Process Mineralogy Today

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Category: Process Mineralogy


Mineralogical Modelling: Rule of Thumb vs Probability Methods (Part 1)

This is the first of two blog posts on mineralogical modelling where we highlight some of the terminology used and misconceptions made.  Part 2 will further develop the theme by comparing the value of using rule-of-thumb and probability -based particle modelling principals.

 

Liberation

Many users of mineralogical analysis focus only on elementary concepts such as grain size.  Yet there are many levels of depth available to analyse liberation data.  In this section we focus on using liberation data in a simulation model.  Critical to understanding mineralogy is the concept of ‘liberation’.  A particle is considered liberated if it consists of only one mineral.  Conversely a particle is considered ‘barren’ if it contains no valuable mineral.  There are a few issues with ‘liberation’ defined in this way.  For a start is it really important if a particle is say 99% valuable mineral rather than 100% mineral?  Because the purest definition (particles consisting of only valuable mineral) is of limited value, the word ‘liberation’ has become generalised, and to some extent over-used.  Yet when discussing ‘liberation’ generally we are simply referring to how distinct the valuable mineral is from the associated gangue.

Various definitions of particle types (Liberated, Binary, MultiMineral)

Fig 1. Various definitions of particle types (Liberated, Binary, MultiMineral)

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Flotation mineralogy: Valid and Valuable?

Following on to the conclusion of another successful MEI conference, Flotation ’13, some interesting comments and feedback have emerged that highlight the continuing interest in and need for mineralogical data in understanding flotation response – and some of the challenges that emerge from trying to obtain that.

 

Barry Wills’ blog of 18th November 2013 refers back to the prediction made by Professor Dee Bradshaw at Flotation ’11 that chemistry would dominate discussions; and how she has seen that shift to a point where mineralogy dominates at Flotation ’13.  This point is further underlined by Dr Chris Greet (30th November 2013), who also makes the essential connection between the realisation of the value of mineralogy, and the hurdles encountered in generating and utilising valid mineralogical data correctly.  Chris sights three commonly encountered hurdles:

 

1) Turn-around time
2) Expense
3) Validity

 

Flotation_Valid and valuable Time to Result AND Validity of Result – does it have to be a trade-off?

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Reinventing the Acid Rock Drainage testing wheel


The Challenge

Acid rock drainage (ARD) testing as practised by the mining industry is in need for reinvention. With the global financial liability associated with ARD estimated at US$100 billion (Tremblay and Hogan, 2001), now is the time to reduce costs, increase knowledge, prevent environmental impacts and reshape environmental ARD testing.  How can Best Practice ARD sampling as recommended by the Australian Government (Price, 2009) be achieved and ARD accurately predicted when using such costly tests and outdated protocols? The scale of the problem increases further when considering that 20-25 Gt of waste rock is produced globally by the mining industry (Lottermoser, 2010). Lower grade deposits are being mined (Mudd, 2007), and whilst much research is conducted as to how to process and extract the value, how should the additional waste rock be most appropriately managed?

 

ARD at Haulage Creek, Tasmania

ARD at Haulage Creek, Mt Lyell Mine, Tasmania

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Operational Health Check Suite

Over the last few months, MinAssist has progressively launched a series of “Operational Health Checks” that have been developed as suite of off-the-shelf process mineralogy studies targeted at giving rapid performance gains for a minimum of fuss.  Each of these fit in to a Suite of programs that are focused on bringing cost savings, recovery improvements and general risk reduction through improved understanding of ore types.

 

Key points within the processing circuit have been identified, and a mineralogical testwork program developed to:

     – target the typical challenges encountered

     – indicate overall circuit efficiency

     – identify possible areas for improvement

 

The sample points have been pre-determined, the analytical testwork process developed, and the critical information to examine identified.  This removes much of the hassle for a busy plant metallurgist looking to undertake a process mineralogical study.  It also reduces the overall time-to-result: providing a concise, metallurgically focussed report of the mineralogy in a meaningful time frame.

 

HC Benefits

The Health Check suite is ideal to for:

     – the busy process metallurgist looking to get the best from a circuit

     – taking a quick look at the health of a circuit to make sure things are running as they should be

     – as a prelude to a more in-depth study based on the findings of the health check

 

A Health Check can be run as a one-off study, or on a routine basis to build up a complete picture over time.

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When to invest in process mineralogy

Over the past few months we have explored the value of investing in Process Mineralogy in some detail.  We have established that best practice dictates that every site should include some Process Mineralogy in their continuous improvement plans but when is the optimum time to start?  The answer is right now.  With budgets stretched due to lower commodity prices this may seem a difficult proposition but in reality it is in difficult times that we need our plants to operate at their optimum efficiency and even a simple Process Mineralogy program can genuinely help an operation run more smoothly, and lead to larger savings, for a relatively small investment.

 

Sadly the value of process mineralogy is often poorly articulated or understood, not least because it can be difficult to directly link to the bottom line.  Its not easy to quantify: “we do process mineralogy routinely, and it saves us $xxx per year” (the blog on 13th August 2013 does highlight some cases where companies have attempted to do this).  It is therefore inevitable that when the financial decision makers are casting an eye around for areas to trim, particularly with a limited budget as so often is the case, process mineralogy can seem an easy target to drop (and therefore be even harder to start!).  In today’s market place, modern mining companies work very hard to lower overhead costs and be careful with expenditure in order to extract ore economically – however the old adage ‘you have to spend money to make money’ does hold true in this instance.

Open Cut Hauling

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What is the Return on Investment of using Process Mineralogy?

In this week’s blog, we seek to respond to a common question that we hear at MinAssist: what is the return I get on investing in process mineralogy?  The short answer is it is not always easy to quantify in reality as there are often many factors at play at any given time, but an effective benchmarking study is of course always a good place to start to give you some indication of the ‘before’ picture – against which to measure changes.  The same benchmarking study can be used to also provide a good indication of where to go next with regards testwork, modelling and flowsheet design.

 

Here, by way of example, we have highlighted 3 recently published case studies that highlight how process mineralogy has been successfully integrated with geometallurgy and metallurgical testwork to provide tangible benefits.  One is from Xstrata based on the Nickel Rim South deposit, one from Rio Tinto’s Kennecott operation, and the third from the Anglo Platinum group’s operating concentrators.

 

ROI Case Studies

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Using mineralogical understanding as a building block for plant process improvement

Developers and operators of mining and mineral processing operations face constant challenges to become more efficient, whilst at the same time being faced with increasingly complex ore bodies.  This complexity is characterised by multiple mineralisation events and complex formation histories, leading to variation in ore mineralogy.  This inconsistency can often be explained by changes in the ore texture, or the relationship between minerals present in the ore.  Understanding the ore texture can be a very useful tool in developing a process flowsheet or optimising an existing circuit.  For complex ore bodies with multiple ore textures this understanding is not only useful, but is essential to manage variability, reduce risk and optimise the operation.

Ore Feed Recovery

MinAssist has complied a short white paper discussing some of the mineralogical influences on feed ore quality and subsequent recovery: The Influence of Rock Texture on Processing

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Value losses due to poor liberation and classification

Ball MillThe crushing and grinding circuit in any process flowsheet is a major contributor to cost and should be a major focus of any continuous process improvement program. While the direct costs (i.e. power and maintenance) within the crushing and grinding circuits are generally the primary consideration for optimisation, the indirect costs associated with insufficient liberation or over grinding can have as profound an impact on downstream processes. Care should be taken when evaluating comminution circuit optimisation that efforts to increase throughput or reduce energy requirements don’t have a negative impact on the liberation characteristics of the material and result in reduced downstream recovery.

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Liberation and Free Surface Area in the Float Feed

The importance of the liberation of target minerals in the feed to a flotation circuit is well recognised and understood by process metallurgists.  This blog seeks to introduce some of the concepts around:

 

– how liberation is defined

  • – what the important parameters to understand are

– how liberation is defined by process mineralogists

 

Liberation measurements estimate the volumetric grade distribution of a mineral as a measure of the quality in a processing stream (Spencer and Sutherland, 2000).  Put simply, it is based on the area % of the mineral grain in the particle:  which brings us to the first key question – what is the difference between a “grain” and a “particle”?

 

The second critical question is to ask whether area % alone is enough to help predict how a particle will behave in a flotation cell – what about free surface area?  A grain may be defined as 90% liberated, but have no free surface area… so will this recover more quickly or more slowly to the flotation concentrate than say a grain that is 60% liberated but has a high free surface area?

 

What is the difference between a “Grain” and a “Particle”?

 

Typically, a “grain” is classed as a single mineral, whilst a “particle” is made up of one or more mineral grains.  The figure below provides an example of a single “particle” that contains four mineral “grains”.

 

Example of a “particle” containing five mineral “grains” (4 black and 1 white) Example of a “particle” containing five mineral “grains” (4 black and 1 white)

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Whats new in Process Mineralogy Technology: The QEMSCAN EXpress

QEMSCAN EXpressAt Process Mineralogy Today we like to keep abreast of what is happening in the world of Process Mineralogy.  A key tool in our field that has driven the development of Process Mineralogy over the last 3 decades are automated mineralogy systems and it is excellent to see that a wider range of solutions are being produced that move away from the research oriented full SEM based systems to more useable options.

 

One of the key industry players, FEI Natural Resources, has announced the release of the latest in their series of automated mineralogy tools – the bench-top QEMSCAN EXpress.  This follows a big year of releases from FEI, with the MLA EXpress a few months ago, and the release of the rugged MineSite systems.  FEI now offers a trilogy of platforms for the QEMSCAN and MLA, from the high-end laboratory system, to the affordable bench-top system, to the rugged mobile platform for remote locations.  This is great news for the industry as it offers a wider range of fit for purpose systems that can service anything from a high-end research laboratory to a mine-site laboratory. ...