Abstract
In this paper, a combined precipitation–flotation system is proposed for the removal of Fe(III), Zn(II), and Cd(II) as hydroxides. The efficiency of precipitation, as a function of pH, metal ion concentration, and dosage of the precipitating agent as the main variables, was evaluated. The results showed that 99% efficiency was attained from a mixture solution containing the three metal ions in sulfate media at pH 10.3 after 15 min of treatment. The sedimentation behavior showed that a larger precipitate facilitated solid/liquid separation at 30 min. The characterization of precipitates was performed by X-ray diffraction (XRD) identifying iron, zinc, and cadmium oxides; hydroxides; and sodium sulfate. For the flotation, a 20 mg/L solution of dodecylamine (DDA) was used as a collector. Such a solution allowed for the removal of 76% of precipitates in concentrate. An increase in the collector concentration diminished the float percentage due to the micelle formation and low adsorption of the collector on the surface of the precipitate. The results provide evidence of the effectivity of the removal of metal ions by the combined precipitation–flotation system as an alternative for the treatment of acid mine drainage (AMD) in less time in comparison with a sedimentation stage.
Highlights
In Mexico, 4.4% of the consumption of water is related to industrial applications, demanding direct exploitation of rivers, streams, lakes, or aquifers [1]
Formation of Fe(III), Zn(II), and Cd(II) hydroxides involve the chemical equilibrium depicted in the following reactions (4)–(6) that are highly dependent on metal ion concentration and pH value:
Cd(II) was evaluated, showing a precipitation efficiency higher than 99% for the three metal ions at a pH value of 10.3
Summary
In Mexico, 4.4% of the consumption of water is related to industrial applications (including the mining industry), demanding direct exploitation of rivers, streams, lakes, or aquifers [1]. Froth flotation, a well-known technique in the mining industry to concentrate ores through the separation of solids of a different nature (hydrophilic or hydrophobic) by adding a compound named a collector [20,21], has been proposed Compounds such as sodium oleate, potassium ethyl xanthate, dodecylamine, and sodium dodecyl sulfate have been used as collectors for the recovery of precipitates [21,22,23,24]. Complete knowledge of the precipitation–flotation system will offer the mining industry an alternative for the efficient treatment of AMD that in the long term contributes to more sustainable mining, reducing its environmental impact in terms of water consumption and the high heavy metal ion concentration in wastewater [34]. A characterization of precipitates, concentrates and tailing after flotation was performed
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