AN OVERVIEW OF GOLD MINING
AND THE GREEN MOVEMENT
By Ron Loya
When it comes to being kind to the environment, to many the very thought of gold mining (or any other mining for that matter) conjures up an image of incompatibility with the long term health of the planet. The very real issue of toxic legacies from past mining practices can make it difficult to consider the concept of “sustainable mining”. In order to ponder the future of gold mining, a factual look at past and present day operations as well as the reagents they have employed can provide a better focus on how going forward, gold mining can co-exist with what has come to be known as “the green movement”.
By and large, even though gold mining has been carried out for centuries using the same basic principles, today’s operations in the western United States bear little resemblance to those carried out in the 1800’s. During the California Gold Rush, what drew the masses to the foothills was the presence of gold in rivers and streams. This gold had formed in quartz millions of years ago and the quartz had been eroded to the point that it lost its hold on the yellow metal. The bits of gold were collected by separating and discarding the worthless gravels in a technique known as “Placer Mining” (placer being derived from the Latin word for beach sand), something that is commonly referred to as “panning for gold”.
The problem with placer mining in waterways has historically been that the gold simply “runs out”. By this I mean that any profitable amounts that make their way into them can become depleted and it may take decades to centuries for the rivers to become “recharged” with gold by further erosion. Placer mining can take place in usually dry places far away from bodies of water under certain conditions. First the area must be a location where water once flowed. Be it a hundred or a thousand years ago, it must be some sort of very old or ancient watershed that has long since changed course or ceased altogether. Water may be introduced to the process to aid in suspending lighter material over and off of the heavier gold, or other dry methods employing vibration or some sort of motion can be used to separate it out.
Hard Rock (also called lode or reef) mining on the other hand, requires auriferous (gold bearing) quartz veins to be excavated before erosion liberates them of the valuable element. Through the process of milling (grinding or crushing), what took Mother Nature eons to accomplish will occur in mere seconds. During California’s Gold Rush, these quartz formations began to be sought out more and more as placer deposits started to diminish. Small teams or “companies” of men would prospect an area to assess whether the gold concentrations found in these formations were worth the amount of labor it would take to extract them.
Now, most gold mining centers on microscopic concentrations in otherwise nondescript placers and low grade quartz ores. In large operations, vast amounts of these materials are processed on a daily basis for a comparatively miniscule amount of gold. In hard rock mining, the material is reduced down to a workable size and is treated with compounds of cyanide to collect the gold. This can result in environmental problems at and adjacent to the mine in terms of air quality, erosion, and waste material toxicity.
TOOLS AND BY-PRODUCTS OF MINING
A compound that in high enough concentrations is acutely toxic and fatal if ingested or inhaled. Around 1000 plant and microorganism contain compounds that produce tiny amounts of cyanide, including flax, sorghum, alfalfa, bamboo, peach, pear, cherry, plum, corn, potato, cotton, almond, and beans. It can be found in table salt, cigarettes and coffee. Insects such as centipedes, millipedes, beetles, moths and butterflies synthesize and excrete cyanide.
Commercially, cyanide can be synthesized from ammonia, oxygen and methane. Eighty seven percent of all manufactured cyanide is used in cosmetics, adhesive, plastics, metal hardening & electroplating, pesticides, dyes and paints, and leather tanning, the other thirteen percent is used in mining operations.
Because of its low cost and its unique ability to dissolve gold in a water solution, cyanide has been the reagent of choice for gold milling and recovery for over 100 years, increasing gold yields by 40 to 50 percent. It is mixed with lead, lime, oxygen and water to dissolve and collects gold by bonding (amalgamating) one gold molecule to two cyanide molecules. The resulting “pulp” is then centrifuged or floated on soap bubbles (froth flotation) to collect the gold bearing concentrate. Carbon or zinc is then introduced into the pulp before being heated. Finally, an electric current is passed through the solution to break the chemical bond and collect the gold.
Although cyanide is quickly diluted and degraded by ultraviolet light and biological oxidation, it can accumulate as a dangerous toxin in bottom sediments left behind as waste material.
Is a heavy metal chemical element historically known as quicksilver and hydrargyrum. It is the only metal that is a liquid at room temperature. Derived from roasting the mineral cinnabar, it has a very low boiling point (674degrees F) for a metal. It also has the peculiar ability to chemically bond (amalgamate ) to some metals, particularly gold and silver.
This metal has been used commercially in thermometers, barometers, float valves, switches, relays, fishing lures, long bows, dental amalgam and fluorescent light bulbs. Prior to the 1900’s it was widely used in over the counter and prescription tonics, ointments and pharmaceuticals.
China is the top marketer of mercury with almost two-thirds of all global production. It is a toxic substance, and so both the mining of cinnabar and refining for mercury are hazardous and have historically caused mass cases of poisoning. It can be absorbed through the skin and/or inhaled, causing chronic to acute poisoning.
Mercury has been used in mining applications as far back as 500 BC to extract gold and silver from ores. Because of its affinity for gold, it is introduced into ore slurries and collected after becoming amalgamated. The amalgam is then heated in a closed system to evaporate, separate and recover the mercury and the molten gold is then collected. While theoretically, mercury can be handled and used in a responsible manner, the fact is that it has a long history of being misused and released in large quantities into the environment in the form of releases of waste water and the disposal of tailings that have not been thoroughly processed.
Currently eleven percent of global environmental introduction comes from gold production through tailings disposal. Other man caused introductions include improper disposal of auto parts, batteries, fluorescent bulbs, electronic parts, sludge incineration, power, cement, iron and steel plant emissions. Natural releases to the environment include volcanoes, which are responsible for about half of all global atmospheric mercury emissions, geothermal springs and in situ cinnabar deposits.
Is an element that has been used in strengthening bronze, copper and lead (mainly batteries and bullets) alloys, semiconductors, pesticides, herbicides, dyes, preserving wood, livestock supplements, pharmaceuticals, fireworks, and glass.
Trace quantities of arsenic is a vital dietary element in some rodents, poultry and goats among other species, including humans. It is said to be present at some level in every living thing, however it can become toxic and even fatal at certain levels.
In nature, it is widely dispersed in soil and ores. Twenty five percent of arsenic emissions into the atmosphere come from natural sources, mostly volcanoes
Commercially, arsenic is produced by roasting dust particles of a variety of soils. It can also be collected for profit as a byproduct of smelting operations. China is the top marketer of arsenic with almost 50% global production. World production is estimated to be over 50,000 tons. It can also be introduced as an air and water pollutant by smelting plants that fail to use emission scrubbers, earth grading and other excavations and by leaching of pesticides or treated ground contact wood.
Although it is not employed in mining, because it is naturally occurring and widely distributed, the act of moving soil can expose arsenic to the atmosphere to be carried away as dust and allow it to be introduced into waterways. Arsenic products such as pesticides and treated ground contact wood can also be a source of pollution by leaching.
A NEW APPROACH TO OLD PRACTICES
Now, several discoveries that mitigate and even eliminate the need for toxic chemicals have led government agencies, private enterprise, and universities to pursue a movement called Green Mining. These new technologies not only can replace toxic chemicals, they can be used to clean up much of the chemical waste left behind in long defunct mining operations.
The movement actually had its roots on Australia in the 1980’s when the government allocated money to research new mining, surveying and drilling techniques. The Government agency “Commonwealth Scientific and Industrial Research Organization”, in existence since the 1920’s was revamped to address the call for environmentally cleaner mining.
A general consensus of the Green Mining Movement goals is:
- To clean up closed mines, shut down illegal and unregulated mines
- Use environmentally friendly mining processes
- Fund research for the development of environmentally friendly mining technologies.
INNOVATION LEADS TO DISCOVERY
An accidental discovery by chemists at Northwestern University employed a benign substance commonly used to remove cholesterol from food items. The process had as yet not been tried on inorganic substances. This proved to be one of the first major leaps in the movement.
Zhichang Liu, a postdoctoral fellow in chemistry hoped to find ways to separate heavy metals from soils and even more broadly, to isolate any number of undesirable chemicals in a variety of applications. Simply stated, he was looking for a chemical lockbox that could trap other molecules and then release them, or “unlock the box” with little effort. After some less than successful experiments with various chemicals, he filled two test tubes, one with cornstarch derived alpha-cyclodextrin, and the other with a dissolved gold salt called aurate. He then mixed them together in a beaker at room temperature and found that “needles” of gold formed because the cyclodextrin isolated the gold from the solution.
For those more technically inclined, the following will give some insight as to how this was accomplished. The needles form when gold atoms bind to bromine atoms in the cyclodextrin solution. Four bromine atoms link to the gold. The gold-bromine combination then links to an ion of potassium, which is surrounded by six water molecules forming a kind of snowflake-like structure. Cyclodextrin molecules then wrap around the whole lot, and link together like train cars. These long wire-like structures line up roughly parallel to each other and form the nanometer-sized needles.
After a research report on the subject was published, makeshift processing plants began to be constructed to test various cyclodextrin systems on mobile platforms at mine sites. Various gold mining corporations are in a research and development phase of converting their milling operations over to this process or have operational plants that employ it on a small scale with future plans to scale up production. The process also has the potential to extract gold from electronic waste which has small amounts of gold, silver and other recyclable metals. Perhaps the most promising thing about cyclodextrin is that it can be used in reprocessing old mine waste (tailings) to not only remove any existing gold but to also remove any heavy metals and other toxins left behind from past operations.
This chemical, also called “Hypo” was once commonly used in developing photography film (to dissolve silver salts) and is currently used in dechlorinating water and paper making. It offers a number of benefits related to gold recovery yields and environmental concerns:
Unlike cyanide which is highly toxic, the chemicals used in the thiosulfate leaching process are benign, offering a safer alternative for dissolving gold, and in some cases can improve gold recovery rates. When used in a closed system it has the added benefit of being an alkaline process which minimizes concerns with corrosion of equipment in the recovery process.
The main chemical components left behind in the thiosulfate leaching process (ammonium thiosulfate and ammonium sulfate) are common fertilizers. This opens up the additional possibility of using mine tailing solutions in agricultural applications.
Pulverized ore is heated and made into a thick slurry with water, air and limestone in large pressure chambers or autoclaves. It is then pumped into large stainless steel tanks where it then comes into contact with the thiosulfate to form a fine bead-like material called resin that attracts the gold. 13,400 tons of ore can be processed daily, with leaching, separation and extraction taking place simultaneously. The thiosulfate processes is being tested on low grade ores and may also be viable for deep ore bodies, where in situ recovery would be safer for workers and the environment.
MOVERS IN GREEN MINING
Besides Northwestern University’s work on environmentally friendly mining techniques, the Massachusetts Institute of Technology (MIT) is spearheading the American Green Mining Movement by setting forth its own goals as a part of its MISSION 2016 effort.
These private companies are among those involved with green mining technologies :
Molycorp, of Colorado has embraced the green mining movement and is working to integrate it into its rare earth and rare metal mining operations.
SurCan Gold of Canada is a privately funded ethical gold mining and exploration company that is committed to using an environmentally friendly approach. It is a major player in championing green gold mining technology by pursuing the strict use of modern facilities without harmful chemicals, and the clean-up of already contaminated land and waters.
Barrick Gold Corporation of Nevada uses thiosulfate to reprocess tailings from defunct mines. It is also working with the Australian government to optimize thiosulfate milling.
PARTICULATE AIR POLLUTION
Besides combustion engine emissions, much of the environmental air pollution generated from mining comes from dust resulting from open pit excavations, transfer of materials and transport vehicle traffic. In the past, large water cannons were used to spray down worksites, using vast amounts of water which caused erosion and loss of wildlife habitat. Now, low water flow “wet earth cannons” send atomized water over large areas to bring suspended dust down without flooding.
THE CHINESE FACTOR
Until 2010 mining in China was almost entirely unregulated in terms of efficiency and environmental sensitivity. The Chinese Ministry of Industry did have stated standards of mining practices, but looked the other way when it came to compliance.
Since then, some steps have taken place to improve air and water quality, first by putting the brakes on illegal and new mining operations. In 2011, due to an unprecedented wave of public protest, mining permits for rare earth elements have been frozen, efforts have begun to shut down illegal and “inefficient” mines, the Chinese government has begun sending envoys to Australia and the United States to learn about Green Mining practices.
Inefficiency in Chinese mines is centered on the way electricity is generated, and so an effort is being made to replace diesel and propane with natural gas. In mines and large factory operations, systems of heat recovery are beginning to be used to power steam turbines to provide a secondary source of electricity.
Proposed mandatory minimum recovery rates for waste water from mines will decrease toxic and radioactive solid wastes by pumping tailings water into evaporation tanks and using the clean condensed water to reintroduce back into the system. This will drastically reduce the need to tap fresh water supplies. Recent “red alert” air pollution alerts have driven to point home that China must make a tangible investment in environmental health.
In the Journal of Cleaner Production, Volume 14, Issues 12–13, 2006, Pages 1158–1167; an abstract reviews alternatives for gold recovery systems. While many inroads and innovations have occurred in the nine years since its publication it provides a useful snapshot of where we were, where we are now as a result of the green mining movement as it relates specifically to gold recovery, and what still needs to be done.
Research report: Selective Isolation of Gold Facilitated by Second-sphere Coordination with A-cyclodextrin , written by Zhichang Liu
Is Green Mining Possible is posted on Green Living Online’s site
A seven minute video outlining Canada’s Green Mining Movement