Industrial wastewater generally contains heavy metals, like iron, cobalt, nickel, zinc etc. that are harmful to living organisms. For treatment of such wastewater, it is possible to use ozone or oxidizer to make them precipitate as M(OH)3. This method has an advantage in that it is possible to precipitate heavy metals separately by using Potential-pH diagram for each heavy metals. That is, heavy metals can be recovered from wastewater for reuse. Another advantage is that ozone will not contaminate water. In this project, ozonation experiments were performed for iron, cobalt and nickel by injecting 20.88 mg/h of ozone in solutions containing 100 ppm of each metal. From the experiments it was found that iron could be separated from cobalt and nickel at pH 5 and cobalt could be partially separated from nickel at pH 8 which iron was removed from 100 ppm Fe2+ to 1.1 ppm Fe2+ at pH 5 after 90 minutes of ozonation. The reaction order and reaction rate constant for Fe oxidation-precipitation reaction were –0.17 and 3.52 10-6 , respectively. In the case of cobalt, it was found that Co2+ concentration was decreased from 100 ppm to 57.1 ppm after 90 minutes at pH 8. The reaction order and reaction rate constant for Co oxidation-precipitation reaction was –0.5214 and 6.82 10-10 , respectively. In the case of nickel it was found that Ni2+ concentration was not almost changed because amount of used ozone was very small in comparison with the required amount.
By
Natthapol Vijitrachalermpongsa
Thanayachai Bounnatee
