| Along with industrialization advancement speeding up,the mineral resources were exploited and utilized constantly,and the environmental hazards caused by thallium pollution have seriously threatened human health and aroused widespread concern.which caused the environmental pollution question of thallium more and more serious.At present,the environmental protection department of Human Province has issued industrial wastewater discharge standards of thallium pollutants.The emission limit was 5?g/L.In recent years,the thallium content in the Xiangjiang River Basin was found to exceed the standard.After the investigation,it was found that some of the thallium pollutants were from the sintering flue gas desulfurization effluent of a Steel Enterprise in Hunan Province.The traditional methods were hard to treat the low concentration thallium in wastewater.However,it was shown that the emulsion liquid membrane(ELM)technique could be applied to wastewater containing low concentration thallium and achieve the best effect.The ELM is comprised of aviation kerosene as the organic solvent,2-ethylhexyl phosphoric acid-2-ethylhexyl ester(P507)as the carrier,polyisobutylene succinimide(T154)as the surfactant,polyisobutylene(PIB)as the additive and sulfuric acid as the internal reagent.Due to the stability of the ELM will directly affect the separated efficiency of metal ions,at first,the concentration of carrier,surfactant and stripping phase and other factors have been investigated.The research showed that T154 could maintain the system more stable than Span80.Among the influencing factors,the surfactant concentration and feed solution phase/emulsion phase volume ratio could affect the stability of emulsion liquid membrane more obvious,the rupture rate exceeded 6%.So increased of surfactant concentration appropriately and reduced the feed solution phase/emulsion phase volume ratio would achieve a steady system.On the basis of the ELM stability tests,the removal efficiency of thallium which existed in sintering flue gas desulfurization wastewater was studied further.Under the optimized ELM operating conditions of 2% of carrier,5% of surfactant,0.5 mol/L of stripping agent,350 rpm of agitation speed,500:40 of volume ratio of feed solution to emulsion phase,3:1 volume ratio of membrane to internal phase and after 15 minutes,the thallium concentration in the treated wastewater was below 5 ?g/L which analysised by the Inductively Coupled Plasma Mass Spectrometry,the removal efficiency of thallium was 99.76%.This indicated that the residues of thallium in effluent could meet the local discharge criteria of Hunan Province.Subsequently,the influence of major calcium and magnesium coexisting ions in wastewater on extraction of thallium ion by ELM was investigated.The result showed that the feed solution would turn into an acidic circumstance in a short time by the rapid ion exchange,which would be in favor of the removal of thallium from calcium and magnesium contained in desulfurization wastewater.The emulsions after reaction were needed to break for reuse.The demulsification conditions which include ultrasonic,centrifugation,heating and demulsifier were studied.The research showed that the single method could not make the system effectively demulsification,however,in the process of heating-demulsifier combined methods which the temperature is 70°C and the oxygen sodium as a demulsifier,the system could be almost completely demulsificated.The removal rate of thallium was over 90% after the oil phase reused.In the end,the interior of ELM was studied and the migration route of thalliumwas interpreted.In conclusion,as one of the highly efficient separation methods,which belongs to liquid membrane technology,the ELM possessed the advantages of fast mass transfer,large mass transfer area,high selective etc compared with traditional methods.The oil phase could be recycled and reused after demulsification.This indicated that the ELM is a very promising technique in the removal of Tl in sintering flue gas desulphurization wastewater drained from ferrous metallurgic industry. |
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