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Chemical aspects between water and minerals in view of building geothermal power plants

Chemical aspects between water and minerals in view of building geothermal power plants. A short introduction into mineralogy from Martin Weber Msc. chem., Switzerland. Analysis of thermal water from the richest mineral source in Switzerland. Place of the fountain: Baden (Switzerland)

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Chemical aspects between water and minerals in view of building geothermal power plants

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  1. Chemical aspects between water and minerals in view of building geothermal power plants A short introduction into mineralogy from Martin Weber Msc. chem., Switzerland

  2. Analysis of thermal waterfromtherichestmineralsource in Switzerland • Place of the fountain: Baden (Switzerland) • Temperature: 46.5°C • pH-data: 6.43 • Total mineralisation: 435 mg/L • Boric and silicic acid: 71 mg/L • Solved gas: 292 mg/L

  3. Analysis of thermal waterfromtherichestmineralsource in Switzerland Kations mg/L • Ammonia 0.78 • Lithium 4.8 • Sodium 720 • Potassium 63 • Magnesia 99 • Calcium 503 • Strontium 6.2 • Iron 0.013 • Manganese 0.016 • Copper <0.005 • Zinc <0.01 • Lead 0.002 • Aluminium 0.018 • Total 1397 Anions mg/L • Fluorine 3.1 • Chlorine 1185 • Bromine 2.5 • Iodine 0.009 • Nitrate <0.5 • Hydrogen- carbonate 487 • Sulfate 1375 • Hydrogen- phosphate 0.05 • Hydrogen- arsenate 0.1 • Molybdate <0.005 • Total 3053

  4. Solid precipitationsfrommineralwatersomefrequentexamples Solvationproduct • Limestone CaCO3 4.7 x 10-9 • DolomitheMgCa(SO4)2 2.6 x 10-6 • Plaster CaSO4 2.4 x 10-5 • Strontianithe SrCO3 1.6 x 10-9 • Barythe BaSO4 1.5 x 10-9 • Silicates CauMgvAlw(SixOy)z • Borates NauCavMgw(BxOy)z

  5. Problems withprecipitatingmineralsfromwater • Formation of mineralic layers and coatings on pipes and heat exchangers. • Reduced heat transitions trough mineralic coatings and sedimentations. • Reduced water flow through the primary water cycle and risk of a transition from a laminar to a turbulent flow.

  6. Formation of limestone CaCO3 • Mineral watercontains Calcium (Ca2+) and Hydro-gencarbonateions (HCO3-). These ionsareeasily soluble andstay in a chemicalequilibriumwith CaCO3, whichisheavily soluble: Ca2+(aq) + 2 HCO3-(aq) CaCO3(s) + H2O + CO2 easily soluble heavily soluble In coldwatertheequilibriumis on theleftside, wherethe soluble particlesexist. Heat will changetheequilibriumfromthelefttotherightside, so theformationof limestone ispreferred.

  7. Formation of Silicates • Mineral watercontainsconsiderableamountsofsilicicacidH4SiO4. The rangeofconcentrationspreadsfrom 5 mg/Litreupto 75 mg/Litre. • Silicicacidismoderately soluble, but bysplitting off waterittendsto form higherpoly-silicates, whichareless soluble andprecipitateassolids: 2 H4SiO4 (aq)  H6Si2O7 (s) + H2O 3 H4SiO4 (aq)  H8Si3O10 (s) + 2 H2O 4 H4SiO4 (aq)  H10Si4O13 (s) + 3 H2O etc.

  8. Formation of Silicates • The anionof (monomeric) silicicacid SiO44-represents a tetrahedralgeometry. • Polysilicicacidsmaybeformedbyconnectingcorners, edgesor planes ofmonomeric, tetrahedralsilicatesasthefollowingpictureisshowingus: schematic structure

  9. Formation of Silicates group- silicate chain- silicate ring- silicate ortho- silicate monomer band- silicate ring- silicate

  10. Formation of Silicates • Connectingofcornersleadstotheformationofeithergroups, chains, bands, rings orlayers, connectingedgesor planes leadstotheformationofcagesfrompolymericsilicicacid: layer structure of polysilicate minerals like clay and mica [(Si2O5)2-]x

  11. Formation of Silicates Combinedwith different kationswecomeacrossthedifferent naturallyexistingsilicateswhichareknownby alternative names. Type ofsilicateformulaof Mineral- nameandformula theanionclassof a representativemineral monosilicates SiO44- OlivinesFayalit Fe2SiO4 groupsilicates Si2O76-Barysilit Pb3Si2O7 ring or cyclosilicates Si3O92- Beryll Al2Be3Si6O18 chainsilicates [SiO32-]xPyroxenesDiopsidCaMg[SiO3]2 band silicates [Si4O116-]xAmphibolesTremolit Ca2Mg5(OH)2[Si4O11]2 layersilicates [Si2O52-]x clays Kaolinit Al2(OH)4[Si2O5] Talcum Mg3(OH)2[Si2O5]2 Mica Biotit K{(Mn)3(OH)2[AlSi3O10]} Asbestos Serpentin Mg3(OH)4[Si2O5] cagesilicates [AlySi4-yO8y-]x Feldspars Orthoclas K[AlSi3O8] CeolithsMordenit Na2[Al2Si10O24] . 6 H2O Quartz SiO2

  12. Weathering decay of silicates • Products fromweatheringdecayofsilicatesare: • SiO2orsilicicacid H4SiO4 • Hydroxide ofaluminium Al(OH)3 • Clay minerals • Weatheringdecayoffeldspar: KAlSi3O8 + 4 H++ 4 H2O  K+ + Al3+ + 3 H4SiO4 • Reformation of Kaolinit (a claymineral) 2 KAlSi3O8 + 4 H++ 9 H2O  2 K+ + AlSi2O5(OH)4 + 4 H4SiO4

  13. Resistivityofweatheringdecayfrom different silicates Iland- silicates Chain- silicates Band- silicates Layer- silicates Cage- silicates Feldspars and Quartz SiO2 Olivins SiO44- Pyroxenes SiO32- Amphiboles Si4O116- Clay and Mica Si2O52- Resistivity of weathering decay increases

  14. Solutions forencounteringmineralicprecipitations on pipesandheatexchangers • Electrophoresis • Exchangeable heat exchangers • Filters for gelatinous polysilicic acids • Cyclone (centrifugal separation)

  15. Thankyouforyourattention!

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