Synthesis Of Boron Extractant And Extracting Boron From Pingluo Underground Brine Located In Sicuan Basin

The Pingluo underground brines located in Sicuan Basin,abundant with potassium,lithium,boron,and rubidium et al,far in excess of the mining industrial grade,has high economical development value.The content of potassium and boron are 53.3 g/L and 4.99 g/L,respectively.In the traditional technology of salts extracting,potassium and boron are always separated as mixed salt and difficult to be purified;meanwhile,in the stage of NaCl salting out,boron lost partially by entrainment,which lead low recovery rate of boron.To solve this problem,solvent extraction was employed to separate boron from brines and product as boric acid before extracting potassium.The extraction efficiency of boron from Pingluo brine was investigated by using a new synthesized boron extraction agent and 2,2,4-trimethyl-1,3-petanediol,and2-butyl-2-ethyl-1,3-propanediol,respectively,andtheoptimalexperimental parameters was obtained.Using formaldehyde and isobutyraldehyde as raw material,triethylamine as catalyst,hydroxypivalaldehydewasmade.Undernitrogenatmosphere,the hydroxypivalaldehyde reacting with sec-butylmagnesium bromide,a new extraction agent 2,2,4-trimethyl-1,3-hexanediol was formed.The new extractant is undissolved in common diluents such as kerosene,sulfonated kerosene and methylbenzene,but it is easy to dissolve in chloroform.The results show that when the concentration of extractant is 1.2 mol/L,the ratio of organic phase to aqueous phase is 1:1,the single extraction rate of boron from Pingluo underground brine is only 20.4%,which is inferior to the expectation.The extraction agent we synthesized was not suitable for extracting boron from Pingluoundergroundbrine.Basedontheexistingextractionagent,2,2,4-trimethyl-1,3-petanediol,and 2-butyl-2-ethyl-1,3-propanediol were chosen as extractant,chloroform as diluents,and the optimal experimental parameters of extracting boron from Pingluo underground brine were obtained.2,2,4-Trimethyl-1,3-petanediol as extractant to extracting boron from the Pingluo underground brines,the optimal parameters are as follows:the concentration of extractant is 0.8 mol/L,the ratio of organic phase to brine is 1:1,the extraction time is8 minutes,the first stage extraction rate of boron is 95.02%,the saturated extraction volume is 46.25 g/L（by H₃BO₃）;after the second stage extraction,the cumulative extraction rate reaches 99.68%.At the re-extraction stage,with 0.4 mol/L sodium hydroxide solution as stripping agent,1:1 of volume ratio of organic phase to stripping agent,the first stage re-extraction efficiency is 81.50%;after the second stage back extraction,the cumulative back-extraction efficiency reaches 97.86%.After continuous operation,the boron from Pingluo underground brine can be recovered 97.55%.Regeneration after second back extraction of the organic phase,the extraction efficiency is 82.59%,and is not high as the first stage,this is due to the extraction agent melting loss in brine and there is still a part of extraction agent and boron band together.The system which contents 2-Butyl-2-ethyl-1,3-propanediol as extractant and chloroform as diluents extraction system is employed to extract boron from Pingluo underground brines.The optimal parameters are as follows:extraction solvent concentration is 1.0 mol/L,the ratio of organic phase to brine is 1:1,the extraction time is 10 minutes,the first stage extraction efficiency of boron reaches 91.36%;after the third stage extraction,the cumulative extraction rate is 99.35%.At the back extraction stage,the stripping agent concentration is 0.3 mol/L,the ratio of organic phase to stripping phase is 1:1,after three stage re-extraction,the boron from Pingluo underground brine can be recovered 98.67%.It is worth noting that the recycling of the organic phase containing extraction agent,the single-stage extraction rate can be reduced with the increase of the organic phase use frequency.The boron total recovery does not always keep a high level,and will gradually decrease.The systems,2,2,4-Trimethyl-1,3-pentanediol+chloroform extraction system,and2-butyl-2-ethyl-1,3-propanediol+chloroform system,are suitable for extracting boron from Pingluo underground brine.Future research should focus on how to reduce the number of extraction solvent soluble loss in large-scale extraction of boron,and choose a more moderate approach boron stripping from the organic phase,in order to early realization the industrial application of boron extraction process.