In this work, Zr4+ cross-linked magnetic chitosan/polyaniline (Fe3O4@CTS-Zr-PANI) composite was synthesized for the first time and used to remove Cr(VI) from aqueous solution. The introduction of polyaniline enhances the stability of chitosan under acidic conditions and its ability to reduce Cr(VI). The addition of zirconium enables ion exchange and electrostatic adsorption to work together to remove Cr(VI). The presence of C=C bonds (benzenes and quinones), Zr-O and Zr-N in its FTIR spectrum confirmed the successful synthesis of it. The removal of Cr(VI) by Fe3O4@CTS-Zr-PANI mainly includes electrostatic adsorption, ion exchange, reduction and complexation. XPS showed that 86.9% of Cr(VI) was reduced to Cr(III) by -OH groups of CTS and C-N groups of PANI at pH=2.0. Then, Cr(III) was removed by complexing with COO- groups of CTS and C-N groups of PANI. The maximum monolayer adsorption capacity of Fe3O4@CTS-Zr-PANI is 531.86 mg g-1 at 298 K (pH=2.0). The adsorbent has excellent stability and regeneration ability, and the adsorption efficiency is still as high as 90.63% after six adsorption cycles. Real chromium-containing wastewater (Cr(VI) 241.21 mg L-1, pH=3.5) was treated with a dosage of 0.08 g adsorbent, and its residual chromium concentration could not be detected.
Abstract The pH scope for neutralization precipitation of chromium ion is comparatively narrow (6.3 ∼ 9.5) and the dosage must be controlled strictly when NaOH or CaO is used as regulator. Slight dissolution of carbonate minerals such as calcite (CaCO3) and magnesite (MgCO3) makes it possible that the solution has buffer pH which can match with the condition of neutralization precipitation of chromium ion. The hydroxide precipitation of Cr(III) occurs more easily in the interface area than in solution because the interfacial solubility product of Cr(OH)3 formed on the surface of MgCO3 () is less than the solubility product in solution (). After the surface precipitation is formed, the dynamic electricity behavior of MgCO3 becomes similar to that of Cr(OH)3. Using MgCO3 as a purifier, the wastewater containing high concentration of chromium ion has been purified and advantages such as good purification effect, fast subsiding speed, and little sediment volume are manifested. Keywords: Carbonate mineralChromium ionWastewater treatment Acknowledgment The authors acknowledge the Key Laboratory of Resources Chemistry of Nonferrous Metals (Central South University) for the laboratories and financial support.
The feasibility of total petroleum hydrocarbon-contaminated (TPH) soil remediation was studied using persulfate oxidation.Factors tested included type of activator, persulfate concentration, number of persulfate applications, and reaction time.Probe chemicals were used to study effi ciency of the persulfate oxidation mechanism.The best activation method used Fe 2+ , which achieved 40.8% TPH degradation at 24 h with an initial TPH concentration of 14,432.5 mg/kg.For alkaline (high pH) and hydrogen peroxide activation treatments, TPH degradation effi ciencies were 35.2% and 21%, respectively.Thermal activation effi ciency was relatively low (15.6%).Kinetic experiments demonstrated that the oxidation reaction was substantially completed within 60 min.A one-time addition of persulfate was superior to multiple applications.The addition of probe compounds produced sulfate radicals, hydroxyl radicals, and reductants.The results indicate that activated persulfate is reasonably effective for remediation of TPH-contaminated soils.
Liquid-liquid equilibrium (LLE) data for ternary system of toluene + phenol + solvent were determined at 298.15, 308.15, and 318.15 K under 101.3 kPa, in which 1,2-propanediol (1,2-PDO) or 1,3-propanediol (1,3-PDO) was screened as the extracting agent. Hand, Othmer-Tobias, and Bachman empirical equations were utilized to corroborate the reliability of experimentally determined LLE data, and two important indicators (distribution coefficient and separation factor) were calculated to evaluate the extraction performance of solvent for separating phenol from coal tar containing toluene. The separation factor was all greater than one, indicating that it is feasible to select 1,2-PDO or 1,3-PDO as extractants for separating phenol from coal tar containing toluene. Meanwhile, solvation free energy and interaction energy among the components were calculated to investigate the separation mechanism of phenol from coal tar containing toluene using 1,2-PDO or 1,3-PDO at a molecular level. The calculation results showed that the solvation free energy of 1,3-PDO–phenol (-13.2 kcal/mol) is more negative than that of 1,2-PDO–phenol (-11.4 kcal/mol), and the interaction energy discrepancy between 1,3-PDO–phenol and 1,3-PDO–toluene (2.5 kcal/mol) is greater than that between 1,2-PDO–phenol and 1,2-PDO–toluene (0.9 kcal/mol), therefore 1,3-PDO can exhibit more superior extraction capacity compared with 1,2-PDO. Furthermore, NRTL and UNIQUAC thermodynamic models were utilized to correlate LLE data for toluene + phenol + 1,3-PDO ternary system at (298.15–318.15) K under 101.3 kPa, and the root-mean-square deviation value was used to evaluate the discrepancy between correlated and experimental values, yielding corresponding binary interaction parameters.
This paper presents numerical simulations of steady and oscillatory lid-driven cavity flow at different Reynolds numbers with a fixed aspect ratio of 1:1. A projection method (P2 pressure correction method) is applied to solve the incompressible Navier-Stokes equations. The code is validated by comparison with published works of steady lid-driven flow at Re = 100, 400 and 1000. Oscillatory lid-driven cavity flow at different Reynolds numbers (100, 400 and 1000) at a fixed oscillation frequency has been investigated. It is observed that the oscillatory lid-driven cavity flow is substantially affected by the Reynolds number.
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