GEOTHERMAL SAMPLING AND ANALYSIS

Halldór ÁrmannssonHalldór ÁrmannssonNovember 2008

SAMPLING AND ANALYTICALSAMPLING AND ANALYTICAL RESULTS

• Only as good as the sampling and analytical techniques

• Imperative that well trained personnelImperative that well trained personnel with insight into possible interferences perform the tasksperform the tasks

• Containers, preservation, correct steam fraction, reading instructions

PRESERVATION OF SAMPLES

• Physical methods • Addition of h i l– Filtration

– Freezingchemicals– Acidification

– Airtight containers– Immediate analysis

– Precipitation– Dilution– Prevention of redox– Gas fixation– Ion exchange– Extraction

CHOICE OF SAMPLING SITES

• Geological setting• Temperature• Springs As close to outflow as possible• Springs. As close to outflow as possible• Fumaroles. Sulphur deposits and

concentrated flows good guides• Wells: Best 1 5 m away from bends or• Wells: Best 1.5 m away from bends or

constrictions

NoNo

Yeses

YYes

S it bilit f li Fumaroles, Theistareykir, IcelandSuitability for sampling

Fumarole vegetation

SAMPLING A FUMAROLESAMPLING A FUMAROLE

Small fumaroles gathered for flow measurement and sampling

On H2S

• Reactive• Metal sulphides generally insoluble and

precipitatedprecipitated• Oxidized to S, SO2, SO3

--, S2O3--, S4O6--

SO t, SO4-- etc.

• Reacts with organic compounds to formReacts with organic compounds to form e,g, complex ions

PRESERVATION OF H2S

• Precipitation with metal ion, e.g. Zn+2, Cd+2. ZnAc2 or CdAc2 added, ZnS or CdS precipitated and preservedp p p

• Addition of hydroxide, NaOH or KOH delays oxidationdelays oxidation

• Removal by acid and N22

• Immediate determination

ANALYTICAL METHODS

• Available instruments• Servicing facilities• Trained personnel• Trained personnel• Comparison of methods

– Speed– ReliabilityReliability– Cost

FIELD LABORATORY

• Volatile constituents: pH, CO2, H2S, NH ONH3, O2

• Urgent constituents, e.g. SiO2Urgent constituents, e.g. SiO2

• Separation efficiency checks, e.g. Na, ClCl

• Apparatus for specific tests, e.g pp p , gaccurate balance, oven

• Facilities for supply of deionized water• Facilities for supply of deionized water. Distillation + deionization apparatus or

f ili istorage facilities

MOST IMPORTANT TECHNIQUESMOST IMPORTANT TECHNIQUES• Gas:Titrimetry (incl. Orsat); Gas Chromatography; Mass

t t R di tspectrometry; Radiometry• Cations: AAS (flame, carbon furnace); FES; ICP/AES;

Ion chromatography; Fluorimetry; Ion selectiveIon chromatography; Fluorimetry; Ion selective electrodes

• Anions: Ion chromatography; Ion selective electrodes;• Anions: Ion chromatography; Ion selective electrodes; Spectrophotometry; Titrimetry, e.g. HCO3

-, either by direct titration with HCl or by back titrationy

• Total solids: Gravimetry; Conductivity• General: ICP/MS large commercial laboratories gaining g g g

ground• Isotopes: Separation + Mass spectrometry

Gas Chromatography Method For Geothermal Gas AnalysisGas Chromatography Method For Geothermal Gas Analysis

Gas Chromatography PE Gas Chromatography PE -- Auto SystemAuto SystemGas Chromatography PE Gas Chromatography PE -- Auto SystemAuto SystemSampleSampleSampleSample

Arnel Injection SystemArnel Injection System

NN G C iG C i H G C iH G C i

Hayesep T ColumnHayesep T Column

NN22 Gas CarrierGas Carrier

Molecular Sieve 5A CoulomnMolecular Sieve 5A Coulomn

He Gas CarrierHe Gas Carrier

TC DetectorTC Detector

He & HHe & H22 GasGas

TC DetectorTC Detector

NN22, Ar, O, Ar, O22 & CH& CH44 GasGas

HeHe First PeakFirst PeakHeHe First PeakFirst Peak

He & HHe & H22 GasGas

InterceptIntercept

NN22, Ar, O, Ar, O22 & CH& CH44 GasGas

HeHe First PeakFirst PeakHH22 Second PeakSecond PeakNN22 Thirth PeakThirth PeakARAR Fourth PeakFourth PeakOO Fifth PeakFifth Peak

HeHe First PeakFirst PeakHH22 Second PeakSecond PeakNN22 Thirth PeakThirth PeakARAR Fourth PeakFourth PeakOO Fifth PeakFifth Peak

Oki DataOki Data

ChromatogramChromatogram

OperationOperationin Vacuumin VacuumConditionCondition

OperationOperationin Vacuumin VacuumConditionConditionOO22 Fifth PeakFifth Peak

CHCH44 Sixth PeakSixth PeakOO22 Fifth PeakFifth PeakCHCH44 Sixth PeakSixth Peak

ChromatogramChromatogram ConditionConditionConditionCondition

Hg

• Spectrophotometry: Dithizone. High concentrations• NAA: Cumbersome but accurate• AAS:

– Cold vapour. Relatively high concentrationsp y g– Gold amalgamation. Sensitive, accurate, but time

consuming• ICP/AES: Not sufficiently sensitive for most geothermal fluids

(0.02-0.1 mg/l)• ICP/MS: Sufficiently accurate but consider preservation• Preservation of prime importance. Present in liquid and

vapour

ISOTOPESISOTOPES• Atomic nuclei are composed of protonsAtomic nuclei are composed of protons

and neutrons• Atomic number = No of protons (Z)• Atomic number = No. of protons (Z)• Mass number = No. of protons +

t (A)neutrons (A)• Isotopes: Same atomic number, p

different mass numbers• Stable or radioactive (decayStable or radioactive (decay

spontaneously)

TECHNIQUESM t t R idl i i• Mass spectrometry. Rapidly moving ions separated on the basis of their mass-to-h ticharge ratios

• Radiochemical methods– Neutron activation: radioactivity induced by

irradiation with neutrons– Isotope dilution: known weight of isotopically

labelled species mixed with sample, isolated as purified compound radioactivity measuredpurified compound, radioactivity measured

– Measurement of natural radioactivity

COMPONENTS OF A MASSCOMPONENTS OF A MASS SPECTROMETER

STABLE ISOTOPES

• D, 18O, 34S and 13C, ,• Ratios (R), not absolute vales

determined by MSdetermined by MS• Comparison with standard, or δsample =

((R R )R )×1000‰((Rsample-Rstd)Rstd)×1000‰• SMOW for D and 18O; PDB for 13C, CDT

34for 34S• Water vapour interferes in MS. Hence p

D2O→D2, and 18O2 →C18O2

CONVERSIONSCONVERSIONS• H2O→H2: Reduction2 2

– Hot uranium. Toxicity, political regulation– Zinc shot. Correct Zn reagent. Laborious

preparation of glass apparatus– Hot chromium

H O H E ilib i P l• H2O→H2: Equilibration. Pt catalyst• O2 →CO2: Equilibration• SO4, H2S : Oxidation→SO2 (SO4

-2+2C →S-2

+2CO2 (vacuum, 1100°C); S-2+Ag→ Ag2S; S-2

2C O 4C SO ( 400°C) 18O+2Cu2O→4Cu+SO2 (vacuum, 400°C). 18O measured in CO2 from first reaction, 34S in SOSO2

Isotope Analysis in GeothermicsIsotope Analysis in Geothermics

SamplesSamplesSamplesSamplesSamplesSamplesSamplesSamples

WaterWater GasGasWaterWater

1818OO DD 1818OO 33HH 3434SS 3434SS 1313CC

GasGas

PP RR QQ1818OOH2OH2O DD 1818OOSO4SO433HH 3434SSSO4SO4

3434SSH2SH2S1313CCCO2CO2

EpsteinEpstein-- ZincZinc SulphateSulphate EnrichmentEnrichment SulphateSulphate

PP RR QQ

pp ppMayedaMayeda ReductionReduction ReductionReduction ElectrolysisElectrolysis

HH221818O + COOO + COO1616 Zn + HZn + H22O O SOSO44 + C + C --

HH221616O + CO + C1616OO1818OO ZnOZnO + H+ H22 SS== + CO+ CO22 LSCLSC

SulphateSulphateOxidationOxidation

SS== + Cu+ Cu22O O Cu + SOCu + SO22

10001000°°CC COCO33–– + H+ H33POPO44

POPO≡≡44 + H+ H22O + COO + CO22

JJ

MASS SPECTROMETERMASS SPECTROMETERRX

KK LL MM NN

SMOWSMOW 1818OOH2OH2O & D& DH2OH2O

CDTCDT 3434SSSO4SO4 & & 3434SSH2SH2S

PDBPDB 13C13C & & 13C13C

INTERNATIONALINTERNATIONALSTANDARDSSTANDARDS

δδ = = -- 1 x 1000 ‰1 x 1000 ‰RX

RST

PDBPDB CH4CH4 & & CO2CO2

Delta V Advantage Mass Spectrometer. University of Iceland 1)Gas conversion, 2) Bomdardment with electrons, 3) Double focussing 4) Faraday cup 5) Digital readout3) Double-focussing, 4) Faraday cup, 5) Digital readout

QUALITY CONTROL

• Precision: Repeat analysis of one sample or duplicate several samples

• AccuracyAccuracy– Standard additions

Diff t th d– Different methods– Standards or reference samples– Ionic balance– Mass balance (TDS Conductivity)Mass balance (TDS, Conductivity)

• Checks: Inter-laboratory comparisons

Methods used for selected constituents by laboratories in IAEA I t l b t C i 2003Interlaboratory Comparison 2003Cl SO4 SiO2 K Mg

Co 2 16 14Tm 23 1IC 5 5 2 2Tu 9Tu 9AA 9 24 21ICP/MS 1ICP/AE 3 3ICP/AE 3 3FE 1•Co: Colorimetric; Tm: Titrimetry; IC: Ion Chromatography; Tu: Turbidometry; AA: Atomic Absorption; ICP/MS: Inductively•Co: Colorimetric; Tm: Titrimetry; IC: Ion Chromatography; Tu: Turbidometry; AA: Atomic Absorption; ICP/MS: Inductively

Coupled Plasma Mass Spectrometry; ICP /AE: ICP Atomic Emission; FE: Flame Emission

ConclusionsExtreme care by trained personnel needed for• Extreme care by trained personnel needed for sampling

• AAS still most popular method for cation analysis butAAS still most popular method for cation analysis but ICP/AES and ICP/MS performed commercially by large laboratories are increasing their share

• Volatiles in field or soon after arrival in laboratory (CO2, H2S by titration)

• Gases by titration and GC• Gases by titration and GC• Isotopes by mass spectrometry after suitable

conversions

Thank you