Figure 17 - uploaded by Robin Francis Grayson
Content may be subject to copyright.
Source publication
The study sets out to identify methods capable now, or in the near future, of recovering gold traditionally lost by placer gold mines and artisanal miners, but without resorting to dangerous mercury or controversial cyanide. The study tracks the rise and fall of gold recovery systems across the world. The study clarifies the meaning of 'fine gold',...
Citations
... Calvez et al. (1998) indicated that the coal-oil agglomeration process can recover gold from sulfide ores if sulfides are less than 5 percent of the feed. Grayson (2007) noted that thiosulphate is capable of leaching gold from refractory ores [in particular, carbonaceous ores and carlintype ores (these are sediment-hosted gold bearing ores)]. ...
Artisanal and small-scale gold mining (ASGM) is present in over 80 countries, employing about 15 million miners and serving as source of livelihood for millions more. The sector is estimated to be the largest emitter of mercury globally. The Minamata Convention on Mercury seeks to reduce and, where feasible, eliminate mercury use in the ASGM. However, the total quantity of mercury used in ASGM globally is still highly uncertain, and the adoption of mercury-free technologies has been limited. This paper presents an overview of new data, derived from Minamata ASGM National Action Plan submissions, that can contribute to refining estimates of mercury use in ASGM, and then assesses technologies that can support the phase out mercury use in ASGM while increasing gold recovery. The paper concludes with a discussion of social and economic barriers to adoption of these technologies, illustrated by a case study from Uganda.
... Chemical and mineralogical characterization allow for a better observation of the different mineralogical characteristics of gold ore and their relationship with the processing steps [28,29]. Grayson (2007) [30] identified about 70 different gold processing methods, except those based on cyanide or mercury, to recover gold lost by artisanal miners without side effects of cyanide and mercury. With the focus of avoiding the side effects caused by the mercury and cyanide, various gravity separation techniques have been tested to increase their suitability in artisanal gold mine [31]. ...
... Chemical and mineralogical characterization allow for a better observation of the different mineralogical characteristics of gold ore and their relationship with the processing steps [28,29]. Grayson (2007) [30] identified about 70 different gold processing methods, except those based on cyanide or mercury, to recover gold lost by artisanal miners without side effects of cyanide and mercury. With the focus of avoiding the side effects caused by the mercury and cyanide, various gravity separation techniques have been tested to increase their suitability in artisanal gold mine [31]. ...
... Manual breaking of gold ores with hammer, African stone grinding mill and old-style table shaking system are largely employed in the gold mining of Miyove (Figure 1b-d) possibly due to financial constraints on investment, lack of technology, and skilled labor [34,35]. For example, modern shaking tables that are very effective and can concentrate sizeable amounts of ore at a time, providing high-grade concentrates and liberated gold, are relatively expensive and require some skill to operate [30]. The use of primitive processing methods results in the generation of solid waste with high gold content [36]. ...
Few investigations have focused on the potential uses of artisanal gold (Au) mine tailings,
despite the fact that artisanal gold mining activity contributes to environmental issues such as greenhouse gas. Mineralogical characterizations of artisanal gold mine tailings in Miyove gold mine (Baradega and Masogwe) in Rwanda were investigated for potential utilization as a source of valuable gold, using the centrifugal separation technique. Results of X-ray diffraction analysis, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, inductively coupled plasma–optical emission spectroscopy, and X-ray fluorescence showed that artisanal gold mine
tailings samples have significant amounts of gold to justify economical gold extraction opportunity. The gold grades in the ores and artisanal gold mine tailings were in the ranges of 37–152 and 2–7 g t−1, respectively. Quartz was a major phase, with minor impurities in two different types of gold ores and their respective tailings. The beneficiation carried out using centrifugal separation, regarded as an extension of gravity separation, showed gold grades in the range of 535–1515 g t−1 for gold
ores and 36–302 g t−1 for artisanal gold mine tailings. The gold recoveries for ores and artisanal gold mine tailings were in the range of 21.8–47.3% and 46.9–63.8%, respectively. The results showed that the centrifugal separation technique was more efficient in boosting gold recovery compared to the present panning approach employed at the site, which sometimes recover as low as 10%. The results suggest that mineralogical characterization of artisanal gold mine tailings allows for the development and design of a suitable methods for improving gold ore beneficiation and artisanal
gold mine tailings reprocessing.
... Over the past decade, other lixiviants have been introduced to AGM for the gold leaching purposes. Alternatives to replace mercury and cyanide in gold processing have been studied in (Sparrow and Woodcock, 1995;Hilson and Monhemius, 2006;Vieira, 2006;Grayson, 2007), but most of them require trained operators or expensive proprietary methods. Consequently, the utilization of these methods is either insignificant or such that no applications have been witnessed in neither conventional nor artisanal operations. ...
Mercury pollution from artisanal gold mining causes severe environmental and health problems, especially to operators and people living around the processing facilities. Over 2000 tonnes/a of mercury is released to the environment by the artisanal miners which is the largest man-made source of mercury pollution. Here we present a novel method using a local plant, cassava, common in many artisanal mining areas in Latin America, Africa, and Asia, to dissolve gold from ores. In our experiments, we used a liquid by-product of cassava flour manufacturing, “manipueira” to leach gold from the gold ore. It contains hydrogen cyanide, generating from the hydrolysis of cyanogenic glycosides in the cassava plant. The results were very promising to replace the use of mercury, as approximately 50% of the gold content was extracted from the ore in 24 hours.
... There are many methods of gold extraction-some, such as panning and sluices, have been used for thousands of years, many others are more recent developments. For instance, Grayson (2007) [22] identified 75 gold separation and leaching methods that do not use mercury or cyanide. ...
... There are many methods of gold extraction-some, such as panning and sluices, have been used for thousands of years, many others are more recent developments. For instance, Grayson (2007) [22] identified 75 gold separation and leaching methods that do not use mercury or cyanide. ...
... Many methods have been described to leach gold replacing mercury and cyanide (Hilson and Monhemius, 2006 [100], Gökelma et al., 2016 [101]). One example is the American Haber method using undisclosed reagents (Grayson, 2007) [22]. Another example is the patented iodide process promoted by the Canadian company EnviroLeach (2020) [102], which has been used to leach gold from e-waste and concentrates from small gold mines. ...
Worldwide there are over 43 million artisanal miners in virtually all developing countries extracting at least 30 different minerals. Gold, due to its increasing value, is the main mineral extracted by at least half of these miners. The large majority use amalgamation either as the final process to extract gold from gravity concentrates or from the whole ore. This latter method has been causing large losses of mercury to the environment and the most relevant world’s mercury pollution. For years, international agencies and researchers have been promoting gravity concentration methods as a way to eventually avoid the use of mercury or to reduce the mass of material to be amalgamated. This article reviews typical gravity concentration methods used by artisanal miners in developing countries, based on numerous field trips of the authors to more than 35 countries where artisanal gold mining is common.
... The bottom sluice section was cleaned up after a total of 42 h of sluicing. " - Clarkson, 1989; "clean-ups to be needed only once every 24 h" - Grayson, 2007), days ("cleanup takes place every 7-10 days" -Weiss, 1985) till weeks ("Usually the head sluices are cleaned up at approximately regular intervals of 1-4 weeks, as dictated by experience, while the tail sluices are cleaned only once or twice per season …" -Taggart, 1945; "about a week before the box is cleaned" -Subasinghe, 1993; "vary from once a day to once every several weeks" -Gupta and Yan, 2016; "…may wait two weeks or more to clean the sluice" - Teschner et al., 2017). ...
... Stewart and Ramsay (1993) describe the important role of settled gangue in trapping fine heavy minerals. A fixed bed of magnetic heavy minerals is used by the Cleangold technology and seems to increase the gold trapping (Veiga et al., 2006;Grayson, 2007). In contrary to fixed obstacles in a sluice (riffles, slings or bristles of mats) the settled gangue and heavy minerals need a certain time to accumulate and to develop their ability, to catch gold flakes. ...
Sluices are common devices for the extraction of placer gold from gravels and sands. To maximize the outcome, a lot of investigations have been made, predominantly dealing with improvements of their technical construction. Recent similar works in a German gravel plant led to the conclusion, that the cycle time respectively the frequency of cleanups is also an important factor for the assessment of the recovery of a sluice-system. In contrary the available literature is low in fact-based data on this subject. Considerations and experiments led to the approach of modelling the enrichment of a sluice with gold by a saturation curve. From the variety of possible mathematical options, the form y = ax/(x + b) has been chosen for its simplicity. By feeding a test mat-sluice under industrial conditions and determining the mass and content of trapped gold after different times of feeding, a set of data pairs has been obtained. Using this data and the method of lowest error squares the parameters “a” and “b” of the assumed saturation curve have been identified. The significance of such an approach for recovery determinations and the gold extracting industry is discussed.
... Many methods in this concentration of gravity, one of which is a shaking table. Recovery gold using a shaking table can reach> 90% in grain sizes 3 mm-70 μm and it can still reach> 70% in 50 μm gold grains [3]. Based on the results of the mineragraphy analysis in this study, Paningkaban epithermal gold deposits have a gold grain size between 10-100 μm. ...
... Gold in Paningkaban deposits has grain sizes between 10-100 microns (from microscopic observations of ore and SEM_EDS), which are categorized as very fine grain size of gold [3] of gold grains> 0.1-100 microns is categorized as microscopic size because they can still be observed using a microscope [5]. ...
... There are many factors that must be considered in the gravity shaking table method, namely the particle size of gold particles, the shape of the grain (flatness), grain surface texture, the presence of other minerals attached to gold, other types of particles, dilution of the feed, and smoothness of the feed. Gravity concentration is not or less effective if the grain is flatness, small grain size or attached to quartz [3]. ...
Aiming to increase the concentration of gold ore from LS epithermal gold deposit Paningkaban, Banyumas, Central Java related to its characteristic, shaking table has been applied in the development of non-amalgamation technique for artisanal miners. Many parameters affect the results of processing the gold concentration using a shaking table. The parameters studied in this research are gold grain size fraction, water flow rate, and shaking table speed. With an objective to determine the optimum condition, this study was designed using statistical approach Response Surface Method (RSM) at which all of the variables were varied altogether. The research method is to process the gold using shaking table with three levels approach, so that in total there were 27 concentrates to analyze using Fire Assay (FA) and further assessed using RSM to distinguish the interaction among parameters and the optimum condition. For the gold ore deposit from Artisanal Small scale Gold Mining (ASGM) in Paningkaban, Banyumas, Central Java with the formation of low sulfidation epithermal, the results showed that the highest gold was 3688 ppm with operating conditions ie gold grain size fraction of -100 + 200 mesh (-149 + 74 micron), water flow rate of 18 l / min and shaking speed of 100 rpm. From the RSM assessment it was obtained that optimum operating conditions is on gold grain size of -100+ 200 mesh (87,2576 micron), water flow rate of 9 l / min and shaking speed of 100 rpm. Thus, shaking table could be an alternative non-amalgamation technique to process LS epithermal gold ore in Paningkaban creating a sustainable ASGM.
The current work focuses on the extraction of gold using alpha-cyclodextrin (α-CD) from the Kimpese quarry in the Democratic Republic of the Congo, through an environmentally friendly gold process as an alternative to the amalgamation process. The ore was sampled and characterized using atomic absorption spectroscopy (AAS) prior to the experiments, and the analysis revealed 0.08% of gold. The ore was then leached with modified aqua regia (MAR). Time, HBr concentration, pH, and stirring speed were all varied during leaching to highlight the parameters that influence the leaching yield. The optimum conditions were determined using analysis of variance (ANOVA) and response surface methodology (RSM), implying time, HBr concentration, pH, and stirring speed of 6 hours, 80g/l, 1, and 800rpm, respectively, and a leaching percentage of 98.6928%. Following leaching, neutralization tests with potassium hydroxide (KOH) were performed by varying the following parameters: time, KOH concentration, and pH. The following factors were varied in the extraction tests after neutralization: time, α-CD concentration, pH. The optimal parameters were as follows: time of 30 minutes, α-CD concentration of 8.8639g/l, and pH of 6, with yield of 89.7350%. This method of recovering gold from ore using α-CD is inexpensive and does not harm the environment.
There are two Artisanal Small scale Gold Mining (ASGM) location in Lamuntet, Brang Rea Subdistrict, West Nusa Tenggara Regency, namely Nglampar and Song location. Nglampar and Song location are included in the low sulfidation epithermal gold deposit system. The research purposes to analyze mineralogy and geochemistry of gold vein deposits and determine system of low sulfidation gold ore in Nglampar, Lamuntet Village. The methods used to determine the mineralogy of gold vein deposits are petrography, mineragraphy and X-ray diffractometer (XRD) analysis, while geochemical analysis using Scanning Electron Microscope (SEM) with Energy Dispersive X-Ray Spectroscopy (EDS), Fire Assay (FA) and Atomic Absorption Spectrophotometry (AAS). The results showed that the minerals contained were quartz (Qz), sericite (Ser), Chalcedon (Chc), chlorite (Chl), pyrite (Py), sphalerite (Sph), galena (Gn) , gold (Au), chalcopyrite (Cp), argentite (Ag), arsenopyrite (Apy), Azurit (Az), Malakit (Mal) and bornite (Bn). Abundant mineral availability such as sphalerite, galena, chalcopyrite and arsenopyrite are characterized by high levels of Zn, Pb, Cu and As the metal in vein deposits. This can be seen on the chemical content of ore in gold vein deposits ie Au 0.1 ppm -27.8 ppm, Ag 3 ppm-185 ppm, Pb 101 ppm - 35,800 ppm, Zn 73 ppm-60,200 ppm, Cu 26 ppm - 1,740 ppm, and As 150 ppm - 6,530 ppm. Based on the results of SEM-EDS analysis shows that the type of gold mineral is the electrum because of the content of Ag> 20%. Based on those characteristics of the mineralogy and geochemistry in this study showed that low sulfidation gold ore in this area is categorized as polymetallic gold-silver system.
Bu araştırmada, ramatlardan altın/gümüş elde etmek için uygulanan ramat geri kazanım prosesinde açığa çıkan cürufta hapsolan altının gravite ayırması ile uygun koşullarda geri kazanımı amaçlanmış, maliyetleri azaltmak ve değerli metallerin geri kazanımını en üst düzeye çıkarmak için yüksek tenörlü/verimli altın ön konsantresi üretiminin mümkün olup olmadığı araştırılmıştır. Gravite ayırması ile zenginleştirme çalışmalarında santrifüj esaslı Knelson konsantratörü kullanılmıştır. Au tenörü 7 g/t olan soda-boraks esaslı cürufun bileşiminde yüksek oranda Fe2O3 (%13,25) ve PbO (%11,38) olduğu, boyuta göre yapılan sınıflandırma sonucu altının -0,5 + 0,212 mm fraksiyonunda yoğunlaştığı (%34) belirlenmiştir. Knelson konsantratörünün işletme parametreleri (yıkama suyu basıncı, santrifüj kuvvet, besleme hızı, pülp katı oranı vs.) ile besleme malı tane boyutunun konsantre/artığın Au tenörü ve altın kazanma verimine etkisi incelenmiştir. Altın kazanma verimi ve artığa kaçan altın miktarları dikkate alındığında yıkama suyu basıncı, santrifüj kuvvet ve besleme hızının ayırma performansına etkisinin sınırlı olduğu, besleme tane boyutunun ise konsantre Au tenörü üzerinde etkili olduğu tespit edilmiştir. 7 g/t Au tenörüne sahip cüruftan en uygun şartlarda %72,4 verimle 16 g/t Au içeren bir konsantre (artığın Au tenörü: 3 g/t) elde edilmiştir. Altının fraksiyonel bazda en yüksek dağılım gösterdiği -0,212 mm boyutunda besleme malı ile çalışıldığında, konsantrenin Au tenörü kayda değer bir artış göstererek 30 g/ton'a ulaşmıştır.
