Abstract
Heavy metal wastewater which is released from research, educational and medical facilities of universities often contains organic acids. The aluminum coagulation-sedimentation process is one of the usual methods to remove heavy metals from inorganic wastewater, however it is interfered by the coexistent organic acids.
In order to improve the heavy metal removal efficiency, this paper proposes a method using the precipitation with aluminum hydroxide after a pH-shift from 10 to 7. In this study, zinc wastewater was examined as an example. Zinc ions are soluble at pH 7, but zinc forms an unsoluble hydroxide at pH 10. When the pH shifts from 10 to 7, the zinc hydroxide will be removed by the aluminum hydroxide before it reaches a dissolution equilibrium. When the treatments were applied to wastewater containing oxalic acid, malonic acid, succinic acid or glutaric acid, the oxalic acid interfered the zinc removal to a great extend in the case of conventional method. However, using the pH-shift method, wastewater containing oxalic acid could be effectively treated.
