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Removal of Heavy Metals from Contaminated Water
I'm a 5th year chemical engineering student, trying to remove chromium (6+) from groundwater stream. My questions are: how to reduce Cr 6 to Cr 3 through treatment since the later is less toxic. I believe that Cr 6 can be removed (by adsorption) at low pH, therefore how to control pH in ground water since it is impossible to add acids to drinking water. What are the most effective adsorbent to remove Cr 6. Any help would be greatly appreciated.
- Abu-Dhabi, United Arab Emirates University, UAE
The simplest and most effective way to reduce hexavalent chromium is to add three electrons to each molecule. This can be accomplished at any pH under 9.0 using an electrolytic reactor with steel plates - electrocoagulation. No other chemical, acids, etc. are needed as long as the water will conduct electricity. The only negative is that the chromium will precipitate as a chromium iron oxide immediately after reduction, along with many other contaminants whether you want to remove them or not.
- Shiner, Texas, USA
Weak and strong base anion exchange resins and activated carbon have all been used for the removal of hexavalent chromium from groundwater. The capacity of these medias before leakage occurs is relatively low however, since the monovalent HCrO4- ion is not held as strongly as the divalent ions CrO4= and Cr2O7=. Since there is an equilibrium between the different ions, a small percentage of the chromium is always present as HCrO4-.Lyle Kirman
consultant - Cleveland Heights, Ohio