Precious Metal Enrichment Research Articles

Simultaneous utilization of copper and non-metals from waste integrated circuits for precious metal melting capture and organics thermal detoxification

Waste integrated circuits, with underlying resource attributes and environmental risks, are complex in composition. Current processes suffer from high resource inputs, excessive pollutant emissions and incomplete treatment of varied species. Therefore, a comprehensive resource recycling and safe disposal process integrated with precious metal enrichment, non-metal resource utilization, and organic detoxification was proposed. The copper and non-metals from waste ICs served as in-situ precious metal collector, slagging former and reducing agent for alternative to partial chemical inputs. Batch experiments indicated that optimized parameters enabled the recycling efficiencies of 94.3 %, 96.8 % and 98.4 % for copper, gold and silver, respectively. Meanwhile, oxide component, yielded as silicate slag, was synthesized into glass ceramics via high-temperature sintering. Furthermore, organic conversion process revealed that high-temperature smelting catalyzed bromine removal and contaminant detoxification, with decomposed reductive hydrocarbons facilitating metal capture in turn. And the capture mechanism was disclosed form thermodynamics and microdroplet motion perspectives. As process evaluation indicates, proposed recycling route allows remarkable reductions in negative environmental response and economic investment. In this work, metal recycling, waste minimization and pollutant detoxification were attained synergistically without residue, which contributes a novel insight into the disposal of comparable e-wastes.

Interfacial self-assembled of covalent organic framework onto MXenes for efficient enrichment and recovery of Au(III) and Pd(II) from aqueous solution

Recovery of precious metal ions in wastewater could not only improve resource utilization, but also could reduce environmental pollution. Herein, a composite of TpPa@Nb2C was constructed by an interfacial self-assembled method and explored the synergistic adsorption effects for precious metals. The structure and morphology of the composites were analyzed by advanced characterization techniques, followed by parametric analysis of Au(III)/Pd(II) adsorption from the simulated wastewater. The results showed that the grafting of COFs with abundant reducing active sites on the MXenes could significantly improve the selectivity and adsorption capacity. Meanwhile, the interaction was found as monolayer way and controlled by chemistry process, and the maximum equilibrium Au(III) and Pd(II) uptake reached up to 910.1 and 386.2 mg/g, respectively. The competitive adsorption study showed that the co-existence of impurities had little effect on the removal rate. The mechanism analysis demonstrated that the precious metal ions were reduced to elemental gold/palladium on the network of TpPa@Nb2C, and they got three electrons or two electrons from the hydroxyl groups through redox reaction, respectively. Thus, this study provided an excellent material for enrichment and recovery of precious metals in waste liquid and the treatment of e-waste.

A combined and sustainable approach and a novel mechanism for recovering Bi, Au and Ag from high-chloride leachate of waste printed circuit board smelting ash

High-chloride leachate is a solution rich in precious metals that is produced in chloride hydrometallurgy. It has high levels of both rare and precious metals and hazardous chloride ions, and resource recovery from this solution and its safe disposal have become key objectives in the field of hydrometallurgy. In this study, a sustainable process involving "ultrasound-assisted precipitation–Pb powder cementation" was proposed for the stepwise separation and high-value utilization of Bi, Au and Ag obtained from high-chloride leachate. Targeted separation and conversion of Bi were achieved by precipitation–re-acid hydrolysis–ultrasonication-assisted coprecipitation–centrifugal purification. Under the optimal process conditions, the removal rate of Bi reached 99.52%, while the loss rates of Au and Ag were only 4.63% and 8.72%, respectively. Single-factor experiments of Au and Ag cementation by Pb powder showed that the recovery rates of precious metals could be improved by increasing the temperature, raising the solution pH, and applying mechanical force and ultrasonication. A possible reaction mechanism for Au and Ag cementation with Pb powder was proposed based on macroscopic kinetic analysis and microscopic mineral characterization. This work provides technical support and a theoretical basis for the separation and enrichment of rare and precious metals in chloride hydrometallurgy.

Recovery of cathode copper and ternary precursors from CuS slag derived by waste lithium-ion batteries: Process analysis and evaluation

The efficient and environmentally friendly recycling technology of waste residue that including abundant heavy metal produced during the recovery of lithium batteries has become a research hotspot. Herein, a novelty process of acid leaching-selective electrodeposition-deep impurity removal-regeneration was proposed to recovery of the CuS slag, which has been efficient transferred to high purity cathode copper and commercially available ternary precursors. Copper cathode with a purity of 99.67% was prepared under electrochemical reaction conditions at −0.55 V for 2 h. A novel impurity remover-Mn powder, which was used to remove the residual impurities and as a feedstock for the ternary precursor. Finally, NCM523 was regenerated by co-precipitation. The process is superior to the traditional process in economy, energy consumption, CO2 emissions, product purity and process duration. This study provides a new approach for solid waste recovery and precious metal enrichment.

Adsorption and reduction behavior and mechanism of Au(III) on reductive cellulose-based aerogel

A reductive cellulose-based aerogel (VTCA) was fabricated from cellulose by introducing valonea tannin through cross-linking reaction. VTCA owned high porosity of more than 96% with the average pore size of 30–50 µm, and it exhibited good adsorption performance for Au(III) at a wide pH values range (1−8) with the max adsorption capacity of 243.1 mg g−1. VTCA showed good adsorption performance for Au(III) under the interference of various co-existing ions. The adsorption obeyed the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model, and temperature rise was favorable for adsorption. The adsorption-reduction mechanisms mainly involved electrostatic interaction, chelation adsorption and reduction. Au(III) could be effectively adsorbed onto the surface of VTCA by electrostatic attraction and chelation, and then reduced in situ to Au0 by phenolic hydroxyl on tannic structure. This study provides a new adsorbent with the advantages of convenient preparation and high efficiency, and it has great application prospects in the enrichment and recovery of precious metals in waste liquid and the treatment of oxidized pollutants.

Textural characteristics of ore mineral dendrites in banded quartz veins from low-sulfidation epithermal deposits: implications for the formation of bonanza-type precious metal enrichment

Textural characteristics of ore mineral dendrites in banded quartz veins from low-sulfidation epithermal deposits: implications for the formation of bonanza-type precious metal enrichment

Volcanogenic massive sulfide (VMS) deposits of the Dunnage Zone of the Newfoundland Appalachians: setting, styles, key advances, and future research

The Dunnage Zone of the Newfoundland Appalachians hosts diverse Cambrian–Ordovician volcanogenic massive sulfide (VMS) deposits. The peri-Laurentian Notre Dame Subzone contains Cu–Zn–Au mafic and bimodal mafic deposits in ∼501–485 Ma ophiolitic rocks and Zn–Pb–Cu–(Au–Ag) deposits in ∼471–465 Ma bimodal rifted continental arc sequences (e.g., Buchans). The peri-Gondwanan rocks of the Exploits Subzone host Zn–Pb–Cu–(Au–Ag) bimodal felsic, felsic siliciclastic, and Zn–Ag–Au hybrid bimodal felsic deposits in the ∼513–486 Ma Victoria Lake supergroup; Cu–Zn bimodal felsic to bimodal mafic deposits of the ∼486 Ma Wild Bight Group; and Cu–(Au) mafic siliciclastic deposits of the ∼466 Ma Great Burnt Lake/South Pond belt. Regardless of age or stratigraphic hosts, all VMS deposits are associated with specific magmatic assemblages and extensional tectonism (i.e., rifting). Gold-enriched deposits of the Rambler-Ming district are associated with felsic rocks that formed via slab melting and subsequent melt-mantle wedge interaction, which likely enhanced precious metal enrichment in these deposits. Whereas many deposits exhaled on the seafloor, some deposits formed via subseafloor replacement of host units or as re-sedimented sulfides generated in sediment-gravity flows. Metals in the deposits were derived from leaching of underlying footwall rocks; however, Au–Ag- and epithermal suite element-enriched deposits show evidence for metal contributions from magmatic hydrothermal fluids. Sulfur in deposits was derived predominantly from leaching of H2S from underlying footwall rocks and from thermochemical sulfate reduction of seawater sulfate, with lesser input from bacteria-derived H2S and magmatic-hydrothermal-derived H2S. Despite recent research advances and historic mining, numerous questions remain unresolved and provide opportunities for future study.

Enrichment of precious metals associated with chalcopyrite inclusions in sphalerite and pyrite

Abstract The results of investigations into enrichment of precious metals in sphalerite and pyrite from the Maluntou epithermal gold deposit, China, are reported. The obtained data suggest intimate associations of Au- and Ag-bearing nanoparticles with chalcopyrite inclusions in sphalerite and pyrite. The origins of chalcopyrite inclusions involved different hydrothermal processes, including recrystallization-driven phase separation from parent chalcopyrite-sphalerite solid solutions and replacement of pre-existing pyrite in the presence of Cu-bearing fluids. The chalcopyrite blebs/lamellae follow sphalerite {111} planes, which define a shared sulfur layer for both chalcopyrite and sphalerite. This study indicates that mixing and boiling during the evolution of ore-forming fluids for the Maluntou deposit are key processes for the abnormal enrichment of precious metals in sphalerite and pyrite. The chalcopyrite micro/nano inclusions enhanced enrichment of precious metals in sphalerite provides new insights into the controls on the enrichment of precious metals in sulfides.

Leaching Behavior of the Main Metals from Copper Anode Slime during the Pretreatment Stage of the Kaldor Furnace Smelting Process

The Kaldor furnace smelting process is currently the mainstream process for treating copper anode slime, but the existence of copper, tellurium and other impurities has adverse effects on the recovery of gold and silver during the Kaldor furnace smelting stage. Therefore, it is necessary to pretreat the copper anode slime to remove these impurities before Kaldor furnace reduction smelting. However, the current pretreatment process of copper anode slime generally has the problem of low removal efficiency of copper and tellurium, and little research on the occurrence state of main metals in copper anode slime. Therefore, this study quantitatively determined the phase composition of Cu, Te, Pb, Bi, As, Sb, Se, Ag and Au, and hydrogen peroxide was introduced to enhance the leaching of impurities. The leaching behavior of each metal in copper anode slime was investigated in detail. The results demonstrate that Cu and Te in the copper anode slime mainly exist in the form of CuO and CuSO4 and Te and AuTe2, respectively. More than 99% of the Cu and 97% of the Te were leached out using 250 g/L H2SO4 and 28.8 g/L H2O2 with a leaching pressure of 0.8 MPa at 150 °C for 2 h, while the leaching of Au and Ag was both < 0.03%. The removal of Cu and Te and the enrichment of precious metals were achieved. This study provides a rich theoretical reference for the optimization of the Kaldor furnace process.

Selective separation of base metals and high-efficiency enrichment of precious metals from scrap copper anode slime

In this study, a clean and effective integrated process for selectively separating base metals and high-efficiency enriching precious metals from scrap copper anode slime was investigated. O2-enriched roasting combined with H2SO4-NaCl leaching was used in the decopperized process to avoid the scattered distributions of As & Sn and enhance the selective leaching efficiencies of Cu, Ni, and As. The obtained leachate containing Cu, Ni, and As can be sent to the existing electrolyte purification process. Then, alkaline xylitol leaching was applied to selectively separate Pb greatly avoiding its negative impact on the subsequent process, and Pb-containing leaching solution was used to prepare lead electrodeposition electrolyte. Sn was recovered in the form of sodium stannate by soda roasting-alkaline leaching. Results of scale-up experiment showed that the direct leaching efficiencies of Cu, Ni, As, Pb, and Sn under the optimum conditions were 99.3 %, 96.9 %, 98.6 %, 98.1 %, and 98.9 %, respectively. Ag and Au were maximally remained in the residue. Furthermore, three leaching solutions generated in the proposed process can be treated in an environmentally friendly way. Therefore, it was a high-efficiency and eco-friendly method for SCAS to realize the comprehensive utilization of the base metals and reduced risks of secondary pollution.

Selective Separation of Base Metals and High-Efficiency Enrichment of Precious Metals from Scrap Copper Anode Slime

Selective Separation of Base Metals and High-Efficiency Enrichment of Precious Metals from Scrap Copper Anode Slime

Effect of pyro-processing conditions on impurity removal and precious metal enrichment in waste printed circuit board (WPCB) recycling process

The combinatorial effects of slag composition and O2-blowing conditions on silicon (Si) and iron (Fe) removal as well as gold (Au) and silver (Ag) enrichment from waste printed circuit boards (WPCBs) were investigated to optimize pyrometallurgical WPCBs recycling process. Regardless of the experimental conditions, the removal rate for Si and Fe was approximately 100%, except in slag-free operation. The Si removal rate was generally higher than the Fe removal rate at a given reaction time irrespective of experimental variables because the O2 affinity of Si is higher than that of Fe in molten copper, thermodynamically. The removal rate of impurities was clearly dependent on blowing conditions and slag composition, and a combinatorial operation of bottom-blowing and highly fluid slag favored the efficient removal of impurities. The maximum enrichment ratio of Au and Ag (CAu,AgMax) was about 10% and the possession rates of Au and Ag, RAu,Ag at CAu,AgMax were greater than 96%. The loss of Au and Ag can be minimized, i.e., RAu,Ag can be maximized by stopping O2-blowing before metal droplets are physically entrapped by molten slag, because metal droplet's entrainment is affected by slag viscosity, which contributes to the settling velocity of metal droplets. Consequently, it is very critical to appropriately control not only the slag composition but also O2-blowing conditions for both impurities removal and maximizing precious metals enrichment and possession.

Investigation of the evaporation kinetics of a lead-silver alloy and elementary substances under vacuum

A novel method for statistically analyzing the evaporation rate of metals is introduced. The variation in the masses of elemental metals and a lead-silver alloy over time is measured by a vacuum thermogravimetric furnace, and the evaporation rates of the metals are obtained through mathematical statistical analysis at temperatures of 1073–1573 K and ambient pressures of 3.5–500 Pa. The experimental results indicate that the logarithm of the evaporation rates of a lead-silver alloy and sample substance are linearly related to the reciprocal of the temperature at the 95% confidence level, which satisfies the dependent linear equation lgω=−CT+ω0. The evaporation rates of lead and silver at environmental pressure conform to the reciprocal of the exponential model, ω=A*exp−PB+ω0'. At an ambient pressure of 10 Pa and temperatures of 1073–1573 K, the evaporation rates of the lead-silver alloy with 10% silver and the sample substance approximately satisfy the following relationship: lgωPb-Ag=95.92%lgωPb+19.01%lgωAg. This work has obtained the basic evaporation kinetic parameters of the lead-silver system components, which provides basic theoretical guidance for the gasification and separation of a noble lead alloy to achieve the removal of impurity lead and enrichment of precious metals.

An integrated and sustainable hydrometallurgical process for enrichment of precious metals and selective separation of copper, zinc, and lead from a roasted sand

The developed hydrometallurgical process for recovering copper, zinc, and lead from the roasted sand of WPCB-SA. • A hydrometallurgical process for recovering valuable elements was proposed. • Copper and zinc were selectively recovered by water leaching. • Lead was efficiently recovered by high-chloride leaching. • The leaching kinetics and conversion mechanism of lead were analyzed. • Gold and silver have been successfully enriched in the leached residue. This study developed an efficient and sustainable hydrometallurgical process for the enrichment of gold and silver and the stepwise separation of copper, zinc, and lead from sulfated roasted sand of waste printed circuit board smelting ash. Selective separation of copper and zinc was achieved by water leaching, and silver dispersion was reduced by controlling the amount of NaCl added during the leaching process. The results of the water leaching showed that the copper and zinc leaching rates were 99.85% and 99.47%, respectively, whereas the loss rate of silver was 2.1% with optimal leaching parameters. The high-chloride-complex method was used to study the efficient conversion and separation of lead from the leached residue, and the leaching kinetics and conversion mechanism of lead were discussed. The results showed that under the optimal conditions, the leaching rate of lead was 99.79%. Leaching kinetics analysis showed that lead leaching in the high - chlorine system was controlled by a chemical reaction; the apparent activation energy was 53.63 kJ/mol. After the leaching of copper, zinc, and lead, 1.66% Ag and 213 g/t Au were enriched in the leached residue; and the precious metal enrichment goal was reached. The chlorinated leachate showed good recycling performance, and a lead leaching rate of 97.93% was obtained after three circulations. After cooling, crystallization, and purification, lead chloride with a purity of 99.89% and high economic and industrial value was obtained from the lead-rich leachate. This process has favorable and sustainable industrial application prospects.

Gold-and silver-bearing assemblages in the Ann-Mason copper porphyry deposit, Yerington, Nevada

Porphyry deposits are an important source of copper and their value may be upgraded by minor contents of precious metals, if they are extractable. The mechanisms for enrichment of precious and base metals in these systems are not well understood. This study investigates the deportment of trace metals in the Ann-Mason porphyry deposit, including gold, silver, palladium, mercury, lead and bismuth. Petrographic and geochemical data are integrated to characterise the size and habit of minerals, the host mineral assemblages, and their association with alteration assemblages. Ann-Mason is one of several ore deposits hosted by the Yerington batholith in Nevada, and is being assessed for copper extraction from bornite and chalcopyrite ore assemblages, associated with potassic alteration. Mineralisation assemblages at Ann-Mason have been categorised as chalcopyrite-bornite, chalcopyrite-pyrite and pyrite > chalcopyrite zones. Limited two-metre assay data indicates that gold is most closely associated with bornite, although it is found in all three mineralisation zones. Analysis by SEM-EDS shows that trace elements are mostly present as microparticles hosted by sulfide minerals. Of the 438 grains measured, 89% are hosted by a sulfide mineral, with 68% hosted by bornite. Silver is most commonly present as hessite and gold as electrum, hosted by bornite and associated with potassic alteration. Palladium, mercury and bismuth are most commonly observed as telluride and selenide minerals. Palladium minerals are associated with potassic alteration, while mercury and bismuth minerals are mostly found with sericitic alteration. High fineness native gold is observed as three round blebs hosted by pyrite or silicates. Observations suggest that the trace metals in the chalcopyrite-bornite zone may have been incorporated by bornite and chalcopyrite, and exsolved upon cooling. In the chalcopyrite-pyrite and pyrite > chalcopyrite zones, the trace metals may have been deposited directly from a mineralising hydrothermal fluid and incorporated into the growing sulphide minerals. These findings have implications for the paragenesis of porphyry deposits, as well as for the milling processes that would be needed to extract precious metals at the Ann-Mason porphyry deposit.

Variant Offset-Type Platinum Group Element Reef Mineralization in Basal Olivine Cumulates of the Kapalagulu Intrusion, Western Tanzania

Abstract The Kapalagulu intrusion in eastern Tanzania hosts a major, 420-m-thick, stratiform/stratabound platinum group element (PGE)-bearing sulfide zone—the Lubalisi reef—within a prominent, chromititiferous, harzburgite unit close to its stratigraphic base. Several features of the vertical base and precious metal distributions (in a composite stratigraphic section based upon two deep exploration drill holes) display similarities to those of offset-type PGE reefs that formed under the overall control of Rayleigh fractionation: (1) composite layering (at several scales) defined by systematic vertical variations of sulfide and precious metal contents and intermetallic ratios, indicating repeated cycles of PGE enrichment and depletion in the order Pd-Pt-Au-Cu, and (2) in the lower part of the reef, stratigraphic offsets of the precious metal peaks below peak sulfide (Cu) content. The form and geochemistry of the reef are consistent with overturns of basal liquid layers within a liquid layering system (i.e., stable density-driven stratification of a magma chamber), plus at least two minor inputs of parental magma during which the resident magma was recharged with sulfur and metals, and the effective depletion of precious metals in the magma midway through reef development. The Lubalisi reef differs from classic offset-type PGE reefs, however, principally because individual Pd, Pt, and Au enrichment peaks are coincident, not offset. The reef is set apart from other offset-type PGE reefs in three additional ways: (1) its association with olivine cumulates that crystallized soon after initial magma emplacement and well below the first appearance of cumulus pyroxene or plagioclase (implying attainment of sulfide saturation and precious metal enrichment without prolonged concentration of sulfur and chalcophile metals by normal magma cooling and differentiation), (2) the probable role of chromite crystallization in not only triggering sulfide segregation during reef formation but also facilitating precious metal enrichment in the early stages of reef development, and (3) its great width. The early stage of fractionation may also help explain the coincident precious metal peaks through its effect on apparent precious metal partition coefficients.

Super-enrichment mechanisms of precious metals by low-melting point copper-philic element (LMCE) melts

低熔点亲铜元素（LMCE）As、Sb、Bi、Hg、Pb、Se、Te、Tl、Sn等，均具有亲铜性、低熔点、半金属的特性，在成矿过程中可以形成LMCE熔体，并对Au、Ag、PGE等贵金属的高效富集沉淀起到一种重要的桥梁作用。作者对前人研究资料与LMCE热力学相图进行了分析，并结合浅成低温热液型、造山型、卡林-类卡林型、碱性-偏碱性侵入岩型金矿床的研究成果，探讨了LMCE熔体形成、类型及其对Au、Ag、PGE等贵金属富集成矿的机理，并提出了LMCE熔体参与成矿的矿物组合与结构特征标志。LMCE熔体可以在岩浆过程、（岩浆）热液过程及变质过程中形成，是贵金属矿床重要的成矿机制之一。LMCE熔体中存在大量原子团簇，团簇间的聚集生长会使熔体难以达到相平衡，形成许多非平衡矿物组合，如包含LMCE的自然元素、金属互化物及含LMCE的多相矿物。Au在LMCE熔体中也可以团簇存在，金团簇聚集形成球状或片状，并形成巨富的金矿体。LMCE熔体形成的矿物常以浑圆状、近浑圆状、不规则状的单个或群体组合的乳滴、珠滴、气泡的微粒包体产在硫化物、硒化物、碲化物、氧化物和硅酸盐矿物内或沿矿物裂隙线形排列，这些LMCE微粒包体是熔体扰动导致熔-熔或熔-液间发生乳化所致，流体沸腾是引起熔体扰动的主要机制。LMCE熔体不能快速淬火结晶，通常在低温下缓慢冷却达到相平衡，形成复杂的矿物组合，该特点即使在微米到纳米级的矿物微粒中也显著存在。熔体-流体包裹体是LMCE熔体参与成矿作用最为直接的证据。固溶体分解结构、熔体退火结构、矿物-熔体二面角结构、溶解-再沉淀结构等也是LMCE熔体参与成矿的标志性结构。;The low-melting point chalcophile elements (LMCE), including As, Sb, Bi, Hg, Pb, Se, Te, Tl, Sn and so on, have characteristics of chalcophile behavior, low melting point and semi-metallic properties, which can form LMCE melt during mineralization process and play an important role for the efficient enrichment and precipitation of Au, Ag, PGE and other precious metals. In this paper, the previous research data and the LMCE thermodynamic phase diagrams were analyzed. Combining research results of epithermal, orogenic, Carlin to Carlin-like and alkaline to meta-alkaline intrusion-related gold deposits, the authors discussed the formation and type of LMCE melts and their mechanisms for the enrichment of Au, Ag, PGE and other precious metals, and summarized mineral compositions and characteristic textures of mineralization that benefited by LMCE melts. The LMCE melts can be formed during magmatic, (magmatic-) hydrothermal and metamorphic processes, and belong to one of the important metallogenic mechanisms for precious metal deposits. There are many ion clusters in the LMCE melts, and aggregation between the clusters precludes the melt to reach phase equilibrium, which results in many non-equilibrium mineral combinations, including the coexistence of native LMCE, intermetallic compounds and multiphase minerals containing LMCE. Gold could also exist as ion clusters in the LMCE melt that gather to form spherical or flakes native gold, and form the super-rich ore bodies. The minerals formed by LMCE melt often exist as single or group combinations of emulsion droplets, beads, and bubbles in round, nearly round, and irregular particle inclusions in sulfides, selenides, tellurides, oxides and silicates, or distribute along fractures of minerals. These LMCE micro-inclusions are derived from melt disturbance that result in melt-melt or melt-liquid emulsification. Fluid boiling should be the main mechanism that causes the melt disturbance since the LMCE melt cannot be quenched and crystallized quickly at this process. It is usually cooled slowly at low temperature to achieve phase equilibrium and form complex mineral compositions. This feature is significant even in micro-to nano-scale mineral particles. Melt-fluid inclusions are the most direct evidence for the involvement of LMCE melts during mineralization. Solid solution decomposition texture, melt annealing texture, mineral-melt dihedral texture, dissolution-reprecipitation texture are also characteristic textures of LMCE melts involved in mineralization.

Textural Characteristics of Barren and Mineralized Colloform Quartz Bands at the Low-Sulfidation Epithermal Deposits of the Omu Camp in Hokkaido, Japan: Implications for Processes Resulting in Bonanza-Grade Precious Metal Enrichment

Abstract The Miocene low-sulfidation epithermal deposits of the Omu camp in northeastern Hokkaido, Japan, are small past-producers of precious metals and represent significant exploration targets for high-grade Au and Ag ores. The quartz textures of ore samples and the distribution of ore minerals within quartz veins were studied to identify the processes that resulted in the bonanza-grade precious metal enrichment in these deposits. In the high-grade vein samples, which are crustiform or brecciated in hand specimen, ore minerals exclusively occur within colloform quartz bands. High-magnification microscopy reveals that ore-bearing colloform bands consist of fine-grained quartz exhibiting relic microsphere textures and quartz having a mosaic texture that formed through recrystallization of the microspheres. The presence of relic microspheres is evidence that the microcrystalline quartz hosting the ore minerals formed through recrystallization of a noncrystalline silica precursor phase. The ore-hosting colloform bands composed of agglomerated microspheres alternate with barren colloform quartz bands that are composed of fibrous chalcedonic quartz and mosaic quartz formed through recrystallization of the chalcedony. The findings of this study are consistent with previous models linking bonanza-grade precious metal enrichment and the formation of bands of noncrystalline silica in low-sulfidation epithermal veins to episodic vigorous boiling or flashing of the hydrothermal system in the near-surface environment.

2-Mercaptobenzimidazole derivative of chitosan for silver sorption – Contribution of magnetite incorporation and sonication effects on enhanced metal recovery

The recycling of precious and strategic metals from secondary resources (including E-wastes) is of critical importance for the recovery of scarce metals widely used in High-Tech devices. Therefore, the development of efficient and selective sorbents is of great importance. The grafting of 2-mercaptobenzimidazole onto chitosan microparticles allows developing highly selective sorbents. The incorporation of magnetite particles is also a strategic aspect for facilitating the use and recovery of microparticles. Sonication (at two different frequencies: 37 kHz and 80 kHz) shows high potential for improving both kinetic and thermodynamic aspects associated with silver uptake on 2-MBI-chitosan materials. Sorption capacities as high as 3 mmol Ag g−1 can be obtained with contact times as low as 20–30 min. The sorption isotherms are successfully fitted by the Langmuir and the Sips equations, while the kinetic profiles are modeled using the pseudo-second order rate equation and the resistance to intraparticle diffusion. The sorption process is exothermic: the sonication (and the frequency of sonic generator) strongly changes the thermodynamic parameters. The sonication also speeds up metal desorption, which is highly efficient using acidic thiourea solutions: the sonication allows also reducing the concentration of thiourea in the eluent required for complete silver elution. The sorbent shows remarkable stability is terms or sorption and desorption for five successive recycling runs. The acid leachates of printed circuit board are efficiently treated with the 2-MBI-chitosan sorbent for the recovery, enrichment and separation of precious metals (Ag, Au and Pd) from base metals (major elements: iron copper, aluminum, tin).

A Middle Devonian basin-scale precious metal enrichment event across northern Yukon (Canada)

AbstractHyper-enriched black shale (HEBS) Ni-Mo-Zn-Pt-Pd-Au-Re mineralization is geographically widespread across the Richardson trough in northern Yukon (Canada), where it discontinuously outcrops at the regional contact between the Road River Group and overlying Canol Formation. Stratigraphic relationships indicate that the contact is Middle Devonian, but there are no precise age constraints for the HEBS. We apply Re-Os geochronology to HEBS mineralization from two localities that are 130 km apart, the Nick prospect and the Peel River showing, to date directly the age of sulfide mineralization. The Nick prospect yields an isochron age of 390.7 ± 5.1 (2σ) Ma, whereas the Peel River showing yields an isochron age of 387.5 ± 4.4 (2σ) Ma. Within error, these ages are identical and overlap with the biostratigraphically constrained age of the sedimentary host rocks, indicating that mineralization and sedimentation were coeval. Significantly, the ages of the HEBS overlap those of Middle Devonian Kačák, pumilio, and Taghanic global-scale biotic events which are characterized by eustatic sea-level rise and black shale deposition. Linkage of the Yukon HEBS to one (or more) of these bio-events indicates that sea-level rise may have been requisite to formation of basin-scale HEBS mineralization in northwestern Canada during latest Eifelian and Givetian time.