Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

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Optimum pH in Merril Crowe (1 reply and 1 comment)

Alex Loutou
6 years ago
Alex Loutou 6 years ago

Dear Mets Expert,

What is the optimum pH in MC process, is the ratio of gold-silver affect in the MC process?

Thak you.

Richard S
6 years ago
Richard S 6 years ago
1 like by David

Alex:  The pH should be above 10, preferably between 10.5 to 11.0, which is the normal range for leaching gold and silver from an ore.  You should have low free cyanide available to keep from using excess zinc.  Additionally, the solution should be well filtered so that optimally the suspended particulates are less than 2 ppm.  Also, the dissolved oxygen should be removed to < 0.2 ppm to prevent the releaching of the gold and silver in the precipitate (which is why the oxygen is removed.  The gold and silver ratio does not matter as zinc will precipitate both well.  Generally Merill-Crowe is used for pregnant solutions that contain a substantially amount of silver as using an alternative such as loading the metal complexes on carbon will cause a large amount of carbon inventory to be processed. You will produce a mixed precipitate that will have the same proportions of gold and silver as in the PLS and in the ore.  Check your barren solutions for metal content.  If there is a barren for gold and silver both, the MC is running well.  If you have a silver barren but there is gold content in the barren, you probably have residual oxygen in the solution going to the precipitate filters.  This is because the gold in the precipitate will leach faster than the silver content in the presence of oxygen and free cyanide.


Alex Loutou
6 years ago

Thanks for your explanation Richard, its helpful.
The pH even up to 11.6 because using lime to improve clarity in CCD beside lime in hpper clarifier. Rather hard to maintain pH at level 11.2 as long as usage higher lime in CCD. FYI currently we treat different ore type as previous which now more clay content in the ore.
The changes that appear during treat this ore were, pH increase, Zn dust and flocculent increase, less zinc press life time and base metal (zinc) content in the dore become higher.
by historical the pH range 11.2-11.5 showed better MC performance thats why I ask if someone has experience for MC operation.

Thanks a lot for your valuable input,


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