Research Of Removing Copper From Wastewater With Mixed Surfactants By Flotation

Flotation (foam separation) is one of methods frequently used for heavy metal removal from dilute aqueous solutions. Collector usually employs chemosynthetic surface-active reagent but rarely used environment-friendly biosurfactants from microorganism and plant. In order to promote the use of green environment-friendly products, the complex of novel biosurfactant and other kinds of surfactants are researched, and the effects to remove heavy metal ions from wastewater with the best mixed system are investigated.The natural nonionic surfactant tea saponin from theaceae plant extraction is mixed with various different chemosynthetic surfactants. The surface tension of tea saponin (TS)/ sodium dodecyl sulfate(SDS) and TS/ hexadecyl trimethyl ammonium bromide(CTAB) are measured. The effect of the concentration and kind of inorganic electrolyte on the surface activity and foam properties of mixture are investigated. The results show the surface tension of the complex mixed by TS and anionic/cation surfactants both reduct. There are synergism effects between TS and anionic/cation surfactant, but the synergism effect is more evident between TS and anionic surfactant: when the mole ratio of TS/SDS is between 1:5and 1:3, it is found that the surface tension and critical micelle concentration (cmc) are both the lowest; the mixtures'foaming ability and stability are both improved, and the optimal foam properties can obtain when the mole ratio of TS/SDS is between 1:5 and 1:4; Inorganic salt had a major impact on surface activity of SDS but rarely on TS's since its steady quality.Flotation is progressed as TS/SDS is 4:1 refer to the rusults of mixing. The control group mixed by SDS and the other nonionic chemical surfactant Tween-80 was set as well. The potential of two complex systems to remove copper from wastewater are investigated respectively. Main physicochemical parameters influencing process, such as the collector-copper ratio(molar ratio), pH of the solution, the ionic strength(NaCl and NaNO3), as well as kinetic parameters(flotation time and air flow rate) are evaluated. Promising results were obtained:under identical conditions, the rate of copper removed by the complex of SDS and TS was significantly higher than by the control group. The removal efficiency increased with increasing molar fraction of SDS to TS and reached to maxium when mixture ratio was 4:1. The maxium value of removal rate and enrichment ratio was 94.8% and 158 respectively when the collector-copper ratio was 3:1, pH was 8.0, and air flotation was 0.2L·min-1. Ionic strength had a remarkable impact on copper removal.Copper removal rate significantly decreased with increasing of inorganic salt concentration from 0.0001 mol·L^-1 to 0.05 mol·L^-1when copper concentration in solution was invariable.Copper recovery rate with alkaline precipitation could reach up to 86.4% when copper concentration in foam concentrated was higher than 50 mg·L^-1.