Process Mineralogy for Metals

8/20/2019 Process Mineralogy for Metals

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Professional Development

Process Mineralogyfor Metals


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Part 1 - Process Mineralogy and

TechniquesIntroduction

The Demand for Minerals

Steps in an engineering process. Yellow arrows represent a transformational process.


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Raw materials for an engineering process. Arrows indicate transformation processes.

Raw materials must be seen from the perspective of local availability and market needs.

Mining engineers must be prepared to see beyond the mining viewpoint and apply mineral

process techniques to transform any kind of raw materials (including garbage) into saleable products.

Mining engineers must be familiar with the uses of raw materials in different industrialsectors to be able to adapt, modify and create new uses.

A holistic vision will also help to address concerns about the environment.

"Ore is a mineral from which it is possible to produce metal by using technologicalmethods that already exist or can reasonably be developed. By convention there is no "clayore" or "gypsum ore". Minerals become ores when technological developments allow themto be mined and treated successfully." ones (!"#$)

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Raw material can be evaluated%

• by source, either primary sources or recycling

• by the nature of the source, either renewable or non&renewable

• by the final use of the material, either structural (pieces, ob'ects, ...) or functional(electronic, magnetic, optical, biomaterials, etc.)

echnology is used to transform raw material (minerals, metals, ceramics, plastics,composites, wood, leather, cotton, garbage, etc.) to fulfill a market need.


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Raw material will be transformed based on market needs and available technology.

Process Mineralogy Definition

"Process mineralogy which combines mineralogy and petrography with processdevelopment engineering generates data for commercial design of the ore processing

plant."

chapiro et al. (!"#!)

"Many metallurgists appreciate the importance of applied mineralogy to a muchlarger extent than some geologists, who regard the study of minerals as a subsidiary

subject necessary only for a degree of geology. nfortunately, many promising prospects have been missed because the basic training of the person who discoveredthem did not include a sound !nowledge of mineralogy."

*iebenberg (!"$+)

rocess mineralogy combines mineralogical techniques with mineral process unit operationsto identify minerals, their associations and characteristics in order to%

• design processing flowsheets

• specify raw materials and marketable products

• troubleshoot plants, predict reagent consumption

• indicate new uses of minerals

• establish feasibility concepts at the early stages of geological e-ploration

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Importance of Process Mineralogy

" echnology is whatever is needed to transform resources into products."

ven if geology and mineralogy are similar, mineral deposits are different. echnology usedin one deposit must be adapted or modified to be used in other similar deposits.

/e mine rocks but we concentrate minerals (with the e-ception of dimension rocks andmaterials for civil construction && this actually represents more than 0+1 of the worldwidemined products).

/e sell and use minerals or mi-ture of minerals. hey have characteristics and specificationsthat make them saleable. 2f these specifications are not met, the mineral product is worthless.

2nformation in geological reports is not quite adequate for the ne-t step of a mining pro'ect,evaluating%

• which valuable minerals can be concentrated

• which contaminants will be together (penalties)

• which technology is available and suitable for that ore

• what impact it could have on the environment

• which market the product is suitable for

• how much will be spent to produce saleable mineral products

rocess mineralogy will not provide all the answers but will give good hints at the earlystages of a geological e-ploration pro'ect.

Process Mineralogy Usefulness

rocess mineralogy has been defined as ... 3Application of a series of tools and techniques toidentify and adapt the quality of the raw material to the market needs.3 hese tools andtechniques can%

. 4haracteri5e raw material quality

. redict quality of concentrates and final products

. 6esign preliminary process flowsheets

. rovide quality control

. Add value to orebody information

. nhance decision making

. redict environmental impacts

. 7ind new applications and new products

. 2ndicate new markets

. 2nvestigate recycling options


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. 2dentify the ore&gangue associations

. 6etermine liberation of ore&minerals

. 8uantify minerals

. 2ndicate (possible) losses

. 2ndicate by&products

. 2dentify available raw materials (and wastes)

. Assist technology development

. redict raw material processing performance

. redict reagent consumption

. rovide hints about hydro and pyrometallurgical reactions

rocess Mineralogy is also known as%

. echnological 4haracteri5ation

. Applied Mineralogy

. 2ndustrial Mineralogy

. Mineralurgie

Techniques, Analysis and Classification

Main Techniques Applied to Process Mineralogy

he main techniques applied to process mineralogy depend on whether we analy5e%

• ores (small amount of the metallic mineral of interest% with e-ception of 7e and Mn,ore&minerals occur in ore deposits in small quantities, usually 9 :+1; e.g. metal grades ofsome ore deposits% +.


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• Mineral factors (characteristics and properties of minerals determine thetechnological routes, mineral liberation and predict quality of concentrates)

he bottom line is to predict and e-plain performance when a mineral is sub'ected to a physical or chemical process.

he main techniques applied to process mineralogy are%

• optical microscopy (transmitted and reflected light)

• instrumental analysis (BR6, M, 6 A, C, 2R, BR7, AA , etc ...)

• mass balance (stoichiometric balance)

• mineral processing unit operations (particle analysis, magnetic separation, flotation,gravity concentration, cyanidation, etc...)

• selective chemical e-traction (diagnostic leaching for gold, sequential e-traction ofhydrous ferric o-ides, etc.)

• laboratory techniques to study mineral properties related to industrial performance(filtration, brightness, oil adsorption, viscosity, etc.)


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Ta le " # Most Used Analytical Methods in Process MineralogyTo Identify and $ometimes %uantify Minerals

Technique Principle Purposeolari5ed Dptical

Microscopyransmitted or reflected polari5ed light

interacts with sample (thin or polishedsection) revealing optical properties ofminerals.

2dentification of minerals and specificfeatures such as alteration, grain si5e,associations, etc. Modal analysis.

B&ray 6iffraction(BR6)

B&ray radiation strikes on a pulveri5edsample and diffraction occurs on allcrystallographic planes of the minerals.

2dentification of crystalline minerals.Modal analysis.

canning lectronMicroscopy

( M)

lectron beams strike on a conductivesample. econdary and back&scattered

electrons generate image. 7luorescent -&rays can be discriminated by energy( 6 ) or wavelengths (/6 ).

2dentification of minerals and specificfeatures. 8uantitative microanalysis of

elements in regions (! Em) of minerals.Modal analysis.

ransmissionlectron

Microscopy( M)

lectron beams pass through a conductivethin sample (9 +.! Em) and provide imageon a fluorescent screen. lectronsscattered by atoms of the sample and -&rays can be analy5ed.

2dentification of clays and clayminerals.8uantitative microanalysis of elements inmineral regions. Resolution of ! Em.

hermal Analysis( ermogravimetry

&

C,6ifferentialhermal Analysis &

6 A)

2n C, mass changes of a minerals aremonitored as a function of temperature.2n 6 A, the difference in temperature

between the sample and a reference isrecorded.

4omplementary tools for quantitativedetermination of minerals (mostly clays).Fseful for amorphous minerals.

2nfraredpectroscopy

(2R )

Absorption of 2R radiation by minerals asa function of the atomic weights, lengths,strengths and interatomic bonds in thestructure of minerals.

8ualitative and quantitative analysis ofminerals (mainly amorphous ones andclays).

B&rayhotoelectron

pectroscopy(B )and Auger pectroscopy

*ow energy -&rays strike on the surface(: Em) of the sample and e'ect electrons

from the inner shells. hese electrons areanaly5ed. he atom rela-ation processcan e'ect another electron (Auger) fromouter shells.

8ualitative and quantitative analysis ofelements (all e-cept G and Ge) at the

mineral surface (chemical bonding,o-idation state, adsorbed species, etc.)


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Ta le & # Most Used Analytical Methods in Process Mineralogy# 'hemical Analysis

Technique Principle Purpose

B&ray7luorescencepectroscopy

(BR7)

B&ray radiation strikes on a pulveri5ed or fused sampleand all elements emit characteristic -&rays that can bediscriminated by their energies ( 6 ) or wavelengths(/6 ).

8ualitative andquantitative analysis ofelements with atomicnumber between 0 and":

Atomic Absorptionpectroscopy

(AA )

ample is digested with acids and elements in solution areconverted into atomic vapor by high temperature flame(!$++ H4). he atoms selectively absorb light from lampsemitting specific wavelengths that are characteristic of theelements of interest. he amount of light absorbed is

proportional to element concentration in the solution.

equential analysis ofelements (mostlycations). 7or goldanalysis, a fusion

procedure I aciddigestion (fire assay)

precedes the AAanalysis.

2nductively4oupled lasma&Atomic mission

pectroscopy(24 &A )

ample is digested with acids and solution is sprayed intoa Argon plasma torch (!+,+++ H4). he atoms are e-citedand decay emitting radiations that are separated by a high&resolution monochromator.

imultaneous analysis of elements (mostlycations).

Fltra&violet &visible

pectroscopy

Atoms and molecules in solution absorb FJ and visiblelight (:++ to !!++ Em). he wavelength of the absorbedradiation is a characteristic of the molecule.

he absorption ofcharacteristicwavelengths allowsquantifying theconcentration of thatspecific molecule in asolution.

elective 4hemical-traction

Reagents selectively dissolve minerals revealing whichmetals are associated with them. Fsually sequentiale-tractions are applied to remove metals%

!) weakly adsorbed on clays;:) strongly adsorbed on hydrous ferric and manganeseo-ides;?) associated with organic matter;


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Atomic $pectroscopy

An element to be analy5ed is convertedinto a neutral atomic or ionic vapor.

lectromagnetic radiation absorbed oremitted by electrons during orbitaltransitions is the analytical signal ofinterest.

Atomic Absorption pectrometry andAtomic mission pectroscopy (e.g. 24 &A ) are e-amples of atomic spectroscopytechniques.

Mineralogical Analysis

%ualitative and %uantitative Analysis

here are appro-imately ?@++ known minerals. his number is slowly increasing as newminerals are discovered by modern analytical methods and new mineralogical environments.

Dnly :@+ to ?++ minerals form common commercial products or occur in significant proportions in ores or mineral deposits. Gowever it is important to know the gangue minerals,

as they can contaminate concentrates or final products as well as cause impact to theenvironment.

here are many diagnostic properties usually applied to hand specimens% crystal habits,cleavage, fracture, hardness, specific gravity, color, streak, luster, etc. ome of these

properties bring more certainty to mineral identification than others.

2n process mineralogy, we need to identify and quantify all minerals present in arepresentative sample.

he main identification techniques are%

• optical microscopy


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• electron microscopy

• -&ray diffraction

Au-iliary methods are also applicable to help identification or to enhance mineralconcentration in the sample%

• qualitative and quantitative chemical analysis

• sequential or selective chemical e-traction

• mineral separation (based on certain properties)

he main quantitative analysis techniques (also called modal analysis) are%

• mineral separation (each mineral species is weighed separately)

• microscopic techniques (point counting and image analysis)

• quantitative -&ray diffraction

• stoichiometric balance

Mineral 'lassification

2n classical mineralogy, chemical composition and internal structure have been the basis forthe classification of minerals. 6anaLs 4lassification, shown in able ! below, is widelyaccepted.

2n process mineralogy, minerals are classified by their uses or functions, as shown in able : below.

Ta le ( # Minerals 'lassified y Use ) *unctions

'lasses Use ) *unction E+amplesore minerals metals e-traction 4u7e :

industrial minerals provide properties for materials,have specific industrial use

kaolin for paper, garnet forabrasives

energy minerals power generation coal

gemstones 'ewelry diamond

gangue minerals headache for miners clayminerals


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Ta le , # Mineral 'lassification

'lasses E+amples

>ative lements Cold, Au

ulfides yrite, 7e :

ulfosalts nargite, 4u ?As <

D-ides Gydro-ides Gematite, 7e : D?; Coethite, 7eD(DG)

Galides 7luorite, 4a7 :

4arbonates 4alcite, 4a4D ?

>itrates >itratite, >a>D ?

Korates Kora-, >a : K


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minerals. Rutile ( iD &) in 2ndia is magnetic. =ircon in >igeria is more magnetic thanilmenite.

'rystal structure . Reactivity of solids to leaching solutions varies from one polymorph toanother. 4alcite is more reactive than aragonite. 6efects in the structure associated with shape

and type of crystal structure bring special properties for some minerals. >atural Q&MnD &,3nsutite3, is adequate for dry batteries and &MnD &, 3pyrolusite3 is not.

Alteration products have a strong effect on all beneficiation processes as well as increasingreagent consumption in metallurgical processes. 4lay minerals mi-ed with hydrous ferrico-ides form a thin layer on gold particles that prevents flotation. he presence of hydrousferric o-ides in o-idi5ed copper ores is one of the main sulfuric acid consumers.

Element Distri ution in $creened *raction

6epending on lithology, minerals tend to have different si5e distribution. 7or e-ample, in placer deposits, ore&minerals tend to have a uniform grain si5e distribution. 2n other ores,valuable minerals do not show concentration in a specific si5e, i.e. they are distributed allover the screened fractions.

A high concentration of the valuable mineral in coarse fractions does not give any indicationabout its liberation. 2n other words, if chemical analysis shows that there is a concentration of a certain element (consequently mineral) in a coarse fraction, this does not mean that thevaluable mineral is coarse and free.

Kut when the particle distribution shows the presence of a valuable element (mineral) in finefractions, this means that the mineral is fine, but it is >D necessarily liberated.

Ta le " # $i!e and tungsten /0 distri ution of a pegmatite sample

otal of highlighted rows & ##1 /,

$ieve si!emesh0

/eight retained10

/10

D/10

I0


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&


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7igure ?. 4orrelation between 4u and Au is a good indication that bulk concentrate of copperminerals can take gold together.

7or e-ample, Au distribution in 7igure < below shows some correlation with Ag distribution.4u in 7igure @ below shows poor correlation with due to the presence of different copperminerals, such as tennantite (4u,7e) "&As ( ", and mooihoekite 4u 57e 5 "4 as well as othernon&copper sulfides such as galena b and pyrite 7e &.

*igure (

Au distribution shows some correlation with Ag distribution.

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*igure 6

4u shows poor correlation with due to the presence of different copper minerals.


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Part 2 - ptical Microscopy

Analysis !y Transmitted "ight

7isi le 8ight

Jisible or white light is an electromagnetic wave with a series of wavelengths between ?"+(purple) and $$+ Em (red), shown in 7igure ! below. Monochromatic light consists of a single

wavelength within this range.he electromagnetic fields associated with light waves are directed at right angles to the

direction of travel of the beam. 2f white or monochromatic light passes through a special polari5ing filter, then the light becomes plane&polari5ed, i.e. the electromagnetic field isconstrained to vibrate in one direction only and this direction is still at right angles to thedirection of travel of the beam.

*igure "

Jisible or white light is an electromagnetic wave.


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Polari!ing 9ptical Microscope transmitted light0

A polari5ing optical microscope (transmitted light), shown in 7igure : below, contains%

• a lens, which is usually !+B

• polari5ing film which can be either slid or flipped into the light path. he vibrationdirection is set at "+H to the lower polari5er.

• a primary magnification system. he lenses permit changes in magnification; usually:.@B or ?.:B, !+B, and


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Refraction

2n isotropic substances, such as glass, liquids or crystals that belong to the isometric crystalsystem, light moves in all directions with equal velocity and hence each isotropic substancehas a single refractive inde-, shown in 7igure ? below.

2n anisotropic substances, light is broken into two polari5ed rays vibrating in perpendicular planes, shown in 7igure


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2n he-agonal and tetragonal (anisotropic) crystals there is only one direction in whichordinary light moves in the same direction as e-traordinary light. his is called the optic a-is,which coincides with the c a-is (see 7igures 0 and $ below). hese crystals are calledunia-ial. Drthorhombic , monoclinic and triclinic crystals have two optical a-es andthey are optically classified as bia-ial.

Unia+ial 'rystals

Fnia-ial crystals, shown in 7igure @ right, are divided into two optical groups% positive andnegative.

• ositive% when the D ray has greater velocity than the ray.

•

>egative% when the ray has greater velocity than the D ray.

*igure 6. Unia+ial crystals . A. he unia-ial indicatri- is a geometrical figure that is helpfulin visuali5ing the relation of the refractive indices and their vibration directions. K. 4rosssections of unia-ial indicatri-. (7rom% /ahlstrom (!"@!))

here are many refractive indices in unia-ial crystals, depending on direction. Fsually 'ustthe two principal indices are represented and the difference between them is called

birefringence . his is better observed with crossed polars.

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ome anisotropic minerals absorb more light (some wavelengths) in one vibration directionthan in the other. his phenomenon is called pleochroism . -amples are tourmaline ,

biotite , and hypersthene .
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Process Mineralogy for Metals

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