Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-03-23T09:55:18+00:00
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Prevent Anode Oxidation (6 replies)

Bill Rico
1 year ago
Bill Rico 1 year ago

How I can prevent oxidation in the anodes in electro-winning cell to get gold in cathodes?

Maya Rothman
1 year ago
Maya Rothman 1 year ago

What are you using for your anode material? Are there other ions like chloride in your EW solution? What is the voltage applied to the EW cell? What is your anode current density? It would help to know more about the chemistry and operational parameters of the process.

1 year ago

In general, as the majority of commercial electrolytic cell extractions using stainless steel anodes that corrode in solutions below pH 12.5, we make sure to have an eluate solution with a pH greater than 12.6.

1 year ago
OberstGruppen 1 year ago

Couple of things, the optimum amperage is somewhere between 30-50 amps per cathode. As you would already know, caustic is added to produce conductivity but should not exceed pH of 12.5 as mentioned already.

Check your water that you use in the electrowinning for chloride levels as any salt or chloride will increase you anode corrosion drastically. The purer the better! Keep in mind, the higher the cyanide levels, the higher the cell operating voltage for optimum cell performance. Cyanide levels are not required to be high.

It is also worth noting that allowing the cathodes to sit in a cell without current being applied to the cell, such as a shut down or major power blackout, a cathodic gold: anodic mild steel corrosion reaction occurs. Anode corrosion forms FE and Cr ions. These ions can be reduced at the cathode which reduces current efficiency. Chromium ions can inhibit quite significantly the gold reduction kinetics.

Of course anodes can be covered in various coating which needs to be buffed off with a wire brush to restore the electrical efficiency of the anode.

Mostly, as already is the chloride level. That and the pH will create the anode corrosion the most.

Jean Rasczak
1 year ago
Jean Rasczak 1 year ago

We had problems with Chromium and chloride. I have worked in many gold mines, and would recommend checking your water quality, and looking for contaminants. One mine I was at the anodes corroded badly, and it was found that someone had left the raw water valve open in a bypass line, and hypersaline water was flowing to the elution circuit. Once remedied, the problem went away.

If the EW was working well in the past, then you have a process change and should be able to remedy the problem with a bit of detective work. If not, then consider testwork with potable water.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

Increases control neutralization to prevent chlorine reaches your electrolytic cells.

1 year ago

In addition to the previous points (low caustic, high chloride levels, and high current density) you will get corrosion if your flow rate through the cell is too low. Typical safe flows are about 7m3/h for a 600x600 cell, 14m3/h for an 800x800cell and 20m3 for a 1000x1000 cell.

The EW reaction produces acid at the surface of the anode so you need enough caustic to neutralize the acid and enough mixing to contact the acid with the caustic before it attacks the anode.

Chloride accelerates and localizes the acid attack.
High current density increases acid production
Low caustic reduces neutralization.
Low flow rate reduces mixing.
Very, very high caustic increases viscosity which reduces mixing.

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