The following text outlines the terrible conditions illegal mining has left on the Amazon rainforest, and our plan to help save the natural resources and the indigenous natives. We are asking for donations to help with this visionary, challenging but feasible project. All Donations are tax deductible.
CONTROL OF MERCURY POLLUTION DURING GOLD MINING OPERATIONS IN THE AMAZONIC RAINFOREST.
BY Chaim Yosef Mariategui-Levi, PhD.
I)-THE PROBLEM:
The activity of the “Informal Miners” in the Amazon Rain Forest is wreaking environmental havoc by exploiting alluvial gold without restrictions or environmental regulations (Ref 1).
Mercury used as a collector for gold in alluvial sand and silt and Cyanides used for gold extraction are extremely toxic to wildlife and even to plants. These species are released into the environment untreated, threatening the integrity of the Amazonian ecosystem.
In Peru, Brasil, Suriname, Bolivia, and Colombia the phenomenon of the informal or illegal miners have been releasing mercury vapor by evaporating the excess mercury of the amalgams. Mercury is toxic and its toxicity can be potentiated by methylation caused by bacteria in aquatic media. The situation could be described as:
“Peru, the largest gold producer in Latin America and the sixth largest in the world, has long struggled with illegal gold mining. Thousands of small, unchecked operations extracting gold from the Amazon are responsible for nearly 200 square miles of deforestation and mercury poisoning to the water so severe that several regions declared a state of emergency last year.”
In Brasil the situation is not better with the “Garimpos”:
Brazilian “garimpos”, or wildcat mines, are operated by small crews of men, often caked in red-brown mud and working with rudimentary pans, shovels and sluice boxes that have been used for centuries.
More sophisticated operations use water cannons and boats sucking mud from the bottoms of rivers. Regardless of the method, searching for gold and other minerals like cassiterite and niobium is dirty, dangerous and often illegal.
“Looking for gold is like playing in a casino,” said a 48-year-old miner.
Miners asked not to be named, saying they feared the police as much of their work is illegal.
He started in the wildcat mines as a teenager in the area around Crepurizao — a ramshackle frontier town of 5,000 with a dirt landing strip that is a gateway for informal mining in the region.
Garimpos are in the spotlight as Brazil debates opening an area known as Renca in the northern Amazon forest to mining, which has met with stiff resistance from environmentalists.
Mines and Energy Minister Fernando Coelho Filho argues that licensed mining will be an improvement over the estimated 1,000 people currently mining in the reserve illegally.
Crepurizao lies hundreds of miles south of Renca, but gives a window into life in the garimpos caught up in the debate.
REUTERS, Nacho Doce, ENVIRONMENT SEPTEMBER 14, 2017 / 11:20 AM /
Some sources calculate the number of illegal miners to be over 1 million
In Suriname the situation is similar and the government is taking a laissez faire attitude regardless the extensive environmental damage.
Apparently the governments of Peru, Brasil, Bolivia, Colombia and Suriname are not capable to enforce environmental regulations.
The two major sources Mercury pollution are:
a)-Mercury left on the sands tailings(relaves) after extraction.
b)-Mercury evaporated from the amalgams to recover the gold.
A minor source is the dissolution of the recovered gold to eliminate the residual mercury. (Ref.2)
We must not forget that in some areas Cyanides are used to extract gold from fine sands. It requires a very different process but similar reagents to eliminate. Sodium Cyanide is oxidized leaving behind Sodium chloride, Carbon dioxide and nitrogen.
The purpose of this work is to minimize the mercury pollution and to suggest a simple method to destroy cyanides in situ.
THE SOLUTION
II)-MINIMIZING THE MERCURY POLLUTION:
2.1)-General Considerations:
Mercury is used as a collector of gold particles in its recovery from alluvial auriferous sands. As we mentioned above, there are three mayor instances of mercury pollution:
a)-Residual mercury in the treated sands and silts. It contains finely divided mercury droplets.
b)-Mercury vapor is generated while removing mercury of the amalgams using heat.
c)-Residual mercury removed from the gold using nitric acid to purify the gold before sales.
The recovery of mercury from each one of these stages is quite different. For Stage 1, the residual mercury in the treated sands there is not recovery but immobilization to protect the environment from free mercury and from the methylated forms that are extremely Toxic. For Stage 2 the process implies distillation and actual recovery. For stage 3, it is only collection, neutralization and precipitation of mercury and the legal disposal of the precipitate. A description of the technology to be used on each stage will be described in the next subsection.
2.2)-Technology Used for Each Stage of the Waste Stream:
2.2.1)-Residual Mercury in Sand and Silt:
Because Mercury has a relatively high vapor pressure and it can go to the atmosphere or be oxidized and methylated by bacteria creating an extremely toxic species of Methylmercury (CH3Hg+) it is imperative to oxidize and immobilize mercury as mercury sulfide (HgS). This stage requires temporary retention of the processed sandy and silty tailings (relaves) to be treated with sodium hypochlorite in the presence of Hydrochloric acid , equation 1.
Hg0 + NaOCl + 3HCl------> NaH[HgCl4] + H2O…. (1)
[HgCl4]2- + FeS ----->HgS + FeCl2 + 2Cl- --------------(2)
Once the reaction is complete some lime (Calcium Hydroxide, CaOH) must be added to raise the pH to 6 or7 (Neutral), then Ferrous Sulfide (FeS) must be added to slowly convert the ion tetrachloro mercury(II) into the highly insoluble mercury sulfide. A better choice is to use Calcium or Magnesium sulfides instead of ferrous sulfide.
(HgS) as shown in equation 2. The matrix where the HgS will be imbedded is a mixture of iron oxides and sulfides.
The products to be sold to the informal miners or garimpeiros will be described in section IV.
2.2.2)- Removal of Mercury from the Amalgam:
The amalgam may contain at least 60% and as high as 90% mercury per
weight. To remove most of the mercury a portable kerosene powered
retort must be used. The actual design will be provided in section
IV. This retort will be transparent the temperature
must be about 680C to eliminate most of the mercury. The final
contains between 13% to 15% of mercury (Ref 3)
2.2.3)-RESIDUAL MERCURY:
The product of sub-section 2.2.2 contains 13% to 15% of mercury per
weight. It is not suitable to be sold. It must be treated with concentrated
nitric acid to dissolve the remaining mercury. The residue is pure gold.
The liquors that contain mercury(II) nitrate and residual nitric acid.
These liquors must be neutralized with a solution of Sodium hydroxide
and a precipitate of yellow mercury oxide is formed. It is easy to
separate this dense and yellow oxide. (HgO) The liquors can be disposed
as a non toxic liquid and the mercury oxide must be legally disposed.
Equipment and reagents in section V.
III) -REMOVING MERCURY FROM THE ECOSYSTEM:
To remove mercury as any of its species it is necessary to use a system that has both adsorption and ion exchange properties. This can remove elemental mercury, dimethyl mercury by adsorption as well as mercury ions and methyl mercury by ion exchange. The system is implemented with biochar which acts as an adsorbent and an ion exchanger.
IV)- CYANIDE:
Sodium and sometimes potassium cyanide are used to extract finely
divided gold from sands or silts.
Chemical reactions
The chemical reaction for the dissolution of gold, the "Elsner Equation", follows:
4 Au + 8 NaCN + O2 + 2H2O → 4 Na[Au(CN)2] + 4 NaOH
In this redox process, oxygen removes, via a two-step reaction, one electron from each gold atom to form the complex Au(CN)− ion
The recovery of gold occurs when Ferrous Sulfate is added to the solution according to the following equation:
Na[Au(CN)2] + Fe2+ ------------------->Au(0) + Fe3+ + Na+ + 2CN-
(Other reducing agents could be used to precipitate gold from he solution such as Aluminum and Zinc powders as well as other reducing agents.)
A part of the excess cyanide is forming hexacyanoferrates but a considerable amount of free cyanide is expected to be in the solution. These species can be eliminated very rapidly if we react them with sodium hypochlorite at pH between 4.4 and 5.0.
V)-EQUIPMENT AND CHEMICALS TO BE SOLD TO
MINERS:
TO BE COMPLETED
VI)-REFERENCES:
1)-Leontien Cremers, Judith Kolen and Margo de Theije.; Small Scale Mining of Gold in Amazonic…. http://www.gomiam.org/omhoogladen/2014/11/20130312-Cuaderno-Small-Scale-Gold-Mining-in-the-Amazon.pdf
2)-P. R. Seidl, O. R. Gottlieb, M. A. Coelho-Kaplan. Chemistry of the Amazon,
ACS SYMPOSIUM SERIES 588, 1993.
3)-R. F. Schneider, Structure of Gold Amalgams determined by Metallographic Methods.
MS thesis, Chemistry Department, University of Illinois 1920,
4)- A Review on Alternative Gold Recovery Reagents to Cyanide.
Mertol Gökelma, Alexander Birich, Srecko Stopic, Bernd Friedrich.
Journal of Materials Science and Chemical Engineering; 2016, 4 pp 8-17,