The simultaneous removal of cadmium (II) and lead (II) from wastewater with the application of green synthesized magnesium silicate hydrate

To the purpose of solving the problems of coal-gangue accumulation in the mine and pollution of cadmium (II) and lead (II) in wastewater, magnesium silicate hydrate (M-S-H) was synthesized from coal-gangue by thermochemical. M-S-H had removed Cd(II) and Pb(II) by adsorption. The characterization of M-S-H and adsorption effects factors, including initial solution pH, initial metal concentration, adsorbent dose, temperature, reaction time, and coexisting ions were explored for adsorption performance. The solution pH was precisely controlled by a pH meter. The adsorption temperature was controlled by a thermostatic gas bath oscillator with an error of ±0.3. These results from this study revealed that M-S-H surface area increased from 8.12 to 26.15 m2/g with a pore volume of 0.12 cm3/g. The maximum adsorptions of Cd(II) and Pb(II) by M-S-H were 59.52 and 83.33 mg g−1, respectively. The adsorption performance for Cd(II) and Pb(II) reached saturation at pH 5, temperature 25°C, M-S-H 6 g/L, reaction time 90 min, and metal concentration 300 mg/L. Cd(II) and Pb(II) adsorption were spontaneous and endothermic and well fitted with the pseudo-second-order kinetic and Langmuir isotherm adsorption models. The adsorption mechanisms were electrostatic interaction, ion exchange, and surface complexation. This research indicated that the synthesized M-S-H from coal gangue was efficiently eliminated metal ions from water, opening up new possibilities for coal gangue reuse

Spatial distributions, fractionation characteristics, and ecological risk assessment of trace elements in sediments of Chaohu Lake, a large eutrophic freshwater lake in eastern China

The concentrations, spatial distribution, fractionation characteristics, and potential ecological risks of trace elements (Cu, Pb, Zn, Cr, Ni, and Co) in the surface sediment samples collected from 32 sites in Chaohu Lake were investigated. The improved BCR sequential extraction procedure was applied to analyze the chemical forms of trace elements in sediments. The enrichment factor (EF), sediment quality guidelines (SQGs), potential ecological risk index (PERI), and risk assessment code (RAC) were employed to evaluate the pollution levels and the potential ecological risks. The results found that the concentrations of Cu, Pb, Zn, Cr, Ni, and Co in the surface sediments were 78.59, 36.91, 161.84, 98.87, 38.92, and 10.09 mg kg(-1), respectively. The lower concentrations of Cu, Pb, Zn, Cr, and Ni were almost found in the middle part of the lake, while Co increased from the western toward the eastern parts of the lake. Cr, Ni, Co, and Zn predominantly existed in the residual fractions, with the average values of 76.35, 59.22, 45.60, and 44.30%, respectively. Cu and Pb were mainly combined with Fe/Mn oxides in reducible fraction, with the average values of 66.4 and 69.1%, respectively. The pollution levels were different among the selected elements. Cu had the highest potential ecological risk, while Cr had the lowest potential ecological risk

The influence of gold mining wastes on the migration-transformation behavior and health risks of arsenic in the surrounding soil of mined-area

Understanding the characteristic heavy metals and their migration-transformation behavior in mining areas is essential for the prevention and control of mining pollution. This study selected a gold mine in the Anqing-Guichi ore-cluster region in the Middle-Lower Yangtze metallogenic belt as the research area, the concentrations, and migration-transformation mechanisms of metalloid As and typical heavy metals (Cd, Zn, Pb, Cu, Cr, and Ni) in gold mining wastes (mine tailings and sewage sludge) and the surrounding soil (farmland soil and soil a mining area) were investigated. The results showed that the concentration of As was high in both mining wastes and soils, and the geo-accumulation index values of As in soils ranging from 1.44–6.70, indicated that As pollution was severe in the soil. Besides, a close correlation between the concentration of As and the content of iron was observed by XRF analysis, in conjunction with SEM observations, most As-bearing phases are embedded in Fe, O, and Si compounds. According to EDS and XPS results, the Fe-O-As particle was suggested to be Fe-(oxy)hydroxides with absorbed or co-precipitated As. Furthermore, the arsenic phase observed in the soils were consistent with the weathering oxidation products in the tailings, demonstrating that the mineral particles in the tailings could migrate into soils via atmospheric transport, rainwater leaching, surface runoff, etc., and consequently result in heavy metal accumulation. The sequential chemical extraction result showed that the residual state of As in the soil exceeded 60%, and As posed no risk to low risk according to the Risk assessment code result. However, due to the high concentration and high mobility of arsenic, its environmental impact cannot be ignored even if its bio-accessibility in mined area soil is low

The partitioning and environmental characteristics of trace elements in a coal-fired power plant: a case study at Huaibei, China

The trace elements (TEs) in coal are of great concern due to their toxicity and bioavailability. The coal, bottom ash, fly ash and gaseous species were sampled to study the partitioning and environmental behaviors of TEs during coal combustion. The mineral and phase characterizations of coal combustion residue were determined by X-ray powder diffraction (XRD) and fourier transform infrared spectroscopy (FTIR), respectively. The gaseous emission, risk assessment code and leaching experiment EN 12457 Part 2 procedure were employed to assess the potential environmental impacts. The concentrations of TEs in all the collected samples were determined by inductively coupled plasma mass spectrometry (ICP-MS). During combustion, the mineral compositions of coal (kaolinite, quartz, illite, pyrite and calcite) were changed to mullite, quartz, hematite, lime, magnetite and anhydrite. Arsenic, Cd, Cu, Pb and Zn were emitted mainly in fly ash and gaseous phases. In the current unconfined deposits, the TEs (As, Cu, Pb and Zn) in bottom ash and fly ash may pose a medium risk to the environment. High regularization and management countermeasures including immobilization/stabilization, re-utilization of combustion ash, and controlled disposal should be conducted to eliminate/minimize environmental and ecological risks in coal activities areas

Mineralogical and morphological factors affecting the separation of copper and arsenic in flash copper smelting slag flotation beneficiation process

Separating copper and arsenic has always been a major problem in the copper slag flotation process, which influences copper slag utilization and the environmental safety. A comparative study of flash smelling furnace (FSF) slag and its flotation products (concentrate and tailing) reveals the factors affecting the separation of copper and arsenic in the beneficiation process from the perspective of mineralogy and morphology. The elemental fractionation in the process shows a positive correlation of As, Cu and Cd and an obvious correlation between speciation transformation of copper and arsenic was observed. The occurrence of arsenic and copper in FSF slag correlate the key phases of arsenic copper alloys, accounted for 88.91 % of total arsenic-bearing phases and 32.28% of copper-bearing phases. Closely-embeded matte and copper-arsenic alloys incerease the difficulty of the separation suggesting the finer grinding is needed for slag. Arsenic is liberated and oxidized into arsenate compounds while the recombination of As-O and Cu-S happened in the process affecting the selectivity of copper and arsenic. Arsenic fixed in silicate minerals is discharged into tailing which suggested to induce and fix arsenic into silicate minerals can facilitate arsenic removal from concentrate. FSF slag and its flotation concnetrate show risks of some of some of HMs which should be cautiously transported, disposed, and utilized

Lead in soil and agricultural products in the Huainan Coal Mining Area, Anhui, China: levels, distribution, and health implications

Heavy metal accumulation in agricultural soil is of great concern, as heavy metals can be finally transferred to the human body through the food chain. A field survey was conducted to investigate the lead (Pb) levels and distribution in soil, agricultural products (wheat, paddy, and soybean), and fish, in the Huainan Coal Mining Area (HCMA), Anhui Province, China, to provide reference information to local inhabitants. The daily intake and target hazard quotients of Pb through food consumption were assessed. Results showed that the mean Pb concentration in soil was higher than the Huainan soil background Pb value but lower than the maximum allowance Pb concentration for agricultural soil (GB 15618-2008). The elevated Pb in soil, especially in rainy months (June to August in Huainan), might be related to Pb leaching from ambient coal gangue piles. Excessive Pb concentration was found in the grains of food crops, which would pose a potential health risk to local inhabitants. Therein, wheat showed higher Pb bioaccumulation ability than other crops. With regard to the Pb levels in muscles, fishes were considered to be safe for consumption. The calculations on daily intake and tolerable hazard quotient of Pb suggest that the potential health hazard posed by Pb is currently insignificant for the inhabitants in the HCMA.</p

Co-combustion of bituminous coal and biomass fuel blends: Thermochemical characterization, potential utilization and environmental advantage

The thermochemical characteristics and gaseous trace pollutant behaviors during co-combustion medium-to-low ash bituminous coal with typical biomass residues (corn stalk and sawdust) were investigated. Lowering of ignition index, burnout temperature and activation energy in the major combustion stage are observed in the coal/biomass blends. The blending proportion of 20% and 30% are regarded as the optimum blends for corn stalk and sawdust, respectively, in according the limitations of heating value, activation energy, flame stability and base/acid ratio. The reductions of gaseous As, Cd, Cu, Pb, Zn and polycyclic aromatic hydrocarbon (PAHs) were 4.5%, 7.8%, 6.3%, 9.8%, 9.4% and 17.4%, respectively, when co-combustion coal with 20% corn stalk. The elevated capture of trace elements were found in coal/corn stalk blend, while the coal/sawdust blend has the better PAHs control potential. The reduction mechanisms of gaseous trace pollutants were attributed to the fuel property, ash composition and relative residence time during combustion. (C) 2016 Elsevier Ltd. All rights reserved

Speciation Characterization and Environmental Stability of Arsenic in Arsenic-Containing Copper Slag Tailing

The increasing presence of arsenic-containing impurities within Cu ores can adversely affect the smelting process and aggravate the environmental impact of slag tailing. This study investigates the geochemical, mineralogical, and chemical speciation characteristics to better understand the association and environmental stability of metal(loid)s in copper slag tailing. The results indicate that the predominant chemical compositions of the selected slag tailing are Fe2O3 (54.8%) and SiO2 (28.1%). These tailings exhibit potential for multi-elemental contamination due to elevated concentrations of environmentally sensitive elements. Mineral phases identified within the slag tailings include silicate (fayalite), oxides (magnetite and hematite), and sulfides (galena, sphalerite, arsenopyrite, and chalcopyrite). The consistent presence of silicate, iron, arsenic, and oxygen in the elemental distribution suggests the existence of arsenic within silicate minerals in the form of Si-Fe-As-O phases. Additionally, arsenic shows association with sulfide minerals and oxides. The percentages of arsenite (As(III)) and arsenate (As(V)) within the selected slag tailings are 59.4% and 40.6%, respectively. While the slag tailings are deemed non-hazardous due to the minimal amounts of toxic elements in leachates, proper disposal measures should be taken due to the elevated carbonate-bound levels of As and Cu present in these tailings