Mill leaching: a viable substitute for mercury amalgamation in the artisanal gold mining sector?

Artisanal small-scale gold miners (ASM) occasionally employ whole ore amalgamation by adding mercury into ball mills to recover gold. In this process, 25–30% of the mercury added is lost to the environment. It is also inefficient less than 30% of gold is recovered. Amalgamation, followed by cyanidation, has been observed at many artisanal mining sites. This combination poses additional environmental and health consequences. Tests with ore samples from Talawaan, North Sulawesi, Indonesia indicate the possibility of replacing mercury by cyanidation in the ball mill, reaching gold extraction of 93% in 6 h of leaching. The gold in the Indonesian ore sample is fine and less than 8% of gold recovery was obtained with gravity concentration of the ore ground 80% below 0.25 mm, which is a reasonably fine grain size for artisanal gold operations. Replacing mercury addition with cyanidation in ball mills was implemented in one artisanal gold mining operation in Portovelo, Ecuador, achieving 95% of gold extraction in 8 h of mill leaching. This technique demonstrated a drastic improvement in gold recovery. It was found to be a simple, inexpensive technique well accepted by local miners. The results from laboratory and field tests are promising; however a thorough investigation into the socio-economic and environmental aspects of this presented alternative must be conducted prior to introduction.     

Mercury balance in amalgamation in artisanal and small-scale gold mining: identifying strategies for reducing environmental pollution in Portovelo-Zaruma,Ecuador

The gold ore mined by artisanal and small-scale miners in Portovelo-Zaruma, Ecuador, is processed in custom mills. Miners can choose between Chilean-mill processing centers, where the ore is ground, concentrated and amalgamated, or “Chancha” Centers, where the whole ore is amalgamated. By weighing mercury before and after all unit operations involved in the amalgamation process, it was possible to determine mercury losses. Analyses in eight centers indicated that 51–59% of mercury introduced into the amalgamation process is recovered when miners squeeze the excess mercury. Around 29% of total mercury is lost when miners burn amalgam and gold is melted, and 15% is lost with the tailings. When only gravity concentrates are amalgamated, 1.4% of mercury entering the process is lost with tailings, whereas 29.5% is lost when the whole ore is amalgamated. Approximately 1.5 tonnes/annum of mercury is released in Portovelo-Zaruma, from which 70% is evaporated and 30% is released with tailings. Mercury-contaminated tailings are leached with cyanide in agitated tanks. A large majority of the processing centers dispose the final tailings with mercury and cyanide into the Calera River and Amarillo River. Mercury dissolved with cyanide likely becomes more bioavailable than metallic mercury. A campaign for reducing mercury emissions must focus on the use of individual retorts – mercury pollution control devices – and the elimination of whole ore amalgamation.     

Cyanidation of mercury-rich tailings in artisanal and small-scale gold mining: identifying strategies to manage environmental risks in Southern Ecuador

In many countries, such as Brazil, Colombia, Ecuador, Indonesia, Venezuela and Zimbabwe, amalgamated tailings are leached with cyanide to recover remaining gold. This paper describes a recently completed study conducted at seven gold processing centers in Portovelo-Zaruma, Southern Ecuador, which involved consultation with local miners. The objective of the study was to understand the behaviour of mercury (with a focus on mercury loss) in artisanal gold mining operations through the evaluation of two cyanidation processes (Merrill-Crowe and Carbon-in-pulp), using a participatory approach. In order to assess the kinetics of mercury dissolution in cyanide, a bottle roll test was conducted in the laboratory. In the Merrill-Crowe cyanidation process, an average of 24.2% of metallic mercury was determined to be trapped at the bottom of the agitation tanks; 33.1% of mercury is lost in association with solid material and 11.7% is lost in solution. Approximately 31.0% of mercury in solution is sent to the zinc precipitation cells from which 27.8% is precipitated on the zinc shavings, with 3.23% remaining in solution. The mercury precipitated on to the zinc is lost to the atmosphere when the shavings are burned at 900 °C. In the Carbon-in-pulp (CIP) leaching system, 11.2% of the mercury is lost with the solid tailings; 31.6% of the mercury is associated with fine particles in suspension and 50.8% is likely dissolved. About 2.68% is trapped at the bottom of the tank and 3.72% is absorbed by the activated carbon. The bottle roll test revealed that mercury dissolution is directly proportional to cyanide concentration. At 10 g/ton of cyanide, approximately 42% of mercury was leached, whereas all gold was solubilized. During this study, miners recognized the risk associated with the cyanidation of mercury-rich tailings, and were aware of how much mercury is discharged to local streams and to the atmosphere. The active participation of miners in this study has led to the strengthening of their knowledge and awareness of mercury contamination, and has enhanced their understanding of the nature of the problem, as well as the weaknesses and strengths of the system they operate.     

Origin and consumption of mercury in small-scale gold mining

Mercury (Hg) is used by small-scale gold miners in more than 50 developing countries, where the accompanied releases affect human health and the environment. The objectives of this paper are to summarize present use of Hg in artisanal and small-scale mining (ASM) worldwide, reveal the origin of part of the Hg used by the gold miners, and propose appropriate actions to reduce the resulting Hg emissions. Significant releases of mercury are associated with inefficient amalgamation techniques. Releases are estimated to range from 800 to 1000 tonne/annum. Of this total, approximately 200–250 tonne of Hg are released in China, 100–150 tonne in Indonesia, and 10–30 tonne each in Bolivia, Brazil, Colombia, Peru, Philippines, Venezuela and Zimbabwe. Mercury usually enters these countries legally – typically imported from countries in the European Union – although in some cases and in some years (e.g., Indonesia, Venezuela, etc.), the reported imports of Hg are far below estimated consumption. Meanwhile, the EU, while gradually replacing Hg products and processes with more environmentally benign alternatives, paradoxically continues to produce virgin Hg at government-owned mines, further exacerbating a general global oversupply of Hg – evident from its historically low market price. Political leadership is needed to avoid the transfer of excess Hg, and related health and environmental risks from the EU to third countries. Otherwise, the present situation will continue or even worsen, with no oversight or control of the global Hg trade in which the transfer of excess EU Hg to artisanal miners is favoured by low Hg prices relative to gold prices.     

Mercury-free gold mining technologies: possibilities for adoption in the Guianas

The rudimentary nature of small-scale gold mining activities often generates a legacy of extensive degradation and deplorable social conditions, both during and after activities have ceased. Small-scale mining usually involves the extraction of secondary gold from placer deposits (alluvial, colluvial or elluvial), which can be liberated and treated using gravity methods. In the Guianas, the most popular form of small-scale gold mining is referred to as “land dredging”, a combination of hydraulicking and suction dredging. This method requires application of large volumes of water for both mining and mineral processing; in most cases, there are no containment structures for the waste tailings generated. Mercury, a dangerous pollutant, is the preferred method employed by small-scale miners for gold recovery. Gold extraction using mercury is comprised of the following four stages: (1) amalgamation, (2) separation of amalgamation, (3) removal of excess mercury, and (4) burning of the remaining amalgam to produce a gold sponge. Mercury can be released into the environment at each stage, which makes the promotion of mercury-free alternatives imperative.Technical alternatives for small-scale gold mining, however, must be thoroughly evaluated, pre-tested, modified accordingly and successfully transferred. Moreover, technology must be inexpensive, relatively simple and easy to adapt, while allowing a rapid rate of return. WWF-Guianas is working with the regulatory agencies and other relevant stakeholders of the Guianas to reduce the environmental footprints caused by small-scale mining. The major aspects of this program are to develop the capacity and regulatory mechanisms within the local government, to promote mercury-free technology, and monitor mercury in the environment. This paper reviews the alternative technologies being investigated by the WWF-Guianas for use in the small-scale gold mining industry.     

Reducing mercury pollution from artisanal gold mining in Munhena,Mozambique

Artisanal small-scale mining (ASM) is responsible for over 90% of gold production in Mozambique. In 2005, a 15-day pilot training project was held in the village of Munhena, a gold mining community. This intervention aimed at raising awareness related to the environmental and health impacts of mercury amalgamation and introduced alternative practices to reduce mercury release and exposure. In 2007, a 9-day evaluation of the pilot campaign was accomplished and knowledge in regards to mining methods, and the ASM government–community operating relations in Munhena were updated. Miners in Munhena are organized in an association of over 3000 members, work on a 25 year Government granted 143 ha concession and generate a substantial income (producing over 5 kg of gold per month). There remain, however, serious barriers towards sustainable community development. ASM associated environmental and health costs are high, as mercury continues to be used and lost to the environment, and cyanide will be introduced soon. The Government of Mozambique has laid the foundation for supporting this sector; however, resources are limited, and thus restrict ability to fully address these issues. Importantly, malaria and HIV/AIDS are not diagnosed and/or treated effectively within the community, and basic necessities are absent. This paper concludes with recommendations focused on enhancing the ASM sector in Mozambique, and overcoming barriers to sustainability in the community of Munhena.     

A matter of approach: the retort's potential to reduce mercury consumption within small-scale gold mining settlements in Tanzania

The mercury-based gold extraction processes prevalent within small-scale mining are both efficient and harmful. While ensuring relatively high levels of gold recovery, they cause environmental and health problems for people living within mining settlements. This mercury consumption can be minimized by using a simple mercury recycling device known as a retort. While mining legislation in Tanzania dictates the use of retorts for gold recovery, virtually no miners use them, indicating the inadequacy of previous introduction attempts. During action research, retorts were introduced in two mining settlements through a thorough and participatory approach. Twenty miners were given retorts and their attitudes and receptiveness to them were studied. Of the recipients, 18 used the retorts over a period of five months, recycling 10 kilos of mercury. Less mercury was spilled into the environment and miners saved money normally spent on purchasing mercury. The findings have implications for the strategies of development interventions targeting mercury-instigated problems within small-scale gold mining.     

Clean artisanal gold mining: a utopian approach?

Artisanal and small-scale mining (ASM) provides an important source of livelihood for rural communities throughout the world. These activities are frequently accompanied by extensive environmental degradation and deplorable socio-economic conditions, both during operations and well after mining activities have ceased. As gold is easily sold and not influenced by the instability of local governments, it is the main mineral extracted by artisanal miners. Mercury (Hg) amalgamation is the preferred gold recovery method employed by artisanal gold miners and its misuse can result in serious health hazards for miners involved in gold extraction, as well as for surrounding community inhabitants, who may be exposed to mercury via the food chain. The rudimentary techniques characteristic of ASM result in a number of occupational hazards, other although most risks are primarily attributed to machinery accidents and ground failure, such as landslides and shaft collapses.Several technologies and methods commonly utilized by large-scale mining operations can be downsized to smaller scale operations. However, the likelihood that miners will adopt these large-scale methods, or those developed specifically for ASM, depends upon some key factors. For an artisanal miner, these factors include: (1) increased or comparable simplicity, (2) quick recovery of the economic mineral, and (3) demonstrated financial gain. Other practical aspects, such as the availability of materials (chemicals, steel rods, piping, generators, etc), capital and operating cost requirements and access to technical support, also influence acceptance of new techniques.This article will review four inter-related areas: first, the limitations and benefits, for ASM, of a number of specific technologies; second, the role of Processing Centers in education, information dissemination and provision of “clean” services; third, benefits and challenges associated with formalization of ASM activities; and fourth, the contribution of ASM to the development of sustainability of communities, primarily through diversification of livelihoods. The appropriate application of technologies, particularly given the diversity of ASM communities around the world, will also be explored.     

Application of sustainable development concepts to an alluvial mineral extraction project in Lower Caroni River,Venezuela

The Caroni River, a tributary of the Orinoco River in the State of Bolivar, Venezuela, has been subjected to mining since the end of the last century. Until the 1990s, hundreds of artisanal miners operated along a 70 km stretch of the river using rudimentary suction dredges to extract gold and diamonds from sediments. Although artisanal miners created considerable wealth along the river, the local community has also been negatively impacted by the social and environmental effects that characterize this sector. The flooding of many parts of the Lower Caroni River, in conjunction with the development of a large hydroelectric-power complex, changed the conditions for dredging operations.A Canada-based company is proposing to open the recently-created hydro-electrical lakes to a Mineral Dredging Project. The early forecasting of potential socioeconomic and environmental impacts would be a valuable tool to build a sustainable business case that facilitates the integration of the project into a sensitive environment. These strategies, currently used in other economic sectors, would contribute to the identification of opportunities to negotiate mutually beneficial agreements with stakeholders of the Project, and reduce the risk of conflict, in this particular case, with the hydroelectric company (EDELCA), former small-scale miners and other stakeholders.This paper, based on the pre-feasibility study of the Project, assesses the applicability of such tools to the mineral dredging and to junior mining company projects in general.     

Policies and regulations for Brazil’s artisanal gold mining sector: analysis and recommendations

In Brazil, artisanal and small-scale gold mining (ASGM) produces in the range of 6 tonnes of gold (Au) per annum, and employs approximately 200,000 people. Most of this mining activity is in the Amazon region, where miners have been extracting gold for more than 40 years. In the Tapajos River Basin, assessments indicate that around 99% of miners operate without the environmental and mining permits required by law. This is a result of a combination of unrealistic or lack of proper policies and regulations, lack of political will, lack of infra-structure to enforce the existing regulations and lack of incentives to miners to comply with legal requirements.In this article, we analyze a group of 20 laws, decrees and resolutions in Brazil, focusing on how idiosyncrasies in these regulations reveal gaps between policy and reality in ASGM areas. Artisanal miners operate in vast and remote areas and the government lacks the resources (personnel, vehicles, information and materials) to enforce the laws. Our analysis emphasizes the need for creating new government commitments and identifying priority areas where government agents can focus their efforts.There is no single solution for the environmental, health, technical and socio-economic problems associated with ASGM. However, a realistic approach should consider improving the level of education of miners, creating government programs to provide technical assistance in the field, simplifying administrative procedures and ensuring adequate measures for enforcement.     

A simplified matrix of environmental impacts to support an intervention program in a small-scale mining site

This paper describes a tool developed to evaluate environmental risks at a Brazilian artisanal small-scale gold mining site. The tool consists of a matrix used to determine the relevance of such risks through the classification of mining activities according to the likelihood that they may cause environmental impacts. The language and method are very simple, and thus appropriate for local stakeholders. It ensures their participation when developing a plan of action for intervention and training. When applied to a pilot site in the Brazilian Amazon, the matrix revealed the variables that pose higher environmental risks. These activities were subsequently addressed in a training program to promote better practices. As a result, the mining activities were improved by 28.8% when comparing compliance to environmental requisites before and after the training program. Specifically, the training program resulted in improved gold recovery, and reduced environmental and health impacts.     

Managing cyanide: health,safety and risk management practices at Turkey's Ovacik gold–silver mine

This paper discusses issues of cyanide management at the newly-constructed Ovacik gold–silver mine in Turkey. The mine, which has been using 120 ton/y of sodium cyanide (NaCN) since May 2001, was the first operation in the country to use cyanide to recover gold. Mine staff strives to continuously plan and provide detailed accounts of the management practices and initiatives being undertaken with regard to handling cyanide. It is believed that the programs and activities that have been implemented at Ovacik will facilitate improvement in this area.     

Towards zero emission pulp and paper production: the BioRegional MiniMill

Growing demand for paper is putting pressure on the World's forests, and although paper made from agricultural residues could meet global demand five times over, today less than 10% is made using these resources. The primary reason for this is the absence of cost effective, small-scale (∼10,000 tonnes per annum), environmentally sound pulping technology. The BioRegional MiniMill was developed in response to this problem. The MiniMill is a modular, regional scale, sustainable pulping process designed for straw and other non-wood feedstocks. The MiniMill innovates in two key areas: (i) preparation, feeding and pulping of straw using a twin screw extruder to reduce energy use, produce pulp in a shorter time and improve pulp quality, and (ii) the inclusion of a small-scale black liquor chemical and energy recovery system, based upon novel fluidised bed technology. The MiniMill is projected to be cost competitive at less than one-tenth the size of the smallest conventional wood-based pulping mill. As with conventional pulp mills, the MiniMill recovers enough renewable energy from the effluent to power the mill and qualifies for carbon emissions credits in accredited countries. In this work we report on some of the key research and development activities, at laboratory, pilot and semi-industrial scale, that have underpinned the design and development of the MiniMill. The ultimate goal of the project is to make available a technically and economically viable process for small-scale cellulose pulp production, that will facilitate the uptake of alternative uses of wheat straw, hemp or flax into the market place.     

Overcoming environmental problems in the gold panning sector through legislation and education: the Zimbabwean experience

Although small-scale mining is often associated with ruinous effects on the natural environment, Zimbabwe’s experience in gold panning demonstrates that though that may be true, the sector, can, through appropriate measures, be encouraged or enticed to develop environmentally friendly methods for gold mining and recovery. A combination of legislation, education, and the promotion of appropriate technology has enhanced the environmental management within the ever-growing gold panning community in Zimbabwe. This paper evaluates the success of attempts to minimise the environmental impacts of gold panning in Zimbabwe through legislation, education and the promotion of appropriate technology.     

Alternatives to cyanide in the gold mining industry: what prospects for the future?

This paper reviews a series of alternative lixiviant systems for the recovery of gold from ores and concentrates. For over 100 years, cyanide has been the leach reagent of choice in gold mining because of its high gold recoveries, robustness and relatively low costs. The environmental damages resulting from its mismanagement, however, have initiated widespread research aimed at identifying and developing less toxic leaching agents. The most widely-researched alternative lixiviants for gold ores are examined in this paper, but it is evident that none has yet made any significant inroad into the dominant position of cyanide as the reagent of choice at the vast majority of gold mines worldwide.     

Material flows in the life cycle of leather

This paper presents a study on the resource and environmental profile of leather for communicating to the consumers about the environmental burdens of leather products. The results indicate that significant environmental impacts were caused during the tanning and finishing of leather as well as the electricity production and transportation required in the life cycle. The use of fossil fuels in the production of energy has greater impact with increased emissions leading to about 15190 kg CO₂ equivalent of global warming and about 73 kg SO₂ equivalent of acidification while producing 100 m² of leather for shoe uppers. Further resource use of 174 kg of coal, 6.5 kg of fuel oil, 17.4 m³ of water and 348 kg of chemicals of which about 204 kg are hazardous are consumed, and wastewater of about 17 m³, BOD of 55 kg, COD of about 146 kg, TDS of 732 kg and solid waste of about 1445 kg are generated during the life cycle for the production of 100 m² of leather. The total solid waste generated is 1317 kg, out of which about 80% is biodegradable contributed by slaughtering, tanning and finishing stage, 14% is non-biodegradable contributed by tanning, finishing and electricity production stages and 6% is hazardous mainly from tanning and finishing stage of leather.     

Quantifying energy use, carbon dioxide emission, and other environmental loads from island tourism based on a life cycle assessment approach

The main purpose of industrial ecology is to evaluate and minimize impacts from economic activities of human society. Tourism as one economic activity, results in a full range of environmental impacts, but few applications of industrial ecology to tourism management have previously been discussed. Life cycle assessment (LCA) is used in this research to explore environmental impacts of island tourism, and then the environmental loads per tourist per trip can be found. Penghu Island in Taiwan is taken as an example to examine this new approach. Various environmental loads in transportation, accommodation, and recreation activity sector are all inventoried and calculated here. In summary, per tourist per trip uses 1606 MJ of energy, 607 L of water, and emits 109,034 g of CO₂, 2660 g of CO, 597 g of HC, 70 g of NO_x. In addition, per tourist per trip also discharges 416 L of wastewater, 83.1 g of BOD, and 1.95 g of solid waste. In terms of energy use, the transportation consumes the largest energy (67%); in particular, the airplane sector. Moreover, per Penghu tourist results in more environmental loads than local people; for example, the amount of solid waste discharge per tourist is 1.95 kg per day, while that of per local people is 1.18 kg. Finally, the advantages and limitations of such LCA approach are also discussed.     

Environmental consequences of different beef production systems in the EU

The aim of this paper is to examine the environmental consequences of beef meat production in the EU, using a life cycle approach. Four beef production systems were studied – three from intensively reared dairy calves and one from suckler herds. According to the results of the analysis, the contributions from the production of 1 kg beef meat (slaughter weight) to global warming, acidification, eutrophication, land use and non-renewable energy use were lower for beef from dairy calves than from suckler herds (16.0–19.9 versus 27.3 kg CO₂e, 101–173 versus 210 g SO₂e, 622–1140 versus 1651 g NO₃e, 16.5–22.7 versus 42.9 m²year, and 41.3–48.2 versus 59.2 MJ, respectively). The breakdown analysis helped identify the key areas in the “cradle to farm gate” beef production system where sustainable management strategies are needed to improve environmental performance. The study also included a sensitivity analysis to preliminarily estimate GHG emissions from beef production systems if land opportunity cost and land use change related to grazing and feed crop production for beef were taken into account. If so, the contribution from the production of 1 kg beef to global warming would increase by a factor of 3.1–3.9, based on a depreciation period of 20 years. This highlights the importance of taking into account the impacts of land use in assessing the environmental impacts of livestock production.     

The regulation of China’s township and village coal mines: a study of complexity and ineffectiveness

An appropriate system of laws and regulations and a suitable institutional structure for administration are important requirements for the effective management of small-scale mines. Over the last twenty years, township and village coal mines in China have made a large contribution to the country’s supply of energy. Yet at the same time they have had substantial negative impacts, such as wastage of coal resources, a high casualty rate amongst miners, and a wide range of environmental damage. Two reasons for the magnitude of these externalities are the highly complex nature of the institutional structure for regulating small-scale coal mines, and the excessive and incoherent burden of applicable laws and regulations.     

Reagent elution combined with positive pressure filtration: A zero-discharge method for cyanide tailings remediation

At present, the cyanide gold extraction process is still the main technology for gold production. Generated cyanide tailings containing highly toxic substances exhibit potential environmental risks. These tailings are in urgent need of purification treatment, especially after being classified as hazardous waste. In this study, the impacts of elution methods, operating time, tailings/water ratios, reagent types on the elution rates of cyanide were investigated. Furthermore, the composite elution ...