title: Anion effects on the electrochemical regeneration of Ce(IV) in nitric acid used for etching chromium.
abstract: The anion impurities such as SO4(2-), Cl(-), and Cr2O7(2-) commonly present in the spent (hazardous) Cr-etch solutions from color filter manufacturing processes may influence the solutions' regeneration by the electrooxidation of Ce(III) to Ce(IV). This study, therefore, investigated the effects of these anions on Ce(III)/Ce(IV) redox reactions at glassy carbon in HNO3. In cyclic voltammetric tests, the presence of SO4(2-) decreased the formal potential but increased the peak potential separation (Delta Ep) of Ce(III)/Ce(IV) couple, and lowered the peak current for Ce(IV) reduction whereas Cl(-) did not change the formal potential and Delta Ep, but the peaks for Cl(-) and Ce(III) oxidation partially overlapped. Cr2O7(2-) slightly lowered the peak current for Ce(III) oxidation but significantly decreased that for Ce(IV) reduction. The Tafel slope for Ce(III) oxidation was approximately 65mVdecade(-1) in the absence of anion impurities. Increasing SO4(2-), Cl(-), or Cr2O7(2-) in solution raised the Tafel slope. The Ce(III)/Ce(IV) equilibrium potential decreased with the increase of SO4(2-) or Cl(-) but was hardly influenced by Cr2O7(2-) addition. These observations from individual anion species together well explained the anions' co-effect (kinetic hindrance) on the Ce(III) oxidation in HNO3, revealing that these anions are unfavorable for the electrooxidation of Ce(III) in the spent Cr-etch solutions.
authors.affiliation: Department of Environmental Engineering and Science, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan.
authors.forename: Te-San
authors.initials: TS
authors.lastname: Chen
authors.forename: Kuei-Jyum C
authors.initials: KJ
authors.lastname: Yeh
authors.forename: Kuo-Lin
authors.initials: KL
authors.lastname: Huang
mesh_terms: D000838:Anions; D002563:Cerium / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods*; D017942:Nitric Acid / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D000838:Anions; D002857:Chromium; D002563:Cerium; D017942:Nitric Acid