Lead-silver anode behavior for zinc electrowinning in sulfuric acid solution

AbstractIn recent years, a renewed interest in studying the electrochemical corrosion behavior of lead anodes during zinc electrowinning is probably due to the particularly high sulfuric acid concentrations in zinc electrolyte where lead alloy anodes have high cell voltage and high corrosion rate of lead. The high corrosion rate of lead alloy resulted in Pb contamination on zinc deposit. In zinc electrometallurgy, the electrolyte from a zinc-rich ore contains a significant amount of Mn2+. Mn2+ in the zinc electrolyte results in forming an oxide film on lead anodes during electrolysis. Pb-0.7% Ag anode is generally used in the zinc industry. To improve the technical performance and decrease product cost, other anodes, such as Pb-Ca or Pb-Ag-Ca or Pb-Ag-Ti or Pb-Ag-Se alloys were tested. Till now, none of them has succeeded in the substitution of Pb-Ag anodes in the zinc electrowinning. As an alloying element, silver in small quantities is considered because of the benefits that generates on the anode during electrolysis. During zinc electrolysis, lead dissolution into the zinc electrolyte can be harmful to the quality of zinc deposit. However, the lead silver alloy anode can decrease the lead content in the zinc deposit by pre-treated methods such as blasting and preconditioning.

Download Full-text

Study on the corrosion of rebars in fly ash concrete during moderate to high corrosion rate

Life-Cycle of Civil Engineering Systems - Life-Cycle of Structural Systems ◽

10.1201/b17618-228 ◽

2014 ◽

pp. 1538-1543

Author(s):

I Zafar ◽

T Sugiyama

Keyword(s):

Fly Ash ◽

Corrosion Rate ◽

High Corrosion Rate ◽

Fly Ash Concrete ◽

High Corrosion

Download Full-text

Electrochemistry of Active Chromium: Part 1—Anomalous Corrosion and Products of Chromium Dissolution in Deaerated Sulfuric Acid

CORROSION ◽

10.5006/1.3287734 ◽

2004 ◽

Vol 60 (3) ◽

pp. 297-303 ◽

Cited By ~ 9

Author(s):

D. M. Dražić ◽

J. P. Popić

Keyword(s):

Sulfuric Acid ◽

Corrosion Rate ◽

Electrochemical Corrosion ◽

Metal Corrosion ◽

Chemical Dissolution ◽

Rate Measurement ◽

Electrochemical Processes ◽

Corrosion Rate Measurement ◽

Anomalous Dissolution

Abstract Chromium corroding in deaerated aqueous solution of sulfuric acid (H2SO4; pH 1 to 3) produces Cr(II) and Cr(III) ions simultaneously in the ratio 7:1, as well as H2. The corrosion potentials of electrochemically activated chromium are determined by the electrochemical processes as expected according to the Wagner-Traud model. However, the real rates of chromium corrosion determined by collecting evolved hydrogen, spectrophotometric determination of the accumulated Cr ions in the solution, or by weight-loss measurements are higher than the electrochemical dissolution rate by up to 12 times for pH 1.0. The effect is smaller for higher pH. This was due to the simultaneous “anomalous” (or chemical) dissolution process of the direct chemical reaction of Cr with H2O molecules, as proposed some time ago by Kolotyrkin and coworkers. Since “anomalous” dissolution cannot be detected by electrochemical means, it has been pointed out that in the presence of “anomalous” dissolution processes during metal corrosion, electrochemical corrosion rate measurements should be taken only as approximate, while the level of approximation should be determined by some other direct corrosion rate measurement method.

Download Full-text

Dissolution of chromium in sulfuric acid

Journal of the Serbian Chemical Society ◽

10.2298/jsc0211777d ◽

2002 ◽

Vol 67 (11) ◽

pp. 777-782 ◽

Cited By ~ 8

Author(s):

Dragutin Drazic ◽

Jovan Popic

Keyword(s):

Corrosion Rate ◽

Room Temperature ◽

Corrosion Potential ◽

Analytical Data ◽

Electrochemical Corrosion ◽

Spectrophotometric Analysis ◽

Weight Loss Method ◽

Loss Method ◽

Anomalous Dissolution

By combining electrochemical corrosion rate measurements and spectrophotometric analysis of the electrolyte it was shown that at room temperature chromium dissolves in deaerated 0.1M Na2SO4 + H2SO4 (pH1) solution as Cr(II) and Cr(III) ions in he ratio Cr(II):Cr(III)?7:1. This process was stable over 4h without any detectable change. The total corrosion rate of chromium calculated from the analytical data is about 12 times higher, than that determined electrochemically by cathodic Tafel line extrapolation to the corrosion potential. This finding was confirmed by applying the weight-loss method for the determination of the corrosion rate. This enormous difference between these experimentally determined corrosion rates can be explained by the rather fast, "anomalous" dissolution process proposed by Kolotyrkin and coworkers (chemical reaction of Cr with H2O molecules) occurring simultaneously with the electrochemical corrosion process.

Download Full-text

Electrochemistry of active chromium, part III: Effects of temperature

Journal of the Serbian Chemical Society ◽

10.2298/jsc0311871p ◽

2003 ◽

Vol 68 (11) ◽

pp. 871-882 ◽

Cited By ~ 7

Author(s):

Jovan Popic ◽

Dragutin Drazic

Keyword(s):

Corrosion Rate ◽

Hydrogen Evolution ◽

Anodic Dissolution ◽

Electrochemical Corrosion ◽

Potential Range ◽

Temperature Dependences ◽

Hydrogen Evolution Reactions ◽

Effects Of Temperature ◽

Best Fit ◽

Anomalous Dissolution

It was shown that the temperature in the range 20 ? 65 ?C has considerable effects on the electrochemical anodic dissolution of chromium in the active potential range as well as on the electrochemical hydrogen evolution reactions on bare and oxide covered chromium surfaces. Also, the chemical dissolution of chromium is strongly affected. The apparent energy of activation for anodic dissolution is 63.1 kJ mol-1, for hydrogen evolution on a bare Cr surface 19.5 kJ mol-1, for the same reaction on an oxide covered surface 44.0 kJ mol-1 and for the chemical ("anomalous") dissolution 66.9 kJ mol-1. The temperature dependences of the total corrosion rate, and the electrochemical corrosion rate alone, are presented in polynomial forms with the appropriate constants obtained by the best fit of the experimental data. For the hydrogen evolution reaction on both bare and oxide covered chromium, the Volmer-Heyrovsky reaction mechanism with the second step as rate determining was proposed.

Download Full-text

A Review of the electrochemical corrosion of metals in choline chloride based deep eutectic solvents

Journal of Electrochemical Science and Engineering ◽

10.5599/jese.1135 ◽

2021 ◽

Author(s):

Mihael Bučko ◽

Jelena Bajat

Keyword(s):

Ionic Liquids ◽

Corrosion Rate ◽

Wide Spectrum ◽

Choline Chloride ◽

Electrochemical Corrosion ◽

Deep Eutectic Solvents ◽

High Viscosity ◽

Metal Corrosion ◽

Melting Points ◽

Separate Class

Deep eutectic solvents (DESs) are a class of mixtures with melting points notably lower than those of their raw constituent components. These liquids have found a tremendously wide spectrum of applications in the last two decades of their research, so their contact and interaction with technical metals and alloys are inevitable. Therefore, the corrosivity of DESs towards metals is an extremely important topic. This review summarizes research efforts collected in the last two decades related to the corrosion rate of various metals in different DESs. Since the DESs are mainly composed of organic raw compounds, and by their physicochemical properties they may be regarded as a separate class of ionic liquids, the literature data about DESs corrosivity has been compared to the data related to the corrosivity of various organic solvents and ionic liquids as well. All the results gained until now show significantly low corrosivity of DESs. This observation is discussed in relation to the chemical composition of DESs. The absence of the oxidizing agents, the inhibitory action of organic ions and molecules, high viscosity and low electrical conductivity have been recognized as the main factors contributing to the low metal corrosion rate in DESs.

Download Full-text

Effect of Heat Treatment and Sulfuric Acid Anodization on Corrosion Resistance of Aluminum Alloy (AA7075)

Nigerian Journal of Technology ◽

10.4314/njt.v40i1.9 ◽

2021 ◽

Vol 40 (1) ◽

pp. 56-62

Author(s):

M. Abdullahi ◽

L.S. Kuburi ◽

P.T. Zubairu ◽

U. Jabo ◽

A.A. Yahaya ◽

...

Keyword(s):

Heat Treatment ◽

Corrosion Resistance ◽

Aluminum Alloy ◽

Sulfuric Acid ◽

Corrosion Rate ◽

Polarization Resistance ◽

Testing Machine ◽

Palm Kernel ◽

Engine Oil ◽

Micro Hardness

This paper, studied the effect of heat treatment and anodization on corrosion resistance of aluminum alloy 7075 (AA7075), with a view to improving its corrosion resistance. Microstructure and micro hardness of the anodic film of the samples were studied with the aid of optical metallurgical microscope and automated micro hardness testing machine. Linear polarization methods were used to assess the corrosion behaviour of the alloy in 0.5M HCl. The microstructure of the annealed sample showed formation of dendrites while precipitation hardened samples in palm kernel oil and SAE 40 engine oil showed precipitates of MgZn2. The SEMS result showed pores and micro cracks on the surfaces of the anodized samples, with the as cast and anodized sample in sulfuric acid exhibiting most compact with few pores. The as cast and sulfuric acid anodized sample shows highest micro hardness value of 205.33 HV, while the least value of 150.67 HV was recorded in sample precipitation hardened in SAE 40 engine oil and anodized in sulfuric acid. Analysis of the potentiodynamic polarization data and curves showed a linear relationship (decrease in icorr, decreases the corrosion rate) between current density and the corrosion rate in all the samples. Higher polarization resistance of 15.093 Ω/cm2 was recorded by the as cast and Sulfuric acid (SA) anodized sample while the precipitation treated in SAE 40 engine oil plus SA anodized sample recorded lowest polarization resistance of 5.2311 Ω/cm2. Heat treatment alone improves corrosion resistance of AA 7075 in 0.5 M HCl solution but heat treatment plus SA anodization does not improve corrosion resistance in the same environment.

Download Full-text