Flotation-separation of toxic metal ions from aqueous solutions using thiosemicarbazide derivatives as chelating agents and oleic acid as a surfactant

Abstract

A simple and rapid procedure was developed for flotation-separation of toxic metal ions namely Hg²⁺, Mn²⁺ and Cd²⁺ from aqueous solutions. Thiosemicarbazide derivatives such as: 1-(amino-N-phenylmethanethio)-4-(pyridine-2-yl)thiosemicarbazide (H₂PPS), N-phenyl-2-(pyridine-2-ylcarbamothioyl)hydrazinecarboxamide (H₂PBO), 1-(amino(thioformyl)-N-phenylform)-4-(pyridine-2-yl)thiosemicarbazide (H₂APO), and 1-(amino-N-(pyridine-3-yl) methanethio)-4-(pyridine-2-yl)thiosemicarbazide (H₂PPY) have been used as organic chelating agents and oleic acid (HOL) as a surfactant. The different parameters affecting the flotation process namely, metal ion, ligands and surfactant concentrations, foreign ions (which are normally present in fresh and saline waters), pH and temperature are examined. About 100% of mercury, cadmium and manganese ions float at room temperature (~ 25 ^oC), at a metal:ligand ratio of 1:2 and at pH ~5. The procedure was successfully applied to recover Hg²⁺, Mn²⁺ and Cd²⁺ ions spiked into some water samples. The flotation mechanism is suggested based on some physical and chemical studies on the ligands and metal-complexes isolated from the floated layers.