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Phaseequilibria of the system KOH–K2CrO4–K2CO3–Al2O3–H2O and its subsystems were investigatedat 150 °C in the high alkali concentrated region. In the concentratedalkali region of the system and its subsystems KOH–K2CrO4–Al2O3–H2O and KOH–K2CO3–H2O, the equilibrium solid-phase K2CO3·1.5H2O was found. In the concentrated alkali region of the complexsystem, potassium aluminate and K2CO3play anevident salting-out role to potassium chromate, respectively, andtheir combined operation lowers the solubility of K2CrO4. The solubilizing effect of K2CrO4onAl2O3in the system KOH–K2CrO4–Al2O3–H2O is similar to that of Na2CrO4on Al2O3in the system NaOH–Na2CrO4–Al2O3–H2O. Thesefindings can provide a significant and precious database for the productionof K2CrO4and K2CO3andthe recovery of alumina from a concentrated alkali solution. [ABSTRACT FROM AUTHOR]

Abstract: In a new vanadium production process using concentrated alkaline solution as reaction media, the effective separation of Na3VO4 and Na2CrO4 plays an important role. The mutual salt solubility data in the NaOH–Na3VO4–Na2CrO4–H2O system at 40 and 80°C therefore were measured and compared with ternary NaOH–Na3VO4–H2O and NaOH–Na2CrO4–H2O subsystems, respectively. With the crystallization areas discussed in detail, a strategy for effective separation of Na3VO4 and Na2CrO4 from the NaOH–Na3VO4–Na2CrO4–H2O quaternary system has been proposed. [Copyright &y& Elsevier]

The phase equilibria for the system KOH–K2CrO4–Al2O3–H2Oand its subsystems at 150 °C in a high alkali concentrated regionwere investigated. In the concentrated alkali region of the systemand its subsystem KOH–Al2O3–H2O, the equilibrium solid-phase K2O·Al2O3·2H2O was found. This is differentfrom the system KOH–Al2O3–H2O at low temperature from which the equilibrium solid-phaseK2O·Al2O3·3H2O was discovered. The salting-out effect of KOH and potassium aluminateto K2CrO4is strong. These findings can providea significant and precious database for the production of K2CrO4and the removal of alumina from the concentratedalkali solution that is produced in the chromate cleaner productionprocess. [ABSTRACT FROM AUTHOR]

The osmotic coefficients of the Na2CrO4−H2O system at 353.15 K were determined using isopiestic method ranging from 0.05 to 7.683 mol·kg−1. The experimental osmotic coefficients were excellently correlated with Pitzer equation to obtain the interaction parameters, the activity coefficients, and the solubility product for Na2CrO4. Furthermore, the solubility of Na2CrO4in NaOH solutions at 353.15 K was predicted using binary parameters, and the predicted values agree with the experimental data, demonstrating the Pitzer equation is capable of optimizing the processes for the removal and recovery of sodium chromate in NaOH solutions at high temperature. [ABSTRACT FROM AUTHOR]

The full alkali concentration range phase diagrams of the Na2O−Al2O3−H2O system were constructed at (150 and 180) °C. The compositions of the clear liquids and wet solid phases were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the results show that, as the Na2O concentration increases, the Al2O3solubility initially increases monotonically, to maximum values of 100 w(mass fraction) = 33.58 and 35.86 at (150 and 180) °C, respectively, and then decreases. At both temperatures, the solid phases were determined to be Al2O3·H2O, Na2O·Al2O3·2.5H2O, Na2O·Al2O3, and NaOH by X-ray diffraction coupled with Schreinemaker’s method. The phase diagrams indicate that, as the temperature increases, the Na2O·Al2O3·2.5H2O phase region shrinks, while that of the Na2O·Al2O3phase expands. [ABSTRACT FROM AUTHOR]

Equilibria data for the NaOH−Na2CrO4−Na2CO3−H2O quaternary system at (40, 60, and 80) °C were measured, and the phase diagrams at (80 and 40) °C were constructed. Furthermore, the crystallization areas in the phase diagrams are discussed in detail. In addition, the solubility of Na2CrO4in NaOH solutions was compared with that in Na2CO3saturated NaOH solutions, and the solubility of Na2CO3in NaOH solutions was also compared with that in Na2CrO4saturated NaOH solutions. On the basis of the phase diagrams, a strategy for effective separation of Na2CO3from the NaOH−Na2CrO4−Na2CO3−H2O quaternary system has been proposed. [ABSTRACT FROM AUTHOR]

Abstract: Phase equilibria for the K2O–Al2O3–H2O system were investigated at 40°C. In the concentrated alkali region of the phase diagram, only the equilibrium solid-phase K2O·Al2O3·3H2O was found besides KOH·H2O. This is different from the fact of the similar system Na2O–Al2O3–H2O. Two invariant points with their respective equilibrium solid pairs (Al2O3·3H2O versus K2O·Al2O3·3H2O and K2O·Al2O3·3H2O versus KOH·H2O) were identified with their corresponding compositions. These findings can provide a significant database for the removal of alumina from the concentrated alkali solution that was produced in the cleaner manufacturing process for chromium compounds. [Copyright &y& Elsevier]

Theseparation of K3VO4and K2CrO4plays an important role in the vanadium cleaner productionprocess using concentrated alkaline solution as reaction media. Equilibriumsolubility data for the KOH–K3VO4–K2CrO4–H2O system at (40 and 80)°C therefore were measured and compared with ternary KOH–K3VO4–H2O and KOH–K2CrO4–H2O subsystems, respectively.Based on the data, a strategy for effective separation of K3VO4and K2CrO4from the KOH–K3VO4–K2CrO4–H2O system has been proposed. [ABSTRACT FROM AUTHOR]

To realize the effective separation of Na 3 VO 4 , Na 2 CrO 4 and the impurity Na 2 CO 3 in a newly developed vanadium production process using concentrated alkaline solution as reaction media, the equilibrium liquid phase solubility and solid phase compositions of the NaOH–Na 3 VO 4 –Na 2 CrO 4 –Na 2 CO 3 –H 2 O system at (40 and 80) °C were measured. The obtained solubility data were afterwards compared with quaternary NaOH–Na 3 VO 4 –Na 2 CrO 4 –H 2 O subsystem to investigate the salting-out effect of Na 3 VO 4 , Na 2 CrO 4 and Na 2 CO 3 . Further, a strategy for effective separation of Na 3 VO 4 and Na 2 CrO 4 from the NaOH–Na 3 VO 4 –Na 2 CrO 4 –Na 2 CO 3 –H 2 O pentabasic system has been proposed on the basis of detailed analysis of crystallization zones. [ABSTRACT FROM AUTHOR]

The phase diagram for the Na2SO4–NaOH–H2O system andsolubility data for Na2SO4in sodium aluminatesolution with Na2O to Al2O3ratios(caustic ratios) of 12 and 15 were studied inthe full alkali concentration region at 80 °C. The contents ofAl and Na in the solution were analyzed by means of inductively coupledatomic plasma emission spectrometry (ICP-OES). The sulfur contentwas determined using ion chromatography (IC) and the ethylenediaminetetraaceticacid (EDTA) volumetric method. The phases of the equilibrium solidswere identified via X-ray diffraction (XRD) as well as Schreinemaker’smethod. The results showed that the Na2SO4solubilitydeclines as the concentration of NaOH in the ternary system increases.At a NaOH concentration exceeding 32.96 % (mass percent), the Na2SO4solubility is lower than 1.13 %. For this system,the corresponding equilibrium solid phase was identified as anhydroussodium sulfate (Na2SO4) and sodium hydroxide(NaOH). The Na2SO4solubility in the quaternarysystem approximates the values obtained in the Na2SO4–NaOH–H2O system. At NaOH concentrationshigher than 30.68 % and 30.76 % the Na2SO4solubilityvalues in the sodium aluminate solution with caustic ratios of 12and 15 are lower than 1.03 % and 1.05 %, respectively. [ABSTRACT FROM AUTHOR]

The solubility of K3VO4in theKOH–K3VO4–Ca(OH)2–H2O system and subsystems at (313.2 and 353.2) K were studiedin awide alkali concentration range, varying from 5 % to 45 % KOH. Fromthe data, it is concluded that the K3VO4solubilitydecreased obviously with the addition of Ca(OH)2when theKOH concentration is low. Also, the calcification of K3VO4can be achieved efficiently only in this KOH concentrationrange. The precipitate phase is mainly presented as Ca10V6O25, and the element K in the K3VO4can be recovered as KOH. Besides, temperature is notthe primary impact factor for the behavior of K3VO4calcification. [ABSTRACT FROM AUTHOR]