Removal of Cadmium, Zinc, and Manganese from Dilute Aqueous Solutions by Foam Separation

As environmental regulations are becoming stricter, new techniques must be developed for the removal of trace concentrations of heavy metals from mineral processing effluents. Foam separation techniques are an interesting alternative to more conventional processes such as ion exchange because of their efficiency to treat dilute aqueous streams. In this paper, the simultaneous removal of Cd2+, Mn2+, and Zn2+ from dilute aqueous solutions was investigated by using sodium dodecyl sulfate as collector and triethylenetetramine as auxiliary ligand via a series of batch-mode flotation experiments. Experimental results showed that Cd2+, Mn2+, and Zn2+ can be completely removed in one step under the following conditions: pH 9.50, flotation time=120 min, auxiliary concentration 0.1 mmol L-1, collector-to-metals molar ratio 2:1, ethanol concentration 0.5% (v/v), and a nitrogen gas flowrate set at 25 mL min(-1). An excess in auxiliary ligand concentration yielded to low removal efficiency. The modeled speciation of the examined system suggested that the metals are separated from the bulk solution to the foam phase via a combination of ion flotation and precipitate flotation.

Automated summary

This study investigated the simultaneous removal of Cd2+, Mn2+, and Zn2+ from dilute aqueous solutions using foam separation technique, demonstrating that these metals can be completely removed under specific conditions. Experimental results showed that parameters such as the molar ratio of collector to metals, auxiliary ligand concentration, and nitrogen gas flow rate significantly affect the removal efficiency. The modeled speciation suggested a combination of ion flotation and precipitate flotation for the separation of metals from the bulk solution to the foam phase.