X-Ray Diffraction (XRD) for Mineral Processing

Interview conducted by Alessandro PiroliniJul 21 2015

 

How is X-ray Diffraction (XRD) currently used in mineral processing?

XRD is used for the identification of the mineralogy of samples from various parts of an ore body or mineral process stream. XRD can identify which minerals are present and in what amount.

This information is then used to inform geologists responsible for feeding the mill and metallurgists responsible for optimisation of beneficiation. Differing mineral mixes and content will significantly impact the methods used to process specific ore.

Why is XRD chosen above other analytical techniques?

XRD provides detailed information about the crystalline structure of minerals. It is an established technique to identify minerals in a laboratory environment. Olympus XRD has made this possible in-the-field.

Olympus analysis requires less skills and qualification compared with other methods. Sample preparation is simple and fast. By comparing samples to a database of known minerals, data interpretation is relatively straight-forward.

With Olympus XRD, sample preparation is relatively simple and is achieved in very little time. The X-ray based technologies are mature technologies which have been around for decades. They are well understood resulting in relative ease of availability.

How does the field portable TERRA from Olympus aid in the rapid identification of minerals?

The Terra is a portable, relatively lightweight XRD system that requires very quick and easy sample preparation. Once the sample is crushed and sieved to a fine powder (<150um) in the field using a simple mortar, pestle and sieves, it is then fed into the XRD for analysis.

Test times are in the order of minutes or tens of minutes, producing a diffraction pattern that can be run through an XRD database and software package to report the results very quickly. This process greatly accelerates the traditional XRD analysis process which routinely involves despatch to a laboratory and significantly more complicated sample preparation procedures.

What makes TERRA unique?

So many things! Portablility and ruggedness – no other XRD is more mobile or tougher. Simplified sample preparation – very basic crushing and sieving is needed using small field tools supplied with the product.

Ease of use – any field technician can prep and load the sample in minutes, and operate the integrated web browser user interface on a phone or laptop to initiate the collection of a diffraction pattern from a sample.

Use of a low x-ray power source ensures safe use, simplifies radiation licensing, eliminates water cooling and enables us to use small lithium ion batteries to operate the unit meaning no mains power is needed. These features ensure an extremely low cost of ownership when compared with other XRD’s.

The Terra’s patented vibrating sample cell which was designed as part of the NASA Mars Curiosity Rover project is perhaps its most unique feature. This allows the Terra to have no movable parts, eliminating the requirement for a large mechanically operated goniometer.

The sample is rotated using sound waves allowing angles between 5 and 55 degrees to be measured with a an x-ray tube and CCD Detector that remain in a fixed position. It is this aspect that contributes to its ruggedness and portability. Rotating the sample also eliminates preferred orientation issues associated with traditional laboratory XRD measurements.

How does TERRA simplify sample collection for XRD?

Sample preparation for traditional XRD systems often requires a very low grind (<10 um) and can involve a very fastidious 20-30 minute procedure to create a very flat surface from which the XRD goniometer must read. The Terra’s requirement for only <150 um grind size reduces sample prep to less than 5 minutes using simple and small tools.

Could you talk a little bit about the involvement of NASA in the TERRA product?

The technology behind the TERRA and BTX-II was developed with NASA for the Mars Curiosity Rover. The Terra evolved out of the NASA’s Mars Science Laboratory

The Curiosity Mars Rover mission contains a remote laboratory which is capable of using XRD to analyze the chemical and mineral composition of the Martian soil samples. The TERRA instrument has its roots from two decades of work developing a compact, portable X-ray diffraction instrument (XRD) suitable for use in space.

The powder vibration system allows the XRD device to be far more compact, sensitive and accurate when used with samples of varying grain sizes. This was a critical requirement for the success of the mission, because Curiosity’s drilling mechanism would not be able to generate consistently sized powder.

What are the benefits of using TERRA over other available XRD products on the market?

Its all about speed, portability and low cost of ownership. All the unique features I mentioned earlier allows those people benefiting from very rapid mineralogical information to obtain it quickly and optimise their operations.

In a way that no competing XRDs can. Mudlogging companies in the oil and gas industry have been the early adopters. Particularly in shale gas segment to guide drilling and ensure they remain in the correct geological sequence for horizontal drilling.

In a mineral processing application, something as simple as quantifying quartz content has proved useful as a guide for ore hardness and inform optimum grind time which ensures appropriate size fractionation for optimal beneficiation.

When copper oxide ore and copper sulfide ore are both present in an ore body, how can XRD help to differentiate between the two?

This allows detailed and advanced notice of movement of oxides to the acid leach circuit and sulphide to the flotation circuit. As well, quantification of acid absorbing mineral such as CaCO₃ will influence the volumes of acid consumed and directly affect costs.

Mineral quantification is important to optimize conditions and reduce costs. Certain minerals can also float when concentrating Cu sulphide ore. This can reduce the grade significantly. Knowledge of these gangue minerals allows the metallurgy manager to add reagents to help separate them out from copper minerals.

With advanced knowledge of these using Olympus XRDs, management can be proactive rather than reactive , reduce reagent costs and streamline the process

How has the TERRA been used in mines in Nevada to assess the permeability and absorption of leach pad material?

The TERRA was used to measure leach pad samples and categorize them to define their likely leaching potential. This was based on the samples relative clay and quartz contents. A combination of high swelling clay and low quartz content in leach pad material results in low permeability and high absorption of leach liquor.

Samples were easily and quickly grouped as Good, Fair, and Bad based on their suitability as leach pad material. This aids leach pad material selection to optimize leach liquor percolation to achieve better Au recovery.

When in the field, is the TERRA easy to operate, and does it require extensive training?

This is what makes the Terra unique. Obtaining a diffraction pattern with this instrument is very simple. Training to achieve this doesn’t take more than a few hours and is focused on the simple sample prep side, sample loading and web browser user interface.

This can be run off any smart web enabled device like an iPhone or iPAD. Having said this, interpretation of the diffraction pattern and quantification of the mineral phases does require specialist training and is the more demanding part of applying this technology to any operation.

For existing XRD users though, it’s very straight forward. It’s done using established mineral databases combined with mineral match software. The analyser produces files that can be run through most established XRD software programs so is completely compatible in this aspect. Training on the interpretation of diffraction patterns in comparison with known databases is necessary and takes a few days.

Do you envisage there being any major advances in XRD in the near future?

The Terra represents a major leap in the advancement of XRD technology. Developing an XRD with no moving parts and putting it Mars to send mineralogical information back to Earth is an impressive accomplishment.

So I think it may be a few years before we see something major. We’ve simplified the hardware, I think the next focus should be simplification of software. Getting mineral quantification results at the press of a button with little need for human interaction with the software is the ideal scenario. That should be the next focus for more widespread use of this technology globally.

About Todd Houlahan

Todd graduated from the University of Newcastle, Australia in 1993 with a Bachelor of Applied Science majoring in soils and hydrology.

After 7 years as a contaminated land consultant remediating heavy metal contaminated sites in the UK and Australia, he first used a Handheld X-Ray fluorescence (XRF) analyser in 2000, to guide excavations of a lead contaminated site in Sydney.

Since that fateful day, Todd has been at the heart of the Portable XRF revolution in the mineral exploration and mining industry over the last 15 years.

Todd was one of a select few who helped secure the scientific credibility of portable XRF technology for minerals applications through industry trials, scientific evaluations and published papers via his early work in Australia through 2000-2004.

In total he worked with Niton analysers for 8 years in various positions based in Australia, Germany and the UK, finally as Global Business Development Manager (Exploration and Mining).

For the last 7 years he has led the International Mining Group at Olympus (formerly InnovX Systems) helping explorers, miners and their shareholders achieve cost efficiencies by using the best portable XRF and XRD technology on the market today. Todd is committed to long term collaborative partnerships and providing unrivalled, geologically focused global support.