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Trouble In Vat Leaching Of Stamp Mill Dump (4 replies)

Wadzanayi
2 months ago
Wadzanayi 2 months ago

The unit operation consists of vat leaching of stamp mill dumps.The dump is created after artisanal miners surrounding the custom milling center have taken out their gravity gold.

Sequence of events is as follows;

  1. Site began experiencing high solution tails is August 2016. the head on average was 1.2 Au g/t but tails would be as high as 0.77 Au g/t. 
  2. Carbon activity was discovered to have been very low at around 54% .No regeneration was being done apart from acid washing of the carbon with dilute HCl before and after elution
  3. The filtration system,pipework and adsoprtion columns were all cleaned out after noticing a bluish sediment within the system.As suspected, copper was the major problem and this was also causing the cyanide consumption to go up from 0.9kg/ton to approximately 1.5kg/ton.
  4. After cleaning out of the whole system, new carbon was put into the adsorption columns( there are 6 adsorption columns each with a carrying capacity of 125kg) and leaching of the cyanide dumps resumed.
  5. After 3 days, the tails have now started to spike at an avergae of 0.3 Au g/t.The head solution grade is still between 1.1-1.3 Au g/t

Please help

 

ThabisoKwenane
2 months ago
ThabisoKwenane 2 months ago

In Gold processing what normally causes solid residues (g/t) is either insufficient cyanide or oxygen into the system. Another important factor that you should consider is that cyanide and oxygen has to be at an acceptable ratio for the cyanidation process to be efficient. One of the things that you can do is to run a bottle roll test or a batch cyanidation process and play around with different reagent dosages and check which recipe suits the ore that you are treating. Also ensure that you are operating your process at a pH of 10.5 to have sufficient cyanide ions in solution. Unfortunately copper is an enemy to gold processing and the best way of dealing with the copper if is in abundance is to have excess cyanide in solution to compensate for it. By doing so copper will not be a negative factor in gold recovery.

Solution grade is presented as "mg/l". So I am not quite sure if you are talking about solids grade (g/t) or solution grade "mg/l". My  above answer is based on solids grade. But if you have issues with solution grade, ensure that you acid treat your carbon with 3% HCL solution and regenerate in a kiln with a temperature of approximately 750 degrees Celsius. Also ensure that your carbon inventory is sufficient. The standard quantity that you can use per adsorption column is 20g/L.

All the best.

 

Jorge Ganoza
2 months ago
Jorge Ganoza 2 months ago

You should review the results and recommendations from the metallurgical testing programs. The study should include the effect of particle size on gold extraction (you did not mention in your comments anything about the particle size). Other valuable information is the cyanide strength, presence of cyanicides (e.g. oxide copper minerals), leaching time. A mineralogical study should have been considered in the metallurgical testing program to assess the gold particle size, liberation, gold bearing minerals, gangue minerals.

According to your information, gold feed grade 1.2 g/t. gold reported in tails 0.7 g/t. Based on this data, the gold extraction was around 42%. In the second case (gold in tails, 0.3 g/t), the gold extraction was close to 75%. It important to know the results from the testing program. Does the ore used in the testing program and the ore treated in the leaching circuit came from the same ore body? You should try to find out it.

Other point to analyze is the vat operation, for example how the material is removed. 

GeoffC
2 months ago
GeoffC 2 months ago
1 like by David

It would appear that copper is the most likely cause of the problem. It can cause a couple of main problems. If there is insufficient free cyanide the copper cyanide species formed are more likely to adsorb onto carbon and can reach a point where it effects the ability of the carbon to adsorb gold. Copper can be removed from carbon by a cold cyanide wash.The insufficient free cyanide also means there is not enough cyanide to leach the gold properly in the first place. In a vat leach it is difficult to ensure there is sufficient free cyanide unless good solution flows are achieved. Unfortunately high cyanide consumption is a requirement when treating cyanide soluble copper ores. Generally as a rule of thumb anything containing over about 0.5% cyanide soluble copper is likely to be uneconomic to treat. Another common problem occurs when cyanide levels are measured using silver nitrate titrations as the copper cyanides break down giving false "free" cyanide readings. If using this method to determine cyanide strengths much higher levels must be used to ensure there is actually free cyanide present.  

On another topic to be aware of when treating stamp battery tailings is the presence of mercury. This can follow gold through the carbon elution and electrowinning stage and be present during smelting operations. It can sometimes be seen in the bottom of electrowinning cells. I have in the past included a retort stage to remove Hg before the smelt or calcine steps.

Mr_Weseni
2 months ago
Mr_Weseni 2 months ago

Good day... 

Mrs Wadzanayi please get in touch with me on +263717214189.... i am also facing that similar problem with our VAT leaching tanks.... Our head grade its 1.30g/t and our tailings are 1.10g/t. Maybe we could put our heads together and come up with something. 

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