Gold Smelting Research Articles

Optimization of direct smelting for mercury-free gold recovery in artisanal and small-scale gold mining

Artisanal and small-scale gold mining (ASGM) faces challenges in accessing capital, technology, and responsible practices, hindering sustainable operations and contributing to environmental and health impacts from mercury use. This study evaluated optimizing direct smelting of gold concentrates as an alternative to mercury amalgamation for efficient and responsible production. 50 kg of ore from Nholi mine was concentrated using a Knelson concentrator and analyzed (XRF, fire assay with AAS, XRD). Response surface methodology with a face-centered composite design investigated smelting temperature (1100–1400 °C), duration (30–90 min), and concentrates-to-flux ratio (1:1–3:1) effects. The impact of sulfide concentration (pyrite varied 6.7–48%) on gold recovery was explored. Low-sulfide concentrates associated with pyrite and sphalerite yielded best recovery (>80%) at 1250 °C for 90 min with 2:1 concentrates-to-flux ratio. Direct smelting with ≤6.7% sulfide enabled over 87% gold recovery, facilitating responsible ASGM production.

Determining priority control toxic metal for different protection targets based on source-oriented ecological and human health risk assessment around gold smelting area

Determining the priority control source and pollutant is the key for the eco-health protection and risk management around gold smelting area. To this end, a case study was conducted to explore the pollution characteristics, source apportionment, ecological risk and human health risk of toxic metals (TMs) in agricultural soils surrounding a gold smelting enterprise. Three effective receptor models, including positive matrix factorization model (PMF), ecological risk assessment (ERA), and probabilistic risk assessment (PRA) have been combined to apportion eco-human risks for different targets. More than 95.0% of samples had a Nemerow pollution index (NPI) > 2 (NPImean=4.27), indicating moderately or highly soil TMs contamination. Four pollution sources including gold smelting activity, mining source, agricultural activity and atmosphere deposition were identified as the major sources, with the contribution rate of 17.52%, 44.16%, 13.91%, and 24.41%, respectively. For ecological risk, atmosphere deposition accounting for 30.8% was the greatest contributor, which was mainly loaded on Hg of 51.35%. The probabilistic health risk assessment revealed that Carcinogenic risks and Non-carcinogenic risks of all population were unacceptable, and children suffered from a greater health risk than adults. Gold smelting activity (69.2%) and mining source (42.0%) were the largest contributors to Carcinogenic risks and Non-carcinogenic risks, respectively, corresponding to As and Cr as the target pollutants. The priority pollution sources and target pollutants were different for the eco-health protection. This work put forward a new perspective for soil risk control and management, which is very beneficial for appropriate soil remediation under limited resources and costs.

Study on the performance of Anerinibacillus sp. in degrading cyanide wastewater and its metabolic mechanism

Cyanide extraction dominates the gold smelting industry, which leads to the generation of large amounts of cyanide-containing wastewater. In this study, Aneurinibacillus tyrosinisolvens strain named JK-1 was used for cyanide wastewater biodegradation. First, we tested the performance of JK-1 in degrading cyanide under different conditions. Then, we screened metabolic compounds and pathways associated with cyanide degradation by JK-1. Finally, we explored the potential JK-1–mediated cyanide degradation pathway. Our results showed that the optimal pH and temperature for cyanide biodegradation were 7.0 and 30 °C, respectively; under these conditions, a degradation rate of >98% was achieved within 48 h. Untargeted metabolomics results showed that increased cyanide concentration decreased the abundance of metabolic compounds by 71.1% but upregulated 32 metabolic pathways. The Kyoto Encyclopedia of Genes and Genomes enrichment results revealed significant changes in amino acid metabolism pathways during cyanide degradation by JK-1, including cyanoamino acid metabolism, β-alanine metabolism, and glutamate metabolism. Differential metabolic compounds included acetyl-CoA, l-asparagine, l-glutamic acid, l-phenylalanine, and l-glutamine. These results confirmed that cyanide degradation by JK-1 occurs through amino acid assimilation. This study provides new insights into the mechanism of cyanide biodegradation, which can be applied in the treatment of cyanide wastewater or tailings.

Antimony and gold substance flows analysis of pyrometallurgical process for antimony-gold concentrates

In this paper, substance flow analysis was used to analyze the production of antimony and gold in the pyrometallurgical process of complex antimony and gold concentrate. The comprehensive recovery and utilization of antimony and gold concentrate were studied in detail by establishing antimony and gold mass balance accounts and substance flow charts. The results showed that the resource efficiency of antimony and gold was 88.85% and 94.86%, respectively. The direct recovery of antimony in the blast furnace, gold smelting furnace, cupellation furnace and reverberatory furnace was 95.44%, 84.95%, 85.11% and 91.22%, respectively. The circular substance flow generated by the cupellation furnace accounted for 72.6% of the total circulation flow. One tonne of antimony accompanied 0.016 tonnes of antimony into water-quenched slag and 0.017 tonnes into the arsenic alkali slag. The proportion of gold entering antimony oxide, precious antimony, antimony matte and water-quenched slag in the blast furnace was 8.4%, 84%, 6.7% and 0.9%, respectively. The proportion of gold entering the gold-bearing products, antimony oxide and antimony slag in gold smelting furnace was 90.6%, 3.6% and 5.8%, respectively.

Study on the treatment of cyanide gold extraction wastewater by persulfate-electrochemical oxidation

The cyanide gold extraction wastewater from a gold smelter was treated using a persulfate-electrochemical oxidation (PS-EO) coupling process. The optimal process conditions and significance level of each factor were determined using orthogonal experiments, and the precipitates and cathodic precipitates in the system were analyzed and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), and the oxidation removal reaction mechanism of cyanide was further explored. The results showed that voltage, time and PS concentration were the main influencing factors of the cyanide removal extent. When the voltage was 5 V, PS concentration 0.5 g L–1, pH 7, plate spacing 2.5 cm and reaction time 240 min, the removal extents of total cyanide (CNT), free cyanide (CN–), Cu and Zn ions in wastewater reached 98.33 %, 100 %, 99.53 % and 98.86 %, respectively. The removal of cyanide was mainly attributed to the indirect oxidation by SO4•–, •OH and O2•– active radicals produced by activated PS and the direct oxidation of S2O82–. The contribution rate of S2O82– direct oxidation was 42.38 %. The oxidation contribution rates of SO4•–, •OH and O2•– active free radicals were 15.75 %, 29.33 % and 12.54 %, respectively. Compared with simple PS and EO treatment processes, the PS-EO combined process reduced the amount of oxidants and helped to improve the current density of the system, as well as the generation of active free radicals such as SO4•–, •OH and O2•–. Additionally, after PS-EO treatment, there were almost no precipitates such as Zn(CN)2, CuCN, Zn(OH)2 and Cu(OH)2 produced in the wastewater. The cyanide ions in complex ions such as Cu(CN)32– and Zn(CN)42– were completely oxidized to N2 and CO2, and then under the influence of an electric field, the released Cu2+ and Zn2+ ions were directed to migrate to the cathode and precipitate.Finally, the treated wastewater could be directly returned to the grinding or leaching the ore process, thus achieving the goals of being harmless and utilizing cyanide wastewater resources.

Heavy Metal Pollution in Soil and Surface Sediments of Meycauayan River, Philippines and Their Relationship to Environmental Indicators

ABSTRACT The City of Meycauayan is an industrial powerhouse in the Philippines. It is considered as one of the most polluted cities in the developing world on the account of industrial discharges of toxic materials to the environment. This work investigated the sources of the heavy metal pollution in Meycauayan by analyzing soil and sediment samples for heavy metals like Chromium (Cr), Mercury (Hg), Nickel (Ni), and Lead (Pb) together with selected environmental indicators such as Total Nitrogen (TN), Total Organic Matter (TOM), and Total Phosphorus (TP) located along the Meycauayan River. Hierarchical cluster analysis (HCA), principal components analysis (PCA), and Pearson correlation analysis (CA) were used to identify the sources of the metals. Our results show delineated locations of severe levels of heavy metal pollution downstream of the river because of the concentration of industrial activities. Cr is due to proliferation of tanneries discharging untreated wastewaters to the river. Significant input of Pb and Hg from Pb-acid battery recycling and gold smelting industries were also found. The risk assessments also indicate severe levels of heavy metal pollution in locations where industrial activities are concentrated. Our findings indicate that the heavy metals have similar impacts to K, TN, TOM, and TP in the soil and sediments. Our study shows the serious need to address heavy metal pollution in Meycauayan aside from the ongoing cleanup of solid wastes as part of rehabilitation efforts by the local government.

Cyanide Release Characteristics of Solid Waste in Gold Smelting Process

To explore the relationship between total cyanide and easily liberatable cyanide in cyanide tailings and its impact on the environment, the leaching and release characteristics of total cyanide and easily liberatable cyanide in a tailings pond were studied using a dynamic leaching experiment, and a dynamic model was established. The results show that the release concentration of total cyanide in cyanide tailings is higher than that of easily liberatable cyanide. With the increase in leaching time, the release of cyanide is more sensitive to leaching intensity. The first-order kinetic, second-order kinetic, modified Elovich, double constant, and parabolic diffusion equations were used to fit the cumulative release of cyanide. According to the kinetic results of cyanide cumulative release, in addition to the first-order kinetic equation, the other four equations revealed good fitting for the cyanide leaching process, which shows that cyanide released under simulated rainwater leaching was not simply via surface diffusion, but controlled by multiple factors.

Paleoecotoxicology: Developing methods to assess the toxicity of lake sediment records influenced by legacy gold mining

The contamination of lakes by industrial emissions is an issue of international concern. Traditional paleolimnology examines sedimentary micro-fossils to infer the biological response to natural and anthropogenic stressors over time. Here, we calculate a theoretical biological effect for historic sediment sections using Probable Effect Concentration Quotient (PEC-Q) and arsenic specific quotient methods and develop novel time-constrained sediment toxicity test methods using a cultured Daphnia sp. combined with a whole cell microbial biosensor to assess the toxicity of past industrial contamination with modern testing methods. These methods were developed using sediments collected from Pocket Lake (Northwest Territories, Canada), a lake known to have exhibited a significant ecological shift following input from nearby gold smelter emissions during the mid 20th century. We then applied these methods to near-, mid-, and far-field sites to assess the response of Daphnia sp. to varying contaminant load. Daphnia sp. mortality exposed to dated sediments indicated a strong concordance with the timing of mining activities, and a strong concordance with PEC-Q and arsenic specific toxicity quotients. In contrast, a decrease in Daphnia mortality was observed during pre-, and post-mining periods when the contaminant burden was lower. Initial assessments of bioavailability using a microbial biosensor indicated that arsenic in porewater is 72–96% bioavailable, and limited evidence that oxidative stress may contribute to the Daphnia sp. toxic response. These results indicate that lake sediment archives can be used to infer missing biomonitoring data in sites of legacy anthropogenic influence, which will be useful for those seeking to conduct cost-effective and efficient preliminary environmental risk assessments.

Complete reconstruction of the process and conditions during gold smelting in the 15th–17th centuries in Złoty Stok based on metallurgical slags

AbstractThis study presents the first complete reconstruction of gold metallurgy in Złoty Stok, Poland. The key parameters of the process (i.e., temperature of smelting and solidification, melt viscosity, oxygen fugacity) are calculated using the remnants of the process: metallurgical slags. The slags consist of silicate phases (i.e., olivine, pyroxene), sulfides and arsenides (i.e., pyrrhotite, Fe2As), as well as glass. These slags are chemically dominated by SiO2 (< 56.60 wt%), MgO (< 18.36 wt%), FeO (< 15.36 wt%), and CaO (< 15.19 wt%). The obtained results indicate that the temperature during the metallurgical process was at least 1300–1350°C, and crystallization of the slags took place until they cooled to < 1200°C. The morphology of olivine crystals in the slags indicates large differences in their cooling rate, from 5 to 300°C/h. Strongly reducing conditions during the metallurgical process (−10.5 to −11.5 log fO2) was confirmed. Low melt viscosity (logƞ = 0.26 – 0.90 Pa s) facilitated the separation of the sulfide melt rich in gold from the silicate melt being the slag precursor. The obtained results allowed existing descriptions of the smelting process in Złoty Stok to be corrected.

Ultra low-cost and bio-sustainable carbonized green algae for wastewater purification in gold smelting industry.

As a promising solar energy conversion technology, solar water evaporation has been regarded as an energy-efficient approach to alleviate the freshwater shortage caused by industrial water pollution. In this paper, we developed a straightforward method with a solar-driven steam generator (SSG) based on the carbonized green algae (CGA) as a light-to-heat conversion material (LHCM) to deal with the industrial wastewater of gold smelting. CGA SSG exhibited excellent light absorption, hydrophilicity, and water evaporation rate (1.66 kg·m-2·h-1). It accomplished the non-selective removal of heavy metal ions (Cu2+, Pb2+, Zn2+, Hg2+) and CN- in the treatment of gold smelting wastewater, and the ion removal rate was 99%. Compared with traditional and complex wastewater treatment technologies, the solar-driven CGA SSG presented many advantages (low cost, simple preparation, and high performance) in water purification, which could be employed in backward areas to obtain clean water.

Harmless treatment of cyanide tailings by a bifunctional strain JK-1 based on biodegradation and biomineralization

Cyanide tailings(CT) are a typical hazardous waste, containing large amounts of heavy metals and highly toxic cyanide. As so far, it is difficult to solve this problem at the same time. In this study, a “two-step” process was proposed for the first time to treat CT, first using microorganisms to degrade cyanide and then using microbially induced carbonate precipitation (MICP) to solidify the CT. We isolated a bifunctional bacterium which exhibited cyanide degradation and high urease activity from CT, identified as Aneurinibacillus tyrosinisolvens strain (named JK-1). We used JK-1 bacteria to treat the CT in a “two-step” process. The results showed that the degradation of free cyanide (F–CN) and total cyanide (T-CN) in CT by JK-1 bacteria reached 94.54% and 88.13%. After the MICP treatment, the spindle-shaped CaCO3 solidified the CT into a block of calcite and sphalerite crystals, and the uncompressed compressive strength (UCS) reached 0.74 MPa; the morphology of heavy metals in the CT changed from the exchangeable state to the carbonate-bound state, and the mobility was significantly reduced. Compared with chemical treatment, the treatment of CT by the new process is highly efficient and green, which can realize the solidification of CT, degradation of cyanide and immobilization of heavy metals at the same time. Compared with chemical treatment, the new process is efficient and green, which can realize the solidification of CT, the degradation of cyanide and the immobilization of heavy metals at the same time; it is of great significance to the harmless treatment of CT and the sustainable development of gold smelting industry.

Late-Holocene diatom community response to climate driven chemical changes in a small, subarctic lake, Northwest Territories, Canada

The paleolimnological record of diatoms and climate, spanning the last 2800 years, was investigated in a small subarctic lake (Pocket Lake) that from AD 1948 to 2004 was contaminated by gold smelting waste. An age-depth model was constructed using a combination of 210Pb, 14C, and tephra to determine a 2800 year history of lake ontogeny (natural aging), biological diversity, and regional climate variability. Diatoms form six strong paleoecological assemblages over time in response to changes in local hydrological and sedimentological conditions (including metals). Selected environmental variables explained 28.8% of the variance in the diatom assemblages, with Fe, Ca, and sediment end member distribution being important indicators. The diatom assemblages correlated to the Iron Age Cold Epoch (2800–2300 cal BP), Roman Warm Period (2250–1610 cal BP), Dark Age Cold Period (1500–1050 cal BP), Medieval Climate Anomaly (ca. 1100–800 cal BP), and the Little Ice Age (800–200 cal BP). The disappearance of Staurosira venter highlights the change from the Iron Age Cold Epoch to the Roman Warm Period. After deposition of the White River Ash (833–850 CE; 1117–1100 cal BP), transition to circumneutral conditions was followed in tandem by a transition to planktic influenced communities. Ten discrete peaks of Cu, Pb, and Zn were observed and attributed to soluble mobility from catchment soils through enhanced seepage and spring snowmelt. The prominent metal spikes were aligned with increases in Brachysira neoexilis. Downward mobilization of arsenic and antimony from contaminated surficial sediments highlight the problem of post depositional industrial contamination of paleosediments. Results demonstrate that paleoclimatic changes in the region, modulated by solar radiation, impacted temperature and precipitation in the lake catchment, influencing temporal shifts in diatom ecology. Changes in diatom taxa richness provided valuable information on the relative influence of water quality (planktic taxa) and sediment input (benthic taxa). The diatom assemblage succession also provides evidence that natural aging over time has played a role in the ecological evolution of the lake.

Green Treatment of Cyanide Tailings Using a “Filter Press BackWash–Chemical Precipitation–Gaseous Membrane Absorption” Method

Based on a “filter press backwash–chemical precipitation–gaseous membrane absorption” process, treatment of harmless cyanide tailings was conducted using cyanide tailings from a gold smelting enterprises (Yunnan Province, China) as the research object. The effects of air-drying time, backwash water parameters, initial pH of acidification, NaHS dosage, cyanide-containing water flow rate, and gaseous membrane stages on the process were investigated. Chemical composition, X-ray diffraction, and X-ray photoelectron spectroscopy analyses of the copper products were carried out. Results showed that the copper content in the copper product was 54.56%, and the chemical composition was mainly CuSCN, CuS, Cu2S, and CaSO4. Five cycles of experiments were carried out under optimal conditions; the results showed that the process can make the treated cyanide tailings meet the requirements of the technical specification for pollution control of cyanide leaching residue in the gold industry (TSPC) standard for storage in a tailings pond and a have certain stability. The average recovery rate of copper and total cyanide in elution water was 97.8% and 99.89%, respectively, and the average removal rate of thiocyanate was 94.09%.

Selective extraction of arsenic and antimony from gold-bearing sludge using two-stage alkaline leaching

In gold smelting industry, coexisting of arsenic (As) and antimony (Sb) in gold-bearing sludge is a serious issue for the smelting process. This study employed a two-stage leaching methods to selective extract arsenic and antimony from gold-bearing sludge. Arsenic was firstly removed through NaOH leaching, following by Na2S-NaOH leaching to remove antimony in the atmospheric conditions. The first step results show that more than 96% of arsenic can be removed under the conditions of 2 mol/L NaOH, the ratio of liquid to solid (L/S) of 5, 60 °C, 400 rpm, 3 h. Meanwhile, the antimony dissolved in the solution is converted into the residue as the state of NaSb(OH)6 during this process. After Na2S-NaOH leaching, the antimony leaching extent is 97.2% during the condition of 2.5 mol/L Na2S, 0.125 mol/L NaOH, L/S = 5, 70 °C and 6 h. In addition, the vulcanization of copper was found in the Na2S-NaOH leaching process, and the CuS appeared in the leaching residue. The results prove that the NaOH leaching following by Na2S-NaOH leaching can selectively extract arsenic and antimony from gold-bearing sludge in the atmospheric conditions.

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.

An environmental-friendly approach to remove cyanide in gold smelting pulp by chlorination aided and corncob biochar: Performance and mechanisms

In this study, a new process was developed using ClO− and corncob biochar (CB) combined with HAS (a stabilizer) to remove cyanide from gold smelting pulp. The Box-Behnken design was employed to optimize the doses of treatment reagents during cyanide removal. Results showed that the optimal doses of the three reagents were as follows: ClO− dose of 20 mg/g dry solid (DS), CB dose of 22 mg/g DS, and an HAS dose of is 24 mg/g DS. The cyanide concentration in the filtrate was the lowest (0.114 mg/L), with a 98.36% removal efficiency after a contact time of 2 h at 25 °C under optimized conditions. Compared with those of ClO− and HAS, it was found that the dose of biochar was the dominant factor influencing cyanide removal. Batch sorption experiments of cyanide to biochar indicated that the Langmuir isotherm model fit the sorption data, and the maximum cyanide sorption capacity was expected to be 2.57 ± 0.06 mg/g. Density functional theory (DFT) calculations (interaction energy was −74.42 kcal/mol) indicated that the adsorption peak resulted from cation-π interactions between the cyanide and CB. This study could lead to a novel environmental-friendly approach for the removal of cyanide from gold smelting pulp.

A Collaborative Training Program to Assess Mercury Pollution from Gold Shops in Guyana’s Artisanal and Small-Scale Gold Mining Sector

A three-phase, 11-day training program designed to monitor elemental mercury (Hg0) emissions originating from gold shops was conducted in Georgetown and Bartica, Guyana, during May of 2019. The first phase consisted of interactive lectures and discussions on mercury use in artisanal and small-scale gold mining throughout Guyana, the region, and the world. In addition, specific training in the theory and use of analytical instrumentation to quantify Hg0 pollution associated with the processing of amalgams and sponge gold occurred. Trainees participated in the mapping of smelting facilities in Georgetown where, outside of one gold shop, Hg0 concentrations exceeded 100,000 ng/m3. During the second phase of training, a subset of trainees traveled to Bartica, where they mapped the town center to identify point sources of Hg0 pollution, all of which corresponded to the location of shops where amalgams and sponge gold were heated and purchased. Once mapped, Hg0 concentrations were measured during the smelting of gold inside the Guyana Gold Board (GGB) facility and two privately-owned gold shops. Maximum Hg0 concentrations at the GGB facility did not exceed 98,700 ng/m3 during the measurement period, while maximum concentrations at the two privately owned shops were measured as 527,500 ng/m3 and 302,200 ng/m3. With guidance from the training team, trainees were responsible for the collection and interpretation of all data. The third phase of the training involved the collaborative production of a report summarizing the findings from the training. This work represents the first formal training opportunity for the assessment of Hg0 concentrations in and around gold shops in Guyana, and provides baseline data to assist the government of Guyana to generate air quality standards for Hg0 emissions.

Recovery and kinetics of gold and iron from cyanide tailings by one-step chlorination–reduction roasting

The experiment on recovery of gold and iron by one-step chlorination-reduction roasting in the muffle furnace was conducted using cyanide tailings from a gold smelting enterprises (Henan Province, China) as research object. The effects of the dosage of calcium chloride, dosage of bituminous coal, roasting temperature, roasting time, and other factors on the high-temperature chlorination efficiency of gold were studied. The effects of iron reduction were also investigated. X-ray diffraction analysis on the roasting products was carried out. Results showed that the high-temperature chlorination efficiency of gold increased with the rising of calcium chloride dosage. The high-temperature chlorination efficiency of iron also increased, leading to iron loss. The concentration of CO and CO2 produced by bituminous coal increased in roasting atmosphere, leading to the decrease of chlorine gas concentration. Thus, the high-temperature chlorination efficiency of gold decreased. During the roasting process, the reduction process of iron oxide is Fe2O3 → Fe3O4 → FexO → Fe, and the wustite can easily react with the silicon dioxide to form iron silicate in the weak reduction atmosphere. Under the condition of calcium chloride dosage of 6%, bituminous coal dosage of 22%, roasting temperature of 1200 °C, and roasting time of 1.5 h, the technical indices of gold high-temperature chlorination efficiency of 83.1%, iron grade of 92.0%, and iron recovery of 84.9% were obtained. The relationship between the high-temperature chlorination efficiency of gold and roasting temperature was established. The high-temperature chlorination reaction of gold was controlled by the interfacial chemical reaction. The apparent activation energy of the high-temperature chlorination of gold is calculated to be E = 20.3 kJ/mol.

Source apportionment of potential ecological risk posed by trace metals in the sediment of the Le’an River, China

From perspective of risk management and control, the ecological risk contributed from various sources can give direct risk information in selecting priority pollutants to control in river ecosystem restoration. However, studies combined receptor model with risk assessment to obtain ecological risk in every source category that is still limited. It is essential to quantitatively and spatially analyse the contributions of various sources to both the content and ecological risk in river system. Ten trace metals in 47 sediment samples were collected in Le’an River, which is the main tributary of the largest freshwater lake in China, Poyang Lake and analysed by laboratory analysis. The potential ecological risk index (PERI) model was used to evaluate the ecological risk posed by sediment trace metals. The positive matrix factorization (PMF) was utilized to identify the source of sediment trace metal and apportion their contribution. The ecosystem risks of the sources were quantitatively analysed by combining PERI and PMF, termed PMF-PERI. In addition, we conducted a spatial dissimilarity analysis of the source contribution distributions. The ecological risk assessment results showed that the metals Cd, Cu, and Hg may cause the main ecological hazards. Source apportionment of the trace metal concentrations indicated that the dominant source of trace metals in the sediment was human activities (55.83%), such as Pb-Zn mining and agricultural activities (30.33%), gold smelting (13.62%) and copper mining (11.89%). Source apportionment of the ecological risks posed by the trace metals indicated that natural sources were the main ecosystem risk sources (64.75%), followed by Pb-Zn mining and agricultural activities (14.65%), copper mining (10.67%) and gold smelting (9.93%). The results of spatial dissimilarity analysis indicated that the significant spatial variation in the contribution compositions was related to the locations of the sources and the river. The results of this study indicated that the emission reduction of agricultural activities should be given priority attention for protecting the watershed environment of the Le’an River. In addition, this study extends the use of risk assessment in receptor model source apportionment.

Variation in thyroid hormone levels is associated with elevated blood mercury levels among artisanal small-scale miners in Ghana.

BackgroundMercury can be very toxic to human health even at low dose of exposure. Artisanal small-scale miners (ASGMs) use mercury in gold production, hence are at risk of mercury-induced organ dysfunction.AimWe determined the association between mercury exposure, thyroid function and work-related factors among artisanal small-scale gold miners in Bibiani- Ghana.MethodWe conveniently recruited 137 consenting male gold miners at their work site in Bibiani-Ghana, in a comparative cross-sectional study. Occupational activities and socio-demographic data of participants were collected using a questionnaire. Blood sample was analysed for total mercury and thyroid hormones.ResultsOverall, 58.4% (80/137) of the participants had blood mercury exceeding the occupational exposure threshold (blood mercury ≥5μg/L). T3(P<0.0001) and T4(P<0.0001) were significantly reduced among the exposed group compared to the non-exposed. TSH showed no significant variation between the exposed and non-exposed groups. Longer work duration (≥5years), gold amalgamation, gold smelting and sucking of excess mercury with the mouth were associated with increased odds of mercury exposure. Blood mercury showed negative correlation with T3(r = -0.29, P<0.0001), and T4(r = -0.69, P<0.0001) and positive correlation with work duration (r = 0.88, P<0.001). Even though a positive trend of association between blood mercury and TSH levels was recorded, it was not significant (r = 0.07, P = 0.4121)ConclusionSmall scale miners in Bibiani are exposed to mercury above the occupational threshold which may affect thyroid hormone levels.