Electrochemical Properties and Microstructure of Al/Pb–Ag and Al/Pb–Ag–Co Anodes for Zinc Electrowinning

doi:10.1007/s40195-014-0050-6

Abstract

Abstract:

The Al/Pb–0.8%Ag and Al/Pb–0.75%Ag–0.03%Co (in mass fraction) anodes used in zinc electrowinning are prepared through the electrodeposition of lead methanesulfonate electrolyte onto an aluminum matrix. The results of anode polarization curves, Tafel curves, and EIS characterizations indicated that the Al/Pb–0.75%Ag–0.03%Co anode has higher electrocatalytic activity and corrosion resistance than the Al/Pb–0.8%Ag anode. SEM observations on the fruit surfaces demonstrated the crystals on the Al/Pb–0.8%Ag anode are larger than on the Al/Pb–0.75%Ag–0.03%Co anode. After 24 h of anodic polarization, SEM observations and XRD analysis showed that the MnO₂–PbO₂ layer on the Al/Pb–0.75%Ag–0.03%Co anode surface is characterized by dendritic crystals, and the PbSO₄–PbO₂ layer under the MnO₂–PbO₂ layer is characterized by uniform and chaotic orientation tetragonal symmetry crystallites of PbSO₄. However, the MnO₂–PbO₂ layer on the Al/Pb–0.8%Ag anode surface is characterized by granular crystals, and the PbSO₄–PbO₂ layer under the MnO₂–PbO₂ layer is characterized by well-organized orientation crystallites of PbSO₄, which are concentrated in certain zones.

Key words: Zinc electrowinning, Corrosion resistance, Electrocatalytic activity

Yongchun Zhang, Buming Chen, Zhongcheng Guo. Electrochemical Properties and Microstructure of Al/Pb–Ag and Al/Pb–Ag–Co Anodes for Zinc Electrowinning[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(2): 331-337.

Figures/Tables 9

Fig. 1 Tafel polarization curves of Al/Pb–0.75%Ag–0.03%Co and Al/Pb–0.75%Ag anodes after anodic polarization for 24 h

Table 1 φcorr corrosion potential and Jcorr corrosion current density of Al/Pb–0.8%Ag and Al/Pb–0.75%Ag–0.03%Co anodes

Anodes	φ_corr (V)	J_corr (A/cm²)
Al/Pb–Ag	-0.545	7.21 × 10^-2
Al/Pb–Ag–Co	-0.533	3.03 × 10^-2

Fig. 2 Anode polarization curves of Al/Pb–0.8%Ag and Al/Pb–0.75%Ag–0.03%Co anodes after anodic polarization for 24 h

Table 2 Parameters of oxygen evolution dynamics of Al/Pb–0.8%Ag and Al/Pb–0.75%Ag–0.03%Co anodes

Anode	η (mV)	b₁ (mV/dec)	b₂ (mV/dec)	i₀ (A/cm²)
Al/Pb–Ag	0.943	357	258	1.288 × 10^-4
Al/Pb–Ag–Co	0.702	495	251	1.905 × 10^-3

Fig. 3 a EIS characterization of Al/Pb–0.8%Ag and Al/Pb–0.75%Ag–0.03%Co anodes after anodic polarization for 24 h b the equivalent circuit

Table 3 Equivalent circuit parameters of Al/Pb–0.8%Ag and Al/Pb–0.75%Ag–0.03%Co anodes after 24 h of anodic polarization according to the EIS spectra

Anode	R_s (Ω/cm²)	C_f (F/cm²)	R_f (Ω/cm²)	C_dl (F/cm²)	R_t (Ω/cm²)	Q_a (S/cm²sⁿ)	n	R_a (Ω/cm²)
Al/Pb–Ag	0.89	0.04	0.55	4.35	0.08	5.10	0.86	3.76
Al/Pb–Ag–Co	0.95	0.03	0.51	18.45	0.10	14.30	0.87	3.53

Fig. 4 SEM images of Al/Pb–0.75%Ag–0.03%Co a–c and Al/Pb–0.8%Ag d–f anodes after anodic polarization for 24 h

Fig. 5 XRD of Al/Pb0.8%Ag a and Al/Pb–0.75%Ag–0.03%Co b anodes after anodic polarization for 24 h

Fig. 6 SEM images on the fruit surface of Al/Pb–0.8%Ag a–c and Al/Pb–0.75%Ag–0.03%Co d, e anodes, line scanning of section of Al/Pb–0.8%Ag anode f

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