Mining for Gold and Copper using Biohydrometallurgy Essay Example

ions in the solution. The extraction of copper occurs by bonding it to a ligand, a larger molecule with smaller groups that possess a lone pair.

The ligand (L) is dissolved in an organic solvent such as kerosene and shaken with the solution producing this reaction:Cu2+(aq) + 2LH(organic) -> CuL2(organic) + 2H+(aq). The ligand donates electrons to the copper, producing a complex - a central metal atom (copper) bonded to 2 molecules of the ligand. This complex, having no charge, dissolves in kerosene and can be separated from the solution. The reversibility of the initial reaction, determined by pH, can be reversed by adding concentrated acid, causing the copper ions to return to an aqueous solution. The copper is then subjected to an electro-winning process to increase its purity. An electric current is passed through the resulting solution of copper ions, causing them to be attracted to the negative cathodes and collect there. Additionally, copper can be concentrated and separated by displacing it with Fe from scrap iron through the reaction Cu2+(aq) + Fe(s) -> Cu(s) + Fe2+(aq). The copper gains the electrons lost by the iron in this process.

Copper acts as the oxidizing agent, accepting electrons, while iron serves as the reducing agent, losing electrons. The excess leaching solution is directed into an uncovered pond, where the oxidation of Fe2+ ions to Fe3+ ions is catalyzed by T. ferro oxidans. This oxidation process recharges the leaching solution, which is then pumped back to the top of the heap for another cycle. Gold can also be extracted using bacteria. Approximately 15 to 30% of the world's gold reserves are trapped in refractory minerals like chalcopyrite.

Initially, the refractory sulphide concentrate is treated with the thermophilic bacterium Sulpholobus acidocalderius. These bacteria facilitate the oxidation of sulphide minerals by dioxygen under specific aqueous conditions at a temperature of 70 o C.

The final and resulting extract underwent cyanidation, resulting in a significant breakthrough where the gold recovery rate improved from 10% to 100%. Subsequently, a mixed culture of moderately thermophillic bacteria from specific samples was introduced. This culture proved effective across various conditions, including different temperatures, pH levels, water salinity, and arsenic concentrations. It was found that the bacteria performed best at a temperature of 46 oC (as excessive heat would denature the enzymes within the bacterial cells) and in solutions with a pH ranging from 0.5 to 1.5. These conditions greatly increased the percentage of gold extracted. Despite having several advantages and disadvantages, one notable benefit of this new process is its significantly lower cost compared to conventional methods.

The cost of mining copper traditionally can range from $130 to $200 per tonne. However, Biohydrometallurgy has reduced this cost significantly to around $70 per tonne. Additionally, conventional mining techniques emit about two tonnes of sulphur dioxide into the atmosphere for every tonne of copper extracted, while biological extraction methods prevent this release. Furthermore, biological mining does not pose any environmental concerns as the entire process is biological except for the stage of copper extraction, which involves Electro winning to separate ions. In contrast, Biohydrometallurgy does have a few drawbacks including its slow pace that spans decades rather than years and a lack of efficient methods for breaking ores into small particles for extraction purposes.

Currently, biological methods are economically viable for extracting minerals from

low-grade ores, even those that are resistant to traditional methods. However, advancements in technology could expand the competitiveness of these methods. The mining industry has been hesitant to adopt this new process due to unfamiliarity with the technology. There are only a few qualified biohydrometallurgists in this area and limited success stories in terms of commercial viability, raising concerns about the reliability of the biological process which requires significant time. Bacterial leaching is used as a secondary method for copper extraction because the conventional process is slow and not efficient enough in generating revenue. Additionally, the traditional method yields more copper from the ore.

The bacterial process for gold extraction is primarily used because of its rapid research and technological development. It is not only more economical, producing more gold and generating higher revenue, but also has lower plant operation costs. Moreover, compared to traditional methods, this entire process is more feasible and economically competitive. However, for the new bacterial leaching process to become commercially viable, it requires approval and regulation from government and political authorities who may also need to provide funding. Before granting permission for implementation, an inquiry may be necessary to assess the mandatory and safe effects of this new technology. In summary, although bacterial chemistry for obtaining metals from ores is a novel technology, it still lacks widespread recognition in the industry.

Compared to conventional methods, this process has the advantage of being cost-effective and eco-friendly. Its impact on shaping our future will be significant.