Compositional Surfactant Formulation Assised Foam Fractionation For Removing Chromium Ions And New Technologies Development

Chromium pollution in wastewater has great potential harm to ecosystem and human health,and has become a major global environmental problem.Foam fractionation technology is a new separation technology for recovering low concentration substances.It can be used to remove heavy metal ions.The key of the technology is effective surfactants.However,most of the capture agents are chemical synthetic surfactants,which will cause secondary pollution to the environment.Biosurfactant has become an ideal substitute for chemical surfactant because of its natural source and good environmental compatibility.Therefore,this paper studies the separation mechanism of biosurfactant for heavy metal chromium,and develops two separation processes with different biosurfactants.The first process is to prepare a binary surfactant mixture by mixing Sapindus Saponin and cetyl trimethyl ammonium bromide,which as a capture agent in foam fractionation process to removal hexavalent chromium in water.The surface activity and foam performance can be improved by the binary surfactant Sapindus Saponin-cetyl trimethyl ammonium bromide,and the best compound mass ratio(Sapindus Saponin: cetyl trimethyl ammonium bromide)is 1:1.The interaction between Cr(Ⅵ)and binary surfactants was analyzed by IR.The results showed that there was strong electrostatic binding between them.The effects of binary surfactant concentration,pH and gas volume flow rate on the separation of hexavalent chromium were investigated.Under the suitable operation conditions of foam fractionation of Cr(Ⅵ)concentration 10 mg/L,binary surfactant concentration 0.17 g/L(mass ratio of Sapindus Saponin to cetyl trimethyl ammonium bromide was 1:1(w/w)),pH 5.0 and volumetric air flow rate 150 m L/min,the removal percentage and enrichment ratio of Cr(Ⅵ)reached 94.05% and 48.15,respectively.The enrichment ratio of Cr(Ⅵ)was increased by 38.6%,but its removal percentage was only decreased by 1.6% compared to the case that cetyl trimethyl ammonium bromide only was used under the same operating conditions.The second process is the integrated technology of biological reduction,micelle enhanced ultrafiltration and foam fractionation.The technology is applied to removal hexavalent chromium from water.Only one biosurfactant rhamnolipid was used in the whole process.First,rhamnolipid was used to reduce hexavalent chromium,and the effects of the amount of rhamnolipid and pH on the reduction percentages of hexavalent chromium were studied.The experimental results show that the reduction percentage of hexavalent chromium is 95.6% when the rhamnolipid concentration exceeds 1.50 g/L and the pH is 6.0.Then the influence of the operating parameters of micelle enhanced ultrafiltration-foam fractionation on the removal percentages of trivalent chromium was investigated.Under the best operating conditions,micelle enhanced ultrafiltration has a transmembrane pressure of100 k Pa and foam fractionation uses a gas distributor with a pore size of 0.125 ± 0.01 mm.micelle enhanced ultrafiltration-foam fractionation can remove 97.5% of trivalent chromium.Therefore,the removal percentage of hexavalent chromium was 93.21% after the combined process of biological reduction-micelle enhanced ultrafiltration-foam fractionation.To sum up,this paper develops two process routes to removal hexavalent chromium from water,which aims at providing some new ideas for the treatment of chromium pollution in water by biological surfactant.It also looks into the prospect of combining bio surfactant with foam fractionation for remediation of heavy metal pollution.