Study On The Boric Acid Complexation Extraction Process Of Magnesium Brine

The boric acid complexation extraction from strong acid brine with high concentration of magnesium and low concentration of boron was studied by using isooctyl alcohol as complexing agent and toluene as dilution agent. A liquid-liquid equilibrium model of boric acid complexation extraction was established and the complexation extraction process was developed for low concentration of boric acid extraction.The effects of concentration of complexing agent isooctyl alcohol and different dilution agents (kerosene, toluene and methyl-phenol) on extraction efficiency, coefficient of distribution and phase splitting time were investigated. The best extraction result was achieved with toluene as dilution agent and the concentration of complexing agent isooctyl alcohol of 0.5 (v/v). Under the conditions of 0.5 (v/v) isooctyl alcohols and extraction phase ratio O/A=1:1 (organic phase: aqueous phase), the effects of pH value of brine and magnesium ion concentration on extraction phase equilibrium were also studied. The boric acid complexation extraction is promoted as the pH<3 and the concentration of magnesian ion is more than 3.3 mol·L-1, while the partition coefficient of boric acid is larger in two phases. The regeneration of extractent with water was also investigated and the regeneration conditions of six-stage countercurrent regeneration were determined while A/O = 0.7:1 (aqueous phase: organic phase).The mechanism of boric acid complexation extraction was studied by the combination of IR and slope ratio method. The components of the complexation were qualitatively analyzed by using IR, and then the composition of the complexation was calculated with slope ratio method. The research results were concluded as the followings: (1) The complexation agent that was composed of isooctyl alcohols and toluene has the chemical extraction ability on the boric acid, but does not have the physical extraction ability. The extraction of boric acid was accomplished by the formation of isooctyl borate through esterification reaction of isooctyl alcohols and boric acid, because the isooctyl borate can be dissolved into the organic phase. (2) The complex compound only includes mono-isooctyl borate and di-isooctyl borate. The biger phase ratio and concentration of the magnesium ion, the biger percentage di-isooctyl borate in the complexation.According to the thermodynamic fundamental and the electrolyte solution theory, a liquid-liquid equilibrium model was established for the boric acid complexation extraction with isooctyl alcohol under the conditions of high concentration of magnesium and low concentration of boron, and the interaction parameters of the model were calculated through regression. The four-stage and eight-stage cross extraction process, as well as the eight-stage countercurrent extraction were simulated by the model. The data deviation between the experiment and the model calculation is less than 5%, which proves the validity of the model.A complexation extraction process of boric acid from the strong-acid magnesium ion brine was developed on the basis of above investigation. The simulation of the process demonstrated that the boric acid concentration of extracted brine can reduce to less than 30 mg·L-1 (based on B2O3). This extraction process makes the brine good material for producing high purity magnesium oxide and recovers boric acid, which realizes the comprehensive utilization of the brine.