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 tailings
To 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 Tailings
Nopiming Park, MB
For abandoned sites: measure and map the surface
area and topography with aerial photography and
GPS
It 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 needed
for 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
25
MW 17
20
Capping
As (ppm)
15
10
NBM
Salzsauler
5
Simpson
0
1994
1996
1998
2000
2002
years
2004
2006
2008
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 Modeling
WATEQ4f 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 Summer
Dig a hole to expose the section
Measure, photograph, describe
Collect 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 Identification
Optical Microscopy in reflected & transmitted light on
polished thin sections (field of view 1.1 mm)
Mineral Identification
Powder X-ray Diffraction (XRD)
10.0
Well-crystalline jarosite &
poorly-crystalline schwertmanite
Intensity(Counts)
8.0
6.0
4.0
2.0
x10^3
47-1775> Schwertmannite - Fe16O16(SO4)3(OH)10!10H2O
22-0827> Jarosite, syn - KFe3(SO4)2(OH)6
10
20
30
40
2-Theta(°)
50
60
70
80
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
sample
Incident X rays
2θ
2θ
Photographic
Film or
Spectrometer
Powder XRD
for identification of
minerals
Refracted X rays
Each parallel plane of atoms refracts atoms based on the Bragg Equation
nλ = 2d sineθ
Where n is an integer (1, 2, 3, etc.)
λ is the wavelength of the Xrays
d is the spacing between successive planes of atoms
θ is the angle of incidence and reflection of the Xray beam
λ 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 spectrum
Values 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
Schwertmannite
Precipitate from
surface water
Jarosite
2 µm
Precipitates from ground water
Schwertmannite
2.5 µm
Micro X-ray Diffraction Analysis
19
18
17
16
15
14
13
Lin (Counts)
12
11
10
9
8
7
6
5
4
3
2
1
0
13
20
30
2-Theta
Y + 3.0 mm - File: Kristin50um18pts_07.raw
85-0796 (C) - Quartz - SiO2
19-1184 (I) - Albite, ordered - NaAlSi3O8
37-0468 (*) - Scorodite - FeAsO4·2H2O
40
Courtesy of
Dr Roberta Flemming
University 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
Schwertmannite
Quartz
Pyrite
Chalcopyrite
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