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F locculants for Water Treatment. Date: May ???,2011 Speaker :Speaker A 、 Speaker B 、 Speaker C. 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

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f locculants for water treatment

Flocculants for Water Treatment

Date: May ???,2011

Speaker :Speaker A、 Speaker B、 Speaker C

objectives
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

colloids
Colloids
  • Colloid:substance microscopically dispersed throughout another one.
  • Colloidal system:consists of two separate phases-a dispersed phase and a continuous phase .
  • Diameter of dispersed-phase

particles:approximately

5 and 200 nm.

properties of colloids
Properties of Colloids
  • Tyndall effect : light scattering by particles in a colloid or particles in a fine suspension.
  • Absorption:another characteristic of colloids.
tyndall effect
Tyndall effect
  • The Tyndall effect can be used to tell the difference between the true solution, and colloid.
flocculants for water treatment
Flocculants for Water treatment
  • Flocculants:causing colloids and other suspended particles in liquids to improve the sedimentation of small particles.
al oh 3
Al(OH)3
  • Al(OH)3:the basis for application of as coagulant in water purification.
  • Alzheimer’s disease:traces 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.
fe oh 3
Fe(OH)3
  • Preparation of Fe(OH)3 :

Fe(NO3)3 + NaOH → Fe(OH)3 + NaNO3

Fe(OH)3

fe oh 31
Fe(OH)3
  • Absorbent for suspension in raw water.
  • Removal of Pb2+ and other heavy metal ions.
hydrolysis of ferric ion
Hydrolysis of ferric ion
  • Ferric ion hydrolyzes in water:

[Fe(H2O)6]3+ + H2O → [Fe(H2O)5(OH)2]2+ + H3O+

[Fe(H2O)5(OH)]2++H2O→[Fe(H2O)4(OH)2]++H3O+

2[Fe(H2O)6]3+→[Fe(H2O)4(OH)2Fe(H2O)4]4++2H3O+

  • When pH value of the solution decreases, the hydrolysis of ferric ions decreases too.
slide11
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

removal of pb 2 zn 2 cr vi
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.
slide13
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.
analyze the pb 2 by icp ms
Analyze the [Pb2+] by ICP-MS
  • The [Pb2+] in the stock solution is 7174 ppm.
slide15

The absorption of Zn2+by Fe(OH)3 is excellent.

  • The higher pH value, the less [Pb2+]
analyze the zn 2 by icp ms
Analyze the [Zn2+] by ICP-MS

The [Zn2+] in the stock solution is 4784 ppm

‧ 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%.

analyze the cr vi by icp ms
Analyze the [Cr(VI)] by ICP-MS
  • There are two species of Cr(VI):

K2CrO4(aq) K2Cr2O7(aq)

  • Both the two species are poisoned.
slide19

0.01M K2CrO4(aq):

[Cr(VI)] in stock solution is 563 ppm

slide20

b) 0.001M K2CrO4(aq)

[Cr(VI)] in stock solution is 56.4 ppm

slide21

The absorptionof 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-

conclusion
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%.

conclusion1
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.

thanks for your attention
Thanks for your attention!!

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