Processing complex slurries
The dilution alternative: Emerging options to improve how we process complex slurries
by Dr Chris Vernon
Pipeline transport of minerals and waste is a major component of mineral processing.
While the transport of ore in dilute turbulent flow is a common practice their design is often based on correlations and engineering experience.
This may not carry over easily to more complex flow scenarios.
Rheologically complex slurries tend to arise when solid phases are ground to finer sizes, solid fractions are increased or when gangue materials, particularly clays, are present.
Falling ore grades and water scarcity are also contributors to the growing prevalence of complex suspensions.
Because of the multiple interactions occurring, these slurries can create unpredictable events within the pipeline that cannot be seen externally or easily monitored, resulting in poor pipeline control and risks to operations.
Due to this lack of visibility and understanding of slurry behaviour, many choose to sidestep these issues through dilution.
However, the ‘dilution solution’ causes its own social, environmental, and financial issues, and is increasingly being seen as not a solution at all.
For those dealing with complex slurries there are other options and emerging technology to help process through pipelines without damage or risk.
Industry changes and downstream problems are increasing risks
In general, mineral processing industries are happy with the current approach to complex slurries.
Understanding these slurries can be difficult. Diluting slurries to diminish complex rheological responses is a familiar and accepted (and, generally, economically feasible) approach.
However, there are cases which need an alternative approach to process complex suspensions.
Some have been motivated by economic reasons to change . For example, the alumina industry reduced the volume and pH of residue going to storage and benefited from the recovery of caustic soda.
Other drivers include:
Excess water usage
There is increasing social and environmental pressure on mineral processing industries to use less water and have smaller disposal footprints.
Tailings storage facilities (TSF) failures
Overtopping TSF with insufficient remaining capacity is linked to several major TSF failures. Poor understanding of how to handle rheologically complex slurries leads to the use of dilution, which may contribute to excess water in a TSF.
Falling ore grade
Mining lower grade ores requires fine grinding which often introduces more problematic gangue. This may give rise to circumstances where it is not possible to operate a dilute slurry pipeline and the process requires more throughput with existing equipment to minimise additional capital expenditure.
These problem are often the consequence of trying to solve another operational issue. For example, external pressure to reduce water consumption and TSF footprint may create circumstances where operating with higher solids concentrations in tailings pipelines is necessary.
Understanding your pipeline can help remove complexities
There are many million tonnes of mineral suspensions produced and transported by pipe every year.
The pipelines most likely to transport complex suspensions are downstream of value processing (e.g. tailings) with only a few in-process streams, such as reactor feeds, that may be problematic.
One of the biggest challenges complex suspensions present is to the stable, trouble free operation of a pipeline.
When unstable operation becomes too common, the draw on human labour becomes significant, reduced throughput threatens upstream processing and downtime due to blockages occurs.
Few operations have an advanced understanding of the behaviour of slurries within their pipelines.
This makes dealing with complex slurries risky and undesirable. Gaining greater understanding of your pipeline will give you better results and performance over its lifespan, reducing the need to turn to dilution.
Mineral processing operations invest in installed pipeline and slurry approaches for many years. Like any long-term relationship, the operator needs to listen to and understand the underlying characteristics of its pipeline.
This can involve characterisation of the slurry rheology and the coarse particle phase. This is not just at target conditions for one ore type, but over the range of conditions that will be experienced over the life of mine, particularly in the twilight years.
This characterisation helps to put the right monitoring and practices in place to successfully pump complex slurries and remove downstream risks.
- If the range of variables contributing to pipeline behaviour can be studied, then the dominant factor/s can be identified. Often this is solids concentration but others may have synergistic interactions.
- Once isolated they can be monitored to indicate how a slurry’s behaviour may change and the operator may react accordingly. This requires an accurate model of the pipeline/slurry system.
- Once this has been established, real time monitoring of rheology and bed formation can be introduced to keep the pipeline within its operating window.
Our developments are helping operations see what they couldn’t before
We believe more operations will adopt the characterisation route in the future. This may be because it is seen as a better option, or it may be due to legislative frameworks created by social and economic needs.
Already at mining industry conferences there are calls for greater control over pipeline discharge. Our online rheology measurement and related instrumentation allow greater control over pipelines and have been discussed as part of a solution.
Our aim is to create the ‘transparent pipe’ through:
- characterisation of a rheologically complex, multi-phase suspension, enabling its response to changes in input to be predicted
- developing a sophisticated model of the pipeline/slurry system, potentially through our PipeTools software
- employing online/real time rheological measurement of slurry pipelines using our online rheometer, the iOR™, and
- using the CSIRO Bed Load Detector for in pipe measurement of flow segregation.
This represents a set of services and instrumentation to map the conditions inside a working pipeline and how it will respond to a process change.
It allows a better understanding and ‘internal view’ of the pipeline, ensuring the right actions are taken according to slurry complexity.
We can help you add value through our expertise and technology in characterisation and monitoring.
These instruments are still in the ‘development phase’. To further enhance product development and ensure they meet industry needs, they are currently being field tested and piloted in real life operations.
We are also seeking further partnerships to test emerging technology at commercial scale.
Field trials and pilots are an integral part of CSIRO’s innovation cycle and our work with the industry and manufactures to introduce technology to the market to drive change in the sector.
By partnering with us, you stand to achieve:
- an improved operating window when working with complex rheological suspensions that may have arisen as a result of water saving, differing ore grades etc.
- reduced down time, and
- a stable system requiring less supervision.
If you’re interested in reducing downstream risks and pursuing alternative options to excessive slurry dilution, or would like to explore the opportunity to test emerging technology and processes at commercial scale, we are in a uniquely positioned and interested in collaborating with you.