Effects of NH_4~+on Ce(IV) electro-regeneration in simulated and real spent TFT-LCD Cr-etching solutions

摘要

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 ℃ 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 NHJ 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_~+, but higher than those of 4 M HNO_3 that contained anion impurities with/without 0.4 M NH_4~+.