Flocculants for Water Treatment

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Flocculants for Water Treatment

• Date May ???,2011
• Speaker Speaker A? Speaker B? Speaker C

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Objectives

• Flocculation of ferric hydroxide(Fe(OH)3)
  colloidal solution ??is affected by the different
  pH values.
• ? research the flocculation of Fe(OH)3(aq) at
  different pH value
• Ferric hydroxide colloidal solution performs
  excellently on the adsorption of heavy metal
  ions.
• ? research the adsorption of lead ions (Pb2),
  zinc ions (Zn2), chromium(VI) ions to decrease
  the huge volume of waste water containing heavy
  metal ions in high school chemistry laboratory

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Colloids

• Colloidsubstance microscopically dispersed
  throughout another one.
• Colloidal systemconsists of two separate
  phases-a dispersed phase and a continuous phase .
• Diameter of dispersed-phase
• particlesapproximately
• 5 and 200 nm.

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Properties of Colloids

• Tyndall effect light scattering by particles in
  a colloid or particles in a fine suspension.
• Absorptionanother characteristic of colloids.

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Tyndall effect

• The Tyndall effect can be used to tell the
  difference between the true solution, and
  colloid.

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Flocculants for Water treatment

• Flocculantscausing colloids and other suspended
  particles in liquids to improve the sedimentation
  of small particles.

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Al(OH)3

• Al(OH)3the basis for application of as
  coagulant in water purification.
• Alzheimers diseasetraces of aluminium are found
  in brain lesions sometimes, so there is concern
  that consumption of excess aluminium
  compounds may cause or contribute to
  the development of this.

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Fe(OH)3

• Preparation of Fe(OH)3
• Fe(NO3)3 NaOH ? Fe(OH)3 NaNO3

Fe(OH)3
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Fe(OH)3

• Absorbent for suspension in raw water.
• Removal of Pb2 and other heavy metal ions.

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Hydrolysis of ferric ion

• Ferric ion hydrolyzes in water
• Fe(H2O)63 H2O ? Fe(H2O)5(OH)22 H3O
• Fe(H2O)5(OH)2H2O?Fe(H2O)4(OH)2H3O
• 2Fe(H2O)63?Fe(H2O)4(OH)2Fe(H2O)442H3O
• When pH value of the solution decreases, the
  hydrolysis of ferric ions decreases too.

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• With the increasing of pH value, the solution
  changes from yellow to brown, reddish brown, and
  finally red-brown, which is the color of
  Fe(OH)3(s).

pH3
pH12
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Removal of Pb2?Zn2?Cr(VI)

• Large volume of waste water containing
  Pb2?Zn2?or Cr(VI) ions is produced by the
  experiments in the high school chemistry course.
• Pb2?Zn2 and Cr(VI) ions are poisoned for human
  body , so we try to use Fe(OH)3 colloid to remove
  them to decrease the volume of waste water.
• Research the absorption ability of Fe(OH)3
  colloid at different pH value.

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• Experiment
• Adjust the pH value of Fe(OH)3(aq) from 6 to 13.
• Prepare the stock solution containing
  Pb2?Zn2?or Cr(VI) ions
• Mix Fe(OH)3(aq) and the stock solution for 5ml
  each at different pH value.
• Mix solutions are stood for a certain time.
• Withdraw 5ml clear mix solution.
• Analyze the concentration of heavy metal ions in
  the clear solution by ICP-MS in the
  Instrumentation Center at National Tsing Hua
  University.

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Analyze the Pb2 by ICP-MS

• The Pb2 in the stock solution is 7174 ppm.

pH 13 12 11 10 9 8 7 6
Experiment 1 0.462 1.17 11.3 14.3 90.2
Experiment 2 0.417 2.39 0.817 2.8 30.7 181 741 979
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• The absorption of Zn2 by Fe(OH)3 is excellent.
• The higher pH value, the less Pb2

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Analyze the Zn2 by ICP-MS
The Zn2 in the stock solution is 4784 ppm
pH 13 12 11 10 9 8 7
ppm 2.67 1178 1490 1669 1579 1827 1947
? The absorption of Zn2 by Fe(OH)3 is
excellent, and is better at higher pH value . ?
At pH 13 ,the zinc ions is left only about
0.056.
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• The absorption of zinc ions is better at higher
  pH value.

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Analyze the Cr(VI) by ICP-MS

• There are two species of Cr(VI)
• K2CrO4(aq) K2Cr2O7(aq)
• Both the two species are poisoned.

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• 0.01M K2CrO4(aq)
• Cr(VI) in stock solution is 563 ppm

pH 13.54 13 12 11 10 9 8 7
ppm 265 262 263 278 277 255 246 197
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• b) 0.001M K2CrO4(aq)
• Cr(VI) in stock solution is 56.4 ppm

pH 13.17 13 12 11 10 9 8 7
ppm 22.1 25.9 25.1 26.4 26.3 23.2 14.6 3.72
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• The absorption of Cr(VI) by Fe(OH)3 colloid is
  far worse than the absorption of Pb2 and Zn2
  ions.
• The best absorption is at pH 7.
• There is a chemical equilibrium between CrO42-
  and Cr2O72-
• 2CrO42- 2H ? Cr2O72- H2O
• Cr2O72- will exist more than CrO42- in the
  acidic solution. Fe(OH)3 will have a better
  capability of absorption for Cr2O72-

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Conclusion

• ? The absorptions of Pb2 ? Zn2 and Cr(VI) ions
  by Fe(OH)3 colloid perform excellent.
• ? The higher the pH value is ,the better the
  absorption of Pb2 and Zn2 ions by colloidal
  ferric hydroxide solution is.
• ? At pH 13 , the lead ions is left only about
  0.006.
• ? At pH 13 ,the zinc ions is left only about
  0.056.

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Conclusion

• The absorption of chromium(VI) ions by
• colloidal Fe(OH)3 solution is far worse
• than the absorption of lead ions and zinc
• ions. And the better condensation effect
• will happen at pH 7.

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Thanks for your attention!!
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