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

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-04-04T06:57:36+00:00
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Cyanide toxicity and environmental impact (15 replies)

John Koenig
2 years ago
John Koenig 2 years ago

Is the use of Cyanide in gold production a real issue, with respect to its toxicity and environmental impact to local Authorities and gold producers? Is there enough concern out there to warrant a total shift towards a much more friendlier reagent?

I suppose responsible handling and disposal thereof, comes at a cost to the Mining Enterprises. Is the strict adherence to the ICMC (International Cyanide Management Code) guaranteed or is it just left up to individual mining enterprises?

JohnnyD
2 years ago
JohnnyD 2 years ago

People have been evaluating alternate reagent schemes for many years. Many have been tried and in certain situations have found good applicability (i.e. Barrick Goldstrike with Thiosulfate.) The fact of the matter is that the process of gold lixiviation from ore is difficult and there are few chemistries that can do it effectively. None of these chemistries are really benign. So regardless of reagent choice, it is incumbent upon the gold miner to handle their reagents responsibly and dispose / destruct of them responsibly.

As far as I know, Sodium Cyanide is the safest and most cost effective reagent for use in gold extraction at commercial scale. We encourage all mines to embrace the processes and disciplines of the International Cyanide Management Code http://www.cyanidecode.org and work only through value chain partners who are signatories. Additionally we encourage mines to evaluate the range of cyanide destruction technologies offered by sodium cyanide producers such as my company http://www.cyanco.com/products.php#detox and by other service providers.

The vast majority of gold mines use NaCN at significant quantity without incident. Those that don't, become environmental disasters which attract unfavorable mining industry market perception and press. Each of these failures are totally preventable. This subject is really all about responsibility from wingtip to wingtip.

David Kano
2 years ago
David Kano 2 years ago

In many underdeveloped countries there may be laws specifying the need to control and manage the use of cyanide. But, the reality is that these regulations are often not enforced. In the Philippines there have been a number of cyanide spills from both large-scale and small-scale mining operations. Many mining companies are unwilling to treat and/or impound their wastes in a responsible manner. Alternative leaching methods are available but may be more costly to implement. With gold mining the the cost of processing with alternative leaching agents should not be an issue.

I disagree that cyanide is the safest leaching agent. However, I agree that there are toxicity and disposal issues with almost all leaching agents.

JohnnyD
2 years ago
JohnnyD 2 years ago

ICMC compliance is policed via a regular auditing and certification process. You can read the actual detailed audit reports on the ICMC website.

Helena Russell
2 years ago
Helena Russell 2 years ago

All chemicals need treating responsibly but the fear of chemicals is even more dangerous.
If you question this see http://www.dhmo.org/facts.html and ask yourself if water can kill are we doing enough to survive?

Bill Fraser
2 years ago
Bill Fraser 2 years ago

The challenge is that cyanide is always relatively safe until you allow humans to manage it. Unfortunately it's not the operation of the leach process that's the problem as that usually complies. It's more often the operation of the tailings storage facility and the particular metallurgical fingerprint of the residual waste. Every mining site is unique and will have a Myriad of cyanide complexes. The long term management of TSF's post closure with respect to ground waters is usually poorly addressed.

JohnnyD
2 years ago
JohnnyD 2 years ago

I agree that the management of tailings storage is one of the primary risks of precious metal extraction. Would you agree that tailings management remains a risk almost regardless of reagent chemistry, due to the levels of residual heavy metals? One of the worst mining ecological disasters of recent years, the Mount Polley tailings dam failure came from a facility which is not a cyanide consumer (despite many erroneous news reports). Understanding of past containment failures and implementation of permanent corrective actions is key to maintaining the industry's license to operate.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

I would but companies always under do the structural geology and groundwater components of potential exposure pathways. And singularly avoid constructing a properly designed and engineered base to these structures. Uranium mines like Ranger NT compacted clay bases and have been very effective in containing metal migration. The problem really comes with high acid producing materials which can increase transmissivity over time in fault zones and such. Not enough is done with ore finger prints and groundwater aquifer signatures

Mining companies avoid spending money on these items to mask losses due to seepage and maintain manageable water balances

Alan Carter
2 years ago
Alan Carter 2 years ago

Lets answers this a different way. The use of cyanide based precious metal recovery is efficient, cost effective and well understood. The environmental issues are understood, monitored and controllable.

From the comments above, we all agree on this. Alternate reagent systems are not well understood, are more costly, and their long term environmental effects are somewhat undefined.

If the tailings dam contains cyanide at Cyanide Code standard, and did fail, its long term water quality effect, is likely lower than other alternate reagent. I could argue, that switching to non cyanide systems would put many precious metal producers out of business, on cost increases alone.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

In addition to your comments there are well proven technologies for cyanide destruction. The INCO process has been in use for 30 years and can achieve very low levels of cyanide contained in plant effluent.

John Koenig
2 years ago
John Koenig 2 years ago

What is the cost of this cyanide destruction process. Doesn't it add a significant chunk to the total cost of production?

Maya Rothman
2 years ago
Maya Rothman 2 years ago

Iif the cyanide destruction process proves expensive you can still implement the cyanide regeneration process. the process allows you to limit the amount of cyanide that passes into the environment and as well as reduces the overall cost of the cyanide since the bulk of the cyanide is regenerated and recycled.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

The cost of cyanide destruction varies depending on the ore type, and what discharge limit you need to achieve. Content of base metals like copper and iron will also have a big impact on operating cost. Ultimately it requires testwork to determine what reagent dosage is required, and then based on location and availability you can determine the cost.

JohnnyD
2 years ago
JohnnyD 2 years ago

Typically Cyanide destruction technologies and support are offered (i.e. Caro's Acid, Combinox) to customers as a value added service or at very reasonable costs. At scale, the cost impact is negligible.

Maya Rothman
2 years ago
Maya Rothman 2 years ago

SO2 air detox using sodium meta bisulphite was very effective when we used it in the mid1990's

Alan Carter
2 years ago
Alan Carter 2 years ago

As a broad rule of thumb in initial costs estimates I used the cost of cyanide destruction (OPEX) as approximating the initial cost of the cyanide in the process. Again this will eventually be optimized by testwork (which in early test programs is usually neglected) as long as you are able to get a reasonable sample during the testwork program . In the development phase of a process it would be wise to include the cyanide destruction test work in the test work flow sheet along with the other tailings test work that the TSF designer requires.


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