Methodology

Sampling and analytical techniques for solid and liquid

mine waste

Sample Records• All samples must have a systematic number and date

which must be recorded in your notebook at the time of sampling. A sample without a number, date and locality is useless

• Decide on a simple systematic numbering scheme at the start of a project and stick to the same system. The numbers should continue through field sampling and lab analysis to tabulated results.

• Solid samples should have number, locality, depth, and way-up arrow for cores.

• Water samples should have sample number, locality date, person collecting sample, and method of preservation. e.g. F.A (filtered acidified), F.U. filtered unacidified

Types of solid waste

• Non acid generating (NAG) waste rock– Contains more carbonate than sulphide– Can be used for road construction, backfill

etc.

• Potentially acid generating (PAG) waste rock– Contains more sulphide than carbonate

Sampling Waste Rock• Systematic sampling of wall rock or waste heaps

necessary for calculation of acid generating potential which will determine utilization or treatment of rock and value or liability

• Difficult to obtain a representative sample due to:– Coarse and variable size– Variability in rock type– Variability in composition within rock type– Variability in weathering

INCO Thompson

Tailings

Fine grained waste from beneficiation– Often highly reactive– Sulphide tailings often acidic– May contain arsenic or selenium – May contain cyanide– High salinity– Dry tailings easily blown– Must be contained

Characterization of tailingsTo predict future probability for acid mine

drainage and/or pollution, we need to know the past and present mineralogical and geochemical reactions occurring in the deposit.

There may be little documented history for abandoned mine sites

Gunner Mine TailingsNopiming Park, MB

For abandoned sites: measure and map the surface area and topography with aerial photography and GPSIt is important to final the size of the deposit, ground and surface water flow to determine acid generating potential and metal mobility

Central Manitoba Mine Tailings

Special techniques are neededfor sampling

Mine tailings are very fine-grained and reactive producing even finer-grained products

Need to collect solid samples and liquids in equilibrium and try to keep them in the same state until analyzed

Water Sampling

Pass through 2 or 45 μm filter to remove solid particles.

These may dissolve in the changed conditions of the collected samples

Use meters with specific probes for pH, Eh, conductivity, and dissolved oxygen (DO)

Test strips for Fe2+, HS- etc.

Preservation

Preserve separate aliquots with:

(1) HNO3for cation analysis

(2) HCl for Fe2+/Fe3+ analysis

(3) H2SO4 for PO4 and nutrient analysis

(4) Zn acetate solution for sulphide analysis

Leave one aliquot unacidified for anion analysis

Keep samples cold but not frozen and analyze as soon as possible

Separation of As(III) and As(V) in the field

• As(III) is toxic and unstable in solution as it oxidizes to As(V)

• Passing 10 ml through a SAX (strong anion exchange) cartridge retains As(V)

• As(III) collected in bottle• Elution of cartridge with 10 ml HCl

in laboratory removes As(V)• Measurement of As concentration

in both portions gives As(III), As(V) and total As

As in groundwater at Snow Lake

• Difference between separating measuring As species from MW 17 in field and lab

MW 17

0

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1994 1996 1998 2000 2002 2004 2006 2008

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As

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NBM

Salzsauler

Simpson

Capping

Water Analysis

• If possible use a certified laboratory such as ALS

• Chemical analysis of cations with Inductively coupled Plasma Optical Emission or Mass Spectroscopy (ICPOES or ICPMS)

• Anions by ion chromatography

• Alkalinity by titration

• Fe2+/Fe3+

Aqueous ModelingWATEQ4f and PHREEQC are based on an ion-association aqueous model and

will provide: • ionic speciation • saturation-indices (SI): indicators of the degree of saturation of water with

respect to a mineral. Minerals in equilibrium with the water and controlling the water chemistry have SI values of –2 to +2 (around zero)

• PHREEQC will also calculate:• batch-reaction and 1D transport involving reversible reactions, which include

aqueous, mineral, gas, solid-solution, surface-complexation, and ion-exchange equilibria, and irreversible reactions, which include specified mole transfers of reactants, kinetically controlled reactions, mixing of solutions, and temperature changes; and inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits.

• Geochemists WorkBench® plots phase diagrams.

• Care must be taken to relate these results to minerals identified from solids

Solid Tailings

Vibration drilling in winter without water or drilling fluid to prevent contamination, and dissolution of soluble phases

In SummerDig a hole to expose the sectionMeasure, photograph, describeCollect samples using a tube pushed into the sediment or small boxes for thin sections

Keep samples cold or preferably frozen until processed to prevent oxidation, and precipitation of tertiary minerals

Laboratory preparation of samples

• Frozen core sliced using a diamond blade

• Water squeezed from core for comparison of water in contact with solids

• Dry samples for thin sections• Impregnate with epoxy resin• Polished thin sections prepared

without water to preserve soluble minerals.

Mineral IdentificationOptical Microscopy in reflected & transmitted light on polished thin sections (field of view 1.1 mm)

Mineral IdentificationPowder X-ray Diffraction (XRD)

x10^3

2.0

4.0

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nsity

(Cou

nts)

47-1775> Schwertmannite - Fe16O16(SO4)3(OH)10!10H2O

22-0827> Jarosite, syn - KFe3(SO4)2(OH)6

10 20 30 40 50 60 70 80

2-Theta(°)

Well-crystalline jarosite & poorly-crystalline schwertmanite

Xray Diffraction Page 311 – 320 Klein and Dutrow (2008)

• Single crystal or fine powder samples• X-rays are absorbed by vibrating electrons and

re emitted as X-radiation of the same energy• Used to identify minerals

(powder) or provide information

about the crystal structure or

atomic order (single crystal

or Rietveld Refinement of

powder pattern)

Powder XRDfor identification of

minerals

Each parallel plane of atoms refracts atoms based on the Bragg Equationnλ = 2d sineθ

Where n is an integer (1, 2, 3, etc.)λ is the wavelength of the Xraysd is the spacing between successive planes of atomsθ is the angle of incidence and reflection of the Xray beamλ is known and 2θ is measured from film, or spectrum

Values of 2θ and intensity (i) of Xrays at each value measured from a photographic film or a spectrumValues of d calculated Values of d and i compared with values from standard tables using a computer program. Suggestions for minerals present given from XRD pattern and sometimes chemical composition of

sample

2θ2θ

Incident X rays

Powder sample

Refracted X rays

Photographic Film or Spectrometer

Precipitates from ground water

Precipitate from surface water

2 µm 2.5 µm

SchwertmanniteSchwertmannite

Jarosite

37-0468 (*) - Scorodite - FeAsO4·2H2O19-1184 (I) - Albite, ordered - NaAlSi3O885-0796 (C) - Quartz - SiO2Y + 3.0 mm - File: Kristin50um18pts_07.raw

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Micro X-ray Diffraction Analysis

Courtesy ofDr Roberta FlemmingUniversity of Western Ontario

Spectroscopic Techniques used for Chemical Analysis of Minerals

Optical Emission Spectroscopy (OES)• Mass Spectroscopy (MS)• Secondary Ion Mass Spectroscopy (SIMS)

• X-ray Fluorescence (XRF)• Scanning Electron Microscope (SEM)• Energy Dispersive X-ray spectroscopy (EDX)• Electron Microprobe (EMP)

Laser Ablation (LA) Inductively coupled plasma (ICP)

• Laser ablation (LA) is the process of removing material from a solid surface by irradiating it with a laser beam.

• Inductively coupled plasma (ICP) is a very high temperature (7000-8000K) excitation source that vaporizes, excites, and ionizes atoms using induction coils in a magnetic field.

• The plasma can then be analyzed by AA, Optical Emission Spectroscopy or Mass Spectroscopy

Optical Emission Spectroscopy (OES)

• Atoms are energized to emit radiant energy of IR-visible-UV wavelengths which are specific to an element

• The energy can be dispersed and collected as a spectrum and compared with standards

• The amount of radiation at differing wavelengths is proportional to the number of atoms of a specific element.

• The material must be vaporized using ICP or LA ICP

Xray Spectroscopy

• A solid sample is bombarded with incident Xrays

• Absorbance of Xray energy causes electrons to be dislodged from the innermost

• K, L, M levels (Fig 14.4 K & D)

• Electrons are replaced by a higher energy level with excess energy of a specific X-ray wavelength being given off (Fig 14.20 K & D)

• This secondary Xray emission spectrum is characteristic of a specific element and the amount of the absorption relates to the proportion of that element.

Mass Spectroscopy

• Measures the mass to charge ratio of ions

• Ionized vapour (plasma) passes through a series of curved magnets

• Ions are separated by being attracted or repelled by the magnetic field

Electron Microprobe• Initial energy source is a focused beam of

electrons instead of an X-ray beam

• X-rays cannot be focused but as electrons are charged they can be focused by magnetic fields

• Volume analyzed

10-20 μm3

Scanning Electron Microscope

• Focused beam of electrons scans the surface of either unpolished specimen or polished thin section and gives an image of the surface

Quartz

Chalcopyrite

Pyrite

Schwertmannite

Energy Dispersive X-ray spectrometer on the Scanning Electron Microscope

• Collect the whole X-ray spectrum at once

• Allow fast analysis of grains visualized by SEM

Secondary Ion Mass Spectrometry

(SIMS)

• Focused beam of ions (O- or Cs+) impinges on the surface of a mineral

• Secondary ions on the surface are ejected

• Mass spectrometer separates by charge and mass (Fig 14.33 K&B)

• Can measure elements from H to U

• Very low detection limits (ppb)

Experimental Data

Model

Test model with further data

Prediction

Recommendations for preservation or remediation