Process Mineralogy Today

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Category: ore characterisation


Direct Measurement of Submicroscopic Gold: Methods and Applications

The ability to recover gold effectively is largely dependent on the nature/carriers of gold and the mineral processing techniques utilized. Gold ores are often classified into two major ore types: free-milling and refractory. Note that many gold deposits contain proportions of both ore types. Free-milling ores refers to those where the majority of gold is liberated through crushing/milling and recoverable by cyanide leaching. Refractory ores are defined as those which yield low gold recoveries, requiring complex and costly chemical pre-treatment prior to cyanidation. Refractoriness is directly controlled by ore mineralogy, generally resulting from the presence of either naturally occurring ‘preg-robbing’ carbonaceous minerals or submicroscopic gold.

 

Figure courtesy of David Holder: SIMS element distribution maps of a colloform pyrite grain showing Au and As in solid solution. Note the pyrite has been stained using KMnO, which can indicate compositional variations within and between pyrite morphologies.

Figure courtesy of David Holder: SIMS element distribution maps of a colloform pyrite grain showing Au and As in solid solution. Note the pyrite has been stained using KMnO, which can indicate compositional variations within and between pyrite morphologies.

 

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Mineralogy: The missing “M” in AMD prediction?

The previous blog of 5th December 2013 Flotation Mineralogy: Valid and Valuable examined the role of mineralogy in flotation.  Indeed, many of these same ideas, challenges and solutions are experienced when dealing with environmental characterisation of ore deposits.  However, the challenge extends further as often environmental managers and superintendents are left with smaller budgets, and fewer staff to undertake such predictive characterisation works.  The key to predicting environmental issues such as formation of acid mine/rock drainage (AMD/ARD) lies in understanding the mineralogy.  If there was just one piece of information or test that one could perform in this field, it would be to obtain mineralogical data, and yet, the current trend is to collect as much geochemical data (i.e., net acid generation and net acid producing potential values) as possible.  Furthermore, when such geochemical data is collected, it is rarely correlated back to the original mineralogy, or indeed to the lithology from which the sample originated. Therefore, how can an ARD block model be produced based on a handful of numbers which do not have any mineralogical or lithological context?

 

Absence of Mineralogy in ARD

 

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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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Rock and Mineral Texture: Controls on Processing

The texture of an ore will define: the grain size distribution(s) and P80 target grind size; the grindability of the ore; the degree of liberation of the target mineral(s); the phase specific free surface area of the target mineral(s); the amount of fines; and the number of coarse composite particles.  These factors will play a major influence on the process flowsheet developed for an ore, from mining strategy through to blending, processing, target grade and recovery, and tailings management.  Understanding these will aid the processing engineer when trying to unlock the maximum value from the rocks, with the minimum of effort, cost and environmental impact.

 

Texture, in the context of geometallurgy, simply refers to the relationship between the minerals of which a rock is composed (Wikipedia definition).  It includes the size, shape, distribution and association of the minerals in the rock.  All textures, including crystallinity, grain boundary relations, grain orientations, fractures, veinlets etc have a bearing on processing ores, but the sizes of the mineral grains, and the bonding between the grains are the main characteristics that influence ore breakage and mineral liberation (Petruk, 2000).  Understanding the geology and history of an ore will help unravel the complex nature of the textures that may be encountered during processing.

 

Example of textural changes due to oxidation and deformation (Butcher 2010).

Example of textural changes due to oxidation and deformation (Butcher 2010).

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What is Geometallurgy?

With today’s increasingly complex ore bodies, it is no longer sufficient to use grade and tonnes alone to manage risk and optimise an operation.  In response to this, Geometallurgy is being increasingly employed; seeking allow a block model of an ore deposit to be developed based on key metallurgical parameters and the predicted response of the rock during mining, processing and subsequent environmental management.  To help explain how and where geometallurgy can be used, MinAssist has compiled a short white paper introducing the subject: What is Geometallurgy?

 

What is Geometallurgy?

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