Lizhang Wang

The influence of TiO2 and aeration on the kinetics of electrochemical oxidation of phenol in packed bed reactor

The electrochemical oxidation of phenolic wastewater in a lab-scale reactor, packed into granular activated carbon (GAC) with Ti/SnO2 anodes and stainless steel cathodes, was interpreted in this study. GAC saturated rapidly if it was only used as sorbent, but application of suitable electric energy for the system simultaneously could recover the adsorption ability of GAC and maintain the continuous running effectively. The titanium dioxide (TiO2) as catalyst and airflow were also applied to the electrochemical reactor to examine the enhancement for phenol oxidation process. Results revealed that the electrochemical degradation of phenol could be reasonably described by first-order kinetics. In addition, it was illustrated that acid region, increased voltage, more dosage of TiO2 and higher aeration intensity were all beneficial parameters for phenol oxidation rates. By inspecting the relationship between the rate constants (k) and influencing factors, respectively, an overall kinetic model for phenol oxidation was proposed. The kinetics obtained from the experiments under corresponding electrochemical conditions could provide an accurate estimation of phenol concentration effluent and better design of the packed bed reactor.

Modeling approach to phenol oxidation by a sand-based packed-bed electrode system (SPBEs)

A comparative study of phenol oxidation using pure electrolysis (PEs) and sand-based packed-bed electrode systems (SPBEs) was performed under conditions of phenol concentration 800 mg L(-1), initial pH 6.5, current density 100 A m(-2) and sodium sulfate (Na(2)SO(4)) 3.0% (w/w) on IrO(2)-Ta(2)O(5)/Ti anode. The results show quartz sand, a non-conducting material is incapable of expanding the electrode area and the phenol oxidation in SPBEs commences only at the electrode surface. From the theoretical description of the mass transport coefficient and chemical oxygen demand (COD), we confirm that the enhancement of the COD removal efficiency, current and space-time yields in SPBEs is due to the improvement of mass transport properties. The proposed SPBEs shows superiority to the PEs on saving energy at the same applied voltage, however, when operated under the same applied current density the energy consumption of the former would be much higher than that of the latter because of the rise of the applied cell voltage.

Highly Efficient Interception and Precipitation of Uranium (VI) from Aqueous Solution by Iron-Electrocoagulation Combined with Cooperative Chelation by Organic Ligands

A new strategy combining iron-electrocoagulation and organic ligands (OGLs) cooperative chelation was proposed to screen and precipitate low concentrations (0-18.52 μmol/L) of uranium contaminant in aqueous solution. We hypothesized that OGLs with amino, hydroxyl, and carboxyl groups hydrophobically/hydrophilically would realize precuring of uranyl ion at pH < 3.0, and the following iron-electrocoagulation would achieve faster and more efficient uranium precipitation. Experimentally, the strategy demonstrated highly efficient uranium(VI) precipitation efficiency, especially with hydrophilic macromolecular OGLs. The uranium removal efficiency at optimized experimental condition reached 99.65%. The decrease of zeta potential and the lattice enwrapping between U-OGLs chelates and flocculation precursor were ascribed to the enhanced uranium precipitation activity. Uranium was precipitated as oxides of U(VI) or higher valences that were easily captured in aggregated micelles under low operation current potential. The actual uranium tailing wastewater was treated, and a satisfied uranium removal efficiency of 99.02% was discovered. After elution of the precipitated flocs, a concentrated uranium solution (up to 106.52 μmol/L) with very few other metallic impurities was obtained. Therefore, the proposed strategy could remove uranium and concentrate it concurrently. This work could provide new insights into the purification and recovery of uranium from aqueous solutions in a cost-effective and environmentally friendly process.

Kinetics for ammonium ion removal using a three-dimensional electrode system

Electrochemical oxidation of ammonium ions (NH(4)(+)) by using a three-dimensional electrode (TDE) composed of IrO(2)-Ta(2)O(5)/Ti anode and bamboo carbon was carried out in this paper. Experimental results reveal that the NH(4)(+) oxidation follows first-order kinetics at lower NH(4)(+) concentration and the rate constant is highly dependent on the applied current density, dosage of chlorine ions and initial NH(4)(+) concentration. In addition, increasing current density, more Cl(-) dosage and higher initial NH(4)(+) concentration are beneficial for NH(4)(+) removal. By inspecting the relation between rate constant and those operating factors, an overall empirical equation for estimation of the rate constant of NH(4)(+) oxidation is presented. The estimated model is in good agreement with the experimental results and it could also be used for accurate design of the TDE system.

Comparative study of kinetic models for electro-oxidation of phenol in a three-dimension electrode reactor

The quite effective electro-oxidation of phenol was experimentally investigated using a three-dimension electrode reactor in this paper. Experiments were conducted to examine the effects of the operating conditions, such as voltage, air-liquid ratio and dosage of NaCl on the phenol removal efficiency. The experimental results shown that the operational factor of applied voltage played the most important rolls in determining the oxidation rate of phenol, and concurrently, the addition of airflow and NaCl could obviously increase the reaction process. Using first-order kinetics to describe the electro-oxidation process of phenol, two different kinetic models were proposed by inspecting the relationship between rate constants and voltage, air-liquid ratio and dosage of NaCl, respectively. Contrasted to the abundant experimental data, a more reasonable kinetic model was obtained for the accurate estimation of phenol concentration outlet during continuous flow of raw wastewater.