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Carbon fouling (3 replies)

8 months ago
Sturmbann 8 months ago

We do acid washing on our carbons and regeneration as well, but our current barren carbon loading is very high compared to the previous loadings. This is a major worry now since our protocols are still being followed as before. I want to know, in the attempt to do acid washing can the carbons be fouled? Or can a decrease or increase in the acid solution lead to fouling because we have done all the necessary calcium and other organic foulant tests and they are within acceptable limits as before. Our barren before recent results were within 30-50ppm but now we are recording about 120-200ppm on the barren carbons. Please i need help as soon as possible. Currently we use the AARL stripping process for our elution.

Maya Rothman
8 months ago
Maya Rothman 8 months ago

The problem is probably in the elution process.
Check the following as a start:

Temperature during the pre-treat and elution wash, should be above 110 C.
Check the pressure on the column, it needs to be high enough to prevent steam formation.
Check pre-treat make up, is there enough NaOH and NaCN.
If AARL elution check water quality.
Check NaCN to make sure that it has not been contaminated.

What elution process are you using, because if it is Zadra then you need to check the electrowinning cell as well.

5 months ago
Bhaduri 5 months ago

All good diagnostic suggestions by Maya. In addition:

a) Has there been a change in ore type & contaminant loading on C...need ICP results for comparison;

b) Has the clay content/CIL slurry pH significantly changed?;

c) Have you attempted increasing soak time for AARL, all other conditions remaining the same?

d) Is your acid (HCl) conc at 3-4 wt%? and how do the current soluble Ca+2 levels in the spent acid compare to previous H+ washes?

3 months ago
jculver 3 months ago
1 like by David

I have found in a zadra strip process the fouling of carbon by silicates due to the very high pH used (11.5-12.2). Acid washing of the carbon showed no benefit, we ended up feeding the fouled carbon to the roaster instead of adding additional cost in regenerating the carbon. Since this is likely not an option for many facilities, investigating very high dosages of anti-scalant proved to slow the rate of fouling of the carbon. 

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