Gold Content Research Articles

Insight into Limited Recoveries in Printed Circuit Board Leaching: Evidence of Gold Adsorption Loss to Polymeric Particles

AbstractSustainable resource utilization ultimately depends on total recovery during recycling operations. PCB leach pulp for target metal recovery contains ceramic and polymeric particles resistant to reagent attack. The investigation herein shows the physicochemical behavior of five polymeric particles namely green, red, black, white, and blue in gold chloride complex [AuCl4]− solution. Gold concentration change was monitored over time to study how the gold solution interacted with the polymeric particles and how the interaction conforms to known adsorption isotherm and kinetic models. The black and green polymeric particles have the highest adsorption per unit mass to about 1.81 mg/g and 2.18 mg/g, respectively. Four adsorption kinetic models evaluated for insight on the adsorption mechanism observed show Elovich and pseudo-second-order (PSO) models fit the kinetic data best compared to other models with correlation coefficients of 0.9867 and 0.9863, respectively. Of the seven adsorption isotherm models evaluated, Sips model shows best fit for the isotherm data with correlation coefficients of 0.9727 and 0.9328 for green and black particles, respectively. Isotherm and kinetic model analyses of the experimental data indicated physisorption and chemisorption as driving mechanism of the interaction between PCB polymeric particles and gold chloride complex aliquot. Graphical Abstract

Gold nanoparticles for photothermal therapy – Influence of experimental conditions on the properties of resulting AuNPs

Gold nanoparticles (AuNPs)-mediated Photothermal Therapy (PTT) is a minimally-invasive therapeutic approach that uses AuNPs to convert light into heat, leading to the thermal ablation of tumors. Thus, the efficacy of this strategy strongly relies on the photothermal conversion potential of AuNPs. The ability to convert light into heat can be enhanced by tuning the physicochemical and optical properties of AuNPs. This can be achieved by changing the conditions of AuNP's synthesis, such as the order of addition of reagents. The present work entails to explore how varying the order of reagents addition modulates the properties of AuNPs, particularly enhancing the photothermal conversion potential of the resulting AuNPs and consequently, improving PTT efficacy. For this, eleven different AuNPs' nanoformulations were synthetized following different sequences of addition of reagents. These nanoformulations were characterized regarding their physicochemical properties namely size, surface charge, gold concentration, surface morphology and maximum absorbance wavelength. In addition, their thermal activation profiles were determined in vitro. Furthermore, the biocompatibility of different nanoformulations was also assessed. Three nanoformulations, with the most favorable photothermal activation profiles (AuNPs 2, 3 and 7), were then selected for preliminary in vitro safety and efficacy assays using a panel of cell lines. These three nanoformulations were deemed safe in vitro at the tested concentrations. At 250 μM of gold content, and after an incubation period of 4 h, followed by 5 min irradiation with a laser emitting at 808 nm (7.96 W/cm2), AuNPs 7 significantly reduced the cell viability of all cancer cell lines tested (MCF-7, HCT-116 and A375) by ≥ 45 %. However, such cytotoxic effect was not observed for the human keratinocyte cell line (HaCat), thus demonstrating its specificity towards cancer cells. Overall, the results herein presented reinforce that the order of reagents addition is highly important for achieving adequate AuNPs for PTT.

Quercetin-mediated green synthesis of Au/TiO2 nanocomposites for the photocatalytic degradation of antibiotic ciprofloxacin

Contaminated water is one of the world’s largest health and environmental problem. Emerging pollutants, such as pharmaceutics, are raising increasing concerns, as they are non-regulated toxic chemicals found in low concentrations that are very resilient to conventional water treatments. In the search for effective methods to address this problem, photocatalysis arises as a possible solution to degrade organic pollutants. TiO2 is one of the most widely used catalysts, but the reduced photoactivation under visible radiation constitutes a major drawback. The inclusion of plasmonic nanoparticles, such as gold (AuNPs), can improve the ability to absorb visible radiation from sunlight. AuNPs synthesis methods include toxic and expensive reagents. Herein, an alternative method is proposed, using the flavonoid quercetin to act as the reducing agent in the deposition of AuNPs on the surface of TiO2 (Au/TiO2). The method is optimised, and different loadings of gold are tested. The characterisation of Au/TiO2 confirms increased absorption in the visible wavelength range with increasing concentrations of gold as well as a reduction in the energy band gap. The photocatalytic efficiency of Au/TiO2 was evaluated for the degradation of the antibiotic ciprofloxacin under UV and simulated sunlight irradiation, obtaining a maximum degradation of 86 and 95%, respectively.

Concentration of gold during the uncovering of titanium-bearing placers of Sikhote-Alin with a mixture of hydrodifluoride and ammonium sulfate

Concentration of gold during the uncovering of titanium-bearing placers of Sikhote-Alin with a mixture of hydrodifluoride and ammonium sulfate

Auranofin is lethal against feline Tritrichomonas foetus in vitro but ineffective in cats with naturally occurring infection

Protozoal diarrhea caused by Tritrichomonas foetus (blagburni) is a prevalent, lifelong, and globally distributed burden in domestic cats. Treatment is limited to the use of 5-nitroimidazoles and treatment failure is common. The repurposed gold salt compound auranofin has killing activity against diverse protozoa in vitro but evidence of efficacy in naturally occurring protozoal infections is lacking. This exploratory study investigated the efficacy and safety of auranofin for treatment of cats with naturally occurring, 5-nitroimidazole-resistant, T. foetus infection. The minimum lethal concentration (MLC) of auranofin against 5 isolates of feline T. foetus was determined under aerobic conditions in vitro. Healthy cats and cats with T. foetus infection were treated with immediate release auranofin (range, 0.5–3 mg/cat for 7 days) or guar gum-coated auranofin capsules (0.5 or 3 mg/cat for 7 days). Adverse effects were monitored by clinical signs and clinicopathologic testing. Efficacy was determined by fecal consistency score, bowel movement frequency, and single-tube nested PCR of feces for T. foetus rDNA. Fecal samples were assayed for concentrations of auranofin, known and predicted metabolites of auranofin, gold containing molecules, and total gold content using HPLC, LC-MS, ion mobility-MS, and ICP-MS, respectively. Auranofin was effective at killing isolates of feline T. foetus at MLC ≥ 1 μg/ml. Treatment of cats with T. foetus infection with either immediate release auranofin or a colon-targeted guar gum-coated tablet of auranofin did not eradicate infection. Treatment failure occurred despite fecal concentrations of gold that met or exceeded the equivalent MLC of auranofin. Neither auranofin, known or predicted metabolites of auranofin, nor any gold-containing molecules >100 Da could be detected in fecal samples of treated cats. Adverse effects associated with auranofin treatment were common but minor. These studies identify that in vitro susceptibility test results of auranofin may not translate to treatment effectiveness in vivo even when achieving gold concentrations equivalent to the MLC of auranofin in the target environment. These studies further establish the absence of any predicted or unpredicted gold containing metabolites in feces after oral administration of auranofin.

Application of magnetic data and satellite spectral imaging in identifying gold mineralization zones and its associated subsurface structures at Fawakheir-Attala area, Central Eastern Desert, Egypt

The Fawakheir-Attala gold mining zone in Egypt’s Central Eastern Desert features a diverse range of rock formations, including Precambrian crystalline rocks and Phanerozoic sedimentary formations. These formations encompass gneisses, metavolcanics, metasediments, a metagabbro-diorite complex, Dokhan volcanic rocks, and granitic rocks, alongside lower and upper Nubia sandstones. Faults and shear zones are pivotal in controlling gold mineralization within the area, indicative of substantial mineral wealth. This study aimed to map subsurface structural characteristics and investigate gold mineralization zones using aerial magnetic data and ASTER remote sensing, the latter of which played a crucial role in highlighting the surface exposure of alteration zones. Geological surveys combined with remote sensing techniques were employed to identify rock types and mineralization zones, while magnetic methods, including aeromagnetic surveys and ground-based studies, were used to reveal underlying structural properties and fault systems. Analysis of aeromagnetic data revealed a large mineralization zone running from the Fawakhir Gold mine through the Attala Gold mine in a NW–SE direction. Various structural trends and faults, including NW–SE, NE–SW, E–W, and N–S directions, were identified, strongly associated with hydrothermal alteration zones and gold mineralization. Shallow basement relief was observed in the eastern and central regions, contrasting with deeper formations and greater relief in the western section. Land magnetic surveys were utilized to identify new areas for gold mineralization, with geochemical analysis confirming gold content in quartz veins and host rocks. The integration of magnetic and remote sensing techniques effectively highlighted alteration zones indicative of potential mineralization, which could have a subsurface continuation, aiding in the identification of gold occurrences connected to faults, lineaments, and mineralization zones.

LA-ICP-MS Analyses of Sulfides from Gold-Bearing Zones at the Perron Deposit, Abitibi Belt, Canada: Implications for Gold Remobilization through Metamorphism from Volcanogenic Mineralizations to Orogenic Quartz–Carbonate Veins

The Perron deposit, located in the northern part of the Archean Abitibi belt, bears some of the highest gold-grade mineralization for orogenic-vein-type deposits worldwide (High-Grade Zone: HGZ). More than 13 gold-bearing zones with different sulfide assemblages, hydrothermal alterations, and gold grades have been recently outlined, and they range from volcanogenic to orogenic in origin. In addition, seven zones are hosted in a restricted volume of ~1 km3, which is called the Eastern Gold Zone. Pyrite, sphalerite, pyrrhotite, and chalcopyrite—each from a different gold-bearing zone—were analyzed with LA-ICP-MS to decipher their genetic links, mineralizing processes, and temperature of formation. The temperatures calculated with the sphalerite GGIMFis thermometer range from 348 to 398 °C. All gold-bearing zones recorded volcanogenic hydrothermal inputs at different intensities, manifested by pyrrhotite. Pyrite was late-metamorphic and related to the orogenic gold system induced by the contact metamorphism of amphibolite facies. The pyrrhotite grains had very homogeneous trace element signatures in all zones, which is a characteristic of metamorphic recrystallization, exhibiting a loss of mobile elements (Au, Te, Bi, Tl, Sn, W, In) but high concentrations of Ni, Co, and As. Conversely, the pyrite was systematically enriched with all elements depleted from pyrrhotite, bearing five specific signatures of element enrichments: W, Tl, Sn, In-Cd-Zn, and Bi-Te-Au. For gold-rich zones (e.g., the HGZ), gold was linked to the Bi-Te-Au signature of pyrite, with Bi enrichment occurring at up to 72,000 times the background level in Archean shale pyrite. It was concluded that gold was transported, at least in part, as Bi-Te melts in the previously documented non-aqueous orogenic fluids, hence accounting for the very-high-grade gold content of the HGZ. Genetically, the metamorphism of primary gold-bearing volcanogenic mineralizations was the main source of gold during the overprinting of amphibolite (600 °C) in a metamorphically induced orogenic mineralizing event. A strong volcanogenic pre-enrichment is considered the main factor accounting for the gold endowment of the Eastern Gold Zone.

Carbonatization and silicification of ophiolitic ultramafic rocks and formation of gold-bearing listvenites in the Arabian-Nubian shield: A case study from the Al-Barramiya district

Late Neoproterozoic mantle section in the Gabal Al-Barramiya area, the northwestern corner of the Arabian-Nubian Shield (ANS), contains variably serpentinized peridotites that are highly altered along shear zones and thrust planes to form gold-bearing listvenites. They can be categorized into carbonate listvenite, silica-carbonate listvenite and silica listvenite (birbirite). Carbonate listvenite is characterized by the presence of schistosity and deformation fabrics similar to the host serpentinites, but such fabrics are absent in the silica-carbonate and silica listvenites, suggesting that they postdate carbonate listvenite and serpentinization. The presence of listvenites along shears zones and the presence of relics of serpentine and Cr-spinel reflects their formation through metasomatism of ultramafic rocks by hydrothermal fluids circulating along the thrust faults. Silica-carbonate listvenite is characterized by the presence of fuchsite and is enriched in Zn, Pb, Cu, Ag, and Au. Rare earth element (REE) contents differ between the studied listvenites. Silica -carbonate listvenite has the lowest total REE (∑₌0.98–2.56 ppm), whereas the silica listvenite contains the highest total of REE (∑ ₌ 15.70–21.42 ppm). Based on the above, carbonate listvenite is the earliest to form by the infiltration of CO2–bearing fluids released during serpentinization of the original fore-arc peridotite slab, followed by formation of silica-carbonate listvenite due to the activities of SiO2–saturation and CO2-bearing fluids released during ophiolite obduction. Fuchsite in silica-carbonate listvenite formed as a result of metasomatic reactions of Si- and K-rich fluids with Cr-spinel due to hydrothermal alteration of serpentinized peridotite. Silica listvenite formed at the final stage by the silicification of the early formed silica-carbonate listvenite. Listvenitization of the mantle section of the Al-Barramiya ophiolite led to concentration of Au, Pb, Zn, Cu and Ag. The silica-carbonate listvenite contains higher concentration of gold (899–2199 ppb) than the carbonate listvenite (119–191 ppb) and silica listvenite (156–233 ppb).

The gold content of mafic to felsic potassic magmas

Many epithermal gold and gold-rich porphyry-type ore deposits are associated with potassic magmas. Hence, potassic magmas are commonly assumed to have been unusually Au-rich or to have contained high Au/Cu ratios. However, these hypotheses remain poorly tested. Here, we report Au concentrations and Au/Cu ratios in silicate melt inclusions analyzed in potassic rocks worldwide. The results suggest that mafic potassic magmas generally contain only 2‒7 ng/g Au, despite common sulfide exhaustion during partial mantle melting. Both the absolute Au concentrations and Au/Cu ratios are comparable to those of mafic calc-alkaline magmas, and they vary little during subsequent magma differentiation because magmatic sulfide precipitation is strongly dominated by monosulfide solid solution that is relatively poor in Au and Cu. We thus suggest that the close association of Au-rich deposits with potassic magmas is not due to Au enrichment in the magma, but rather due to selective Au precipitation at the hydrothermal stage.

Gold concentration during polyphase deformation: Insights from Boulanger Project, French Guiana

The Boulanger gold deposit is hosted within the Rhyacian greenstone belts from the Guiana shield located within the North Guiana Through, French Guiana. The Boulanger deposit is characterized by a complex polyphase deformation and mineralization history involving a coaxial shortening phase, D1, followed by a transcurrent deformation event, D2. The main ore bodies consist of a series of quartz-tourmaline-pyrite-carbonate extension and shear veins in response to NNE-SSW shortening event (D1), and adjacent altered host-rocks. The proximal alteration bordering the vein system is characterized by pyrite-tourmaline (main ore assemblage). This shortening event is followed by transcurrent deformation, D2. Locally, D2 is expressed by the formation of N020-030 narrow zones (F2 axial trace) along which D1 structures are reoriented. The structural analysis performed on both S1/0 foliation and on geophysical data interpretation highlights the presence of Type-1 interference patterns. These zones are associated with significant gold enrichment and the presence of a new ore assemblage dominated by pyrrhotite-pyrite. Quantitative structural analysis approach, based on measured foliations (S1/0) and gold grade demonstrates that D2-related folding is associated with important gold endowment. These findings suggest that the characterization of the exact fold interference pattern is fundamental for the targeting of favorable enriched zones at the deposit scale.

Beach gold transport and aeolian concentration, southern New Zealand

ABSTRACT Aeolian concentration of iron-titanium oxides (black sand) is a common phenomenon on coasts around the world but associated aeolian detrital gold is relatively rare. In contrast, Holocene and active dunes at Waipapa beach on the coast of the southern South Island of New Zealand host aeolian black sand layers with locally abundant finely particulate (<200 µm) gold and platinum, some of which have been mined historically. Aeolian concentration of black sand, gold and platinum is driven by strong prevailing westerly winds (gusts >100 km/h) on annual or decadal time scales. Holocene fluvial recycling of aeolian sands has been important in upgrading the black sand, gold, and platinum contents. Surf concentration of black sand on the beach is minor and merely feeds the aeolian system, and this differs from other beach gold deposits around the world, which are surf-dominated. Most of the Waipapa beach gold (>90%) has flaky morphology with abundant superficial transport-related deformation reflective of fluvial transport, probably down the nearby Mataura River (∼200 km transport) between Miocene and Holocene. Minor distinctive wind-sculpted toroidal gold, and the platinum, arrived from the west (∼300 km transport) via the Waiau River and Foveaux Strait.

Redistribution of fine gold from hydrothermal sources to sedimentary sinks, Rakaia River, Canterbury, New Zealand

ABSTRACT The Rakaia River in the South Island of New Zealand is a unique catchment in which to trace active detrital gold transport, deformation and concentration from near-coeval orogenic sources. The catchment hosts widespread small late Cenozoic hydrothermal alteration zones, some of which are gold-bearing, in actively rising and eroding mountain headwaters. Detrital gold liberated from the sources is distinctively porous with abundant micron-scale silicate inclusions, especially albite. Fine gold (∼200–100 µm) has been transported >100 km downstream, but coarse gold remains highly diluted in proximal fluvial sediments. Fine gold is also diluted by coarse fluvial sediments that form the upper kilometre of the Canterbury sedimentary basin southeast of the mountain front. Minor re-concentration of fine gold occurs in a bedrock gorge at the mountain front, and on steep ocean beaches beyond the river mouth. Despite the long-distance transport, the fine gold particles have been only superficially modified by surface smearing and minor flattening. The gold may have travelled in suspension in the river, buoyed by electrostatically adhering fine micas, in contrast to detrital garnets that were rounded in bed-load. In contrast, detrital gold on the western side of the mountains has been flattened to thin flakes during bed-load transport.

GOLD RECOVERY USING CITRUS SINENSIS PEELS AS BIOADSORBENT

The recovery of gold from electronic waste using locally available and environmentally friendly materials were investigated. Bio-adsorbent for gold recovery was prepared from Citrus sinensis peels through mechanical processing and chemical modification. Some ceramic computer processor units were leached using aqua-regia as lixiviant. Gold was recovered from the solution using the prepared bio-adsorbent and Sodium Meta Bisulphite (SMB). The recovery efficiency of the bio-adsorbent was determined and results compared to that of SMB. The adsorption of gold at different contact times was determined and the concentration of gold in solution was found using Agilent 4100 Micro Plasma Atomic Emission Spectroscopy (MP-AES). The results obtained showed that the bio-adsorbent has an adsorption capacity of 98.4% for gold and an adsorption kinetics correlation coefficient of 0.99989. This is comparable with SMB which has 95.4%. adsorption capacity and an adsorption kinetics correlation coefficient of 0.98597. The higher adsorption capacity of the bio-adsorbent is attributed to the binding sites and the chemical modification which increases the reducing properties of the functional groups present in the Citrussinensis peels.

Technogenic gold deposits of the Trans-Baikal Territory

Relevance. The need to expand the mineral resource base of the Trans-Baikal Territory. Aim. To study the geochemical composition of technozems of tailings dumps of gold deposits of the Trans-Baikal Territory, their correspondence, in terms of gold content, to technogenic deposits, to calculate the exceeding the maximum permissible concentrations of toxic elements in technozems of tailings dumps. Objects. Technozems of tailings dumps of gold deposits of the Trans-Baikal Territory. Methods. Silicate, X-ray fluorescence ISP-AES methods in analytical laboratories of the Geological Institute of the SB RAS (Ulan-Ude) and JSC "SGS Vostok Limited" (Chita). Results. It was found that in terms of gold content (Au&gt;0.4 g/t), the technozems of the tailings of the gold deposits of the Trans-Baikal Territory, in general, correspond to technogenic gold deposits. The largest volumes and contents of gold (1.2 g/t) are characterized by technozems of the Baleysky tailings dam deposits with insignificant gold contents are technozems of Darasunsky (0.36 g/t) and Kariysky (0.35 g/t) deposits. It is determined that the chemical composition of the technozems of the tailings depends on the composition of the host rocks developed in the areas of deposits. They correspond to the rocks of both basic and medium compositions. The distinctive features of the content of impurity elements in the technozems of tailings are due to the different compositions of the initial ores of gold deposits. These differences are reflected in the values of exceeding the maximum permissible concentrations relative to soils. Among the toxic elements, arsenic is characterized by maximum exceedances of the maximum permissible concentrations. In the technozems of the Lyubavinsky deposit, the excess of the maximum permissible concentrations of arsenic relative to the soil is 933 times, and the Baley deposit is 397 times.

Gold occurrence in the footwall of the Lappberget Deposit, Garpenberg Mine, Sweden: Implications for recovery efficiency

By-product metals have a significant potential to bring additional economic benefits to mines. However, a detailed characterization of their distribution is generally required to fulfill this potential and should preferably be integrated into a geometallurgical assessment. This contribution presents a detailed mineralogical and textural investigation of gold-bearing phases at the footwall of the Zn–Pb–Ag–(Cu–Au) Lappberget Deposit, Garpenberg Mine, Sweden, using optical microscopy, scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), and bulk chemical analysis applied to drill core and Knelson concentrator samples. Gold is a by-product at the Garpenberg mine, but it is unclear how the mineralogy, occurrence, and distribution of gold-bearing phases impact on gold recoveries during mineral processing. Our results show that Au-dominant electrum is the most abundant gold-bearing phase in the footwall of the Lappberget deposit, occurring strongly associated to sulfides in a variety of textures and grain sizes. Electrum grains commonly occur within sulfide borders, as inclusions, intergrowth and overgrowths of chalcopyrite, pyrite, galena, sphalerite, and pyrrhotite. Gangue minerals may also contain disseminated electrum and inclusions. Electrum grain sizes range from ∼5 µm to 300 µm, predominantly below 100 µm. The potential of sulfide lattice-bound invisible gold in the form of solid-solution gold and colloidal gold was also investigated, showing Au depletion within the analyzed sulfide carriers. The analysis of the concentrate samples from the Knelson gravity concentrator showed 584 and 431 ppm of gold content. High degree of liberation is observed among the gold-bearing phases in the concentrate, and gold recovery is highest among fractions coarser than 106 µm mesh. Pyrite and galena are the most abundant minerals in the concentrate samples. The gold-bearing phases were categorized based on its mineralogy, texture, grain size, and association and their influence on gold processing, especially textures and grain size, which implicates its liberation in milling and recovery by the gravity separator.

Computational fluid dynamic model for the prediction of the unsteady operation process of a non-dispersive gold extraction from wastewater

The current study tries to investigate gold extraction in a membrane extractor in unsteady mode. The model was successfully validated using experimental results. The results showed that the diffusive flux on the zone close to the membrane surface is dominant in the first minutes of extraction but later the convective flux is the main flux, particularly at the centre of the shell side. The extraction time of one hour was not ample to extract all gold from the aqueous solution when the volume of solutions was 2000 mL and 3000 mL. Finally, the change in feed flow rate in the range of 30–55 cm3/min did not have a significant influence on the gold extraction time. However, the outlet dimensionless concentration of gold after one hour was increased from 0.24 to 44 with the increase of feed flow rate from 30 cm3/min to 55 cm3/min.

Biogenic synthesis and characterization of gold nanoparticles using transformed mesophilic Escherichia coli BL21 and thermophilic Thermus thermophilus HB27

Gold nanoparticles have numerous applications, many of which are notable in industries. The biosynthesis of gold nanoparticles offers an easy, effective, green, and eco-friendly approach. In organisms capable of synthesizing nanoparticles, enzymes and proteins are responsible for the structural and functional modifications that lead to their formation. These include ABC transporter, peptide-binding proteins, which are dependent on abiotic parameters. This study uses the purified ABC transporter, peptide-binding protein transformed from Thermus scotoductus SA-01 and expressed in mesophilic Escherichia coli BL21 and thermophilic Thermus thermophilus HB27 hosts for the biosynthesis of gold nanoparticles at different concentrations, temperatures, and pH values. Gold nanoparticle formation was evaluated with a range of gold (III) concentrations (0–10 mM), incubated at temperatures ranging from 30–85 ºC and pH levels from 3.6–9.0. Transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and UV–Vis absorption spectroscopy were used to characterise the formation of nanoparticles. In all of the protein reactions, UV–Vis absorbance peaks at approximately 520–560 nm confirmed the formation of gold nanoparticles. Optimum nanoparticle synthesis was observed at pH values ranging from 5.5 to 9.0, gold (III) solution (HAuCl4) concentrations from 0.5–2.0 mM, and a maximum temperature of 65ºC in the mesophilic host and 85ºC in the thermophilic host, indicating the significance of temperature in both hosts for the expression and bioactivity of the purified ABC transporter protein. However, the biogenic formation of gold nanoparticles using E. coli and T. thermophilus hosts was not monodispersed, suggesting a necessity for further development of the procedure.

Study of the influence of temperature and duration of chlorinating roasting on the extraction of gold from E-waste

In this work, based on experimental studies, the effect of roasting temperature and duration on the chlorination of gold from E-waste under low-temperature conditions was studied. It has been established that in the low-temperature range of 150-300 °C, the gold content in the residue shows a sharp decrease, reaching its minimum of 8 ppm at 250 °C. A further increase in temperature does not affect the gold content in the cinder. It has been shown that during chlorinating roasting above a temperature of 250 °C, side reactions should be expected to occur with the formation of additional phases representing chlorides of copper, iron and other elements. The results of SEM and XRD analyzes of the solid phase obtained after chlorinating roasting at a temperature of 250 °C and a roasting duration of 20 minutes showed the presence of copper and iron chlorides in them. Optimal technological parameters and modes of the process of chlorinating roasting of E-waste with gaseous chlorine have been established: temperature – 250 °С; roasting duration – 20 minutes; chlorine consumption is 1.5 times more than the stoichiometrically required amount (SRA) for gold chlorination. Under optimal roasting conditions, a high, up to ~97.6%, recovery of gold in the form of gold chloride (AuCl3) was achieved. The results of the experiments can be a basic basis and make it possible to conduct more representative experiments (scaling) in the future, taking into account the established optimal technological parameters. This will provide a chance to evaluate the possibility of extracting gold from E-waste of different types and compositions and to conduct further research on obtaining pure gold from the collected representative amount of gold sublimate AuCl3 by smelting.

Study on adsorption of kaolinite and gold thiosulfate

The adsorption behavior of gold thiosulfate ions on the surface of kaolinite was studied using a combination of experimental research and quantum chemical calculations. Under the condition of a stirring time of 30 min, a stirring speed of 500 r·min−1, and a mass ratio of 30% kaolinite in the slurry, when the initial gold concentration of 56.50 mg·L−1,the adsorption rate of gold-thiosulfate ions from a kaolinite-containing solution was 7.44%. The results of Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS) showed that the physical and chemical adsorption of kaolinite and gold thiosulfate occurred in solution. Quantum chemical calculations were performed using the CASTEP module in Materials Studio. The adsorption energy of gold thiosulfate on the surface of kaolinite (001) was calculated as − 438.01 kJ·mol−1.The calculated H76–O289 distance was 1.615 Å. Mulliken Charge population analysis and bond population analysis showed that gold thiosulfate ions form relatively stable bonds on the kaolinite surface (001). In the process of thiosulfate immersion, part of gold is adsorbed by kaolinite, which affects the extraction of gold. These results indicate that during the leaching process of gold thiosulfate, kaolinite has the ability to "catch" gold, which affects the leaching efficiency.

Pozyskiwanie złota ze słowackiego koncentratu przy użyciu innowacyjnej metody

The complicated processing of concentrates with low gold content and the long-time use of non-ecological methods was the motion for finding a more efficient process for this noble metal obtaining. From this point of view, this research was focused on obtaining of nano gold from the concentrate White Hill (Detva, Slovakia) using mechanical activation and mechano-biological activation in a molecular hydrogen solution. Gold in this complex concentrate occurs physically enclosed in the intercrystalline space of minerals and is also isomorphic and fills defects in their structure. The exclusion of gold from such complex mineral matrixes of the concentrate can be achieved using a mechano-biological process. This innovative method for obtaining of nano gold with the application of a molecular hydrogen solution is an advantageous alternative to the non-environmental reagents used. Compared to the most used worldwide toxic cyanide reagent, a solution with molecular hydrogen represents a low-cost and above all completely harmless reagent with very good kinetics. Mechanical processes use high-energy milling, which has an effect on the more intensive formation of surface and bulk defects in solid substances. The main advantage of mechanical processes is a smaller number of technological operations, a shorter time required to obtain the desired product at favorable environmental temperatures, and also the formation of nanostructures. The use of a biological process with the application of limnetic algae showed that algae with siliceous structures make it possible to obtain gold from the White Hill concentrate with nanoscale size. Limnetic algae (diatoms, golden algae) are part of aquatic ecosystems and create the largest matter of biomass from all plants on the Earth. The mechano-biological process is a method that enabled to obtain of gold nanoparticles with an average size of 100 nm from the Slovak gold-bearing concentrate from the White Hill deposit (BV-1). Mechanical activation of this concentrate and siliceous shells of the specified limnetic algae (Dinobryon, Surirella) in a molecular hydrogen solution caused changes in the physical-chemical properties of gold minerals as well as in the constituents of algae minerals. These structural changes had a decisive influence on the exclusion of gold nanoparticles into the molecular hydrogen solution under the defined reaction conditions. The gold nanoparticles were subsequently fixed in the cellular matrix of mechanically activated algae shells. The explanation of this phenomenon was the action of biomolecules, which the algae cells secreted in the course of reactions with metal ions present in the molecular hydrogen solution. Gold nanoparticles from the investigated concentrate were obtained by a new mechano-biological procedure already for four hours. In the case of mechanical activation of the concentrate, but without activation of the used algae, gold nanoparticles were excluded after sixteen hours. It follows from this knowledge that the application of an absolutely ecologically harmless aqueous solution enriched by molecular hydrogen and the use of limnetic algae confirmed the suitability of the innovative method for obtaining of nano gold from the concentrate. From the achieved research results significantly more effective kinetics is evident in the case of activated algae. Nanoparticles of gold obtained by the mentioned procedure can have important practical utilization, such as accelerating of the decomposition of dangerous substances or neutralizing pollutants in contaminated water, soil, and air. Simultaneously, obtaining of gold nanoparticles would also be beneficial for removing algae from the aquatic environment, where they are very dangerous for all living organisms.