via Small-scale miners’ mercury use scars environment – NewsDay Zimbabwe January 13, 2016
ARTISaNAL and small-scale gold miners, out to extract as much gold as possible and make quick profits, have over the years resorted to using mercury in extracting the precious mineral and, in the process, exposed both the environment and humans to health risks.
BY BYRON MUTINGWENDE
World leaders agreed through the Minamata Convention that it was imperative to protect human health and the environment from the anthropogenic emissions and releases of mercury and mercury compounds, according to Environmental Management Agency (EMA) education and publicity manager Steady Kangata.
“In 2001 the United Nations Environment Programme (UNEP) conducted an initial assessment of mercury and its compounds, including information on the chemistry, health effects, sources, long-range transport and prevention or control technologies relating to mercury,” Kangata said.
“It was noted that there were significant adverse global impacts from mercury and its compounds to warrant further international action to reduce the risks to human health and the environment from the releases of mercury and its compounds.
Through the years, deliberations continued and finally in October 2013, the Minamata Convention was opened for signing at the Conference of Plenipotentiaries which was held in Japan. Zimbabwe is a signatory to this.”
Article 3 of the Minamata Convention on mercury supply sources and trade states that the chemical’s export and import shall be through consent from the receiving party.
“Each party shall not allow the export of mercury except to a party that has provided the exporting party with written consent and only for the purposes of, and to, a use allowed to all parties under this Convention.”
Zimbabwe Miners’ Federation chief executive officer Wellington Takavarasha said there was need to train small-scale miners on proper storage and use of mercury.
Environment, Water and Climate minister Oppah Muchinguri-Kashiri said while mercury was a naturally occurring element in the environment, it was very hazardous.
“Mercury is a naturally occurring element that is found in the air, water and soil. However, human activity is the main cause of mercury releases, particularly coal-fired power stations, residential coal burning for heating and cooking, industrial processes, waste incinerations and mining for mercury, gold and other metals,” Muchinguri said.
Exposure to mercury causes serious health problems and threatens child development in the uterus and early in life. Mercury may have toxic effects on the nervous, digestive and immune systems, and lungs, kidneys, skin and eyes.
Mercury is considered by the World Health Organisation (WHO) as one of the top 10 chemicals of major public health concern.
Severe neurological effects were already seen in animals in the notorious case from Minamata, Japan, prior to the recognition of the human poisonings, where birds experienced severe difficulty in flying and exhibited other grossly abnormal behaviour.
These effects caused countries to come together and negotiate the Minamata Convention on mercury which calls for a ban on new mercury mines, the phasing-out of existing ones, control measures on air emissions, and the international regulation of the informal sector for artisanal and small-scale gold mining.
The Minamata Convention has been signed by 128 countries so far, Zimbabwe being one of the first countries to sign it in October 2013 in Japan. The government is calling for a reduction in the use of mercury particularly in artisanal and small-scale mining.
Minemet Mineral Processing and Metallurgical Consultancy firm’s managing consultant, Nozipho Ndlovu, said artisanal and small-scale miners use mercury to extract gold from ore by forming a mercury-gold mixture also known as gold amalgam.
“Acid digestion of the mixture using acid and/or heating the gold amalgam evaporates the mercury leaving only gold. This mercury-based process is favoured by small-scale miners over other methods of gold extraction because it is inexpensive, accessible, simple to use and allows miners to produce gold quickly often in a single day,” she said.
“Mercury has also become the biggest profit earner of these miners. Buying mercury at an average price of $120/kg one can pocket from $120 to $180 profit, translating to about 100-150% profit. Millers resell mercury at an average price of $15/50g.”
Ndlovu said small-scale miners believe it is the best method when it comes to recovering fine gold from gold ore. At times mercury is also used by the medium and large-scale miners to recover gold from slag.
A research by Minemet revealed that gold ore is crushed and screened by a stamp mill or hammer mills and the pulverised gold ore is screened and pulp gravitates into the separator otherwise known as the concentrator.
Ndlovu said there were simple and effective alternative practices that can be implemented immediately to substantially reduce mercury use and exposure.
“These include eliminating the worst practices, where mercury is either unnecessary or wasted, such as whole ore amalgamation, open burning amalgam without the use of retort or other mercury vapour capture systems and the use of cyanide after mercury amalgamation, or in processing in mercury-rich tailings without first removing mercury,” she said.
She said to facilitate the elimination of mercury-intensive practices, and the adoption of low mercury and mercury-free alternatives, restrictions on mercury supply were needed.
The legal and economic structure for small-scale gold miners may need revision in some countries in order to obtain the required co-operation and investment, she noted, indicating that fees must be reviewed as the gold prices continue to drop.
Miners also need to be taught that mercury can contaminate the miners themselves, their families, their communities, the environment and people staying afar.
Burning amalgam in open pans can cause significant mercury soil contamination up to 2km away. Mercury vapour can travel even a greater distance and fall down with the rain.