A study of adsorption mechanism of dodecylamine on sphalerite

• A new flotation mechanism of sphalerite using dodecylamine as collector is proposed.
• Dodecylammonium ions could chemisorb with sulfur atoms (in ZnS form) by N atoms.
• The neutral molecular dodecylamine could screen the electrostatic repulsion between positive-charged head groups.
• Negatively charged dodecylamine precipitates inhibit sphalerite flotation.

Long-chain primary amines are not only good collectors for silicate minerals, but, they can also float some metallic sulfides. However, the flotation mechanism of sulfide minerals using long-chain primary amines as collector is uncertain. In this paper, the flotation performance and adsorption mechanism of dodecylamine in the flotation of sphalerite was studied using micro flotation tests, zeta potential measurements, XPS analysis and FTIR measurements. The dodecylamine showed better sphalerite flotation performance over a wide pH range even at a low collector dosage. The spectroscopic data in combination with zeta potential showed that: (1) chemisorption occurred between the N atoms in dodecylammonium ions (RNH3+) and the sulfur atoms in ZnS over the pH range from 1 to 13. The molecular dodecylamines (RNH2) could also adsorb via H-bonds with other sulfur atoms; (2) the molecular dodecylamine absorbed onto the sphalerite surface may screen the electrostatic repulsion between the positive-charged head groups (−NH3+) absorbed onto the sphalerite surface, which increased the density of absorbed amine and further enhanced the surface hydrophobicity; (3) in the alkaline pH range, the dodecylamine colloidal precipitates appeared, and the zeta potential of the colloidal precipitates changed from positive to negative as the pH increased. As a result, positively charged precipitates electrostatically adsorbed onto the negatively charged sphalerite surface thus enhancing the flotation recoveries, while negatively charged precipitates inhibited sphalerite flotation.

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