Comprehensive Utilization Of Major Elements In Pingluo Underground Brine Of Marine Deposit In Sichuan Province

There are rich underground brine resources located in Sichuan basin of western china.Pingluo underground brine,which was discovered in 1990,belongs to marine deposit in Pingluoba structure of Chengdu salt basin,is rich in major elements as potassium,sodium,calcium,magnesium,boron,bromine and chlorine,and also has trace element as lithium and rubidium.The brine resources were famous for its high grade of useful elements,abundant inorganic species and large reserves until been discovered,which has showing great prospects for industrial applications.However,key techniques about the comprehensive utilization and exploration of the brine resources still have not been resolved,further research efforts are required to extract useful chemicals in industrial scale from this complex salt-water system.Aiming at utilization of the Pingluo underground brine,extensive research was carried out to extract elements as sodium,potassium,boron and bromine efficiently,and process for four kinds of products as industrial salt,potassium chlorine,borax and bromine been proposed,preliminary conclusions were as the follows.?1?A principle comprehensive utilization process for the main elements in Pinluo underground brine has been settled.Study on isothermal evaporation of the brine at 55??328K?shows that the crystallization sequence of Pinluo brine is: NaCl;NaCl + K?Cl,Br?;NaCl + K?Cl,Br?+ H₃BO₃.The crystallization paths and the precipitation regularities of salt were consistent with theoretical analysis of quinary system Na⁺,K⁺,Mg²⁺ //Cl^-,Br^--H₂O at 328 K.The analysis of the phase diagram and the isothermal evaporation data show that bomine-potassium separation and boron-potassium separation are two key techniques for the Pinluo brine comprehensive utilization.Therfore,the extraction methods,and process route aiming at utilization of Na⁺,K⁺,Br^-,B₂O₃ were proposed,and a principle technological process has been settled.?2?The process of the first-stage vacuum evaporation for the industrial salt extracting has been established.Analysis,calculation results of the quaternary system Na⁺,K⁺,Mg²⁺ //Cl^--H₂O at 298 K,323K,348 K and 373 K were consistent with the vacuum evaporation data.The segment point between sylvite and rock salt is 38.72% weight loss of original brine during evaporation.The industrial salt obtained from evaporation meet with first grade of QS after washing with original brine.?3?Due to large amout of bromine loss in solid phase with formation of K?Br,Cl?during evaporation,a novel process of bromine manufacturing method was established by chlorine oxidation-steam distillation method,optimization parameters as chlorine quantity,oxidation potential,feed temperature,vacuum degree were determined as follows: chlorine quantity is 115 120 %,brine temperature is 373 K,the flow ratio of steam to brine is 0.14 0.16,the redox potential is 1060 ¹080 mV and vacuum degree in flash tank is-14 ^-10 kPa.The concentration of bromine in liquid phase is 0.321g�L^-1 after steam distillation finished under optimized conditions and the recovery efficiency of bromine reaches 91.67 %.?4?Extensive studies carried out to separate boron from bromine extracted brine,and the extaction process of boron was settled using fatty alcohol solvent extraction method.Fatty alcohol mixed with Exxsol D80 solvent was selected as organic phase.IR spectrum test of 1-octanol H₃BO₃ complex and 2-ethyl-1,3-hexanediol H₃BO₃ complex shows that interaction mode between H₃BO₃ and fatty alcohol was formation of extract complexes and dissolution,physical transfer of H₃BO₃ from water to oil phase does not exist.Effects of the experimental factors on extraction and the stripping equilibrium were discussed,it was concluded that lower pH of brine is beneficial to extraction efficiency and the alkaline environment can accelerate the hydrolysis of boric acid ester,which could greatly improve the stripping efficiency.Based on extraction mechanism and reaction equilibrium of boric acid with alcohol,the optimized parameters of borax preparation and process were determined.According to countercurrent extraction/stripping mathematical model,derivation formula of extraction/stripping series was established and the calculation results were verified through process of 12 stages solvent extraction and 5 stages stripping operation.The extract efficiency reaches 93.52%,stripping efficiency reaches 94.18%,recovery rate reaches 83.86%,industrial borax product meet first grade of QS.The solvent extraction process proposed in study is very efficient,economical and simple,especially suitable for extraction of boron from underground brine or saltlake brine.?5?The process of �second stage vacuum evaporation � recrystallization� for potassium chlorine preparation was established,simplified salt-water system can be described by quaternary system Na⁺,K⁺,Mg²⁺ // Cl^--H₂O at 348 K,phase diagram analysis and calculation results including water evaporation,carnallite precipitated point were consistent with data from verified experiments,it is remarkable that the crystallization and precipitation regularity of Rb+ co-precipitated with Carnallite to form sulotion?K,Rb?Cl�MgCl₂�6H₂O,the phenomenon occurred is also confirmed by studies of Xudong Yu and Ying Zeng?2010?.Based on theoretical analysis and calculation,preparation process of potassium chlorine by hot crystallization method was proposed,optimized parameters were obtained through verified experiments,product of potassium chlorine reaches first grade of QS with purity of 98%,and recovery efficiency of K⁺ is greater than 80%.The general comprehensive utilization process of Na⁺,K⁺,Br^-,B₂O₃ of Pingluo underground brine were: the first-stage vacuum evaporation for the industrial salt,the chlorine oxidation-steam distillation for the bromine,the fatty alcohol solvent extraction for the borax and the second stage vacuum evaporation � recrystallization for potassium chlorine and the industrial salt.The separation problem of bromine and boron with potassium were resolved successfully,research achievements have been applied in industrial scale at Qionglai pilot plant in west Sichuan province,where the scale of industrial salt,bromine,borax and potassium chlorine were 68000t/a,900t/a,13000t/a and 30000 t/a respectively.