An Efficient Separation for Metal-Ions from Wastewater by Ion Precipitate Flotation: Probing Formation and Growth Evolution of Metal-Reagent Flocs

Abstract Hazardous metal pollutions became a severe environmental issue in China. An efficient precipitation-flotation process was developed to achieve fast removal for metal-ions from wastewater. Structure and strength of precipitate particles/flocs significantly influence the flotation removal of metal-ions. Formation and growth-evolution of precipitate flocs in precipitate flotation were studied by stage analysis of precipitate particles-formation, flocs-regulation and flotation separation. The results demonstrate that early formed precipitates MHA(humics-metal complexing particles) have small particle size, high fractal dimension, low strength and recovery factor. The addition of Fe3+ and CTAB(cetyl trimethyl ammonium bromide) reagents make the precipitate particles aggregated to flocs(MHA-Fe, MHA-Fe-CTAB) much more large, loose, coarse, and small-density. The final generated MHA-Fe-CTAB flocs are hard to be broken up, easy to be recovered and efficient to be separated by flotation process. The flotation removal of MHA-Fe-CTAB flocs is clearly higher than that of MHA or MHA-Fe. The flotation results of MHA-Fe-CTAB are as follows: flotation removal of 98.7±0.40%∼99.9±0.10%, residual TOC of 0.96±0.38∼1.35±0.41 mg/L and turbidity of 0.44±0.09∼0.63±0.16 NTU. Introducing Fe3+ and CTAB reagents into flotation solution contributes to the growth-evolution of precipitate flocs, which could intensify the metal-ions removal via precipitate flotation process and result in more ideal purification indexes for metal-containing wastewater.