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An Examination and a Solution to replace the use of Mercury in Artisanal Ore Processing

Written by

Bruce A. Cosgrove, M.Sc., (Solution Chemistry)

Published on

March 23, 2023

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The use of mercury in artisanal ore processing causes damage to the nervous system, digestive system, immune system, lungs, thyroid, and kidneys; causing memory loss, insomnia, tremors, neuromuscular changes, and paralysis.

It is well documented that whole ore mercury amalgamation Chilean processing centers use of mercury in ore processing to recover gold is the Planet’s largest anthropogenic source of local biodiversity destruction, human health threats, and deadly global atmospheric mercury pollution which is documented in 2021 by Oxford University earth scientists[1] to stay airborne up to one year.

In this Article, the Author presents a scalable ESG-driven climate action initiative which has been designed to safely leach crushed and milled ore to; (i) sustainably recover more gold and silver than by using mercury[2], a deadly neurotoxin[3], which today is widely used as a lixiviant[4], and; (ii) to leach precious metals from tailings waste generated during ore processing.

The following flow chart depicts the design schematics for the world’s first mercury free “Sustainable Manipueira Precious Metals Leaching Center” for processing ore bearing precious metals and tailings wastes employing a modified version of the Merrill-Crowe leaching process

This 80 tonnes per day leaching circuit incorporates state-of-the-art cyclone and gravimetric technologies used to separate and recover fine gold from crushed and milled ore slurries and uses manipueira, a plant-based extract solution from the bitter cassava plant[5] as a lixiviant, documented by Marcello Veiga & Pariya Torkaman[6] to recover 99.6%  of the tailings waste gold and 99.3% of the gold in a slurry in 2 hours.

| Unique Solution | Cyanogenic Plants |

“We propose to use a solution extracted from plants, bitter cassava, as a gold leaching lixiviant for the first time in the history of the mining industry.” Dr. Marcello M. Veiga, P. Eng.

Marcello conceived using the bitter cassava plant extract solution, commonly known as manipueira, as a lixiviant who together with Pariya Torkaman, a UBC Ph.D. student and researcher, developed the leaching process protocol. 

It is well documented more than 2,000 plants species including edibles such lima beans, bamboo, flax, and the cassava plant, which is used to make starch, toasted cassava, porridge, dough, beer, and other foodstuff all contain cyanogenic glycosides. These can be converted to aqueous free cyanide by enzymatic hydrolysis[7] which is the plants‘ defense mechanism when the integrity of the cellular structure is compromised by predators including by humans from hand crushing.

The disruption of the plant cell structure coalesces the glycosides with the corresponding β-glucosidase enzymes, producing sugars, and cyanohydrin that spontaneously decomposes into hydrocyanic acid and a ketone according to Bolarinwa, I.F., et  al 2016 publication[8].

In Tadó, Dept. Chocó, Colombia, small-scale alluvial gold miners produce Green Gold[9] using the Balso (Ochroma pyramidale) and Malva (Hibiscus furcellatus) leaves which they crush by hand, mix with water to make a foamy liquid which is added to the gold pan (batea) lowering the solution surface tension allowing the fine alluvial gold to float over the be recovered instead of using mercury. More than likely, aqueous free cyanide is a contributing factor.

According to P. Torkaman et al. publication Leaching gold with cassava: An option to eliminate mercury use in artisanal gold mining[10], manipueira does not contain cyanide, it generates hydrogen cyanide from the hydrolysis of the cyanogenic glycoside linamarin in the bitter cassava plant.

According to Marcello and Pariya 2021 previously cited, the liquid extract from bitter cassava (Manhiot esculenta Grantz) manipueira is “rich in cyanide reaching 2,000 mg/liter by comparison, the cassava we eat has less than 20 milligrams of cyanide per kg of cassava”.

The manipueira extract liquid solution represents 30 – 35% weight per weight of the plant containing 267 milligrams of free cyanide per liter of extract which today is recklessly disposed on the grounds around the mills by the starch manufacturers causing environmental damage, contaminating the soil and waters[11], destroying the local flora, impacting the fauna and when fermented, creates a nasty odor which attracts insects. 270 million tonnes of the bitter cassava plant are harvested annually.

The extract solution has a pH of 3.5 which is recklessly discharged to the environment by the starch processors.

The generation of cyanide from linamarin[12]  is usually enzymatic[13] and occurs when linamarin is exposed to linamarase[14], an enzyme normally expressed in the cell walls[15] of cassava plants.

The symbiosis of artisanal ore processors and flour makers is a win-win situation to reduce environmental pollution, human health threats, and mitigating an unintended consequence of harvesting the bitter cassava plant.

| Enzymatic Hydrolysis of Linamarin produces aqueous free Cyanide |

The conversion of the Chilean processing center to manipueira leaching utilizes the existing leaching circuit including floatation cells and a majority of the ore processing equipment. This equipment is integrated with state-of-the-art centrifugal and gravity technologies which have been proven to recover more fine gold and silver using a modified version of the Merrill-Crowe process, than by using either mercury or cyanide salts.

The starch in the manipueira extract solution is removed by flotation to prevent preg-robbing[16] and in a properly controlled pH- environment of 10.5 which also prevents free cyanide generation and accelerates the gold and silver leaching process ultimately consuming all the free cyanide.

The use of manipueira as a lixiviant is proposed to replace the use of both mercury in ore processing and cyanide salts used to remediate tailings in order to recover more gold and silver sustainably and without the formation of toxic mercury-cyanide complexes, mercury sodium or potassium amalgams all of which, provide mercury mobility when discharged directly into the rivers after tailings remediation,

Ore processors globally use either the Merrill-Crowe or the Carbon in Pulp (CIP) leaching processes which use cyanide salts to precipitate gold and silver from tailings waste which contains mercury. The Company pre-leaching process safely removes the mercury.

Technically, the modified version of the Merrill-Crowe process precipitates more gold and silver using the bitter cassava plant aqueous free cyanide solution than cyanide salts. This solution does not require filtration nor deaeration.

A properly controlled pH-environment of 10.5 is required to precipitate gold, silver, and other precious metals which mitigates any release of toxic cyanide fumes to the atmosphere.

However, under the current practice, the processors rely on the smell of the toxic cyanide fumes as a leading indicator that the cyanidation process is working. This indicator however demonstrates the chemistry of the process is negated and creates a dangerous environment.

| Climate Action Initiative |

Supports the replacement of;

  • mercury with the use of manipueira to safely leach gold more from ore than by using mercury which only amalgams with only the liberated gold in the slurry, and
  • cyanide salts used to remediate tailings wastes containing mercury and which salts, amalgam with mercury providing mercury mobility when discharged to the rivers after remediation,

and;

  • supports gold toll milling, a transactional process which promotes the coexistence by and between ore processors and artisanal miners which provides the miners a fair and equitable payment for the gold and silver content in their ore and dehydrated tailings wastes (“assets”) while eliminating their contact with, and their use of mercury permanently which,
  • supports the UNEP GMP overall goal to protect human health and the environment from anthropogenic releases of mercury to the air, land, and waters.

The leaching center circuit process:

  • uses manipueira, a cyanogenic plant-based extract solution as a lixiviant for the first time in the mining industry to leach and recover more gold and silver safely and sustainably from ore than by using mercury and from tailings wastes than by using cyanide salts which are difficult to handle and without introducing man-made toxins to the tailings wastes which are discharged after remediation;
  • uses a modified version of the Merrill-Crowe process with a properly controlled pH[17] leaching environment preventing the release of toxic cyanide fumes to the atmosphere whereas today, the smell of fumes to the artisanal miners is a leading indicator the process is working;
  • consumes all the free cyanide during the leaching process mitigating future releases of cyanide to the rivers.

Manipueira extract solution:

  • does not contain sodium or potassium salts which, when combined with the mercury in the tailings wastes, form toxic mercury salt complexes providing mercury mobility when the remediated tailings are discharged directly into the Calera and Amarillo rivers;
  • leaches 70% more gold from the crushed or milled ore slurry than by the current practice which uses up to 100 times more mercury than what is technically required to amalgam with the liberated gold in the slurry and only recovering 30%, missing out on the gold in the ore which is lost to tailings;
  • does not lose gold in the form of mercury flour[18] as pursuant to the current practice;
  • unlike today, removes the mercury from the tailings waste prior to leaching preventing the formation of methylmercury[19] which is produced from human bacteria and anaerobic microbes contact with mercury in a moist environment, the result of which is 100 times more potent than elemental mercury, and with unknown biomagnification effects.

| Ore Processing using Mercury |

It is well documented and know by all the processing center owners that 70% of the artisanal miner’s gold is lost to tailings waste during ore processing as demonstrated in the following link to a YouTube video; Artisanal Mining: Poverty Driven Destruction[20], shot during 2015 in a typical Chilean processing center in Portovelo, Ecuador.

Here, in the Portovelo-Zaruma mining district, all Members with tailings ponds keep the artisanal miner’s tailings wastes for subsequent cyanidation to recover that “unknown” quantity of gold in exchange for equipment usage fees. This fact has created distrust of the Members by the local miners.

Artisanal miners are aware they are not enjoying the benefits from their production efforts as they do not have the money to pay for the Merrill-Crowe cyanidation process, or the time to accumulate the carbon required in the carbon in pulp (CIP) leaching process and the related leaching costs to recover their tailings gold, nor the time to wait for the process as 4 – 6 weeks has passed since they started mining ore, they are impoverished, exhausted, and need the cash immediately.

This scalable ESG-driven climate action initiative will result in the reduction of mercury human health and environmental threats and support the UNEP Global Mercury Partnership’s overall goal, while simultaneously eliminating the miner’s exposure to mercury and increasing both the ore processors and miner’s wealth for the benefit of their communities, and ultimately our Planets’ health.

| Need – Problem |

Mercury is everywhere: in the rain, snow, our food, our waters, even in the human placenta, brain, and the central nervous system! Mercury is poisoning life on Earth. Bruce Cosgrove

Processing gold bearing ore by artisanal miners is the Planet’s largest anthropogenic source of deadly mercury pollution overtaking coal fired plants mercury emissions during 2017.

It is well documented that an estimated 20 million impoverished artisanal miners all largely suffer from undiagnosed mercury poisoning. This fact is based upon scientific studies in 80 Countries. This figure includes 4.5 million women and 600,000 children under the age of 15 using mercury to produce 20 - 25% of the world’s supply of gold used in our jewellery, computers, iPads, iPhones, and other electronic devices. Under this model, each miner earns between $4-$5 dollars per day and typically has 5 – 6 dependents.

The Company’s climate action initiative addresses the artisanal ore processors continued use of mercury as a lixiviant to extract gold from ore and mitigate the discharge of toxic mercury laden tailings waste to their rivers, its vaporization to the atmosphere causing deadly global pollution, the local and global biodiversity destruction caused, and the threats to human and unborn children’s health, who are at particular risk.

The human health threats, local and global biodiversity destruction, and global toxic mercury pollution caused by the artisanal ore processors is well researched and  a change in ore processing and gold recovery is yet to occur. Funding for the right solution and additional stakeholders are required to implement a change.

This ESG-driven climate action initiative can help mitigate ongoing;

  • water and food security threats,
  • human and unborn children health threats,
  • local and global biodiversity destruction,
  • mercury atmospheric pollution,
  • anaerobic production of methylmercury,
  • fluvial disbursements of mercury, mercury-cyanide, and mercury cyanide salt complexes discharged into the local waters polluting and contaminating the biosphere.

By adopting the Company’s initiative and switching from mercury ore processing and tailings remediation using cyanide salts to manipueira leaching, artisanal miners and specifically ore processing center owners will (i) recover more gold safely and sustainably, (ii) generate more income, (iii) improve their own health and the health of their neighbors, (iv) improve their community’s well-being, and (v) the health of the Planet and its inhabitants.

| Proof of Existence |Evidence |

  • Newlox Gold Ventures Corp. (“Newlox Gold”) wholly owned Costa Rica operating subsidiary, Oro Roca, S.A., built a 50 tonne/day environmental reclamation facility[21]  based on the extensive R&D process at University of British Columbia Norman B. Keevil (Chairman Emeritus) Institute of Mining Engineering spearheaded by Dr. Marcello Veiga, (“Marcello”) P. Eng., Professor Emeritus.
  • Newlox Gold’s environmental reclamation facility in Costa Rica using manipueira as a lixiviant to leach tailings waste acquired using Marcello’s coexistence model, is projected to yield approximately 6,500 ounces of gold per year at full-scale operations processing 80 tonnes per day of tailings feedstock.
  • The Daily Dive featured Ryan Jackson – Gold Production In Costa Rica[22] - Newlox Gold Ventures Corp., Costa Rica sustainable tailings waste leaching plant. 
  • On October 14, 2021, Marcello Veiga, inventor of the manipueira leaching process along with Pariya Torkaman, a UBC Doctoral Candidate and codeveloper of the manipueira procedure and protocol to safely use as a lixiviant presented the Newlox Coexistence Model for Artisanal Mining at a live podcast at the planetGOLD Platform previously cited.  
  • On October 7, 2021, Marcello along with co-Author Pariya Torkaman in conjunction with Newlox Research & Development Corp. (NERD) submitted to the planetGOLD Exhibition Opportunity Alternatives to Eliminate the Use of Mercury in Artisanal Gold Mining previously cited designed to “assist artisanal and small-scale miners to transition to gold production technologies that do not use mercury”. 
  • On July 01, 2021, SKILLINGS MINING REVIEW published an 8-page interview[23]  featuring this Author  introducing the global mining industry the use of manipueira as a lixiviant in artisanal ore processing to replace the use of mercury. 

| Research |

  • August 15, 2021, P.Torkaman, Marcello M. Veiga, L.R.P. de Andrade Lima,  L.A. Oliveira, J.S. Motta, J.L. Jesus, L.M. Lavkulich published Leaching gold with cassava: An option to eliminate mercury use in artisanal gold mining previously cited in the Journal of Cleaner Production.
  • November 18, 2020, Marcello, and Aaron J. Gunson published Gravity Concentration in Artisanal Gold Mining[24] in Minerals. 
  • According to Marcello and Pariya’s’ presentation Alternates to Eliminate the Use of Mercury in Artisanal Gold Mining previously cited, using a modified version of the Merrill-Crowe process resulted in a 99.6% removal of gold from Newlox Ventures tailings material in 2 hours and 99.3% of the gold from the ore.

| The Perspective|

On September 22, 2017, Indonesia ratified the Minamata Convention on Mercury,[25] a legally binding obligation to protect human health and the environment from the adverse effects of mercury.

According to a 2019 New York Times interview[26] with Yuyun Ismawati, a co-founder of an Indonesian environmental group, Nexus3 Foundation, and a recipient of the 2009 Goldman Environmental Prize, Indonesia produces so much black-market mercury that it has become a major global supplier, surreptitiously shipping thousands of tons to other parts of the world.

Accordingly, for years, Mr. Cece was a pioneer in a network of illegal mercury producers, traders and smugglers who used to supply gold miners across Indonesia with mercury to extract gold from crushed ore.

Ms. Yuyun estimates that illicit manufacturers in Indonesia produce more than 10,000 tons of mercury a year. About a third is used in gold mining in Indonesia, she said, the rest smuggled overseas “to S. America through Bolivia. The government banned the use of mercury in gold mining in 2014, but has done little to curb its use, clean up contaminated sites or warn the public of the danger.

“On a single day, operating a furnace he (Cece) constructed in his backyard, he could produce a ton of black-market mercury worth more than $20,000, he said.” As long as that financial carrot hangs, the longer and harder it will be to eradicate mercury production in Indonesia.

The Gravity Borax Method[27] (“GBM”), enhanced gravimetric method, or the Filipino method for sustainable gold recovery uses an environmentally benign low-cost powder known as Borax® (sodium borate decahydrate) as a flux for smelting replacing the use of mercury as lixiviant.

Essentially, Borax® is mixed with the gold ore concentrate in a plastic bag, placed in a crucible, smelted between 1150 – 1450º Celsius causing chemical reactions wherein which borax in the molten state easily dissolves the metal oxides forming a slag removing the impurities purifying the gold concentrates with no toxic tailings wastes.

Reportedly, the GBM was developed by an artisanal miner in the province of Benguet, Philippines on the island of Luzon in the 1950s and more recently, introduced to artisanal small-scale miners by scientists conducting mercury-amalgamation vs. the GBM competitions.

According to Appel and Na-Oy 2012 publication[28], gold extraction using borax for ASG miners has been successfully tested and operational in the Philippines, Indonesia, Tanzania, Bolivia, Sudan Africa, Kenya, and Zimbabwe for decades.  In a small area of Luzon, the main island in the northern portion of the Philippines, approximately 15,000 ASG miners use this method exclusively typically reporting 3 (three) times more gold recovery than using mercury and producing no toxic tailings waste. 

Additionally, Peter W. U. Appel et al 2015 publication[29] reports in Sorata Bolivia, a mercury-amalgamation competition vs. the GBM was held with the winner being the GBM which extracted 5 (five) times more gold.

Just by using borax, no mercury flour containing gold is produced, hence gold recovery increases.

Peter and his team are doing an excellent job promoting the GBM and produced an informative English video[30] released in 2011 detailing the GBM which has approximately 1.25 million views and a Spanish version released in 2013 with 886,017 views. However, to date, the GBM is reportedly used by only 30,000 artisanal small-scale gold miners collectively in 7 Countries who consistently report recovering 3 (three) times more gold which provided those miners incentive to immediately switch from using mercury.

The use of the GBM for sustainable gold recovery was discovered in the 1950’s approximately 65 years ago although according to Pure Earth [31], has been in use in the Philippines for a century.

In 2015, it is estimated 30,000 artisanal and small-scale gold (“ASG”) miners collectively in 7 countries switched to using the GBM which at this rate and budget, will take an estimated 41,000 years to convert all the 19 million ASG miners in 80 Countries.

Pure Earth  (f.k.a) Blacksmith Institute is a leading global-non-profit focused on pollution issues in low-and middle-income countries.

Pure Earth has “addressed toxic pollution in over 120 project locations through assessment, remediation, risk mitigation, awareness raising and more. These projects have impacted approximately 5 million people with 20% of those being children under six. Families in many of these communities will live longer, have less intellectual impairment, cancer, and other diseases.”

Pure Earth “has identified mercury as one of the world’s top toxic threats. Because much of the mercury released into the environment is the result of artisanal and small-scale gold mining (ASGM), Pure Earth’s global mercury work focuses on ASGM mining communities around the world.”

Pure Earth’s 20 years of effort in 50 countries[32] to date has trained 1,500 miners to use the Benguet method otherwise known as the Gravity Borax Method (“GBM”) for sustainable gold recovery. “Miners especially women, report increased earnings” using the Benguet method being taught in the Philippines by Leoncio D. Na-Oy.

Extrapolating Pure Earth’s efforts to convert the 19 million ASG miners in 80 countries to using the mercury free Benguet method based on continuous funding, will take an estimated 253,000 years.  

The planetGOLD programme is working to eliminate mercury from the supply chain of gold produced by artisanal and small-scale miners by supporting improvements in these four areas.

“The gap in applicable guidance for cyanide management in the ASGM sector requires urgent attention, especially considering cyanide’s accessibility and effectiveness at gold extraction, and in light of the trend in uptake of cyanidation in the small-scale gold mining sector worldwide.”

Globally, artisanal ore processing centers produce 80% of the artisanal gold supply and are largely responsible for the release and discharge of the estimated 2,000 tonnes of mercury to our environment annually. ASG miners who produce an estimated 20% of the artisanal gold supply are incorrectly assumed to be the main culprits of the mercury pollution, however, it is the ore processing centers with the greatest impact.

Based on the Authors forecast model[33] for converting an average of 4 Chilean processing centers in the Portovelo-Zaruma mining district every 7 years, the time to convert 65% of the Members 68 centers or 44 centers that use mercury to sustainable manipueira leaching will take 77 years costing in excess of $USD 44 million.

The Company estimates converting 65% of the  Asociasion de Mineros de Muluncay Society[34]  (“Society”) members 32 centers or 21 centers using mercury  owning 32 centers located near the town of Malvas which is 9 km west of Zaruma situated on the Miranda, Arcapamba, and Botoneros streams all of which are direct tributaries of the Calera river. will take 49 years costing in excess of $USD 21 million.

There are  80 Chilean processing centers in the El Pache mining district bordering Portovelo which, by the same calculation, will take an estimated 91 years costing in excess of $USD 52 million to convert 65% of the centers.

Given the hypothesis that the center owners adapted the Company coexistence model, AMGI principles estimate that 150,000 artisanal miners’ whose ore is processed by the approximate 199 centers in these 3 mining districts would no longer use, or be in contact with,  mercury.

| Conclusion |

Building on the experience of our contemporaries who continue to address the mercury human health threats and biodiversity destruction caused by artisanal miners gold ore processing; the Author has drawn the conclusion the only way to address this issue on a scale large enough to drive change, is through the gold ore processing facilities. 

The Company is #Crowdfunding to secure impact investment capital to implement and promote the scalable ESG-driven climate action initiative in Zaruma, Ecuador with the JV conversion of a whole ore mercury amalgamation Chilean processing center into the world’s first sustainable and profitable precious metals ore and tailings waste leaching center using a plant-based extract as a lixiviant to replace the use of mercury and hard to handle cyanide salts.

| References |

[1] Oxford University earth scientists Influencing global policy on mercury University of Oxford Research 2021.

[2] Mercury

[3] Neurotoxin

[4] Lixiviant

[5] Bitter Cassava Plant

[6] Alternatives to Eliminate the Use of Mercury in Artisanal Gold Mining Marcello Veiga & Pariya Torkaman NERD (Newlox Research and Development Corp.) Presentation.

[7] Hydrolysis

[8] A Review of Cyanogenic Glycosides in Edible Plants, Islamiyat Folashade Bolarinwa, Moruf Olanrewaju Oke, Sulaiman Adebisi Olaniyan, and Adeladun Stephen Ajala, Department of Food Science and Engineering, Ladoke Akintola University of Technology (LAUTECH), P.M.B. Ogbomoso, Oyo State, Nigeria, October 26th, 2016, http://dx.doi.org/10.5772/64886

[9] Green Gold—Dirty Gold, Tadó, Dept. Chocó, Colombia, William E. Brooks, Julio Andrés Sierra-Giraldo, Franciso Mena Palacios November 2015 Natural Resources 6:534-542 DOI: 10.4236/nr.2015.611051

[10] Leaching gold with cassava: An option to eliminate mercury use in artisanal gold mining. P.Torkaman, M.M.Veiga, L.R.P.de Andrade Lima, L.A.Oliveira, J.S.Motta, J.L.Jesus, L.M.LavkulichJournal of Cleaner Production Volume 311, 15 August 2021, 127531 https://doi.org/10.1016/j.jclepro.2021.127531

[11] Leaching of Cyanogens and Mycotoxins from Cultivated Cassava into Agricultural Soil: Effects on Groundwater Quality,  Elie Fereche Itoba Tombo, Seteno K. O. Ntwampe, John Baptist Nzukizi Mudumbi

In book: Aflatoxin-Control, Analysis, Detection and Health Risks Chapter: 8 Publisher: INTECH Open Science Editors: Lukman Bola Abdulra'uf DOI: 10.5772/intechopen.68715

[12] linamarin

[13] enzymatic

[14] linamarase

[15] cell walls

[16] preg-robbing - the phenomenon whereby the gold cyanide complex, Au(CN)2−, is removed from solution by the constituents of the ore. The preg-robbing components may be the carbonaceous matter present in the ore, such as wood chips, organic carbon, or other impurities, such as elemental carbon.

[17] pH - potential of Hydrogen, the term is used to indicate basicity or acidity of a solution on a scale of 0 to 14, with pH 7 being neutral                

[18] Mercury-Free Gold Extraction Using Borax for Small-Scale Gold Miners Peter W. U. Appel & Leoncio Na-Oy January 2014 Journal of Environmental Protection 05 (06):493-499 DOI: 10.4236/jep.2014.56052

[19] Methylmercury

[20] Artisanal Mining: Poverty Driven Destruction YouTube Brandon Nichols Dec 03, 2013 (18 Min., 50 Secs.)

[21] Newlox Gold Environmental Facility

[22] Gold Production In Costa Rica

[23] Skillings Mining Review Interview

[24] Gravity Concentration in Artisanal Gold Mining, Marcello M. Veiga and Aaron J. Gunson, Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada Minerals 2020, 10(11), 1026; Published: 18 November 2020 https://doi.org/10.3390/min10111026

[25] Minamata Convention on Mercury

[26] 2019 New York Times Interview

[27] Gravity Borax Method GBM Mercury Free Gold Recovery 911 Metallurgist

[28] The Borax Method of Gold Extraction for Small-Scale Miners. Peter W.U. Appel, PhD; Leoncio Na-Oy Journal of Health and Pollution (2012) 2 (3): 5–10 https://doi.org/10.5696/2156-9614-2.3.5

[29] Introduction of Mercury-free Gold Extraction Methods to Medium-Scale Miners and Education of Health Care Providers to Reduce the use of Mercury in Sorata, Bolivia, Peter W. U. Appel, Astrid Andersen, Leoncio D. Na-Oy, and Rudy Onos. Journal of Health & Pollution 2015 Dec. 21  DOI: 10.5696/2156-9614-5-9.12

[30]  Gold extraction with BORAX for small-scale miners - Rather Rich & Healthy than Poor & Poisoned October 17, 2011, 1,246,767 Views (9 Min., 48 Secs.)

[31] Pure Earth     [32] Pure Earth 20 years of effort in 50 countries     [33] Authors Forecast Model

[34] Association of Autonomous Miners Muluncay Society

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