons:
- Locked in floatable mineral
- Naturally floatable mineral in this process and/or reagent suite
- Recovered as entrained fines in the flotation water
- Recovered as a larger particle entrapped in a non-draining froth
- Other reasons which may include process inefficiency
The process engineer can now use these data to suggest a course of action to improve the performance.
Grobler says, “We have been able to live up to our motto of being a “sustainable company that contributes” by using the data we obtain from the MLA. It helps us in the service we are able to offer through our chemicals. It has made it possible for us to help our clients track their continuous improvement programs and help with troubleshooting campaigns. It has also made it possible for us to develop new approaches in the chemical solution we are able to offer our clients. We have developed some really good reagent suite solutions. Process mineralogy is critical for us to help our clients operate efficient flotation plants.”
* MLA Dataview software is part of the FEL MLA Suite software package.