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Anode corrosion (4 replies and 6 comments)
It will help if you give more details on the process of electrolysis itself and the cells materials. If you suspect something, see if you can test and confirm the presence of a product. Please, which acid are you using?
the stripping process is zadra process we use kemix stainless cells;
we use chloridric acid we confirm the presence of chloride in the solution over 300 ppm.
we suspect chloride to provoke anode corrosion and low cell amperage.
have you seen this before ?
is there any process to eliminate the chloride before cells?
neutralisation is doing in the acid wash column with caustik soda and followed by water rincage to eliminate NaCl and others
after this we always notice the precence of cl- over 300ppm
Hi!
1. If there are suspicions of chlorides, change the sequence of operations: first desorption, then acid washing.
2. Concentration of NaOH and pH should be maintained not only at the beginning of the process, but also in the middle and at the end.
3. Increase the concentration of NaOH, up to 3.5-4.0%.
Is this heavy anode corrosion a new phenomenon or has it been present from the start of the mine.
If it is new then you are looking for recent changes in procedures or materials.
The materials can include ore types and water sources as well as the anode plates themselves.
Usually a new effect like this is due to a supplier slipping in a batch of lower grade anodes or a change in the ore type, if the latter you will expect to see heavier sludge levels in the EW box.
FWIW, you can test for chlorides at any step using silver nitrate to known volume of sample and then weigh dried precipitate of silver chloride, which drops >99.9% of chloride. Test is confounded if any cyanide, ammonia or other silver complexing agents are present.
Also, expanding anode active surface are by any means will reduce polarization and thus corrosion.
That's expanding surface AREA. This can be done be making sure areas have become passive be any coating, adding more anode, etc...
Be aware the pH requirement is to maintain above pH > 12.6 and this should always be measured by titration and not the use of a pH probe.
Chlorides will attack the grain boundaries of your anodes and reduce the chromium levels and enhance corrosion. So removal is essential. While HCl washing before elution is critical, you need to ensure it is fully waged with low chloride water before transferring it to your elution circuit.
Chloride builds up in your elution water and period dumping of the whole equate tank (every three strips) is essential.
The grade of stainless should be the low hydrogen version. Keeping a trickle current on your anodes between strips and keeping them submerged at all times will also help.
Worse case you can upgrade to other more expensive anodes
HI;
In our plant we noticed a massive corrosion of electrolysis cells anodes ; however, we comply with all Operations instructions: pH> 12; 1-2% NaOH.
We suspect the presence of chlorides from the acid wash.
Is there any process that would allow us to remove the chloride before the electrolysis cells.
thanks