关键词: 电絮凝, 靛蓝染色废水, 废水处理, 铝镁合金电极, 絮凝效率, 电极活化, 电极钝化, 极化曲线

Abstract:

Objective The passivation of Al anodes during electroflocculation reduces the dissolution rate and current efficiency, negatively impacting flocculation yield, contaminant removal efficiency, and increasing energy consumption. In order to solve the above problems, Al-Mg alloy electrodes with varying Mg content were selected as anodes, and the electroflocculation system for indigo dyeing wastewater was constructed together with graphite cathode. The wastewater treatment efficiency of Al-Mg alloy anode and the Mg doping on the inhibition of anode passivation were investigated to understand the activation mechanism of Al-Mg alloy electrode by Mg element, providing a new path and theoretical basis for the performance and effect optimization of the electroflocculation system for indigo dyeing wastewater.

Method Al and four types of Al-Mg alloy electrodes with different Mg contents, namely 5052 (Mg 2.2%-2.8%), 5A03 (Mg 3.2%-3.8%), 5083 (Mg 4.0%-4.9%), 5A06 (Mg 5.8%-6.8%), were selected as anode. The performance of alloy electrode on chemical oxygen demand (COD), total organic carbon (TOC) removal and energy consumption was analyzed. The influence of Mg doping on the dissolution and passivation of the alloy anode during the electroflocculation process was investigated with EDS energy spectroscopy, thermal infrared imaging, open circuit potential and polarisation curve tests.

Results Under the same electroflocculation operating parameters i.e.,applied voltage of 10 V, electrolytic time of 20 min and plate space of 3 cm, the electroflocculation treatment results showed that Al-Mg alloy 5A03 and 5083 did not have significant performance on COD removal rate, chromaticity and flocculation yield. Therefore, Al, 5052 and 5A06 were selected for the experimental verification and characterization analysis of Mg doping, which is conducive to improving electrode activity and electroflocculation effect. Within the same operational conditions, the loss rate of the Al-Mg 5052 was lower than that of Al and 5A06. After electroflocculation with 5A06 and 5052 anodes, the TOC removal rate was 49% and 48%, respectively, and the chromaticity was 50 times for both cases, which were both better than pure Al. In addition, the COD removal rate with 5A06 anode was higher than the electroflocculation system of pure Al anode. After the electroflocculation process, the corrosion potentials for Al, 5052, and 5A06 electrodes shifted positively. The polarization curves of the Al electrode showed current plateau due to the inhibition of metal ion dissolution by passivation. However, it was not detected in that of Al-Mg alloy electrodes. Following treatment, the Al anode surface showed a decrease in Al content and an increase in O content, alongside the presence of Al₂O₃ spherical particles in the electrode's dissolved pits, with Al₂O₃ content exceeding that of the Al-Mg alloy surface.

Conclusion The wastewater after electroflocculation using Al-Mg alloy 5A06 and 5052 achieved effectively improved TOC removal rate and chromaticity compared to the pure Al anode electroflocculation system. Notably, the COD removal efficiency with the 5A06 anode exceeded that of pure Al. The polarization curve of the Al-Mg alloys electrode after electrocoagulation showed no current plateau, and the open-circuit potential was negatively shifted. The performance is attributed to the addition of Mg, which increases the electrode dissolution rate and inhibits passivation. Thermal infrared imaging revealed more pronounced passivation at the electrode plate edges compared to the center, with the passivation area of the Al electrode being significantly greater than that of the Al-Mg alloy electrode. In conclusion, the electroflocculation system constructed with 5A06 as the anode improved the treatment effect of indigo dyeing wastewater to a certain extent and effectively inhibited the passivation process of the electrode.

Key words: electrocoagulation, indigo dyeing wastewater, wastewater treatment, alumium-magesium alloy electrode, flocculation efficiency, electrode activation, electrode passivation, polarization curve