91�� Research - Process Mineralogy

High-Resolution Scanning Electron Microscopy and Microanalysis

mathenyk@hazenresearch.com — Tue, 23 May 2017 21:36:59 +0000

Textural properties of ores and other materials typically feature microscopic, sometimes nanoscopic, attributes. Hence, detailed materials and ore characterization, metallurgical testing, and mineral processing are prime uses for the imaging and analysis tool.

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A scanning electron microscope (SEM) produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the sample's surface topography and composition with a magnification range that encompasses that of optical microscopy and extends it to the nanoscale.

The FEI Quanta 650F SEM is equipped with a large specimen chamber, two Bruker XFlash 6-series high-speed energy dispersive x-ray spectrometers (EDS), and automated quantitative image analysis and microanalysis software.

Dust-Coated Fibers
Main image horizontal field width (HFW) is 1.58 mm; inset HFW is 109 µm.

Particulates on Filter Membrane
Membrane aperture size is 0.02 µm (20 nanometers).

Complex Particle in Zinc Rougher Concentrate (sphalerite, galena, and mica)
Main image HFW is 265 µm; inset HFW is 69.5 µm.

Resolution Standard (gold on carbon substrate)

Introduction Copy:

91��'s scanning electron microscopy (SEM) and microanalysis facility provides detailed information for characterization and processing.

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X-Ray Diffraction

hazen-research-admin — Fri, 07 Jun 2013 22:09:19 +0000

Two problems that were readily solved by x-ray diffraction analysis are discussed below. Talc is a major ingredient in certain cosmetic products. If it contains quartz or other abrasive minerals, it is unsuitable for cosmetic applications. Chemical analysis cannot differentiate between SiO₂ present as quartz and SiO₂ present as talc. X-ray diffraction analysis is an easy and reliable way to ascertain the presence and quantity of quartz. The peaks in the x-ray pattern below reveal that a minor amount of quartz (brown), along with some chlorite (green), is present in the talc (blue). Through special procedures and with the use of quartz and talc standards, the amount of quartz can be quantitatively determined to levels of less than 1%.

In other industrial mineral applications, health hazards such as respirable silica and asbestos in dust samples or products of commerce can be determined by x-ray diffraction. Crystallization chemistry is a complex science used in the production of compounds ranging from table salt and potash to borax and Epsom salts. Minute changes in the crystallization system can cause significant changes in the product that may not be detectable by chemical analysis or microscopy. One project required that we determine quickly whether the particles forming in a sodium carbonate process were hydrated, anhydrous, or a mixture of the two. The pattern below was obtained by x-ray diffraction analysis and showed the presence of both forms. This permitted us to change the process to generate the desired product.

Introduction Copy:

X-ray diffraction is a means of identifying crystalline compounds. It can be particularly useful when these compounds are very fine-grained components or mixtures.

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Electron Probe Microanalysis

hazen-research-admin — Fri, 07 Jun 2013 21:56:36 +0000

This information cannot be obtained by x-ray diffraction or optical microscopy. The electron microprobe and high-resolution SEM are essential for process mineralogy problem solving; we have used them to:

Locate submicroscopic gold in sulfides and other minerals;
Determine the disposition of heavy metals such as uranium, lead, chromium, cadmium, etc., at low levels in contaminated soils or hazardous wastes;
Analyze slags or furnace and boiler deposits to determine the cause and mechanism of detrimental scale formation;
Locate valuable or hazardous elements occurring at low levels or as substituting ions in minerals for which they are not an essential constituent.

The following example illustrates a problem that was solved with the electron microprobe. For some copper deposits, the extraction obtained by acid leaching is frequently not as good as expected. One of the primary reasons is that copper sometimes occurs associated with iron oxides in acid-insoluble form. This association is illustrated below by means of backscattered electron and x-ray images of the elements of interest.

X-Ray Map Showing
Copper Distribution in the
Same Goethite Grain

X-Ray Map Showing Variable
Concentrations of Iron in the
Same Goethite Grain

Backscattered Electron
Image Showing Heavy
Element Concentration

This image shows a goethite (FeOOH) particle in an oxide copper ore. Areas of greater brightness correspond to heavier elements; darker areas correspond to lighter elements. The structure of the grain is typical of goethite derived from the oxidation of sulfides.

The spatial correlation between copper and iron occurrence illustrates a submicroscopic, perhaps structural, association of copper with the hydrated iron oxide. This copper would not be recoverable by conventional leaching. In a standard analysis for acid-soluble copper and sulfide copper, the copper associated with hydrated iron oxides is frequently misinterpreted as sulfide copper.

Introduction Copy:

In an electron microprobe, a one-micron electron beam scans the surface of a mineral specimen to detect a specific element or to determine the elemental composition at the spot under the beam.

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Optical Microscopy

hazen-research-admin — Fri, 07 Jun 2013 21:52:41 +0000

Below are photomicrographs taken through the optical microscope during process studies.

Leitz Orthoplan Microscope

The Leitz Orthoplan microscope allows us to observe minute details such as intergrowth characteristics or inclusions as fine as 0.5 micron.

Chalcocite and Pyrite, 200x

Dark veinlets of chalcocite (Cu₂S) transecting a pyrite particle. Froth flotation of this ore yielded unacceptably low copper concentrate grades due to insufficient pyrite-chalcocite liberation and attendant pyrite carryover into the concentrate. Based on the results of microscopic studies of this ore, the mill operators learned to properly blend ore types and optimize the grind to improve profitability.

Titanomagnetite, 800x

A complex intergrowth of titanium and iron oxides. The brownish-gray continuous phase is the titanium mineral (ulvöspinel), and the light crystallites are magnetite with several black laths of gangue. No amount of grinding would make a physical separation possible, so the potential investors decided not to acquire the deposit as a titanium resource.

Solvent Emulsion, 100x

Optical microscopy detected the cause of a very stable solvent-extraction emulsion. Adding blue stain to the aqueous phase revealed that tiny bubbles of organic phase were trapped in coagulated clay particles. These studies led to methods to improve solvent recovery.

Gold Encapsulated in Pyrite, 200x

A pyrite particle (cream) that contains encapsulated gold (yellow), demonstrating why extraction by cyanidation was poor. Very fine grinding was needed to improve recovery.

Introduction Copy:

The intimate details of the structure of minerals can be observed under the high magnification of an optical microscope.

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QEMSCAN

hazen-research-admin — Thu, 06 Jun 2013 17:24:09 +0000

QEMSCAN^® uses advanced electron beam technology and combines this with high-resolution backscattered electron (BSE) imaging and two energy dispersive spectrometers (EDS). The components are then integrated using electronic control systems and the unique iExplorer software suite to provide a comprehensive tool capable of identifying most ore- and rock-forming minerals on a micro-scale in just milliseconds.

The EDS and BSE data are collected at user-defined stepping intervals across the sample (typically 1 – 30 micrometers). The analyses at each point are correlated with a library of mineral/phase identifications such that each data point is mapped as a specific mineral or phase. The output of the analysis is a false-colored image with associated quantifiable data. The iExplorer software suite not only controls the operation of the hardware but also analyzes the data generated to provide information about the chemical and mineral composition of the sample, as well as the textures, mineral abundances, mineral associations, grain sizes, liberation characteristics, surface exposures, and shapes through the analysis of digital mineral maps.

QEMSCAN has the ability to handle a wide range of sample types, usually set in epoxy, as blocks or thin sections, and even set on conductive tape. It can be used for analyzing almost anything from core samples, offcuts, and rock chips to soil, manufactured products, and dust.

Introduction Copy:

QEMSCAN technology can be used to generate a quantitative picture of sample mineralogy for use in development and in industry, allowing 91�� to aid its clients in characterizing a deposit, designing a milling process, troubleshooting refractory leach behavior, or addressing other commercial project concerns.

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The QEMSCAN facility.

A color-enhanced particle map of a sample. Each color represents a different mineral.

Process Mineralogy

hazen-research-admin — Mon, 03 Jun 2013 21:43:42 +0000

Practical processes for the efficient recovery of metals and minerals from ores are a fundamental requirement for the health of any industrial society. These processes have been developed in response to declining ore grades, the need for new materials, increased environmental awareness, and changing market requirements. Much of this progress was achieved by scientific inquiry into the nature and behavior of minerals and ores, aided by the development of new instruments and research techniques. The characterization of minerals according to their behavior during treatment is called process mineralogy, a combination of classical mineralogy and process engineering. It provides detailed knowledge of minerals to guide their separation, purification, and recovery.

Much as a detective gathers and evaluates different kinds of evidence to solve a crime, 91��’s professional staff applies its knowledge and skills in process mineralogy to answer metallurgical questions, such as the causes of unexpectedly low grades or poor yield of product from a process. We use optical microscopy, electron probe microanalysis, and x-ray diffraction analysis to uncover and evaluate the evidence. These diagnostic techniques are augmented by chemical analyses and physical separation procedures based on specific gravity, magnetic susceptibility, electrical conductivity, and flotation properties. Process mineralogy can also provide insight into reaction mechanisms and can guide research and development programs. 91�� specializes in the field of process mineralogy. We have the skilled staff and equipment necessary to develop optimum processes for new ore deposits and to improve the profitability of operating commercial facilities.

Introduction Copy:

91��’s process mineralogy capability provides clear answers for our mining clients, allowing for iterative process development and troubleshooting.

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91���� Research - Process Mineralogy

High-Resolution Scanning Electron Microscopy and Microanalysis

FEATURES

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X-Ray Diffraction

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Electron Probe Microanalysis

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Optical Microscopy

Leitz Orthoplan Microscope

Chalcocite and Pyrite, 200x

Titanomagnetite, 800x

Solvent Emulsion, 100x

Gold Encapsulated in Pyrite, 200x

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QEMSCAN

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Process Mineralogy

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91�� Research - Process Mineralogy

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