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

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-03-23T09:50:58+00:00
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Processing Refractory Gold (14 replies)

Bill Rico
1 year ago
Bill Rico 1 year ago

May be increasing gold recovery from refractory gold ore (with grade 2-3 g/t) to 90-95%?

Actual data of top refractory gold ore mines show, that gold recovery is 70% and less. What is reason? It is a problem in minerals processing or it is a global science problem? So if you work with refractory ore, what do you think about low recovery? If you do not work, the gold recovery from "light" ores is 90...95%. You right, that need pre-treatment for "hard" ore. But known processes can't liberate gold fully. Processing Refractory Gold is so hard!

Low recovery is very common with refractory ores, in fact a 70% recovery could be considered good. Refractory ores are normally have either a high sulfide content that masks the gold preventing cyanide leaching of the gold, or high organic content that also block gold leaching (reabsorbs the gold), or it can have a high clay content that also soaks up the cyanide. Other issues can be locked particles that are not exposed for leaching, or coarse particles that take a long time to fully leach.

If the issue is the sulfides or organics bioleaching, roasting or other pre-treatment maybe needed. 

Marshal Meru
1 year ago
Marshal Meru 1 year ago

There are a number of factors that cause refractory behaviour in gold ores.

Typically when we start investigating these ores the first step would be to undertake a mineralogical analysis that will tell you if your ore is sulphide refractory (and the grain size you are needing to target for liberation), if you have pregnant solution robbers or if you have a more complex telluride or double refractory ore. Have you completed this step yet?

Armed with this information, and possibly with the added data from diagnostic leaching done on your tail, you can then identify the correct technology to "unlock" the remaining value - through regrind, pre-leach oxidation (whether POX, bacterial, roasting, or some of the newer hydrometallurgical processes such as Albion), or through the removal or deactivation of preg robbing materials.

The following is an excellent introduction to the concept of refractory ore processing:http://www.altamet.com.au/wp-content/uploads/2013/09/Developments-in-the-Processing-of-Refractory-Complex-Gold-Ores.pdf

When it comes to diagnostic leaching the following is a good open source review, although if you can get hold of the reference article by Lorenzen et al that is the definitive text:

https://prezi.com/dbm6l0pbpzoh/extraction-of-gold-from-ores/

There is a significant amount of literature devoted to refractory ore processing - if your question is specific rather than a more general comment then a web search followed by a chat with your local metallurgical laboratory should set you on the path to identifying and then solving the problem. As always, I heartily recommend a read of Marsden and House's "Chemistry of Gold Extraction" as a starting point - partially available on Google books.

Generally speaking I haven't yet come across a refractory ore where "full" recovery is impossible to achieve - however, it is frequently economically not feasible.

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

Is true refractory ore are very complex in terms of recovery. There is always a process route but as stated earlier by Kock the economics are not feasible. Although series of testwork has confirmed a lot of highly recovery route, the most important one that we are all deviating from is still the old technology. Roasting.

Roasting is able to carter for the all the challenges. I have reviewed lot of document where recovery was less than 10% but after roasting process recovery was greater than 95%. I am currently working on a highly refractory ore where recovery is less than 45% even with high oxygen busting. But surprising to get recovery over 98% by roasting.

The key challenge is the environment. Instead of Engineers to find means and ways to innovate a technology to cater for the released toxic gas and evaluate the economics of scale, we rather shifted the blame to biological oxidation. There is a big hope in roasting and the latest upcoming microwave pre-treatment. We need to research and innovate simple and robust extractors which can convert all the CO, H2, S2 etc. into stable element or compound.

If anyone is much interested in such innovation and wish to join hands for such a broad research I am always available in Ghana to assist. Also if people can sponsor such work, I will be very grateful to join such team. In conclusion, roasting can be the most economical way of maintaining higher gold recovery on refractory ores if research work is carried out well. 

Bill Rico
1 year ago
Bill Rico 1 year ago

Actual industrial low recovery we have after you said tests. I think this tests don’t give full knowledge about refractory ore. The first problem is gold particles behaviour in pre-treatment processes (roasting, POX, BIOX.)

In roasting ore gold particles will be flay or dissolve in solid minerals (pyrite, arsenopyrite). Germany geologists said, that gold particles less 10 nanometers is dissolved in pyrite.

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

Anyone who having any project in site of CIL, Crusher or grinding or detox or etc. concerning metallurgy at its procedure.

Jean Rasczak
1 year ago
Jean Rasczak 1 year ago

It seems as if when refractory is mentioned, most people think of pyrite. It is very important to define well, what kind of refractoriness it is, is it physical, chemical or due to carbonaceous materials. Mineralogy will be able to help and from those results different methods may be used. Physical fine grinding can deal with invisible gold by milling up to the size of the gold grains an actually energy intensive process.

Dizzy Flores
1 year ago
Dizzy Flores 1 year ago

As already said; mineralogy test is the major key. When you have an idea about your gold particle size and the rate of liberation by your equipment, then the process of roasting can be commenced. Roasting does not dissolve it only changes physical state and some chemical composition. I am only expressing the BIG idea of finding new innovation for roasting.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

Refractory is wide and cannot be treated as a generic. Gold which has formed an alloy with other metal forming a solid solution is considered refractory, by definition if you can’t get recoveries beyond 80% then you can call it a refractory ore, whether it’s a mineral processing problem or not will depend on the type of refractory, I will consider a mineral processing problem those ores which have micro gold particles which cannot be liberated for a leaching agent to access. Roasting is one of the technologies which has been phased out in most countries as the amount of acid and arsenic gases being produced are detrimental to the environment. If you have a pyrite or arsenopyrite structure you can consider many environmental friendly processes such as Bio-oxidation using microorganisms such as acidothiobacillus ferooxidants or pressure oxidation whereby your main aim is to destroy the matrix and make it accessible, a lot of research is also being channelled to ultra-fine grinding especial in treatment of high grade ores, it is important to consider the grade of the ore when you propose any technology. In this case 2g/t ore it is not economical possible to do roasting unless you can upgrade through floatation or other processes.

Ace Levy
1 year ago
Ace Levy 1 year ago

The term 'refractory' has become a name that is commonly applied to ores that are more challenging to treat economically. Typically referring to gold deposits.

Any ore can be treated by methods that will generate high recovery, but the part that we are all challenged by is achieving this with a positive economic outcome.

In reality this is our real task.

For example: you could fire assay your entire gold orebody creating a lot of beads, the recovery would be 100%, but the costs!

As we all should know every orebody is unique in its mineralogy/lithology/alteration, and as such needs an appropriate solution. While many work with gold, there are similar challenges in all metal ores.

Consider for example very fine grained complex sulphide Cu/Pb/Zn ore bodies, once untreatable by floatation, but now often achieved. I never heard of these being named refractory.

My view is the word refractory is used as a simple term, replacing challenging.

We seem to use it to explain appropriately complex plants to others.

If we can identify the challenge, test it, develop an economic process solution, then the ore is not refractory (just challenging).

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

Refractory comes from direct cyanidation reference without any other process considered the opposite of refractory being free milling.

Carl Jenkins
1 year ago
Carl Jenkins 1 year ago

"Roasting is one of the technologies which has been phased out in most countries". I admire your sentence above. There were challenges that caused the phased out of the process (Roasting) during those times and in such countries. The major cause was it's environmental gas production and in-stability of the by-product.

Looking at the current generation and the rate of development of high tech, we can revisit the process and develop the best out of it. Biox is good but the initial cost, it can't cater for all minerals. At some places where carbonaceous minerals are present recovery is as low as 65% to 75%. If you can review previews document on roasting, you will realized that the process can cater for every ore type and recovery above 90%.

Yes, I accept that during those times roasting was for high grade and currently we are dealing with low grade. But so wonderful is the process of flotation which can help us to get a high concentrate. Hence flotation after roasting will be very great.

I finally still wish our industry to re-candle the deeper research of roasting and how to overcome the environmental challenges. There is still a BIG hope in roasting. Where there is roasting and refractory, there is HIGH recovery. Always let us remember that fire assay is our final way of preparing our ore to know the mineral content. Fire assay is a pyro-metallurgical process which cater for all the outline challenges, so will roasting when deeply researched is undertaken. I will always be willing when some investors wish to resume the deeper research into ROASTING.

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

It is not a global problem. Have any laboratory tests been done; examine the each test and the result which will give a clue on what is to do next; the last question would be "is it economically feasible".

Bill Rico
1 year ago
Bill Rico 1 year ago

If feed grade 2g/t and recovery 95%, that tail grade will be 0.1g/t. It is not possible.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

I agree; just let the tails be examined for mineralogical identification/ whether any particle is in liberated state and if not even partially exposed. This would give a lead to come to a conclusion whether we can recover anything more or not.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

I had worked on bioleaching of arsenopyrite ores, concentrates and tailing in which case it was observed that bacterial leaching helped in a big way in improving the extractability of gold. In ores and concentrates (30-40 gm /ton), the extraction increased up to 77-78% from 65-70% of the ores/concentrates without bioleaching. The results were more pronounced in tailings having gold in 1-2 gm / ton basis. The extraction of gold in tailings improved to 84-85 % from initial 70% range. In all the cases, the particle size remained same for ores/ concentrate and tailings (with or without bioleaching). The observation which was significant was the adaptability of the bacteria (TF & TT) which played major part in liberating gold for extraction. However, the challenge was to adapt the bacteria to the higher poisonous conditions of arsenic which was a very slow process initially and required a lot of patience. But once adapted to the conditions, they became quite active and process was smooth.


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