Transcript Fe(OH) 3
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 (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 • 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(NO3)3 + NaOH → Fe(OH)3 + NaNO3 Fe(OH)3 Fe(OH)3 • 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). pH3 pH12 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 absorption of Pb2＋ by Fe(OH)3 colliod 1000 ppm 800 600 400 200 0 6 7 8 9 10 11 12 13 pH • The absorption of Zn2＋ by Fe(OH)3 is excellent. • The higher pH value, the less [Pb2+] 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%. absorption of Zn2＋ by Fe(OH)3 colliod 2000 ppm 1500 1000 500 0 7 8 9 10 11 12 13 pH • 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)： K2CrO4(aq) K2Cr2O7(aq) • Both the two species are poisoned. a) 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 absorption of Cr6＋ by Fe(OH)3 colliod 300 250 ppm 200 150 100 50 0 7 8 9 10 11 pH 12 13 13.54 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 absorption of Cr6+ by Fe(OH)3 colliod 30 25 ppm 20 15 10 5 0 7 8 9 10 11 pH 12 13 13.17 • 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- 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. TThanks a t te n t io n !! h anks ffor or your attention!!