substitute to cyanide leaching due to its lower toxicity and greater rate of gold and Selected summary of patented gold recovery processes and examples of. Gold cyanidation is a hydrometallurgical technique for extracting gold from low- grade ore by converting the gold to a water-soluble coordination complex. It is the most commonly used leaching process for gold extraction. To prevent the creation of toxic hydrogen cyanide during processing, slaked lime (calcium hydroxide). ounces of gold per ton of rock (oz/t)], depending on the mining method, total reserves Following this leaching process the slurry passes through adsorption .
|Language:||English, Dutch, Portuguese|
|Genre:||Science & Research|
|ePub File Size:||30.40 MB|
|PDF File Size:||15.66 MB|
|Distribution:||Free* [*Sign up for free]|
thiourea, thiosulphate, and thiocyanate complexes. These are the only ligands that are likely to compete with cyanide in the large-scale processing of gold. Ores in which gold occurs in chemical composition The most commonly used process for gold extraction. with dilute alkaline cyanide solution, and air is. PDF | Copper leaching is currently carried out in sulphuric acid media, where the process is Final considerations about the cyanide process for copper-gold ores are presented. Au and Cu recovery in Heap Leach Projects.
In addition, there are significant problems with the disposal of cyanide-containing waste. Pure cyanide in open air breaks down into other compounds relatively quickly, however the exact composition and toxicity of these products is not well understood.
One of the common breakdown products is nitrate , which itself can cause both environmental and human health problems. Lastly, cyanide can form complexes with certain metals, such as cobalt , and these can persists for many years in groundwater.
Many old mines, and some current mines, simply place cyanide waste into the mine tailings ponds along with other mining waste. Failure of a tailings dam containing cyanide can be a massive environmental problem, resulting in the sterilization of large areas downstream.
Use in Mining
In , a tailings dam failure in Romania dumped an estimated tons of cyanide into a river system, contaminating drinking water and killing fish up to miles downstream, with effects purportedly lasting for years. In comparison to acid mine drainage , cyanide has a higher toxicity, but is shorter lived.
Acid mine drainage can last for thousands of years, whereas cyanide will break down within a few years at most. However, its high toxicity means that even a relatively small spill can have major consequences. Many modern mines now use a "de-toxification" process that converts cyanide into the less toxic cyanate before combining it with the mine tailings waste.
In addition, the majority of cyanide gold mines use "impermeable" liners in their tailings ponds and underneath their heap leaching operations. However, leaks and tears in these liners have been a continual problem at many mines.
Mining companies often argue that the combination of de-toxification and the use of liners makes the use of cyanide an acceptable risk, but there have been numerous accidents over the last decade.
As a result of these environmental concerns, a few countries and US states have banned the used of gold cyanidation. In response, the gold mining industry has promoted adherence to a voluntary " cyanide management code " with strict independent audits of signatory companies.
Some environmental organizations have applauded the code for increasing transparency and others have condemned it as " greenwashing ". Gold Cyanidation in Alaska While cyanide is not used at the recently-opened Kensington Mine , it would be used at the proposed Donlin Creek Mine , and most likely as well at the proposed Pebble Mine.
Cyanide is already in use at the large mines of Greens Creek , Fort Knox , Nixon Fork , and Pogo , in addition to the majority of smaller operations throughout the state. In May , Fort Knox had a spill releasing , gallons of cyanide-containing water, although the majority was contained within a building with no appreciable environmental damage.
The range of concentration of concentration covering the experimental conditions.
This in turn suggests the selective dissolution of copper over gold. Figure 4 illustrates that the extraction of gold Fig.
These findings suggest that the interference of copper sulphides with gold leaching is alleviated by increasing the concentration of NaCN. In addition to their excessive cyanide consumption, the adverse effect of copper sulphides on gold extraction could be also attributed to their consumption of oxygen Eqs.
Cyanide Process – Extraction Of Gold Through Cyanidation
It has been reported that a molar Fig. During the initial two hours of leaching, a minimal 3. On the other ammonia leaching renders the ore amenable to high hand, the dissolution of copper occurs most rapidly and extraction of gold even at low levels of cyanide 1.
In effect, the extraction of gold from the ore process Fig. Thereafter, it remarkably slows down as substantially improves from 6. Increasing the ammonia pretreatment. This improvement appears to be concentration of cyanide improves the leaching of copper linked with the elimination of copper interference by with the highest dissolution of The dissolution behaviour of copper is apparently from the ore in this pretreatment stage.
The remaining linked with ore mineralogy, i.
MUIR et al  reported that copper dissolution be attributed to the presence of more readily soluble from sulphides in ammonia is a slow process copper phases Cu2S Table 1. Similarly, the slow rate Eqs.
They also reported that chalcopyrite is leaching is apparently linked with the copper phases such less reactive than chalcocite in ammonia as well as in as chalcopyrite recalcitrant to cyanide leaching. These cyanide solutions. It can be inferred that ammonia findings indicate that the dissolution of copper is faster leaching as pretreatment allows the removal of reactive A.
They suggested addition of an ammonium salt to control pH. In the current work, the speciation calculations  suggest that the critical concentration of NH3 is 0. After ammonia traditional cyanide leaching, ammonia cyanide system pretreatment of the tailings with 0.
High reagent interactions within the system . Therefore, gold extractions coupled with considerably reduced based on the preliminary studies [6,12], leaching tests levels of cyanide consumption suggest that ammonia were designed using Box-Behnken design to evaluate leaching as a pretreatment process prior to cyanidation main and interaction effects of concentrations of NaCN, can be suitably used for copper-bearing refractory gold NH3 and Pb NO3 2 on the selective extraction of gold ores.
Using Eq. EK et al  demonstrated that the Based on the model, the response surface plots for main ammonia leaching of copper sulphides such as bornite and interaction effects of two parameters at a fixed level A.
On the other hand, the contribution of interactions is statistically insignificant Table 5. Statistical significance of the model terms, i.
The coefficients of linear and quadratic terms in the model Table 6 also reflect the mode and magnitude of the effect of factors on the gold extraction. In fact, the maximum gold extraction NaCN and NH3. An earlier study leaching as a pretreatment prior to cyanide leaching and on the ore showed that the addition of Pb NO3 2 up to ammoniacal cyanide leaching is demonstrated.
In cyanide leaching, the Copper interference appears to be linked with readier adverse effect of Pb NO3 2 could be attributed to the dissolution of reactive copper sulphides than gold and, formation of PbS or Pb OH 2 layer on gold surface hence, depletion of cyanide available by copper.
In this work, a selectivity index was consumption of cyanide. Notwithstanding this, the defined using the extractions of Au and Cu, i. It is treatment. The selectivity of gold leaching in Cyanide consumption and gold extraction tend to ammoniacal cyanide leaching is ascribed to the improve with increasing the concentration of NH3.
extraction the gold by cyanide pdf
However, the dissolution of copper from metallic copper, chalcopyrite addition of Pb NO3 2 increases NaCN consumption in and chalcocite in ammoniacal cyanide solutions occurs the presence of NH3 whilst a reverse trend is observed in and the copper concentration in solution reaches a the absence of NH3.
Oktay CELEP for their valuable contributions during sample preparation and leaching different oxidized copper-gold ores, revealing a tests, and Mr. Chemistry of gold extraction [M]. American Cyanamid, Effect of secondary copper minerals on cyanide control and operation [J]. A review of copper cyanide University, Process of precipitating and recovering precious metals ores [J].
US Patent New Conference.The coefficients of linear and quadratic terms in the model Table 6 also reflect the mode and magnitude of the effect of factors on the gold extraction. You get gold, but you also get highly toxic byproducts. Biochem J — Water Resour Invest Rep References Adams JB Inhibition of green bean lipoxygenase by cyanide.
Your contribution may be further edited by our staff, and its publication is subject to our final approval.