Development of a system to reduce the volume of mercury containing waste water from laboratories

Abstract

Mercury-containing wastewater from universities needs to be handled carefully in order to prevent the contamination of the surrounding environment and to reduce the high cost for its proper disposal. In this study, a practical system to reduce the volume of mercury-containing wastewater, which can be used in laboratories, was proposed and reduce the cost of waste-water treatment was achieved. Mercury ion in wastewater is vaporized by bubbling with air after the addition of a reductant. The vaporized mercury is then trapped and concentrated in a KMnO₄ solution. In this study, the concentration of the KMnO₄ solution, selection of the reductant, volume of the reductant solution, aeration flow rate, and bubbling time were investigated. Recovery of mercury was observed to be >90% for a 0.01-0.1% 10-mL KMnO₄ solution. Thus, 0.1% KMnO₄ solution was used as the mercury-collecting solution. Among the examined reductants, including NaBH₄, NH₂OH·HCl, and SnCl₂, SnCl₂ was found to be suitable for treating strong acidic wastewater. The flow rate and bubbling time were investigated for 500 mL of the sample solution. After the addition of SnC1₂ to the sample in a reaction vessel, almost all of the mercury in the sample solution was vaporized and trapped in the KMnO₄ solution via bubbling with air at 0.4 L/min for 30 min. Based on these results, a system that reduces the volume of wastewater containing mercury was installed in a laboratory; it was confirmed that approximately 20 L of waste water can be reduced to 10 mL using this system.