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Controls on Lead Contamination in Natural Waters

Controls on Lead Contamination in Natural Waters. Lead Ore - Galena Oxidation Processes Solubility Controls What to look for in Teesdale. Lead Ore – Galena. Chemical formula: lead sulfide, PbS

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Controls on Lead Contamination in Natural Waters

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  1. Controls on Lead Contamination in Natural Waters Lead Ore - Galena Oxidation Processes Solubility Controls What to look for in Teesdale

  2. Lead Ore – Galena Chemical formula: lead sulfide, PbS cubic, metallic grey, very high density, very soft, occurs in mineral veins, forms at high temperatures at depth

  3. Oxidation processes Lead sulfide is not stable when exposed to conditions present in surface environments PbS + 2O2 +  Pb2+ + SO42- Oxidation of sulfide  sulfate Reduction and oxidation always happen togetheroil-rig Oxidation is loss of electrons : S2-  S6+ - 8e- Reduction is gain of electrons: 2O2 + 8e- 4O2- This not and acid generating process! Pb-salts are relatively insoluble and can be a barrier to further oxidation, unless ore is crushed and processed – Mining!

  4. Solubility of Lead Examine the solubility product of PbSO4 in absence of any other species (i.e in distilled water): PbSO4 (solid)  Pb2+ + SO42- (Aqueous) rewrite this solubility product equation Ksp = [Pb2+][SO42-] = 2 x 10-7 (2 x 10-7 - from experiments) from equation, [Pb2+] = [SO42-] = x x2 = 2 x 10-7x = 2 x 10-7 [Pb2+] =1 x 10-4 moles/litreor ~29 mg kg-1

  5. Solubility of Lead continued But, Presence of other dissolved species reduces Pb-solubility. Also, Pb-solubility in environment is very dependant on pH. At circumneutral pH, Pb will strongly sorb to other mineral surfaces – especially fine grained clay minerals that have very high surface areas

  6. What to Look For on Site PbS + 2O2 +  Pb2+ + SO42- What are products of Galena oxidation? What is major control on Pb solubility? What species should we try to measure?

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