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SULFUR AND SULFATE

SULFUR AND SULFATE. ENVE 202 Dr. A. Kerç. SULFATE. One of the major anions occuring in natural waters Cathartic effect  müshil etkisi Upper limits  250 mg/L. SULFATE ( continue ).

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SULFUR AND SULFATE

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  1. SULFUR AND SULFATE ENVE 202 Dr. A. Kerç

  2. SULFATE • One of themajoranionsoccuring in naturalwaters • Catharticeffect müshil etkisi • Upperlimits  250 mg/L

  3. SULFATE (continue) • Importantforpublic + industrialwatersupplies duetotendency of waterto form scaling in boilersandheatexchangers • Twoseriousproblems in ww.Odor sewercorrosion

  4. SULFATE (continue) • Reduction of sulfatestohydrogensulfideunderanaerobiccondition • SO4-2 + org.matter S-2 + H2O + CO2 • S-2 + H+  HS • HS- + H+  H2S (Primaryionizationcons. KA1 = 9.1x10-8 ) Anaerobicbact

  5. SULFATE (continue) • Inbiochemicaloxidation ( foranaerobic ) if DO and NO3- do not exist, sulfatesserve as oxygensource (electronacceptor) • Relationshipsbetween H2S, HS- , S-2arepHdependent

  6. SULFATE (continue) • IfpH > 8 HS- and S-2 [(H2S) is small] no odor problem • IfpH < 8 equilibriumshiftright @pH 7 80% H2S • Ifconcentration > 20 ppmtoxic

  7. SewerCorrosion • Hightemperature, longdetentiontimessulfatecausecrowncorrosion in concretesewers • H2S responsible (indirectly) forcrowncorrosion • H2S is weakerthancarbonicacid littleeffect on goodconcrete

  8. SewerCorrosion (continue) • Gravitysewersprovideunusualenvironment • Biologicalchangesoccurduringtransportationrequireoxygen • Ifwellvent. no problem H2S + O2  H2SO4

  9. Methods of Analysis • Ionchromatograph • Formation of insoluable BaSO4 • Accordingtothequantity of BaSO4formation • Gravimetric precipitate is weighed • Turbidimetric • Methylthymolbluemethod

  10. Methods of Analysis (continue) • Gravimetric : > 10 mg/L • Ba+2 + SO4-2  BaSO4 • Add BaCl2 in slightaccess • Acidify w/HCL  eliminate BaCO3ppt • Keepnearboilingpoint

  11. Methods of Analysis (continue) • ExcessBaCl2  commonioneffect • Formed BaSO4  colloidal form can not be removedbyfilter • Digestion @ temperaturenearboilingpoint  crystallineforms • Filterthecrystalswithspecialfilter

  12. Methods of Analysis (continue) • Turbidimetric : • Colloidalformation is enhanced in the presence acidicbuffersolution • (Magnesiumchloride, potassiumnitrate, sodiumacetate, aceticacid) • Calibrationcurve

  13. Methods of Analysis (continue) • AutomatedMethylthymolBlue • Continuousflowanalyticalinstrument • BaCl2 added @lowpH BaSO4 • pHadjustedto 10 • Methylthymolblueadded

  14. Methods of Analysis (continue) • CombineswithexcessBarium bluechelate • Umcomplexedmethylthymolblueremaining greycolor (automaticallymeasured)

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