geothermal sampling and analysis halldór … 2008/18... · choice of sampling sites • geological...
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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
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
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