title: Effects of NH₄⁺ on Ce(IV) electro-regeneration in simulated and real spent TFT-LCD Cr-etching solutions.
abstract: 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)(+).
authors.affiliation: Department of Environmental Engineering and Science, National Pingtung University of Science and Technology, 1 Hseuh Fu Road, Nei Pu Hsiang, Pingtung 91201, Taiwan.
authors.forename: Te-San
authors.initials: TS
authors.lastname: Chen
authors.forename: Kuo-Lin
authors.initials: KL
authors.lastname: Huang
authors.forename: Yu-Chan
authors.initials: YC
authors.lastname: Lai
authors.forename: Yi-Ming
authors.initials: YM
authors.lastname: Kuo
mesh_terms: D002586:Cesium / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry*
chemical_list: D000644:Quaternary Ammonium Compounds; D012996:Solutions; D002586:Cesium