Dissolved Air Flotation For The Study Of Heavy Metal Ions From Wastewater

In this paper, trace of heavy metal ion Cr6+ and Pb2+ in the simulation wastewater was removed using ion flotation and precipitate flotation by especially designed dissolve-gas flotation column in a laboratory. The influence of factors such as the kinds and concentration of surfactant, pH value, flotation time, the pressure of solute gas, the kinds and mol concentration of coagulase on flotation behaviors of heavy metal ion were investigated. And then at the optimized flotation conditions, the correlative analysis of macroscopical dynamies of Pb2+ ion was discussed. The processing method of dissolved-gas flotation of heavy metal ion which can meet the national discharge standard was obtained.Results of research on flotation of single metal ion showed that:the removal of effect wasn't satisfied to two metal ions by ues of ion flotation, which was only 40% about to Cr6+ and Pb2+. The effiency of precipitate flotation was significantly better than that of the ion flotation. When the concentration of Cr6+ion was 10mg/L, pH value was 9, the concentration of Sodiumdodecyl benzene sulfonate was 15mg/L, the mol concentration of Ferroussulfate heptahydrate was nFe2+:nCr6+=5:1,flotation time was 35min, the pressure of solute gas was 0.38MPa, the removal efficiency of Cr6+was 93.13%. When the concentration of Pb2+ ion was 20mg/L, pH value was 8.5,the concentration of Sodiumdodecyl sulfate was 15mg/L, the mol concentration of Aluminum sulfate was nAl3+:nPb2+=2:1,the pressure of solute gas was 0.37MPa, the removal efficiency of Pb reached 97.73%.Results of research on flotation behavior of the mixed metal ions indicated that:when the concentration of Sodiumdodecyl sulfate was 15mg/L, pH value was 9, the mol concentration of Ferroussulfate heptahydrate was 5:1,the pressure of solute gas was 0.38MPa, the removal efficiency of Cr6+and Pb2+ was 96.59% and 95.34%, respectively.And the concentration of Cr6+ and Pb2+ in residual solution was 0.34mg/L and 0.87mg/L, so that they can meet the national discharge standard (Cr6+≤0.5mg/L, total Pb2+≤1.0mg/L).In the paper the orthogonal experiment of Pb precipitate flotation demonstrated that:the range the mol concentration of Aluminum sulfate was the most important factor. The sequence of significance level of all factors was nAl3+:nPb>the pressure of solute gas>the concentration of surfactant>pH value. The analysis of macroscopical dynamies of Pb2+ flotation was investigated. The result proved that the process of foam separation could be regarded as first order reaction at the optimized flotation conditions, and the equivalent speed equation was vA=0.190cA and equivalent speed constant was k=0.190min-1.By measuring and analyzing the distribution of residence time and the fluid flowing in flotation column, the average residence time was tm=11.68min, variance wasσθ2=0.528.The distribution density function of residence time was confirmed combined with the relevant experiments.