Oxidation leaching of chromium from electroplating sludge: Ultrasonic enhancement and its mechanism

Abstract

The oxidation leaching of chromium from electroplating sludge was investigated, and ultrasonication was introduced for the enhancement of the leaching process. Two different types of Cr-bearing electroplating sludge were selected for the study, and the effects of the reagent dosage, temperature, and ultrasonic pulse ratio on the leaching efficiency were tested through oxidation leaching experiments. The experimental results show that hydrogen peroxide and sodium hypochlorite exhibit different leaching effects on different types of electroplating sludge. The control of reagent dosage is crucial for the oxidation leaching of Cr, while the effect of temperature turns out to be small. Hydrogen peroxide turns out to be a more effective oxidizer for chromium sludge, and the leaching efficiency of Cr could be promoted from 77.52% to 87.08% using ultrasonic enhancement under optimum conditions. Interestingly, sodium hypochlorite exhibited better leaching efficiency than hydrogen peroxide for the mixed sludge since the organic matter in the mixed sludge will lead to the rapid decomposition and consumption of hydrogen peroxide. The leaching efficiency of Cr from the mixed sludge could also be promoted from 56.82% to 67.10% using ultrasonic enhancement under optimum conditions. According to the scanning electron microscope imaging, ultrasonic enhancement can create voids and cracks on the surface of the sludge particles, hence promoting the contact between electroplating sludge and leaching agents, and promoting the oxidation leaching efficiency. In addition, ultrasound seems to be able to remove the coverings on the surface of the mixed sludge particles, which may facilitate the oxidation reaction.

Stainless Steel Activation for Efficient Alkaline Oxygen Evolution in Advanced Electrolyzers

“…The leaching of Fe leads to the progressive surface exposure of Ni and Cr species, as evidenced by the appearance of an additional broad oxidation peak associated with Cr(III)→Cr(VI) at ≈0.38 V Hg/HgO . [ 40 ] Importantly, in alkaline media, Cr (VI) is found in the form of dissolved CrO 4 2− , [ 41 ] as proved by monitoring Cr leaching through ICP measurements of the electrolyte (Figures S6 and S7, Supporting Information). The anodic leaching of Cr species has been previously reported as an effective route to improve the overall catalytic activity of SS electrode by creating a high‐purity NiFe catalyst layer.…”