Study On The Process Of Extracting Arsenic From Alkaline Solution By Modified Quaternary Ammonium Salt

The ash dust with high arsenic content in copper smelting industry can selectively enter into the solution through alkali leaching process,so as to effectively separate from other valuable elements.However,the high arsenic content in the alkali leaching solution also needs to be treated.In order to solve this problem,the process of extracting arsenic from alkaline solution by modified quaternary ammonium salt was studied in this paper.This paper mainly studies the selection and transformation of extractant,the extraction,stripping and reaction mechanism of arsenic,as well as the recycling and utilization of organic phase of extractant.A new closed-circuit recycling extraction process which can effectively deal with high arsenic content in alkaline system is obtained.The contents are as follows:?1?In this paper,Trioctylmethylammonium chloride?TOMAC?was selected as the extractant of arsenic in the alkaline system.In order to improve the arsenic extraction ability of the extractant,the experiment transformed the Cl^-type TOMAC into the CO₃^2-type TOMAC.In this paper,the scheme of direct transformation of Cl^-type TOMAC with Na₂CO₃ solution was proposed,and the transformation effect of different concentrations of Na₂CO₃ solution on the extractant was investigated.Finally,under the condition of 25?,the ratio of 1:1 was selected Using 12%Na₂CO₃ solution to directly transform the Cl^-type TOMAC for 6 to 8 times,and the contact time of oil and water is 8 min,the ability of extracting arsenic from alkaline solution by the transformed CO₃^2-type TOMAC has been greatly improved,and the single-stage extraction rate can reach 86.91%.The results show that the more carbon atoms are,the better the polarity of the solution is.During the extraction,different polar improvers have an effect on the extraction performance of arsenic.The experiment shows that the more carbon atoms,the better the polarity improvement effect of the solution.Dodecyl alcohol is more conducive to improving the arsenic extraction performance of the extractant than secondary octanol.The extraction mechanism of arsenic was also studied by means of saturated capacity method and equimolar series method,combined with GC-MS spectrum of the extract.It was clear that the main components of the extract were(C₂₅H₅₄N)₂HAsOS₂ and(C₂₅H₅₄N)₂HAsO₂S.?2?Through a series of screening of the stripping agent of arsenic in the organic phase loaded by the quaternary ammonium salt extraction system,the stripping agent that can meet the requirements of both high-efficiency stripping and direct generation of recycled organic phase is selected:low concentration H₂O₂ solution+saturated Na₂CO₃ solution.The experimental results show that H₂O₂ is an important reason to realize the high efficiency of stripping with supported organic phase.The trace H₂O₂??4%?can oxidize the arsenite in the system to arsenite rapidly,and whether H₂O₂ is added first or later does not affect the experimental results.The extraction experiment of As???and As???reveals the mechanism of as stripping in the supported organic phase:there is a difference in the association ability between As???and As???and quaternary ammonium salt cations.In contrast,the association ability between As???and quaternary ammonium salt cations is stronger than that between As???and quaternary ammonium salt cations,which made the thioarsenite in the aqueous phase of the extraction process easy to exchange with CO₃^2-in the organic phase of the extractant to obtain high-efficiency extraction In the process of stripping,the thioarsenite in the loaded organic phase was oxidized to thioarsenate by H₂O₂ of low concentration,and then was rapidly exchanged by CO₃^2-in the stripping agent solution,thus showing a high stripping rate.In addition,the preliminary thermodynamic study of the stripping process shows that the stripping process belongs to endothermic reaction.In the temperature range of 0?³5?,the rise of temperature is conducive to the stripping of arsenic.?3?The results show that when 4%H₂O₂+saturated Na₂CO₃ solution is used as the stripping agent,under the condition of 25?at room temperature,1:1 and 7 min contact time between oil and water,the stripping rate of arsenic is more than 99%.At the same time,the organic phase of CO₃^2-type TOMAC which can be directly used is formed.Through FTIR,NMR and UV-vis analysis of the whole extraction process,the mechanism of transformation,the mechanism of transformation,extraction and stripping can be demonstrated,and the closed-loop extraction process flow chart can directly reveal the law of recycling extraction behavior,show the characteristics and advantages of the whole extraction process and flow,and the recycling experiment of organic phase also reflects The performance of the organic phase is good.The process can not only make the organic phase of the extractant be recycled efficiently,but also Na₂CO₃ solution can be recycled repeatedly.The overall process material is simple and does not produce waste liquid,showing the characteristics of short process,good circulation performance,low cost and high efficiency.