Mercury Losses Research Articles

Evaluation of conditions to minimize mercury losses from leaching test eluates

A series of experiments are described that provide recommendations of modifications to leaching test specifications to minimize losses of mercury from eluates during leaching tests and management of analytical samples. EPA methods of the Leaching Environmental Assessment Framework (LEAF) were used as a reference point for what steps are most likely to see losses, including filtration, storage of unpreserved mercury contaminated material, and materials of construction for vessels. The potential sorption of mercury to borosilicate glass and PTFE lab materials was tested to determine what materials are suitable to replace HDPE and polypropylene. The experimental findings indicate that bottles constructed of PTFE and Type I (borosilicate) glass are recommended as extraction and containment vessels for mercury-containing liquids. Type I syringe filtration of aqueous mercury samples at pH 2 through 9 through 0.45 µm PTFE filters housed in polypropylene is acceptable; however, sorption losses were observed to occur at pH > 9. Storage of unpreserved liquids containing mercury over extended leaching test intervals did not lead to significant losses of mercury when coupled with minimized headspace. All mercury-containing eluates should include preservation with Optima HNO3 to a 1 % concentration and gold (III) standard to a concentration of 200 µg/L, followed by refrigeration at <6 °C prior to analysis.

Investigation of Gold Recovery and Mercury Losses in Whole Ore Amalgamation: Artisanal Gold Mining in Nambija, Ecuador

Mercury is a highly toxic pollutant that can negatively affect human health and the environment; informal mining is one of the main sources of anthropogenic mercury release due to the separation or concentration by amalgamation that is still used to recover gold directly from ore. In the Nambija mining district, there is still informal mining based on practically no technical knowledge, which uses amalgamation as a processing technique for gold recovery. The production tasks that directly affect the handling of mercury during the in situ grinding–amalgamation process are monitored here. Experimental grinding tests were initially carried out in a “chancha” bar mill for a range of ore sizes and as a function of time; then, experimental tests were performed at the macro-level on grinding cycles in Chilean mills. Considering the characteristics of the ore mineral and the operation of the Chilean mills, it was determined that it is possible to reduce the Hg input to mill by up to 20% (at source). Experimental grinding–amalgamation tests were carried out at different times along with a grain size analysis of the ore; the recovery establishes the grinding time and the fraction in which the gold is extracted in a greater proportion, which affects the control of the amalgamation times. The mercury dosage used by the miners in the amalgamation process should be reduced, considering trials where there is better gold recovery and with the purpose of also reducing mercury losses; eventually, it is possible to jointly achieve an increase in gold recovery.

Estimation of Mercury Losses and Gold Production by Artisanal and Small-Scale Gold Mining (ASGM)

Artisanal and small-scale gold mining (ASGM) utilizes mercury (Hg) for the extraction of gold (Au) and is responsible for the largest anthropogenic source of emissions and releases of Hg to the environment. Previous estimates of Hg use in ASGM have varied widely. In this effort, Hg losses in ASGM were derived from the difference between estimates of total Au production and the production reported by conventional gold mining. On the basis of this result, the average ratio of Hg lost to Au produced in ASGM was estimated to be 1.96 in Africa, 4.63 in Latin America, and 1.23 in Asia. The difference among regions can be attributed to the amalgamation procedure used by the miners, in which whole-ore amalgamation is predominant in Latin America and Asia. The obtained estimated ratio of Hglost:Auproduced suggested the possibility to detect either Au or Hg smuggling from one country to another. On the other hand, the importance of considering cyanidation in ASGM was also suggested.Graphical

System Dynamics Modelling of the Global Extraction, Supply, Price, Reserves, Resources and Environmental Losses of Mercury

How mercury flows from geological sources to society and to the environment was modelled for this study. The industrial dynamics of mercury was modelled and included in the integrated assessment model WORLD7. The simulated mercury losses were used as input for a simplified global model for environmental pollution. The outputs were analysed and used to assess mercury pollution amounts and supply to society. In fossil fuels, there are a potential stock of 2 million tons in coal and other hydrocarbons, and 450,000 tons of that could be released to the environment if the fossil fuels are all to be burned. Such release would potentially cause major environmental damage and a significant human health risk. The simulations suggest that environmental mercury flows may peak in 2025, and slowly decline as mercury gets immobilized in nature. The simulations show that the pollution from technical use is eliminated by putting the 2013 Minimata Convention into effect, but that environmental pollution from fossil fuels combustion and from environmental re-emissions will remain a significant problem for the next decades.

Historical mercury losses from the gold mines of Victoria, Australia

Health and ecological risks associated with the use of mercury in gold mining are well known, with much recent attention focussed on contemporary small-scale artisanal mining. Legacy tailings from historical gold mining may also present ongoing risks, as the industry used large quantities of mercury with minimal environmental regulation to limit its discharge. This occurred in both alluvial (placer) mining and in processing auriferous ores. Analysis of historical data on mercury use in the mining industry in Victoria, Australia, indicates that at least 131 tonnes of elemental mercury were discharged into the environment as mine tailings between 1868–1888, with the total amount lost over the historic mining period likely to be much higher. The processing of pyritic ores also concentrated mercury losses in a small number of mining centres, including Bendigo, Ballarat, Castlemaine, Clunes, Maldon and Walhalla. This analysis provides a basis for further research needed to support improved management of legacy mine tailings.

Determination of Mercury in Sediments by Slurry Sampling Electrothermal Atomic Absorption Spectrometry

The concentration of mercury in suspensions of sediments is determined by electrothermal atomic absorption spectrometry (ET-AAS) using a novel chemical modifier (ChM) based on activated carbon treated by iron(II) formate. The efficiency of chemical modifiers based on activated carbon, also modified by Ag(I), Au(III), Pd(II), Co(II), and Ni(II) compounds is studied. The optimum conditions are found for the temperature and time program of the atomizer; they prevent mercury losses at the stage of drying sample suspensions and also exclude spectral interferences at the stage of atomization and measurement of the analytical signals. The minimum characteristic mass of mercury (52 pg) is reached using an iron-containing chemical modifier based on activated carbon. The conditions of ET-AAS analysis using this ChM are tested on certified reference materials of sediments and a sample selected near the sea port of Temryuk (Sea of Azov). The limit of detection found by the 3s-test was 0.05 mg/kg and the relative standard deviation was 5% at the concentration of mercury in the sample 149 mg/kg.

Reduction of soil erosion and mercury losses in agroforestry systems compared to forests and cultivated fields in the Brazilian Amazon

In addition to causing physical degradation and nutrient depletion, erosion of cultivated soils in the Amazon affects aquatic ecosystems through the release of natural soil mercury (Hg) towards lakes and rivers. While traditional agriculture is generally cited as being among the main causes of soil erosion, agroforestry practices are increasingly appreciated for soil conservation. This study was carried out in family farms of the rural Tapajós region (Brazil) and aimed at evaluating soil erosion and associated Hg release for three land uses. Soils, runoff water and eroded sediments were collected at three sites representing a land cover gradient: a recently burnt short-cycle cropping system (SCC), a 2-year-old agroforestry system (AFS) and a mature forest (F). At each site, two PVC soil erosion plots (each composed of three 2 × 5 m isolated subplots) were implemented on steep and moderate slopes respectively. Sampling was done after each of the 20 rain events that occurred during a 1-month study period, in the peak of the 2011 rain season. Runoff volume and rate, as well as eroded soil particles with their Hg and cation concentrations were determined. Total Hg and cation losses were then calculated for each subplot. Erosion processes were dominated by land use type over rainfall or soil slope. Eroded soil particles, as well as the amount of Hg and cations (CaMgK) mobilized at the AFS site were similar to those at the F site, but significantly lower than those at the SCC site (p < 0.0001). Erosion reduction at the AFS site was mainly attributed to the ground cover plants characterizing the recently established system. Moreover, edaphic change throughout AFS and F soil profiles differed from the SCC site. At the latter site, losses of fine particles and Hg were enhanced towards soil surface, while they were less pronounced at the other sites. This study shows that agroforestry systems, even in their early stages of implementation, are characterized by low erosion levels resembling those of local forest environments, thus contributing to the maintenance of soil integrity and to the reduction of Hg and nutrient mobility.

Forest Structure Affects Soil Mercury Losses in the Presence and Absence of Wildfire.

Soil is an important, dynamic component of regional and global mercury (Hg) cycles. This study evaluated how changes in forest soil Hg masses caused by atmospheric deposition and wildfire are affected by forest structure. Pre and postfire soil Hg measurements were made over two decades on replicate experimental units of three prefire forest structures (mature unthinned, mature thinned, clear-cut) in Douglas-fir dominated forest of southwestern Oregon. In the absence of wildfire, O-horizon Hg decreased by 60% during the 14 years after clearcutting, possibly the result of decreased atmospheric deposition due to the smaller-stature vegetative canopy; in contrast, no change was observed in mature unthinned and thinned forest. Wildfire decreased O-horizon Hg by >88% across all forest structures and decreased mineral-soil (0 to 66 mm depth) Hg by 50% in thinned forest and clear-cut. The wildfire-associated soil Hg loss was positively related to the amount of surface fine wood that burned during the fire, the proportion of area that burned at >700 °C, fire severity as indicated by tree mortality, and soil C loss. Loss of soil Hg due to the 200,000 ha wildfire was more than four times the annual atmospheric Hg emissions from human activities in Oregon.

Die invloed van verpoeiering op die kwikinhoud van verskeie gesertifiseerde verwysingsmateriale

The majority of analytical techniques, aimed at establishing the mercury contents of geological materials, require comminution of samples prior to analysis. This typically involves a process of crushing, followed by milling. It is known that heat is generated during milling in conventional milling apparatuses; therefore mercury losses may be expected due to the element’s volatility. To investigate mercury losses during milling, we analysed the mercury contents of nine certified reference materials of igneous rocks before milling and after respectively 3 and 10 minutes of milling, using a direct mercury analyser. The results of the experiments suggest that: (1) mercury losses are insignificant after 3 minutes of milling, (2) mercury losses become significant when samples undergo excessive milling, (3) mercury losses do not appear to be mineralogically controlled and (4) for samples with low mercury contents, contamination during milling plays a much more significant role in the analysed mercury contents than milling time.

Mercury photochemistry in snow and implications for Arctic ecosystems

Mercury is a toxic and bioaccumulative environmental contaminant, which may be transported to remote regions around the world, such as the Arctic. Snowmelt is a major source of mercury to many surface water environments, but the amount of mercury in snow varies considerably. This variation is due to the balance of mercury retention and losses from snow, which is largely controlled by photochemical mechanisms controlling speciation. As such, quantifying these photochemical reaction rates and the factors affecting them will allow for the prediction of mercury speciation and movement into receiving water bodies. This will consequently improve our ability to predict exposure of aquatic organisms to mercury. This review highlights knowledge gaps in the quantification of mercury photochemical kinetics and the specific research required to advance the science of mercury photochemistry in snow, while examining the physical and chemical snowpack variables that influence snowpack mercury reactions. At present, our lack of mechanistic and kinetic knowledge of mercury reactions in snow is one of the greatest gaps preventing accurate predictions of mercury fate in regions containing seasonal snowpacks.

Artisanal gold mining in Antioquia, Colombia: a successful case of mercury reduction

Abstract Five municipalities in Antioquia, Colombia, with population of 162,000 inhabitants, were the world's largest mercury polluter from artisanal gold mining in 2010, releasing and emitting an average of 92 (73–110) tonnes/a of mercury. UNIDO – United Nations Industrial Development Organization joined forces with the Government of Antioquia, National University of Colombia and University of British Columbia to start The Colombia Mercury Project to reduce mercury use and losses. 1 The actions consisted of assessment of mercury losses, health monitoring and awareness campaign. This was supported by technical demonstrations of methods to reduce the amount of mercury used in the processing centres (“entables”). Enhanced enforcement of existing local and federal regulations accompanied these activities. Demonstrations of cleaner methods to miners and owners of “entables” generated 39 new mercury-free processing plants. The presence of the company Gran Colombia Gold buying ore from the miners at a fair price also contributed considerably to observed reductions in mercury use. Mercury entering in the whole ore amalgamation in the 323 “entables” was reduced on average 43% from 2010 levels. In 2013, mercury losses were reduced by 63%, resulting in 46 to 70 tonnes/a, less mercury entering the environment than in 2010.

Mercury pollution assessment in soils affected by industrial emissions using miniaturized ultrasonic probe extraction and ICP-MS

A combination of probe ultrasonic extraction, optimized by surface response methodology, and Inductively coupled plasma mass spectrometry (ICP-MS) detection is described in this work as an effective methodology for mercury monitoring in soils affected by industrial emissions. Minute amounts of samples (typically 20 mg) can be extracted in 3 min by 1 mL of HCl-based extracting solution, without risk of mercury losses, and sub sequentially assayed by ICP-MS. The method was successfully tested on soil standard reference materials and then applied to mercury monitoring in a large set of real soil samples collected during a long-term monitoring survey (2007–2011) around the industrial area of Puchuncavi, Chile. The method proved to be useful for investigation of spatial and temporal mercury variability in the area, showing an intermediate to high mercury contamination with potential impact on the surrounding ecosystem.

Processing centres in artisanal gold mining

The aim of this paper is to reflect on efforts made worldwide to construct processing centres where artisanal miners can visit to have gold extracted from ore “free” or for a nominal fee. These centres use inefficient grinding and amalgamation processes to extract less than 30% of the gold to give back to the miners. As payment, miners typically leave the tailings (residues) at the centres that are processed by cyanidation to extract at least 90% of the residual gold. The cyanidation of contaminated tailings produces mercury–cyanide complexes that are rarely recovered in the process of activated charcoal or zinc precipitation. As a result, tailings discharged into the local water streams carry mercury either as soluble cyanide complexes or mercury droplets. There are a few processing centres, particularly in southern Ecuador, which use responsible and cleaner gold extraction integrating mining and processing techniques, but the vast majority of the processing centres in developing countries are only creating more pollution. Processing centres from different countries were assessed: Nicaragua, Peru, Colombia, Indonesia and Ecuador and the technical procedures to process ores and extract gold are described. The main environmental issues posed by poor practices are: (1) inappropriate cyanide management, (2) amalgamation of the whole ore, which increases the mercury losses with tailings, (3) usage of cyanide to extract residual gold from Hg-contaminated tailings, (4) dumping tailings with mercury, other heavy metals and cyanide into the local natural drainages, and (5) decomposition of amalgams without any condenser or filter.

Impacts of Land Uses on Mercury Retention in Long-Time Cultivated Soils, Brazilian Amazon

Many studies have shown the relationship between fire clearing and mercury contamination of aquatic ecosystems in the Brazilian Amazon. This study aimed at quantifying mercury content in long-time cultivated soils and at assessing the potential of a fire-free alternative clearing technique on mercury retention for long-time cultivated soils compared to traditional slash-and-burn. This case study included five land uses: one crop plot and one pasture plot cleared using slash-and-burn, one crop plot and one pasture plot cleared using chop-and-mulch, and one 40-year-old forest as a control. Low mercury concentrations were recorded in the surface horizon (24.83 to 49.48 ng g−1, 0–5 cm depth). The long-time cultivation (repeated burnings) of these soils triggered large mercury losses in the surface horizon, highlighted by high enrichment factors from surface to deeper horizons. The predominant effect of repeated burnings before the experimental implementation did not let us to distinguish a positive effect of the chop-and-mulch clearing method on soil mercury retention for crops and pastures. Moreover, some processes related to the presence of the mulch may favor mercury retention (Hg volatilization decrease, cationic sites increase), while others may contribute to mercury losses (cationic competition and dislocation, mobilization by the dissolved organic matter).

Complexation and oxidation strategies for improved TXRF determination of mercury in vaccines

A thorough investigation of strategies to overcome the effect of mercury losses during TXRF analysis was carried out. The vaporisation of mercury on sampling targets, associated with too low concentrations determined, depends on the nature of the respective Hg species and the dwell time of the analytes on the target. To prevent vaporisation, oxidation with ammonium persulfate and complexation with ethylenediamine tetraacetate (EDTA) and dimercaptosuccinic acid (DMSA) were investigated. Whereas both approaches were effective in reducing the Hg losses by vaporisation, the complexation approaches turned out to be particularly efficient. Both EDTA and DMSA retain the different mercury species quantitatively over several hours. Based on this approach, a method for mercury determination by TXRF in liquid samples was developed, successfully validated by inductively coupled plasma optical emission spectrometry and applied to the analysis of a mercury-containing vaccine sample.

Environmental Issues within the Chlor-Alkali Manufacturing Industry -

At present is estimated that around 12000 tones of mercury are contained in mercury cells used for chlorine production in the EU. Mercury contamination risk, remains active for long periods after the removing of the pollutant source, and is recognized as extremely dangerous for humans and environment due to the toxicity of various mercury compounds that can accumulate in the trophic chains. Almost all facilities using mercury -cell process reports unaccounted for mercury losses. The annual mercury balance for a site is never zero. This is because mercury accumulates in plant equipment and structures during the life of the plant. The majority of mercury losses occur, in the various process wastes. Considerable emissions of mercury can also occur with run-off water. The soil at many sites is contaminated with mercury due to deposition of atmospheric diffuse emissions and/or historical disposal of mercury contaminated wastes. An even greater problem is represented by the decommissioning of obsolete facilities when large quantities of mercury can escape in the environment despite all precaution measures.

Using street theatre to increase awareness of and reduce mercury pollution in the artisanal gold mining sector: a case from Zimbabwe

Abstract An illustrative example of street theatre used in international development as an awareness-building tool is Nakai , a drama produced by the United Nation's Industrial Development Organization's Global Mercury Project (GMP) in Zimbabwe to increase knowledge of the hazards of mercury use amongst artisanal gold miners in the Kadoma-Chakari region, Zimbabwe. Nakai performed to almost 9000 people, but its influence on behavioral change in the GMP project area could not be studied due to the extremely unstable political situation at the time in Zimbabwe. Nakai evolved as a non-participatory didactic drama with the belief that a transportable equipment-demonstration school would serve as a more effective platform for participation and empowerment. About 700 miners were trained in these demonstration units and learned how to process gold more efficiently and reduce mercury losses when the whole ore is amalgamated and when the amalgams are burned in open air. Indicators of success were not very evident since the repression of the police on miners and theatre players limited sound assessment of the awareness initiatives. The system of mineral processing centers in the region inhibits behavioral change because the centers' owners reap benefits from recovering gold from tailings using sophisticated techniques such as cyanidation, while rudimentary mercury amalgamation techniques are reserved for the artisanal miners. In practice, national and local elites can easily consolidate power and direct project benefits to themselves, reducing the possibilities empowering the miners.

Mercury isotope fractionation in waters and sediments of the Murray Brook mine watershed (New Brunswick, Canada): Tracing mercury contamination and transformation

Mercury isotope fractionation was investigated in different environmental compartments of a mining-impacted ecosystem, the watershed of the Murray Brook deposit in northern New Brunswick, Canada. Mercury contaminated ground water, surface water as well as sediment and samples of suspended particulate matter were collected alongside Gossan Creek downstream of mine tailings and analyzed for mercury isotopic composition. While leachates from the tailings and ground water samples showed a uniform and similar mercury isotopic signature confirming the predominant role of the mining residues in the contamination of the surrounding environment, samples collected from the surface flow system provided evidence of significant mass-dependent fractionation of mercury with distance from the source. As dissolved mercury contents steadily decreased from 31.1 to 1.4μg Hg L-1 with distance from the headwaters of the stream, δ202Hg in the creek water progressively increased resulting in a fractionation of ~0.9‰ over 1.6km. As a result, mercury isotopic ratios in the creek appeared to closely follow a Rayleigh model assuming a constant fractionation factor α(reactant/product) of 1.00038. Stream bed sediments also demonstrated an enrichment of heavy isotopes along the creek with an isotopic shift of ~1‰ over the distance of Gossan Creek (3100m). Although mercury losses from the water column result partly from partitioning to the sediments, measured mercury isotopic ratios differences between dissolved and solid phases were likely small and this study did not observe significant fractionation due to partitioning processes. Results rather suggested that fractionation observed in the surface water system of Gossan Creek is most likely the result of a combined effect of reduction and volatilisation processes, the lighter isotopes being preferentially reduced and evaporated from the water column. Additional sediment samples collected along reaches of Eighteen Mile Brook and the Upsalquitch River that receive water from Gossan Creek, and from tributaries unaffected by the mine contamination were analyzed for mercury isotopic composition. Data obtained from those sediments clearly demonstrated that mercury derived from mining activities is isotopically different from mercury naturally present in the area. Measured isotopic differences can ultimately be employed to trace sources of mercury, notwithstanding potential fractionation caused by natural transformation processes.

Total and inorganic mercury determination in fish tissue by flow injection cold vapour atomic fluorescence spectrometry

A simple and reliable method for Hg determination in fish samples has been developed. Lyophilised fish tissue samples were extracted in a 25% (w/v) tetramethylammonium hydroxide (TMAH) solution; the extracts were then analysed by FI-CVAFS. This method can be used to determine total and inorganic Hg, using the same FI manifold. For total Hg determination, a 0.1% (w/v) KMnO4 solution was added to the FI manifold at the sample zone, followed by the addition of a 0.5% (w/v) SnCl2 solution, whereas inorganic Hg was determined by adding a 0.1% (w/v) L-cysteine solution followed by a 1.0% (w/v) SnCl2 solution to the FI system. The organic fraction was determined as the difference between total and inorganic Hg. Sample preparation, reagent consumption and parameters that can influence the FI-CVAFS performance were also evaluated. The limit of detection for this method is 3.7 ng g−1 for total Hg and 4.3 ng g−1 for inorganic Hg. The relative standard deviation for a 1.0 µg L−1 CH3Hg standard solution (n = 20) was 1.1%, and 1.3% for a 1.0 µg L–1 Hg2+ standard solution (n = 20). Accuracy was assessed by the analysis of Certified Reference Material (dogfish: DORM-2, NRCC). Recoveries of 99.1% for total Hg and 93.9% inorganic Hg were obtained. Mercury losses were not observed when sample solutions were re-analysed after a seven day period of storage at 4°C.

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.