Flocculants 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 Ferric hydroxide colloidal solution performs excellently on the adsorption of heavy metal ions. → research the adsorption of lead ions (Pb 2 ＋ ), zinc ions (Zn 2 ＋ ), chromium(VI) ions to decrease the huge volume of waste water containing heavy metal ions in high school chemistry laboratory

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 Tyndall effect : light scattering by particles in a colloid or particles in a fine suspension. Absorption ： another characteristic of colloids.

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

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 ： 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 Preparation of Fe(OH) 3 ： Fe(NO 3 ) 3 + NaOH → Fe(OH) 3 + NaNO 3 Fe(OH) 3

Absorbent for suspension in raw water. Removal of Pb 2 ＋ and other heavy metal ions.

Hydrolysis of ferric ion Ferric ion hydrolyzes in water ： [Fe(H 2 O) 6 ] 3+ + H 2 O → [Fe(H 2 O) 5 (OH) 2 ] 2+ + H 3 O + [Fe(H 2 O) 5 (OH)] 2+ +H 2 O → [Fe(H 2 O) 4 (OH) 2 ] + +H 3 O + 2[Fe(H 2 O) 6 ] 3+ → [Fe(H 2 O) 4 (OH) 2 Fe(H 2 O) 4 ] 4+ +2H 3 O + 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). pH12 pH3

Removal of Pb 2 ＋ 、 Zn 2 ＋ 、 Cr(VI) Large volume of waste water containing Pb 2 ＋ 、 Zn 2 ＋ 、 or Cr(VI) ions is produced by the experiments in the high school chemistry course. Pb 2+ 、 Zn 2 ＋ 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 Pb 2 ＋ 、 Zn 2 ＋ 、 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 The [Pb 2 ＋ ] in the stock solution is 7174 ppm. pH Experiment Experiment

The absorption of Zn 2 ＋ by Fe(OH) 3 is excellent. The higher pH value, the less [Pb 2+ ]

The [Zn 2+ ] in the stock solution is 4784 ppm Analyze the [Zn 2 ] by ICP-MS Analyze the [Zn 2 ＋ ] by ICP-MS pH ppm ‧ The absorption of Zn 2+ 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.

Analyze the [Cr(VI)] by ICP-MS There are two species of Cr(VI) ： K 2 CrO 4(aq) K 2 Cr 2 O 7(aq) Both the two species are poisoned.

a)0.01M K 2 CrO 4(aq) ： [Cr(VI)] in stock solution is 563 ppm pH ppm

b) 0.001M K 2 CrO 4(aq) [Cr(VI)] in stock solution is 56.4 ppm pH ppm

The absorption of Cr(VI) by Fe(OH) 3 colloid is far worse than the absorption of Pb 2 ＋ and Zn 2 ＋ ions. The best absorption is at pH 7. There is a chemical equilibrium between CrO 4 2- and Cr 2 O 7 2- ： 2CrO H +  Cr 2 O H 2 O Cr 2 O 7 2- will exist more than CrO 4 2- in the acidic solution. Fe(OH) 3 will have a better capability of absorption for Cr 2 O 7 2-

Conclusion  The absorptions of Pb 2 ＋ 、 Zn 2 ＋ and Cr(VI) ions by Fe(OH) 3 colloid perform excellent.  The higher the pH value is,the better the absorption of Pb 2 ＋ and Zn 2 ＋ 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 attention!! T o hi ank sfno ryo u rate t t n!!