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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How to Raise the pH of Silver Heap (6 replies and 4 comments)

D
Ching Chong
7 years ago
Ching Chong 7 years ago

We have a heap that we are planning to leach. The heap contains silver bearing ore. The pH of the heap is at pH 3. we want to raise the pH to 11 before we start to add cyanide to leach the silver. What is the best possible chemical to use?

J
Jorge
7 years ago
Jorge 7 years ago
2 likes by SIMetallurgist and BAUD

The first stage is to perform bottle roll tests to evaluate the silver extraction. If the silver dissolution is as high as 75% to 80%, you could could consider the heap leaching option. The main parameters to evaluate in the testing program are the effect of particle size on silver extraction, cyanide strength, pH (lime can be added to regulate the pH). If the silver extraction is acceptable, the next stage is to perform column leach tests.

It is important to indicate that the rate of silver dissolution is slower than gold. For that reason, a testing program should provide some indication on the metallurgical performance.

Other points to consider in the evaluation process are related to the silver grade, the presence of gold, and other minor elements such as copper, mercury and zinc. 

 

 

F
Siddiquf
7 years ago

Lime.

David
7 years ago
David 7 years ago

If you are crushing before placing on the heap, use addition of pebble lime in the crusher.

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D
Ching Chong
7 years ago

The silver is already on a heap pad. It was abandoned three years ago when the company shut down. The Owners lowered the pH to " control cyanide". We have taken over and we are trying to restart. The heap has a run off at pH2.7 to pH3. So everything is stacked and we want to reduce the pH before leaching the silver.

Marshal Meru
7 years ago
Marshal Meru 7 years ago

Why wouldn't you use lime or caustic in leach solution?

Do one irrigation cycle to see if your pH stabilises before pumping the cyanide to it.

D
Ching Chong
7 years ago

I am planning to use lime to raise the pH. I was wondering if I could add some lime or caustic directly onto the heap to speed up the process. Will adding lime cause cementation?

(unknown)
7 years ago
(unknown) 7 years ago

Use caustic and leach solution 10-11 pH, but with heap pH so low now indicates presence of sulfides; acid rock drainage (ARD).

With Fe bad news for CN leach, maybe there is a reason it is still there, testing first before trying to leave heap

D
Ching Chong
7 years ago

Thanks a lot. Please provide additional info. Do I spread the caustic on the heap? Will the Fe stop the leaching of silver or it will just consume too much cyanide?

David
7 years ago
David 7 years ago

Hi /dbouchard/

You say “we took over”.

Did you actually pay for this before figuring out what to do with it? Really?

No pre-purchase testing? Due diligence?

You said "It was abandoned three years ago when the company shit down."

I suggest you start testing in laboratory if you do not want to be the next "company to ... shut down".

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N
Nurettin
6 years ago
Nurettin 6 years ago

The best chemical? I hope you do not mean cheapest.

first of all what is the chemistry in actual stack. Situation of sulfites, sulfides, sulfates. First of all it is important to examine.

Lime is easiest way but you can coat particals with gypsum And also produce channelings. Your percolation can decrease and totally your recovery will decrease very much. 

it is an only idea but rinsing with the water(as possible as pure) up to a level may be pH5. After that rinsing with around pH9 water. in these sequences when you reach around pH7 you may start ph10-11 solution irrigation 

Do not add lime from surface as solid. You will loose your first 5 meter percolation rate and you will have a channeling baby for all stack. 

As possible as less quantity of chemical is better

 


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