Study On The Metastable Zone Property Of Boric Acid In Systems Of Sodium Potassium Calcium Ammonium At Low Temperature

Salt lake resource is a precious resource on the Qinghai-Tibet Plateau,and the boron content of Nanyishan oilfield brine is relatively high.Boric acid is dispersed and precipitated during the evaporation of Nanyishan oilfield brine,instead of being enriched in brine in the form of borate.In response to above phenomena,the solubility and the metastable zone width of boric acid in polybasic systems of NH₄Cl-CaCl₂-H₃BO₃-H₂O,CaCl₂-NH₄Cl-NaCl-H₃BO₃-H₂O and KCl-NH₄Cl-CaCl₂-H₃BO₃-H₂O were studied in the range of-18°C to 36°C by infrared laser turbidity method.The solubility equation of boric acid in the above systems were fitted,the effect of different concentrations of NH₄⁺,K⁺,Ca²⁺on the properties of the metastable zone of boric acid were investigated,the nucleation kinetics equation and the nucleation kinetic parameters of boric acid in the above systems were obtained.The results demonstrate that the ammonium chloride has little effect on the solubility of boric acid,the solubility of boric acid becomes higher as the mass fraction of KCl increases while the solubility of boric acid is significantly reduced with the increase of CaCl₂ concentration.In different systems,when the mass fraction of other components coexisting with boric acid is constant,the metastable zone width of boric acid reduces as the concentration of H₃BO₃ increases.In NH₄Cl-CaCl₂-H₃BO₃-H₂O system,when the mass fraction of H₃BO₃ and CaCl₂ is constant,with the increase of the mass fraction of NH₄Cl,the pH of the solution is basically unchanged,the metastable zone width of boric acid decreases first and then becomes larger;In KCl-NH₄Cl-CaCl₂-H₃BO₃-H₂O system,when the mass fraction of NH₄Cl,H₃BO₃,CaCl₂ is constant,with the increase of the mass fraction of KCl,the pH of the solution doesn't change significantly,and the metastable zone width of H₃BO₃ becomes larger.In CaCl₂-NH₄Cl-NaCl-H₃BO₃-H₂O system,when the mass fraction of H₃BO₃,NaCl and NH₄Cl is constant,with the increase of mass fraction of CaCl₂,the pH of the solution decreases,the width of the metastable zone of boric acid becomes narrower.The nucleation series m and nucleation constant K of boric acid in different systems were obtained by Nyvlt self-consistent equation theory.The solid-liquidinterfacial energy?and constant A of boric acid nucleation were calculated according to the classical three-dimensional nucleation theory.