The Gravity-Borax Method GBM is still unknown to most Artisanal and small-scale gold miners (ASGMs) worldwide as most still use mercury to extract gold. “Whole-ore amalgamation” is a technique that requires the use of 10–25 g of mercury to produce 1 g of gold. Within the last eight years, it has become evident that this technique is more widely used than earlier anticipated, and artisanal small-scale gold mining (ASGM) is now considered the single largest contributor to global mercury pollution with the environmental release of 2,000,000 lbs of mercury per year. The United Nations Environment Programme has estimated that ASGM contributes a 37% share of the anthropogenic emission of mercury to the atmosphere.
Whole-ore amalgamation is commonly practiced in the Philippines. The ore is mixed with water and crushed in a rod mill (a rotating drum with metal rods inside), after which mercury is added and milled with the ore. The gold dissolves in the mercury and forms amalgam. After the milling, the content is poured into a tub where the mercury (holding the gold) sinks to the bottom. Excess mercury is recovered, and by blowtorching the remaining bit of amalgam, the mercury evaporates leaving behind the gold.
In Benguet province, a group of miners has been using the mercury-free gravity-borax method (GBM) for gold extraction for decades. This method basically requires the same equipment as the amalgamation methods. However, after the rod milling, an ore concentrate holding the heavy minerals is produced by using a launder (gold sluice) or a gold trommel. The heavy mineral concentrate is mixed with borax powder. By blowtorching the mix, the borax melts and the gold sinks to the bottom. It has recently been demonstrated that under identical conditions, GBM yields more gold than the traditional amalgamation method. Despite this advantage, GBM is not widely used outside Benguet. No earlier studies have documented that GBM can be implemented in an area using whole-ore amalgamation. Earlier technology transfer projects have promoted retorting of amalgam as a preventive technology in ASGM.
A project area in Mindanao, 20% of the miners have already converted to the mercury-free method.
Unfortunately, this method is ineffective in areas using whole-ore amalgamation, since up to 90% of the mercury is lost to the tailings (the waste product consisting of fine sand) and only 10% is lost by blowtorching of amalgam. Thus, only a small fraction of the mercury spill from whole-ore amalgamation can be recovered with a retort. The introduction of cyanidation techniques has also been suggested as a way to reduce or eliminate the use of mercury in ASGM. Although most cyanide compounds decompose into nontoxic forms, cyanide itself is highly toxic, and exchanging one toxic chemical with another may be regarded as a controversial solution.
BORAX RECOVERS MORE GOLD than MERCURY
We present the results of a project in which GBM was introduced in two mining communities in the Philippines where whole-ore amalgamation was widely practiced. The main objective of the project was to reduce mercury pollution from small-scale gold mining by encouraging ASGMs to use a mercury-free method.
This article aims to:
- describe the changes in mining practice in two ASGM communities after two years of project implementation.
- describe the activities undertaken to encourage the communities to adopt mercury-free gold mining using the borax method.
- explore enabling and hindering factors in phasing out mercury use.
- teach basic placer mining methods
Obtain the Full Story: Mercury Pollution from Small-Scale Gold Mining Can Be Stopped by Implementing the Gravity-Borax Method – A Two-Year Follow-Up Study from Two Mining Communities in the Philippines.
Testing Local Conditions for the Introduction of a Mercury-free Gold Extraction Method using Borax in Zimbabwe
Special thanks to:
Rasmus Køster-Rasmussen, MD PhD
The Research Unit for General Practice
University of Copenhagen
Øster Farimagsgade 5
P. O. Box 2099
It is estimated that between 10 and 15 million artisanal and small-scale gold miners worldwide (most of which cannot afford quality mining equipment) include 4.5 million women and 600,000 children. According to UNIDO, as much as 95 percent of all mercury used in artisanal gold mining is released into the environment. UNIDO estimates that mercury amalgamation from this kind of gold mining results in the release of an estimated 1000 tons of mercury per year.
Watch and Learn all about BORAX MINING USA
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- Mercury pollution from artisanal gold mining
Alternative to Mercury – GOLD MINING EQUIPMENT without Hg
Also see UNEP.