Te-San Chen

Regeneration of Ce(IV) in simulated spent Cr-etching solutions using an undivided cell.

This study investigated regeneration of Ce(IV) from Ce(III) oxidation at 0.05-0.5Acm(-2) in 4M HNO(3) with/without anion impurities (SO(4)(2-) (0.01-0.2M), Cl(-) (0.01-0.08M), and/or Cr(2)O(7)(2-) (0.005-0.016M)) in an undivided cell. Both Ce(IV) yield and current efficiency (CE) were significantly lower in 0.1M than in 1-4M HNO(3) and different on anode materials (in order Pt>IrO(2)/Ti>glassy carbon). The apparent rate constants for Ce(III) oxidation on the Pt anode (k(1)) and for Ce(IV) reduction on a stainless steel cathode (k(2)) were (0.40-1.80)x10(-4) and (0.08-1.01)x10(-4)s(-1), respectively, corresponding to the apparent mass transfer coefficients of (2.0-9.0)x10(-3) and (0.4-5.1)x10(-3)cms(-1), respectively. For Ce(III) oxidation at 0.3Acm(-2) in 4M HNO(3) containing multi-impurity (0.025M SO(4)(2-)+0.08M Cl(-)+0.016M Cr(2)O(7)(2-)), the k(1) was lowered by one order of magnitude although the k(2) remained unchanged, and both Ce(IV) yield and CE were reduced by approximately 89%. The decrease of Ce(IV) yield and CE by the uni-impurity was in order Cl(-)>Cr(2)O(7)(2-)>SO(4)(2-). The obtained parameters are useful to design undivided batch reactors for the Ce(IV) electro-regeneration in spent Cr-etching solutions.

Kinetic and Mass-Transfer Parameters for Ce(III) Electro-oxidation in Nitric Acid with∕without Anion Impurities

In this study, Koutecky-Levich (K-L) and cyclic voltammetry (CV) techniques were used to measure the kinetic and diffusion parameters for Ce(III) electro-oxidation on glassy carbon in 4 M HNO 3 with/without SO 2- 4 , Cl - , or Cr 2 O 2- 7 impurities. It was found that the apparent diffusion coefficients (D) of Ce(III) determined using the K-L and CV approaches were 1.65 X 10 -5 and 1.12 X 10 -5 cm 2 s -1 , respectively, while the D values varied by -5 to +15% and -2 to -26%, respectively, for the single-impurity cases. For the three-impurity case, the D value (1.59 X 10 -5 cm 2 s -1 ) from K-L estimation was approximately three times that from the CV approach. The standard rate constants (k°) for Ce(III) oxidation estimated from the K-L and CV approaches were 2.63 and 1.80 X 10 -3 cm s -1 , respectively, whereas the k° values were lowered by 35-91% and 38-80%, respectively, for the SO 2- 4 case and by 46-49 and 33-58%, respectively, for the Cl - case. The multi-impurity case had the lowest rate constant around limiting current for Ce(III) oxidation. The obtained kinetic and diffusion data are useful for the design of Ce(III) to Ce(IV) electro-regenerating systems and the evaluation of using spent Cr-etching solutions as candidate electrolytes in zinc-cerium redox flow batteries.

Electro-Regeneration of Ce(IV) in Simulated Spent Cr-Etching Solutions Containing Abundant Ce(III)

This study investigated the effects of the initial Ce(III) concentration, nitric acid concentration, anion impurity, and cell device on Ce(IV) regeneration in simulated spent Cr-etching solutions from thin-film transistor liquid crystal display manufacture. Increasing HNO 3 (electrolyte) concentration (0.5-4 M) favored 0.2 M Ce(III) electro-oxidation, Ce(III) diffusion [(0.37-3.32) X 10- 6 cm 2 s -1 ], and internal cell resistance reduction. The amount of Ce(IV) regenerated from Ce(III) electro-oxidation and the current efficiency (CE) at 0.13 A cm -2 electrolysis on Pt increased with increasing initial Ce(III) concentration in 4 M HNO 3 without impurities in a divided cell with an anion-exchange (AMI-7001) separator. Both Ce(IV) yield and CE were lowered in the copresence of multiple impurities, and the adverse influence of a single anion impurity on the Ce(IV) yield and CE was in the order Cl- > SO 2- 4 > Cr 2 O 2- 7 . The apparent rate constant of Ce(III) oxidation without impurity (1.32 X 10 -4 s -1 ) was approximately fourfold that with multiple impurities; nevertheless, the two cases exhibited similar Ce(IV) yields or CEs at 0.13 A cm -2 electrolysis for 300 min. For the Ce(IV) regeneration, the divided cell was superior to an undivided cell in the absence/presence of multiple impurities, and the AMI-7001 was better than a cation-exchange separator (CMI-7000).

Degradation of N,N-diethyl-m-toluamid (DEET) on lead dioxide electrodes in different environmental aqueous matrixes

This study investigates the electrochemical degradation of N,N-diethyl-m-toluamide (DEET) on PbO2 and Bi-PbO2 anodes. The difference in electrode crystalline structure was responsible for the better DEET degradation and TOC removal on PbO2 than on Bi-PbO2. In 1 M Na2SO4, the degradation efficiency and apparent rate constant (kapp) of DEET oxidation on PbO2 increased with the increase in current density or temperature (activation energy = 24.4 kJ mol−1). The kapp values in DEET-spiked environmental matrixes (municipal wastewater treatment plant secondary effluent (MWTPSE), groundwater (GW), and river water (RW)) were the same (6.05 × 10−4 s−1), but significantly smaller than that in 1 M Na2SO4 (2.23 × 10−3 s−1). The TOC removal efficiency was better in MWTPSE than in RW and GW; however, the mineralization current efficiencies in MWTPSE and RW were similar but higher than that in GW. During electrolysis, the aromaticity was lower in GW than in RW.

Effects of NH+4 on Ce(IV) electro-regeneration in simulated and real spent TFT-LCD Cr-etching solutions

This investigation studies the electro-regeneration of Ce(IV) from Ce(III) in 4 M HNO(3) in the presence/absence of NH(4)(+) and real spent thin-film transistor liquid-crystal display (TFT-LCD) Cr-etching solutions. On Pt, at 2 A and 70 °C for 100 min, the Ce(IV) yield and apparent rate constant of Ce(III) oxidation in 4 M HNO(3) without NH(4)(+) were 100% and 5.54 × 10(-4) s(-1), respectively (and the activation energy was 13.1 kJ mol(-1)). Cyclic voltammetric and electrolytic measurements consistently support the noticeable inhibition by NH(4)(+) of Ce(III) oxidation and lowering of the Ce(IV) yield, respectively. The apparent diffusion coefficients for 0.2 and 0.02 M Ce(III) oxidation in 4 M HNO(3) that contained 0-0.6 M NH(4)(+) were (0.38-0.25) × 10(-5) and (1.6-0.9) × 10(-5) cm(2) s(-1), respectively. Because of combined effects of NH(4)(+) and anion impurities, the 100 min Ce(IV) yield of a real spent TFT-LCD Cr-etching solution (with [NH(4)(+)]/[Ce(III)] = 0.74 M/0.39 M) was 82%, lower than that of 4 M HNO(3) without NH(4)(+), but higher than those of 4 M HNO(3) that contained anion impurities with/without 0.4 M NH(4)(+).

Electro-regeneration of Ce(IV) in real spent Cr-etching solutions

This paper presents the electro-regeneration of Ce(IV) in real (hazardous) spent thin-film transistor liquid-crystal display (TFT-LCD) Cr-etching solutions. In addition to Ce(III)>Ce(IV) in diffusivity, a quasi-reversible behavior of Ce(III)/Ce(IV) was observed at both boron-doped diamond (BDD) and Pt disk electrodes. The Ce(IV) yield on Pt increased with increasing current density, and the best current efficiency (CE) was obtained at 2A/2.25 cm(2). The performance in terms of Ce(IV) yield and CE of tested anodes was in order BDD>Pt>dimensional stable anode (DSA). At 2A/2.25 cm(2) on Pt and 40 °C for 90 min, the Ce(IV) yield, CE and apparent rate constant (k) for Ce(III) oxidation were 81.4%, 21.8% and 3.17 × 10(-4) s(-1), respectively. With the increase of temperature, the Ce(IV) yield, CE, and k increased (activation energy = 10.7 kJ/mol), but the specific electricity consumption decreased. The Neosepta CMX membrane was more suitable than Nafion-117 and Nafion-212 to be used as the separator of the Ce(IV) regeneration process. The obtained parameters are useful to design divided batch reactors for the Ce(IV) electro-regeneration in real spent Cr-etching solutions.