Experimental Study On Synthesizing Hydramine And Extracting Boron From The Potassium Riched Pingluo Brine

The Pingluo underground brines,abounded with lithium,potassium,boron,and rubidium et al,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 Na Cl 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 brines was investigated by using a new synthesized hydramine extraction agent and2-ethyl-1,3-hexanediol,respectively.By organic synthesis,four hydramine compounds were made,they were N,N-bis（3-hydroxy propyl）hexadecylamine（marked as BHH）,N,N–bis（2,3-dihydroxy propyl）hexadecylamine（marked as BPH）,N,N–bis（2,3-dihydroxy propyl）-2-ethyl-hexylamine（marked as BPO）,N,N–bis（3-hydroxy propyl）-2-ethyl-hexylamine（marked as BHO）.Their extraction efficiency was close to each other.Extracting boron from the Pingluo brine with BHH was studied in detail.In the organic phase,iso-octyl alcohol,the volume ratio of which accounted for one quarter,was dissolved into sulfonated kerosene;the concentration of BHH was 0.01 mol/L.We found that the extraction rate increased from 16.09%to 19.72%with the ratio of organic phase to aqueous phase（O/A）increased from 1:1 to 1.5:1.Meanwhile,though the extraction effect could be boosted by adding salting-out agent,increasing the acidity of aqueous phase or diluting the aqueous phase,optimization of the external conditions couldn’t improve the extraction effect to high level.Because the ability of combining boric acid of hydramine was lower than expected and the quite suitable diluent hadn’t been found yet,it was necessary to optimize the structure of compounds and the current operation scheme further to make the new synthesized extractant be efficient on extracting boron from Pingluo brine.Among the various boron extractants,it was reported that aliphatic diol is of eminent extraction capacity.2-Ethyl-1,3-haxanediol was therefore used for the recovery of boron from the Pingluo underground brines.And the optimal parameters were obtained as follows.At room temperature,we used 2-ethyl-1,3-haxanediol as extractant,sulfonated kerosene as diluting agent,when the volume ratio of extractant in organic material reaches 30%,and the ratio of organic phase to brine is 1:1,the first stage extraction rate of boron is 95.01%,the saturated extraction volume is69.81 g/L（by H₃BO₃）;after the second stage extraction,the overall extraction efficiency reaches 99.37%.At the back extraction stage,with 0.5 mol/L sodium hydroxide solution as stripping agent,1:1 of volume ratio of stripping agent to organic phase,the first back extraction efficiency is 69.58%;after the third stage reextraction,the overall back extraction efficiency reaches 99.33%.After continuous operation,the boron from Pingluo underground brines can be recovered 98.70%.In our research,iso-octyl was added to the water-immiscible organic solvent with aliphatic diol,since aliphatic diol cannot be fully dissolved in diluting agent and its solution loss is large in the follow-up process.The results showed as the following:at room temperature,we used 2:3:5 volume ratio of 2-ethyl-1,3-haxanediol,iso-octyl and sulfonated kerosene as organic phase,when the ratio of organic phase to brine is1:1,the first stage extraction rate of boron is 93.35%,the saturated extraction volume is 67.30 g/L（by H₃BO₃）;with two stages extraction,the extraction efficiency of boron can reach 99.82%.At the back-extraction stage,with 0.5 mol/L sodium hydroxide solution as stripping agent,1:1 of volume ratio of stripping agent to organic phase,the first back extraction efficiency is 90.58%;after the third stage reextraction,the overall back extraction efficiency reaches 99.02%.The boron from the Pingluo underground brines can be recovered 98.84%.It should be noted that the extraction efficiency decline gradually with the increase of cycle times when the organic phase was used circularly,so the total recovery rate of boron couldn’t always keep high and it decreased gradually.The structural advantage of aliphatic diol makes it combine boric acid more effectively.In view of this,we can try to synthesize new diols,the structure of which is optimized and the overall performance becomes better.The synthesized diols may extract boron from Pingluo brine more effectively,economically and environmentally.