Extraction Of Silver Research Articles

Effect of flotation and potassium hydroxide pretreatment of an antimonial refractory ore on the extraction of silver by cyanidation

In this study, potassium hydroxide leaching as pretreatment before cyanide leaching of a flotation concentrate of an antimonial refractory gold-silver ore was investigated. The ore assaying 1157 g/t Ag and 3.96 g/t Au was found to be composed of predominantly quartz, barite, kaolinite, clay, mica/chlorite, and dolomite/ankerite. Electrum, pyrargyrite, acanthite, and tetrahedrite were identified to be the most important silver-bearing phases in the ore. A flotation concentrate with a high silver grade (0.6% Ag) at 94.8% silver recovery, as well as high recoveries of antimony (86.8%), zinc (98.6%), and lead (84.7%), was produced in flotation tests. Gold recovery to the concentrate was limited to be 74.4%. The cyanide leaching of the concentrate has yielded consistently low extractions of silver (≤13.8%) confirming the refractory nature of the ore. Alkaline pretreatment of the concentrate was performed in which effects of potassium hydroxide concentration (0.05–3 mol/L) and temperature (20–80 °C) on the removal of antimony and subsequent cyanide leaching of silver were investigated. Extraction of antimony was substantially enhanced from 11.5 to 93.8% with increasing the concentration of KOH and temperature. The activation energy (Ea) for leaching of antimony was calculated to be ≈17 kJ/mol with the implication of a diffusion-controlled leaching reaction. Silver extraction in the cyanidation improved from 13.8% to 95.7% as a consequence of the removal of antimony (i.e. 93.8%) by the alkaline pretreatment. This improvement in the silver extraction can be attributed to the decomposition of silver-bearing antimonial minerals i.e. pyrargyrite, and tetrahedrite in the concentrate. These findings confirm that potassium hydroxide leaching is a suitable approach for the pretreatment of antimonial refractory silver ores.

Effects of pretreatment and leaching medium on the extraction efficiency of Au and Ag from a chalcopyrite leaching by-product

Precious metals such as gold (Au) and silver (Ag) are essential to our modern society due to their unique properties, such as high conductivity and physical and chemical resistance. They are teofn concentrated in by-products during the extraction of base metals. In the present work, a chalcopyrite leaching residue, constituted mainly of elemental sulfur and jarosites, was subjected to different pretreatments and leached with different leaching media to recover Au and Ag. The solid residue was pretreated by desulfurization,peroxidation,desulfurization+peroxidation and leached with cyanide, cyanide+glycine, and glycine. For comparison, samples without pretreatment were also leached using the same leaching media. Changes in the mineralogical species were followed to explain the effects of pretreatment and leaching medium on the dissolution of Au and Ag. Results indicate that the highest extraction of gold and silver (Au:99.50%, Ag:46.71%) is achieved by using a combined desulfurization+peroxidation pretreatment and cyanide as leaching medium.

A Cyaphide Transfer Reagent

The cyanide ion plays a key role in a number of industrially relevant chemical processes, such as the extraction of gold and silver from low grade ores. Metal cyanide compounds were arguably some of the earliest coordination complexes studied and can be traced back to the serendipitous discovery of Prussian blue by Diesbach in 1706. By contrast, heavier cyanide analogues, such as the cyaphide ion, C≡P–, are virtually unexplored despite the enormous potential of such ions as ligands in coordination compounds and extended solids. This is ultimately due to the lack of a suitable synthesis of cyaphide salts. Herein we report the synthesis and isolation of several magnesium–cyaphido complexes by reduction of iPr3SiOCP with a magnesium(I) reagent. By analogy with Grignard reagents, these compounds can be used for the incorporation of the cyaphide ion into the coordination sphere of metals using a simple salt-metathesis protocol.

Sending Laurion Back to the Future: Bronze Age Silver and the Source of Confusion

Silver-bearing lead ores at Laurion in Attica were considered to have been first exploited with the introduction of coinage sometime around the birth of Classical Greece. However, in the late 20th century this chronology was radically revised earlier, to the Bronze Age, largely supported by lead isotope analyses (LIA). Here, we acknowledge that lead and silver metallurgy emerged from the earliest times but we propose that any correlation between these metals in the archaeological record is not a consequence of a geological association between lead and silver in ores such as galena until the middle of the first millennium BCE. We suggest that ancient metallurgists recognised that silver minerals (such as horn silver) dispersed in host rocks could be concentrated in molten lead and that LIA signatures of Bronze Age silver artefacts reflect the use of exogenous lead to extract silver, perhaps applying processes similar to those used to acquire silver in Bronze Age Siphnos. We further propose that lead from Laurion used for silver extraction resulted in the inadvertent transfer of its LIA signature (probably aided by roving silver prospectors) to silver objects and metallurgical debris recovered around the Aegean. New compositional analyses for the Mycenaean shaft-grave silver (c. 1600 BCE) support these conclusions. We believe that reverting to the mid-first millennium BCE for the first exploitation of silver from argentiferous lead ores is consistent with the absence of archaeological evidence for centralised control over Laurion until the Archaic period, the paucity of lead slag associated with silver-processing debris at Bronze Age sites, the scarcity of silver artefacts recovered in post-shaft grave contexts at Mycenae and throughout the Early Iron Age Aegean, the few Attic silver coins with LIA signatures consistent with Laurion until after 500 BCE and a single unambiguous mention of silver in the Linear B texts.

Extraction of silver in processing of dust from the firing of nickel concentrate in fluidized bed furnaces

In 2018 in order to prevent the accumulation of lead in the products of the main technology of JSC Kola MMC the technology of hydrometallurgical processing of fine dust from the nickel concentrate roasting in fluidized bed furnaces was implemented. In the process of roasting, along with lead, silver is concentrated in the fine dusts of electrostatic precipitators. The distribution of silver on intermediate products of the technology is studied and recommendations are given to exclude irreversible losses of this element. It was found that when water leaching of dust, silver is not extracted into the solution, while the treatment of the aqueous leaching residue with sodium chloride solutions under conditions that provide high recovery of lead, results in recovery up to 32% of silver in chloride solution. It is shown that it is not possible to quantitatively concentrate silver in the chloride leaching residue. It is recommended to send the chloride leaching residue based on nickel (II) oxide, free of lead and containing refractory silver compounds, for pyrometallurgical processing in the process of the main technology. It was found that the production of lead cake by interaction of chloride solution with sulfate-containing reagents is accompanied by coprecipitation of silver present in it to form a product containing up to 9.4% (wt.) of this element. The efficiency of treatment of lead cake with sodium sulfite solution for extraction of more than 90% of silver is shown. By treatment of sulfite silver-containing solutions with sodium sulfide, a rich silver-containing concentrate is obtained. A schematic diagram of extraction of silver from lead cake with obtaining of silver-containing concentrate for production of additional products with high added value, as well as suitable for the sale of lead cake. The results of the research allowed to identify the main channels of silver losses during hydrometallurgical processing of dust from nickel concentrate roasting and to recommend ways to prevent them, which will generally increase the complexity of the use of nickel raw materials. The authors are grateful to the staff of FRC KST RAS (N. Yu. Neradovsky, V. Ya. Kuznetsov, I.V. Glukhovskaya, E.S. Kshumaneva) and JSC Kola MMC (I.A. Basova), who took part in conducting research and analytical support of work.

Chemical studies of Chinese coinage II: from Qin to Yuan (221 BCE\u20131368 CE)

This paper surveys of the chemical composition of the copper alloy coinage in China from the Qin Dynasty to the end of the Yuan Dynasty (221 BCE–1368 CE). It shows a dramatic change in the alloying practice used to cast these coins from the Qin unification (after 221 BCE), compared to that practiced in the pre-Qin. There are a number of shifts in the quality of the coinage from dynasty to dynasty, such as the obvious debasement of the Southern Song coinage (1127–1279 CE) when compared to that of the previous Northern Song dynasty (960–1127 CE). Particular attention is paid to the low levels of zinc in the coinage over the period. Although not as obvious as the switch to brass coinage in the Ming, certain periods do show occasional values of zinc up to 2–4%, which we suggest could reflect the sporadic input of recycled brass (Cu–Zn alloy) into the raw material melt. There were several major suppressions of Buddhism during this period, when Buddhist brass statuary was recycled into the coinage, providing a plausible mechanism for the injection of small quantities of zinc into the coinage alloy. A diachronic study of the amounts of iron in the metal, taken to indicate changes to the manufacturing process of copper, also show changes over time. The median levels of iron jump from the Qin (221–206 BCE) to the Western Han (206 BCE–9 CE), possibly reflecting the adoption of slagging processes in the production of the copper, followed by a gradual decline to the Northern Song (960–1127 CE), and a rapid increase during the Southern Song (1127–1279 CE). Finally, a study of changes in the content of silver over time reveals differences in the sources of lead, or changes in lead and silver extraction technologies, over the period.

Identification of microstructure and chemical composition of a silver object from Shahrak-e Firouzeh, Nishapur, Iran (~2nd millennium BC)

Nishapur is a historical city in the ancient Khorasan region, located in the northeast of Iran. Due to its location on the Silk Road, Nishapur enjoyed great economic prosperity and as a result contains many archaeological sites from prehistoric to post-Islamic periods. Shahrak-e Firouzeh is one such site, dating back to 2nd millennium BC, containing numerous metallic objects and metallurgic remains from silver refining by cupellation. This study investigates the manufacture of a unique silver lidded dish decorated with bas-relief mythological designs. Different techniques, including SEM-EDS, micro-PIXE, and Metallography were used to characterize the dish. Results obtained by micro-PIXE and SEM-EDS reveal the use of an intentional silver alloy containing about 92 wt.% silver and about 3.80 wt.% copper. Date also suggested the use of an advanced silver extraction process to obtain high purity silver. The presence of elements such as calcium were associated with exposure to the burial environment and the extraction process. Metallographic examination revealed that this extremely thin object was decorated with complex bas-relief designs which had been produced by cold working, and annealing based upon the presence of twin straight lines on some parts of the surface and the changing gradation in tiny grains and twin uneven lines on the raised parts.

Formation of Formic Acid from Glucose with Simultaneous Conversion of Ag2O to Ag under Mild Hydrothermal Conditions.

Formation of formic acid from renewable biomass resources is of great interest since formic acid is a widely used platform chemical and has recently been regarded as an important liquid hydrogen carrier. Herein, a novel approach is reported for the conversion of glucose, the constituent carbohydrate from the cellulose fraction of biomass, to formic acid under mild hydrothermal conditions with simultaneous reduction of Ag2O to Ag. Results showed that glucose was selectively converted to formic acid with an optimum yield of 40.7% and glycolic acid with a yield of 6.1% with 53.2% glucose converting to carbon dioxide (CO2) immediately at a mild reaction temperature of 135 °C for 30 min. In addition, Ag2O was used as a solid oxidant for glucose oxidation, which avoids the use of traditionally dangerous liquid oxidant H2O2. Furthermore, complete conversion of Ag2O to Ag can be achieved. This study not only developed a new method for value-added chemical production from renewable biomass but also explored an alternative low-carbon and energy-saving route for silver extraction and recovery.

The Chemical Technology for Producing Precious Metals from Enrichment Rejects of Copper-Pyrite Ores

The chemical technology for recovery precious metals Au and Ag from mature flotation tailings of copper-pyrite ores by two-stage sintering with chlorine-ammonium reagents and leaching of bakes with water is developed. The chemical extraction of gold and silver is carried out, using NH4Cl and NH4NO3 reagents in the ratios of 1:1 at a temperature of 250 °C, and 2:1 at 200 °C. In accordance with the obtained results, a chemical technology of enrichment rejects of copper-pyrite ores processing and a scheme of primary apparatus chain for implementing this technology are proposed. The economic effect of the technology realization is calculated. This effect is 96.3 million rubles with a payback period of 8 years when processing enrichment rejects of copper-pyrite ores in amount of 109.5 thousand tons per year under the conditions of JSC “Uchaly Mining and Metallurgical Combine”.

Design of Multistage Extraction System for Simultaneous Separation of Silver and Gold from Thiourea Solutions

This study is focused on the extraction and recovery of gold and silver from thiourea acid leaching ore liquors. In a first step, extraction is performed using di(2-ethylhexyl)dithiophosphoric acid (D2EHDTPA). The extraction of gold and silver takes place simultaneously, allowing the removal of both metals in a single equipment under the same operational conditions. Each metal is then recovered by selective stripping, using NH4SCN/H2SO4 solutions to separate the silver from the D2EHDTPA. Such treatment is followed by a second stripping system, where a (NH4)2S2O3 solution is used to recover gold. A mathematical model is developed to represent all the operations in the process flowsheet. Through this model, it is predicted that, for properly selected operating conditions, recoveries higher than 99.9% for silver, gold and thiourea (to be recycled) can be obtained. The data predicted by the model has a good fit with previously reported experimental data. The proposed process is a more sustainable approach, in comparison with the traditional process involving cyanide, and has potential to be economically feasible.

Research on Hydrometallurgical Processing of Gold-Concentrate of Jamgyr Deposit

Laboratory studies have been carried out on the processing of gold-bearing concentrate from the “Jamgyr” deposit using the JIN CHAN reagent. The influence of the concentration JIN CHAN, the duration of leaching, the temperature of the solution were studied. As a result of research, the extraction of gold and silver into solution using cyanide-free technology was 97,5% and 96%, respectively. The processing of the obtained solutions by the method of sorption was carried out on the MA940BG (gold) ion-exchange resin with the extraction of target components from the solution into the ion-exchange resin: Au – 100,0%, Ag – 77,5%

Investigation of elemental composition of ancient metal objects found in Khorasan-e Razavi Province of Iran using micro-PIXE technique

In this work, elemental composition of 18 metallic objects belonging to the Bronze Age found at the Kalate Shoori site in Neyshabur, northeastern Iran, is investigated using micro-PIXE technique. The aim of the analysis is to identify the type of alloys employed in the fabrication of the investigated objects based on their elemental composition and to measure their contents of trace elements. The results of the micro-PIXE analyses indicate that the investigated objects could be categorized in two main groups: The objects of the 1st group (11 objects) are made of copper–silver alloys in which copper content varies within 30–60 wt% while silver content varies within 25–40 wt%. The objects of the 2nd group (7 objects) are made of nearly pure copper with copper content varying within 85–97 wt%. Though all the investigated metallic objects are found in the Bronze Age layers of the Kalate Shoori site, amazingly, no traces of tin were observed in their elemental composition. The measured impurities in the investigated objects could be either due to the raw materials and minerals used in the extraction of copper and silver or due to the soil surrounding the buried objects. Examination of trace elements contents in the investigated objects reveal that objects with the base of copper–silver alloys (i.e., objects of the 1st group) were all fabricated from the same raw materials, while objects with the base of nearly pure copper (i.e., objects of the 2nd group) were fabricated from different mineral materials with either no arsenic content or with varying arsenic contents of more than 1.5 wt%. Comparison of the results of this work with the published data in the literature indicates that similar samples with the base of copper–silver alloys belonging to Bronze Age have already been found in Altin Tepe, Turkmenistan. It could then be concluded that similar techniques might have been employed in the two regions. Moreover, archeological findings at the Kalate Shoori site reveal that there should be cultural and commercial exchanges between this region and the Central Asia.

Extraction of Metals from Scrap Marble Cutting Segments in Nitric Acid Solutions

Extraction of cobalt, copper, and silver from scrap saw-blade segments using nitric acid solutions (0.1–0.4 M, 20–60°C) were investigated using response surface methodology. Extraction of cobalt and iron was more extensive than copper and silver, i.e., 35.7–96.2% Co and 72.6–100% Fe versus 8.50–35.4% Cu and 8.11–22.5% Ag. Statistical analysis of the experimental data has shown that increasing the acid concentration or temperature enhances the rate and extent of leaching of metals. Under suitable conditions, almost complete leaching of cobalt (99.9%), as well as high extractions of copper (95.9%) and silver (94.9%), were achieved. The activation energy, calculated to be 40.3 kJ/mol, indicates that nitric acid leaching of these metals occurs as a chemically controlled reaction. These findings have demonstrated that nitric acid as an effective oxidant/leaching agent could be suitably used for the extraction of cobalt, copper, and silver from scrap segments.

Experiment of Gold and Silver Extraction from Cyanide Tailings by Melting Chlorination

Cyanide tailings produced in gold smelting process contain a large number of heavy metals and cyanides, which are more and more harmful to the environment. In order to reduce environmental pollution, valuable metals from cyanide tailings are recovered. The amount of calcium chloride, chlorination time, the way of adding calcium chloride and other factors on the influence of gold and silver extraction by chlorination were studied by using the raw material of cyanide tailings with melting chlorination process in this paper, and how to reduce the melting chlorination temperature was explored, and a comprehensive experiment was carried out under the best conditions. The results showed that when the chlorination temperature is 1500°C, the chlorination time is 1 h, and the addition amount of CaCl₂ is 7%, the volatilization rate of gold is 85.38%, the content of gold in slag is 1.83 g/t, the volatilization rate of silver is 77.36%, and the content of silver in slag is 4.12 g/t; when the chlorination temperature is 1500°C, 7% CaCl₂ is added, and the chlorination time is 15 min, the volatilization rate of gold is 87.78%, the content of gold in slag is 1.23 g/t, the volatilization rate of silver is 59.40%, and the content of silver in slag is 7.39 g/t; the addition of 5% CaO can change the slag type, reduce the chlorination temperature by 50~100°C, increase the volatilization rate of gold and silver slightly, and decrease the content of gold and silver in slag; when CaCl₂ is added in five times, the volatilization rate of gold increases to 95.53%, the content of gold in slag decreases to 0.56g/t, the volatilization rate of silver increases to 77.80%, and the content of silver in slag decreases to 4.04 g/t; 7% CaCl₂ was added in five times, and the melting chlorination time was 15 min. the amount of CaO was 5%, and the melting chlorination temperature was 1450°C, the gold volatilization rate is 95.69%, and the gold content of slag is 0.54 g/t, the silver volatilization rate is 77.06% and the silver content of slag is 4.20 g/t.

РОЛЬ РЕГИОНАЛЬНОГО ФАКТОРА В ОТВЕТАХ НА ИСТОРИЧЕСКИЕ ВЫЗОВЫ РОССИИ

The article traces the role of the Ural-Siberian region in Russia’s responses to historical challenges in the era of modernization. It is concluded that this role has been steadily increasing over the course of four centuries — from traditional society to the end of the historical period of modernization. Such a chronologically large and meaningfully diverse process is revealed for the first time in historiography. Addressing it made it possible to assess the strategy of a particular region in ensuring the country’s responses to world challenges at the expense of its own resources. Historical experience has shown that the region stayed in history as a reserve territory of the deep rear. These tendencies are traced on the materials of the procurement of furs, extraction of silver and gold, and ferrous metallurgy products. These resources contributed to Russia’s entry into the world market, the formation of its military-industrial complex, and responses to the challenges of the times and global competitors. The exploitation of such wealth controversially influenced the modernization processes and overcoming the country’s lag behind the advanced states of the world, although imperial Russia sometimes outstripped its opponents in some indicators, in particular, in the production of ferrous metals. Each of the five macro problems posed in this text requires further elaboration precisely from the standpoint of challenges. It is necessary to continue studying the perception of these problems in our country and the ways of organizing responses to them, as well as the reaction of the world community to Russia’s responses. This is the task for specialists in both Russian and general history.

ЛЕЖАЛЫЕ ХВОСТЫ ФЛОТАЦИИ МЕДНО-КОЛЧЕДАННЫХ РУД ИЗВЛЕЧЕНИЯ ЗОЛОТА И СЕРЕБРА: АНАЛИЗ РЕСУРСНОГО ПОТЕНЦИАЛА

The article analyzes the possibility and efficiency of processing stale tailings of flotation plants of the copper pyrite complex. The resource potential, material composition and technological capabilities of processing a number of technogenic objects are considered. The interrelation and influence of mineralogical and technological factors on the choice of tailings processing technology are analyzed. The results of chemical, mineral and phase analysis of stale flotation tailings of the studied pyrite ores are presented. According to the complex studies’ results, it is established that the stale flotation tailings of copper pyrite ores belong to a refractory type of geo-resources due to the high content of pyrite and low, at the level of ppm, gold and silver content, which are present mainly in the “resistant” minerals - chalcogenides, sulphides, their intergrowths. The article presents a factor analysis and conditions for the elemental composition of tailings formation: mineralogical, technological and environmental. The territorial accessibility and technological capability of the investigated technogenic formations are analyzed. In the course of experimental studies, the elemental composition of stale tailings has been revealed - the main components of which are: iron, sulfur, silicon and aluminum. According to the results of X-ray phase analysis, it has been found that the main ore mineral of the tailings is pyrite. At the same time, it is noted that the main share of gold in the stale flotation tailings is presented in the form of sulphides in the form of finely dispersed and isomorphic inclusions. The heterogeneous morphometric and mineral composition of sulphide aggregates, their difficult opening and high dispersion characterize stale tailings as a raw material that is difficult to float. The revealed features of the material composition of stale tails indicate the impossibility of extracting valuable components (gold and silver) from this resource using existing traditional technologies. It has been proved that it is possible to effectively extract precious metals from this category of raw materials only after their deep opening by chemical processing. The relevance of the research lies in the need to process gold-containing man-made waste in order to significantly expand the raw material base of mining enterprises, as well as to improve the ecological situation of the city-forming mining enterprises of the South Urals. The aim of the research is to study the material composition of stale tailings and develop a technology for selective extraction of gold and silver. The object of research is the stale flotation tailings of copper-pyrite enterprises of the Southern Urals. The subject is the mineral composition, the content of useful components of lying tailings and the technology of gold and silver selective extraction from them. Material and research methods. During the experiments, a set of physicochemical and chemical methods of analysis has been used: thermodynamic analysis, synchronous thermal analysis using a combined thermal analyzer of the Netzsch STA 449 F3 Jupiter brand, UV spectroscopy with an automated data processing system), qualitative chemical and assay analyzes

ЛЕЖАЛЫЕ ЗОЛОТОНОСНЫЕ ХВОСТЫ КОМБИНАТА «БАЛЕЙЗОЛОТО»: ПРОБЛЕМА УТИЛИЗАЦИИ

The relevance of the research is the need to recultivate the waste from the enrichment of gold-bearing ores that lie in the immediate vicinity of the residential areas of Baley city, which have a negative impact on the environmental situation in it, as well as to develop a technological approach to the extraction of gold and silver. The purpose of the study is to study the material composition and develop a technology for extracting precious metals. The object of the study is the stale tailings of the ZIF-1 plant “Baleizoloto”. The subject of the study is mineral composition of stale tailings, content of useful components and their extraction technology, the method and methodology presented by mineralogical and chemical analyses of enrichment tailings. Results. The analysis of the tailings dumps’ state of the gold recovery factories of the Baleizoloto plant was carried out. The contents of gold and other chemical elements, among which arsenic, zinc, copper, antimony, and lead predominate, were determined. The gold content prevails in the stale tailings of the ZIF-1 factory, which processed the ores of the Baley deposit, and is in the range of 1.09-1.37 g / t, on average – 1.17 g/t. This determines the prospects for their primary processing. The gold in the clay-sand fraction of the stale tailings is mainly found in thin accretions with quartz, carbonates, pyrite, arsenopyrite, sulfosols, and tellurides. The field of application is processing of technogenic raw materials. Conclusions. It was determined that the sizes of gold inclusions are in the range of 0.7-0.03 mm, the gold penetration varies from 63 to 91.15, and on average is 82.13; the main impurity in gold is silver with a content of 8.85-37%; the average silver content in the tailings of the ZIF-1 factory is 1.85 g/t; the recommended technological scheme for processing stale tailings of ZIF-1 of the Baleizoloto plant has been developed, including the following operations: photoelectron-activation preparation, pelletizing with active solution, heap leaching, two-stage sorption with bubbling with ozone

On the variability of technological indicators in the extraction of precious metals

in the conditions of significant variability of processed polymetallic ores of the Akbastau Deposit, it is essential to minimize the variability of technological indicators of enrichment. Due to the multifactorial nature and non-linearity of the flotation process, the use of classical regression models does not provide the necessary level of reliability, therefore, there is a significant variability in the extraction of precious metals. To solve this problem, the paper substantiates the use of the neural network modeling methodology, which allows to estimate the variability of gold and silver extraction depending on the variation of the content of metals in the ore.

Sº and jarosite behavior during recovery of values from the direct leaching residue of sphalerite using cyanide and glycine

This paper reports the effect of the components of a direct leaching residue (jarosite and elemental sulfur), on the recovery of valuable metals such as gold and silver. Leaching media such as cyanide and mixtures of cyanide with glycine were used to recover the gold and silver from the residue; however, a low recovery of these metals was obtained. This occurred due to the negative effect of its components which caused problems in the extraction process such as encapsulation of silver (due to jarosite) and the formation of thiocyanate and re-precipitation of silver (due to sulfur). Various treatments prior to leaching were tested, finding that when the residue was desulfurized with perchlorethylene and subjected to an oxidizing alkaline hydrothermal treatment, the gold extraction increased from 39.73 to 88% and the silver extraction of 64.76 to 94.29%. Additionally, it was determined that when cyanide was assisted by glycine, the latter decreased the cyanide consumption by inhibition of the dissolution of iron and sulfur in cyanide.

Surface processes at a polymetallic (Mn-Fe-Pb) sulfide subject to cyanide leaching under sonication conditions and with an alkaline pretreatment: Understanding differences in silver extraction with X-ray photoelectron spectroscopy (XPS)

Leaching of polymetallic sulfides is often challenging due to the complexity of these systems. The main issues are related to the formation of surface by-products or to the presence of different metals that require a greater consumption of chemicals compared to that needed to extract the target metal during leaching. This latter case is followed in the present work using X-ray photoelectron spectroscopy (XPS) during the leaching of a silver-containing polymetallic (Mn-Fe-Pb) sulfide under three different cyanidation procedures: (1) conventional leaching, (2) ultrasound-assisted leaching, and (3) leaching of a sample pretreated in alkaline media. In all cases, leaching results in the build-up of Pb compounds (oxides/hydroxides) on the surface of the minerals, suggesting a mechanism in which Pb is first leached by hydroxide and cyanide and later is re-adsorbed as an external layer on the minerals. On the other hand, the effect of each process on Mn was quite distinct: 1) Conventional leaching leads to the oxidation of the sulfide (pyrite) surface and a slight increase of surface Mn species; 2) Ultrasound-assisted leaching decreases surface Mn by dissolving oxidized species, which exposes fresh sulfide surfaces and increases Ag extraction; and 3) An alkaline pretreatment at high temperature exposed fresh sulfide surfaces and decreased the surface concentration of Mn. The fact that ultrasound-assisted leaching and leaching after an alkaline pretreatment allow for a higher Ag extraction (60% and 75% of total Ag, respectively, as opposed to the 25% extracted via conventional leaching), indicates that leaching is more efficient if the surface is not oxidized and if Mn is removed from the samples, either before or during leaching.