Recovery of Boron from Underground Brine by Continuous Centrifugal Extraction with 2-Ethyl-1,3-hexanediol (EHD) and Its Mechanism

In order to economical and environmental-friendly recycle of boron from underground brine, the extraction of boron was carried out in this work by the continuous centrifugal technique using 2-ethyl-1,3-hexanediol (EHD) + sulfonated kerosene (SK) extraction system, and the extraction mechanism was also investigated by the combination of FT-IR with slope method. The results showed that boron can be effectively extracted from underground water with the concentration of boron 5.43 g·L −1 by five-stage centrifugal extraction using 30% EHD + 70% SK at pH = 2.0–3.0, R (O/A) = 1 : 2, and the extraction rate reached 98.46%. Boron in the organic phase can be well five-stage back-extracted by 1.0 mol·L −1 ·NaOH at R (O/A) = 1 : 1 with a back-extraction rate of 97.00%. About 88.32% boron in the aqueous phase obtained by back-extraction can be recycled in H 3 BO 3 form by evaporation crystallization after acidified to pH < 2.5. The extraction mechanism indicated that the extraction is completed mainly based on the esterification reaction between alcoholic hydroxyl in EHD and -OH in B(OH) 3 at the stoichiometric ratio 1 : 1 to generate a stable six-membered ring structure of boric acid ester.