Phase Diagram for the Na2SO4-NaOH-H2O System and Na2SO4 Solubility in Sodium Aluminate Solution with Caustic Ratios of 12 and 15 at 80 °C

摘要

The phase diagram for the Na2SO4-NaOH-H2O system and solubility data for Na2SO4 in sodium aluminate solution with Na2O to Al2O3 ratios (caustic ratios) of 12 and 15 were studied in the full alkali concentration region at 80 °C. The contents of Al and Na in the solution were analyzed by means of inductively coupled atomic plasma emission spectrometry (ICP-OES). The sulfur content was determined using ion chromatography (IC) and the ethylenediaminetetraacetic acid (EDTA) volumetric method. The phases of the equilibrium solids were identified via X-ray diffraction (XRD) as well as Schreinemaker's method. The results showed that the Na2SO4 solubility declines as the concentration of NaOH in the ternary system increases. At a NaOH concentration exceeding 32.96 % (mass percent), the Na2SO4 solubility is lower than 1.13 %. For this system, the corresponding equilibrium solid phase was identified as anhydrous sodium sulfate (Na2SO4) and sodium hydroxide (NaOH). The Na2SO4 solubility in the quaternary system approximates the values obtained in the Na2SO4-NaOH-H2O system. At NaOH concentrations higher than 30.68 % and 30.76 % the Na2SO4 solubility values in the sodium aluminate solution with caustic ratios of 12 and IS are lower than 1.03 % and 1.05 %, respectively.