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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Gold loss at copper precipitation from pregnant leach solution using SART method (2 replies and 2 comments)

F
Fachrifaa
7 years ago
Fachrifaa 7 years ago

Hello everyone, I was doing some lab testwork to reduce copper concentration at pregnant leach solution after cyanidation leaching using SART ( Sulphidization-Acidification-Recycling-Thickening) method, and found out that the gold also precipitated up to 5%. is it at a normal range? some paper said that there should be less than 1% gold being loss from the solution after SART. or is there some method to avoid or reduce the gold loss?

J
Jorge
7 years ago
Jorge 7 years ago
1 like by Fachrifaa

It is important to evaluate the effect of NaHS on the precipitation process. I mean, if you don't control the copper, there would be any problems later. The addition of sulphuric acid to get the appropriate pH is necessary to keep in mind. If the PLS contents silver, it is possible to get a silver precipitate. Before adding NaHS, a solution may content 0.45 mg/L gold, 3.4 mg/L silver. After adding NaHS the solution reports 0.40 mg/L gold and less than 0.02 mg/L silver. A typical precipitate contents approximately 62% copper, 0.35% silver, and 11 mg/kg gold. Don't forget that the mineralogy has an impact on the SART process.

 

F
Fachrifaa
7 years ago

Actually, i was using Na2S (150% - based on copper stoichiometry at the solution) to precip the copper and other base metals, and the reaction take place at pH 4.5 with retention time 10 minutes.
my lab testwork also show similar result as what you said Mr Jorge, except for the gold (i hope u can help me to review it, i will add up some attachment below) , and i was wondering why the gold is also precipitated? and in what chemical compound the gold precipitated? does the gold react with the Na2S or maybe is it because the effect of pH on the solution that break the bound of Au-CN?

here is some data of the lab-testowrk result:

Before
Au 3.53 mg/lt
Ag 2.9 mg/lt
Cu 37.95 mg/lt
Zn 16.1 mg/lt
Fe 2.7 mg/lt

after
Au 3.36 mg/lt
Ag 0.1 mg/lt (maybe lower, the AAS reading limited to 0.1 mg/lt)
Cu 15.45 mg/lt
Zn 5.6 mg/lt
Fe 0.1 mg/lt (the same as Ag)

How to reduce more copper without adding excess na2s into solution?

J
Jorge
7 years ago
Jorge 7 years ago
2 likes by Fachrifaa and David

Regarding the gold behavior in a sulphide medium, you should review the Eh-pH Diagram for Sulfur and Alkaline Sulfide Gold, In my opinion, it is necessary to perform additional precipitation tests using NaHS. Other point that you should keep in mind is the dosage of sulphide, try to evaluate the optimum dosage of sulphide because the precipitation of copper and zinc is not very efficient. 

F
Fachrifaa
7 years ago

I've done some calculation for this, and the recoveries of Cu, Zn, and other basemetals are make sense for the addition of Na2S 150% based on copper stoichiometry at the solution. maybe the recoveries is low, because the ratio between Cu concentration with other base metal concentration (I'm talking about mol units) is close, and this means the addition of Na2S wouldn't be enough to precip the Cu and other basemetals higher. if you compare it to the others SART Plant (which usually had to reduce the copper up to 300 ppm, I guess) it's certainly having high recoveries due to the ratio between Cu concentration with other base metal concentration is far away.

it's only my opinion, though. what do you think?

about the gold behavior in sulphide medium and the additional test using NaHS, i'll add it up to my note. thank you so much Mr. Jorge!


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