Project Amazonia:  Solutions - Mining

Problem:

Contaminants from current mining practices (i.e. mercury, cyanide) leak from mining operations into the surrounding environment, poisoning the flora and fauna.

Solution:

The Haber Gold Process. (HGP)

Named after the developer, Norman Haber, HGP is a solution aimed at minimizing the use of mercury and cyanide in the process of extracting gold. Details of the exact technique employed in this method are not indicated here as the technique is proprietary and exclusively owned by Omai Gold Mines of USA.  Basically, “the process operates by extracting the gold from it ores by dissolving the gold into water. It can then be recovered.”1

HGP offers competitive advantages over present techniques by extracting gold in bulk in less time than possible with cyanide. The process involves the use of non toxic chemicals that dissolve gold rapidly. It also does not lead to the release of heavy metals such as mercury, cadmium and lead as in the use of cyanide. “The use of this non toxic process substantially reduces environmental hazards and a serious risk of contaminating ground water which has repeatedly occurred with conventional cyanide gold extraction.”1

The problem with HGP, however, is that it “is not a universal lixiviant. Every gold ore has different properties. Therefore, the lixiviant is preferably adjusted in order to optimize efficiency, recovery and extraction cost. A modified process can be used for extracting other precious metals.”1

It may be possible to apply this method to mines in the Amazon Rainforest.  However, because the process is currently being patented and unavailable to public perusal, it is difficult to surmise whether its use is practical.  The only possible solution to this hurdle would be a joint venture between Orex and Brazil.

Solution to AMD (Acid Mine Drainage)

A leading method of reclamation that has been used in other parts of the world and which can be used in the Amazon is the creation of artificial wetlands that cans survive in the acidic conditions and support microbes that can actually convert the acid into less toxic compounds.

Treatment may also involve chemical neutralization of the acidity followed by precipitation of iron and other suspended solids. Treatment systems include:

  1. equipment for feeding the neutralizing agent to the Acid Mine Drainage

  2. means for mixing the two streams (Acid Mine Drainage and neutralizing agent)

  3. procedures for ensuring iron oxidation

  4. settling ponds for removing iron, manganese, and other co-precipitates

The quantity of AMD to be treated, the chemical characteristics of the Acid Mine Drainage, climate, terrain, sludge characteristics, and projected life of the plant are some of the factors that dictate the level of sophistication of the treatment system that is necessary to ensure that effluent standards will be met. The chemicals usually used for Acid Mine Drainage treatment include limestone, hydrated lime, soda ash, caustic soda, and ammonia.


Physical Reclamation

Reclamation is the process by which formerly uninhabitable land (caused by mining) is restored to its former (and in some cases surpasses) productivity. All the waste/overburden is taken and formed roughly into what the landscape used to look like. New topsoil is then imported and then laid on top of the overburden. This is then sprayed with a mixture of grass seed, water, fertilizer and a binding material to prevent erosion until the plants can hold. Once grass has taken hold, trees may then be planted.

Phytoremediation

This method uses plants to absorb contaminants such as mercury, pesticides, herbicides, explosives, solvents, radioactive cesium and strontium. Therefore, this is a solution that will be applied in areas where mercury is a mainly used for mining gold. Scientists have developed a plant by building a synthetic gene, merApe9 that absorbs mercury using its roots. This new species can be modifies to suit the environment and climate of the Amazon Basin Rainforest.

This plant species absorbs highly toxic mercury ions from a growth medium and reduces them to less toxic and relatively inert metallic mercury. Once converted to its metallic state, the mercury is transferred into the atmosphere as a vapor.

Mercury pollution is particularly suited for cleanup using Phytoremediation because unlike with most chemicals where the plants that grow on the contaminated medium accumulate large amounts of the toxic substance into their biomass, which must then be disposed of, because of mercury's volatility, it does not accumulate in the plants. Metallic mercury vapor is emitted by the plants as they grow; outdoors, this vapor would diffuse into the atmosphere, quickly reaching nontoxic levels.

The problem with this is the consideration of the safety of evolution of metallic mercury into the air as a safe remediation strategy. In particular, there is concern that mercury vapor in the air will precipitate into the Earth's waters where it can enter aquatic food chains. Through the process of biomagnification, this mercury can reach toxic levels in the predatory fish that humans consume. There is some argument, however, that the mercury vapor released during a phytoremediation cleanup would be insignificant on a global scale. There is also a need to introduce these genes into high biomass plants and show that it works on soil. Though some phytoremediation schemes have been field-tested, mercury-removing plants have only been grown on agar under laboratory conditions. In addition, Arabidopsis, a common test plant, does not reduce enough mercury and lacks the field cultivation to make it a practical choice for phytoremediation cleanup.



Cyanide recycling

This can be done by tailing washing where the tailing flows by gravity to a two-stage washing circuit to recover cyanide. The washed tailing is pumped to a reaction vessel for cyanide destruction. The Inco/S02 air process with two stages of washing is used in order to provide an effluent containing less than 5ppm cyanide for discharge to the tailings pond.

By using methods such as high density thickening as much as 90 % of the cyanide that is found in tailings can be recovered. These recovery methods will result in the following advantages:

Cyanide recovery will make the current cyanide concentration solution ponds unnecessary reducing the risk to wildlife and water.

Reduced cyanide in tailings will make it easier for quicker and cleaner mine closure and reclamation

Recovery and recycling of cyanide makes it less necessary to import cyanide from abroad and this increase the profitability of the mines.

Sources:

http://cas.bellarmine.edu/tiejien.PPT/Ecology/ecological_effects

http://www.mining-technology.com

http://www.rec.org/ecolinks/bestpractices/PDF/kazachstan_altynalmas.pdf

http://www.osmre.gov/amdtcst.htm