Assessing potential hydrogen cyanide exposure from cyanide-contaminated mine tailing management practices in Thailand's gold mining

Cyanide removal of gold cyanide residues by manganese compounds as new decyanation reagents

Plenty of the toxic gold cyanide residues are produced by cyanidation process of gold extraction. As a kind of hazardous solid wastes, cyanide residues must be treated to remove cyanide before disposal. In this study, the removal of cyanide in gold cyanide residues by manganese compounds (KMnO4 and MnO2) was investigated. It was found that both KMnO4 and MnO2 could be used as new decyanation reagents for cyanide removal. To make the residue after cyanide removal meet the national standard, it needed KMnO4 1.8 wt% for 60 min reaction or MnO2 1.0 wt% for 30 min reaction with about pH 8.0. The mechanisms of two processes were investigated by X-ray photoelectron spectroscopy (XPS). The results show that KMnO4 concentrates on the reactions with pyrite in the cyanide residue, the products are mainly Fe(II), Fe(III), SO42- and MnO2. KMnO4 added in the slurry could be consumed by pyrite before oxidation of cyanide, resulting in relatively low cyanide remove efficiency and high KMnO4 consumption. On the surface of the residue after MnO2 treatment, there are mainly pyrite, Fe(II), Mn(II), Fe-CN and CN-, showing that the MnO2 process focuses on the removal of cyanide in the cyanide residue. The MnO2 process has the advantages of low reagents consumption, short reaction time and high cyanide removal efficiency, presenting a promise use for cyanide removal of cyanide residues in a range of applications.

Evaluation of the danger of a tailings pile belonging to an active mine through its characterization and a dispersion model

Mining is one of the principal economic activities in Mexico, which in addition to bringing benefits to the population, causes health and environmental problems. This activity produces a lot of wastes, but the main one is tailings. In Mexico, these wastes are disposed of in the open air, and there is no control over them, so the particles of these wastes are dispersed by wind currents to the surrounding population. In this research, tailings were characterized, finding in them particles smaller than 100 microns; in this way, tailings can enter into the respiratory system and hence can cause diseases. Furthermore, it is important to identify the toxic components. The present work does not have previous research in Mexico, and it shows a qualitative characterization of the tailings from an active mine using different analytical techniques. In addition to the data obtained from the characterization of the tailings, as well as the concentration of the toxic elements found, which were Pb and As, a dispersal model was generated and used to estimate the concentration of particles in the wind generated at the studied area. The air quality model used in this research is AERMOD, where it uses emission factors and available databases provided by Environmental Protection Agency (USEPA); Moreover, the model was coupled with meteorological information from the latest generation WRF model. The modeling results estimated that the dispersion of particles from the tailings dam can contribute up to 10.15 µg/m³ of PM₁₀ to the air quality of the site, which, according to the characterization of the samples obtained, could be dangerous for human health and can be estimated up to a concentration of 0.04 µg/m³ of Pb and 10.90 ng/m³ of As. It is very important to make this kind of research to know the risk which people around this disposal sites are exposed to.

Phytoremediation potential of Gossypium hirsutum on abandoned polluted chromium sludge soil with the amalgamation of Streptomyces tritici D5

The phytoremediation potency of Gossypium hirsutum was explored in this research under the influence of pre-identified metal tolerant Streptomyces tritici D5 in Cr enriched sludge soil using various treatment sets (I to V) in a greenhouse setting. Interestingly, the G. hirsutum remarkable remediate the Cr metal from the Cr enriched sludge soil under diluted (50:50) condition in 90 days of greenhouse experiment. The S. tritici D5 also effectively support the growth and phytoremediation competence of G. hirsutum. This was evidenced by the under the diluted (set III) condition the growth and major biomolecules such as protein, carbohydrate, and chlorophyll content of G. hirsutum were considerably increased in quantity. Hence, the phytoremediation potential of G. hirsutum was effective at soil diluted with fertile and xenobiotics free soil with dilution ratio of 50:50 (set III) and followed by 75:25 (set II) ratio. Thus, under diluted conditions (50:50) G. hirsutum seed coated with S. tritici D5 showed an outstanding phytoremediation process. Therefore, this method can be implemented to the field level study to assess the metal removal prospects of this environmentally friendly method.

Effect and Mechanism of CaO on Iron Recovery and Desulfurization by Reduction Roasting-Magnetic Separation of High-Sulfur Cyanide Tailings

The increasing demand for iron ore in the world causes the continuous exhaustion of mineral resources. The utilization of iron in secondary resources has become of focus. The present study was carried out to recover iron from high-sulfur cyanide tailings by coal-based reduction roasting-magnetic separation. The mechanism of CaO to increase iron recovery and reduce sulfur was investigated by observing CO and CO2 gas composition produced by the reaction, mineral composition and microstructure, distribution characteristics of sulfur, and the intercalation relationship between iron particles and gangue minerals. The results showed that the addition of CaO could increase the gasification rate of the reducing agent, increase the amount of CO2 gas produced, promote the reduction of iron minerals, and improve the metallization degree of iron. When CaO was not added, sulfur was mainly transformed into troilite, which was closely connected with iron particles and was difficult to remove by grinding and magnetic separation. With the addition of CaO, CaO preferentially formed oldhamite with active sulfur, which reduced the formation of troilite. Oldhamite was basically distributed in an independent gangue structure. There was a clear boundary between iron particles and gangue minerals. Oldhamite could be removed by grinding-magnetic separation.

Dispersion modeling of particulate matter from the in-situ burning of spilled oil in the northwest Arctic area of Canada

In-situ burning can be used to prevent oil spreading in oil spill response. In this study, a steady-state Gaussian plume model was applied to analyze the concentration distribution of fine particulate matter produced by in-situ burning, as well as to assess the health risks associated with different combustion methods and ambient conditions, in reference to three simulation scenarios. The spatial and temporal distribution of emission sources can affect the dispersion pattern. The distribution into an array of different burning locations ensures better dispersion of emissions, thereby preventing the formation of high concentration regions. The wind and atmosphere stability play an important role in pollution dispersion. Lower wind and temperature inversion can seriously hinder the diffusion of pollutants. The health risk to technical staff adjacent to the burning areas is a serious concern, and when the community is more than 20 km away from the burning zone, there is few risks. Through simulation, the influences of combustion methods and natural factors on the concentration and diffusion of pollutants are evaluated. The results can help provide an optimized burning strategy for oil spill response in the Arctic area.

Efficient purification of hydrogen cyanide by synergistic effects of electrochemical and liquid phase catalysis

In this study, Co, Cu, Pd, and Pd/Cu composite metal ions were used to synthesize metal nanoparticles with high efficiency in purifying hydrogen cyanide gas. The pure liquid phase catalytic purification of hydrogen cyanide gas was studied. According to the removal rate, the Pd/Cu composite metal ions had the best purification efficiency among the nanoparticles of different metal types. The removal rate order was Pd/Cu>Pd>Cu>Co. The gas after reaction were analyzed by gas chromatography, and it was found that HCN was converted into CO₂, N₂ and NH₃ by nanoparticles. Then, Pd/Cu composite metal ions with the highest purification efficiency were used to study the electrochemical synergistic liquid-phase catalytic purification of HCN gas. The effects of electrochemical conditions and current on the electro-hydraulic synergistic purification were studied. The removal efficiency of HCN by electrochemical synergistic liquid phase catalysis was better than that by pure liquid phase catalysis. The different nanoparticles before and after HCN absorption were characterized and analyzed to explore the purification process of HCN. The purification mechanism of hydrogen cyanide by Pd-Cu catalyst under applied voltage was studied under certain conditions. During the catalytic reaction, the nano-catalyst was partially dissolved in liquid phase and partially HCN reacts with metal ions on the free or nanoparticles to form complex [Mc(CN)n]^2-n. Homogeneous and quasi-homogeneous reactions in liquid phase interweave together to form a more complex reaction system.

Influence of Mining Activities on Arsenic Concentration in Rice in Asia: A Review

Crop and livestock farming on contaminated soil has been found to induce the accumulation of trace elements in edible parts of plants, with subsequent risk to human and animal health. Since rice crop is a major source of energy in worldwide diets and is consumed by more than 3 billion people, the soil–rice pathway is regarded as a prominent route of human exposure to potentially toxic elements. This study provides an overview of arsenic contamination in paddy rice from mining-impacted areas in several Asian countries that are primary rice consumers. From this review, it may be concluded that mining activities, along with the associated residual waste, significantly contribute to arsenic contamination of this food crop as rice samples from these regions were highly contaminated, with the highest total arsenic concentrations recorded being 3–4 times higher than the maximum levels proposed by the Codex Alimentarius Commission. While the contamination in China, Korea, Indonesia, and Thailand appeared to be slightly affected by mining activities, the elevated levels of arsenic in rice from mining areas in India, Bangladesh, and Vietnam could be derived from arsenic-contaminated groundwater.