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- Diosana, Joseph A.L., et al.
(author)
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Strategies on reducing mercury use and exposure in small-scale gold mining -- experiences from Mt Diwata, the Philippines.
- 2006
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In: Abstracts of Eighth International Conference on Mercury as a Global Pollutant. - 1932078657 ; , s. 574-
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Conference paper (other academic/artistic)abstract
- The discovery of gold 1983 in the unpopulated Mt Diwata, the Philippines, resulted in that the mountain within a few years became populated with up to 200 000 persons, making their living from gold extraction. The methods used, amalgamation with mercury and cyanide leaching with rudimentary equipment, result in large emissions of mercury and cyanide and related deterioration of environment and health. Our objective is to relateobservations made in 2005 in relation to mercury supply and use in Mt Diwata and propose possible actions to reduce the deterioration of health and environment. There are no reliable records on Hg actually used or emitted in Mt Diwata. In 2004, theEnvironmental Management Bureau in Davao City certified 367 tonnes Hg for the enduse of mining in Mt Diwata. The quantities actually used were much smaller, but not registered. Sales from authorized Hg dealers in neighboring cities and smuggled Hg, notably via Indonesia, complicates the inventory. Based on documents, interviews, package labels, and quantities of gold extracted, the following observations were made.The consumption of Hg for gold mining has decreased by up to 50% since 2003 as a result of the increased Hg price. Still, more than 10 t Hg is annually used for gold mining in Mt Diwata. A significant fraction of this originates from the EU, notably the Spanish state company MAYASA. The continued use of Hg is not technically or economicly motivated, because amalgamation recovers only a minor part of the gold available, resulting in subsequent cyanide treatment of the ore. Moreover, the cyanide leaching is less efficient on amalgamated ores. Magnetic sluices could replace Hg for partial recovery of gold before submission of the ore to an environmentally adapted cyanidation process. Economic means in form of credits are necessary to permit investment in safer cyanidation equipment. Information is needed to the miners about safer extraction methods and a general use of retorts could reduce but not eliminate hazardous mercury exposure. Restricting the present Hg supplies from Spain and other countries of the EU and from the USA would intensify the transition to Hg free gold mining methods.
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| 2. |
- Hylander, Lars Daniel, 1954-, et al.
(author)
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Consequences of a soaring gold price for gold producing countries and the global environment.
- 2009
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In: Securing the Future and 8<sup>th</sup>ICARD. - Skellefteå. ; , s. 67-68
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Conference paper (other academic/artistic)abstract
- The presently soaring gold price adds to hazards threatening the sustainability of fishing and agriculture as means of support to living. This is by increased gold mining and related emissions of mercury and cyanide into the environment. Amalgamation, practiced in more than 50 countries, results in that metallic Hg is emitted to air, soil, and water and subsequently transformed to very toxic methyl-Hg and bio-accumulated in fish. Thereby, this highly nutritive feeding source eventually is ingested and becomes a poison to man. Four methods for gold recovery: amalgamation, cyanide leaching, a shaking sluice, and Cleangold® sluices, were compared in a case study performed at the largest gold mining village in the Philippines. The results show that the amalgamation method is presently used on all ores, in spite of gold recovery rates of 10–35% of initial gold content of the ore. With a light microscopy and photomicrographs, we documented that the following factors contribute to the low recovery: small and occluded gold grains and gold grains with oxidized surfaces that do not amalgamate. As a consequence, the miners are sending all amalgamated ore tailings for cyanide leaching. This was the most efficient of the methods studied, recovering up to 95% of initial gold content. The Cleangold® sluices recovered more gold than amalgamation, although gravimetric methods have limitations on the actual specific ore. Therefore, a combination of manual panning and/or Cleangold® sluices followed by cyanidation is the best solution under present conditions, followed by cyanidation alone. The used cyanide solution must be properly handled to not threaten the food security. Transition to less hazardous gold mining is urgent, considering that gold is a limited stored resource. Agricultural fields and fish populations are at the contrary fund resources, which will yield a return for an indefinite future if properly managed. Loans for investment in safe and efficient gold extraction technology, information and practical training of the miners, political and scientific guidance of the informal mining sector, restrictions on Hg availability and on sales from industrialized countries are suggested to counteract the present worst case situation, where amalgamation is followed by cyanidation. This combination increases the bioavailability of Hg lost. into the environment.
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