Flocculants Flocculants for for

Water TreatmentWater Treatment

Date: May ???,2011Speaker :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

• 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

ColloidsColloids• 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 Properties of Colloids Colloids

• Tyndall effect : light scattering by particles in a colloid or particles in a fine suspension.

• Absorption ： another characteristic of colloids.

Tyndall Tyndall effecteffect

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

Flocculants for Water Flocculants for Water treatment treatment

• Flocculants ： causing colloids and other suspended particles in liquids to improve the sedimentation of small particles.

Al(OH)Al(OH)33

• 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)Fe(OH)33

• Preparation of Fe(OH)3 ：

Fe(NO3)3 + NaOH → Fe(OH)3 +

NaNO3

Fe(OH)Fe(OH)33

Fe(OH)Fe(OH)33

• Absorbent for suspension in raw water.

• Removal of Pb2 ＋ and other heavy metal ions.

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.

• 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).

pH12pH12pH3pH3

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.

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 [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

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

• The higher pH value, the less [Pb2+]

absorption of Pb2 by Fe(OH)3＋colliod

0

200

400

600

800

1000

6 7 8 9 10 11 12 13

pH

ppm

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

Analyze the [ZnAnalyze the [Zn22 ＋ ] by ] by ICP-MSICP-MS

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%.

• The absorption of zinc ions is better at higher pH value.

absorption of Zn2 by Fe(OH)3＋colliod

0

500

1000

1500

2000

7 8 9 10 11 12 13

pH

ppm

Analyze the [Cr(VI)] by ICP-MS

• There are two species of Cr(VI) ：

K2CrO4(aq) K2Cr2O7(aq)

• Both the two species are poisoned.

a) 0.01M K2CrO4(aq) ：

[Cr(VI)] in stock solution is 563 ppmpH 13.5

413 12 11 10 9 8 7

ppm 265 262 263 278 277 255 246 197

absorption of Cr6 by Fe(OH)3 colliod＋

0

50

100

150

200

250

300

7 8 9 10 11 12 13 13.54

pH

ppm

b) 0.001M K2CrO4(aq)

[Cr(VI)] in stock solution is 56.4 ppmpH 13.1

713 12 11 10 9 8 7

ppm 22.1 25.9 25.1 26.4 26.3 23.2 14.6 3.72

absorption of Cr6+ by Fe(OH)3 colliod

0

5

10

15

20

25

30

7 8 9 10 11 12 13 13.17

pH

ppm

• 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 Cr2O7

2- ：2CrO4

2- + 2H+ Cr2O72- + H2O

Cr2O72- will exist more than CrO4

2- in the acidic solution. Fe(OH)3 will have a better capability of absorption for Cr2O7

2-

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%.

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 Thanks for your attention!!attention!!TT oohh iiaannkkss ff nnoorr yyoouurr aa ttee tttt nn !!!!