Effect of temperature on the leaching of heavy metals from nickel mine tailings in the arctic area, Norway

The leaching of heavy metals from tailings deposit due to the oxidation of sulphidic tailings and formation of acidic leachate is considered a high risk to the surrounding environment. Temperature plays an important role in the leaching of heavy metals from tailings in changing acid-based environment, especially in the Arctic area. To investigate how the temperature variation affected metal release from tailings in the Arctic area, a series of column leaching experiments was conducted under four temperature situations (5°C, 10°C, 14°C and 18°C). Physicochemical properties, Fe, Zn, Ni and Mn concentrations of leachates at each cycle were measured, and multivariate statistical analysis was applied to research the effect of temperature on heavy metals leaching from tailings in the Arctic area. The results showed that higher temperatures encouraged tailings to oxidation and sulfuration of and promoted heavy metal release from the tailings through precipitation and erosion. Ni, Zn and Mn have similar releasing resources from tailings and positive correlation in the leaching activity. Rising temperature accelerated Fe leaching; Fe leaching promoted leaching of the other metals, especially of Mn. Appropriately increase temperature will accelerate oxidization and sulfidization of the tailings, promote acid generation and increase TDS and, finally, promote the release of heavy metals. Climate change, with rising temperatures increasing the risk of heavy metals leaching from the tailings, should be given greater attention. Keeping tailings away from the appropriate temperature and in a higher alkalinity is a good method to control the leaching of heavy metals from tailings

Start-up Strategies for Anaerobic Ammonia Oxidation (Anammox) in In-Situ Nitrogen Removal from Polluted Groundwater in Rare Earth Mining Areas

The tremendous input of ammonium and rare earth element (REE) ions released by the enormous consumption of (NH4)2SO4 in in situ leaching for ion-adsorption RE mining caused serious ground and surface water contamination. Anaerobic ammonium oxidation (anammox) was a sustainable in situ technology that can reduce this nitrogen pollution. In this research, in situ, semi in situ, and ex situ method of inoculation that included low-concentration (0.02 mg·L−1) and high-concentration (0.10 mg·L−1) lanthanum (La)(III) were adopted to explore effective start-up strategies for starting up anammox reactors seeded with activated sludge and anammox sludge. The reactors were refrigerated for 30 days at 4 °C to investigate the effects of La(III) during a period of low-temperature. The results showed that the in situ and semi in situ enrichment strategies with the addition of La(III) at a low-concentration La(III) addition (0.02 mg·L−1) reduced the length of time required to reactivate the sludge until it reached a state of stable anammox activity and high nitrogen removal efficiency by 60–71 days. The addition of La(III) promoted the formation of sludge floc with a compact structure that enabled it to resist the adverse effects of low temperature and so to maintain a high abundance of AnAOB and microbacterial community diversity of sludge during refrigeration period. The addition of La(III) at a high concentration caused the cellular percentage of AnAOB to decrease from 54.60 ± 6.19% to 17.35 ± 6.69% during the enrichment and reduced nitrogen removal efficiency to an unrecoverable level to post-refrigeration

Traffic-related dustfall and NOx, but not NH3, seriously affect nitrogen isotopic compositions in soil and plant tissues near the roadside

Ammonia (NH3) emissions from traffic have received particular attention in recent years because of their important contributions to the growth of secondary aerosols and the negative effects on urban air quality. However, few studies have been performed on the impacts of traffic NH3 emissions on adjacent soil and plants. Moreover, doubt remains over whether dry nitrogen (N) deposition still contributes a minor proportion of plant N nutrition compared with wet N deposition in urban road environments. This study investigated the delta N-15 values of road dustfall, soil, moss, camphor leaf and camphor bark samples collected along a distance gradient from the road, suggesting that samples collected near the road have significantly more positive delta N-15 values than those of remote sites. According to the SIAR model (Stable Isotope Analysis in R) applied to dustfall and moss samples from the roadside, it was found that NH3 from traffic exhaust (8.8 +/- 7.1%) contributed much less than traffic-derived NO2 (52.2 +/- 10.0%) and soil N (39.0 +/- 13.8%) to dustfall bulk N; additionally, 68.6% and 31.4% of N in mosses near the roadside could be explained by dry N deposition (only 20.4 +/- 12.5% for traffic-derived NH3) and wet N deposition, respectively. A two-member mixing model was used to analyse the delta N-15 in continuously collected mature camphor leaf and camphor bark samples, which revealed a similarity of the delta N-15 values of plant-available deposited N to N-15-enriched traffic-derived NOx-N. We concluded that a relatively high proportion of N inputs in urban road environments was contributed by traffic-related dustfall and NOx rather than NH3. These information provide useful insights into reducing the impacts of traffic exhaust on adjacent ecosystems and can assist policy makers in determining the reconstruction of a monitoring network for N deposition that reaches the road level. (C) 2019 Elsevier Ltd. All rights reserved

Pollution and health risk assessment of rare earth elements in Citrus sinensis growing soil in mining area of southern China

Background Analyzing the pollution and health risk of rare earth elements (REEs) in crop-growing soils around rare earth deposits can facilitate the improvement of REE mining-influenced area. In this study, pollution status, fraction and anomaly, plant accumulation characteristics, and potential risks of REEs (including heavy and light rare earth elements, HREEs and LREEs) in C. sinensis planting soil near ion-adsorption deposits in southern Ganzhou were analyzed. The influence of the soil environment on REEs in soil and fruit of C. sinensis was also explored. Methods The geo-accumulation index (Igeo) and ecological risk index(RI) were used to analyze the pollution potential and ecological risks of REEs in soils, respectively. Health risk index and translocation factor (TF) were applied to analyze the accumulation and health risks of REEs in fruit of C. sinensis. The influence of soil factors on REEs in soil and fruit of C. sinensis were determined via correlation and redundancy analysis. Results Comparison with background values and assessment of Igeo and RI indicated that the soil was polluted by REEs, albeit at varying degrees. Fractionation between LREEs and HREEs occurred, along with significant positive Ce anomaly and negative Eu anomaly. With TF values Anxi > Wuyang and of LREE in fruit higher in Wuyang. Correlation and redundancy analysis indicated that K2O, Fe2O3 and TOC are important soil factors influencing REE accumulation by C. sinensis, with K2O positively related and Fe2O3 and TOC negatively related to the accumulation process

Dissolved hydrolyzed amino acids in precipitation in suburban Guiyang, southwestern China: Seasonal variations and potential atmospheric processes

Proteinaceous compounds are particularly interesting because of their ubiquity and importance in many atmospheric processes. We investigated hydrolyzed amino acid (HAA), dissolved organic nitrogen (DON), nitrate (NO3-) and ammonium (NH4+) concentrations in precipitation samples collected in a suburban site in Guiyang over a 12 month period. Annually averaged total HAA, DON, NO3- and NH4+ concentrations were 3.7 mu mol L-1, 151.1 mu mol L-1, 68.9 mu mol L-1 and 117.3 mu mol L-1, respectively. Regarding the HAAs in precipitation, glutamic acid, glycine and proline were present in relatively high concentrations, followed by aspartic acid and alanine. The concentrations of total HAAs in precipitation showed a clear seasonal cycle, with a minimum level in winter and a maximum level in spring. Based on seasonal variations of total HAAs together with back-trajectory analysis, the air mass origins did not significantly impact the precipitation HAA levels. The NO3- concentrations recorded a better positive correlation (P < 0.01) with both the DON and total HAA concentrations than the NH4+ concentrations, possibly revealing that the sources for precipitation amino acids in suburban Guiyang were more linked with NO3- sources (from biomass burning, microbial activities and agricultural activities) than with NH4+ sources (from biomass burning and agricultural activities). In particular, in some specific periods, such as spring, abundant pollen releases may have been responsible for the relatively high precipitation amino acid concentrations. The average air temperature and the highest air temperature showed a positive correlation with the total HAA levels in precipitation. Clearly, the increase in precipitation total HAAs with higher air temperatures may indicate the enhanced temperature-induced degradation of high molecular weight atmospheric proteinaceous matter. Moreover, the volume-weighted precipitation glycine and total HAA levels were positively correlated with the product of atmospheric ozone and nitrogen dioxide, indicating that atmospheric proteinaceous matter may be inextricably bound up with both ozone- and nitrogen dioxide-related atmospheric processes. In conclusion, this study improves current knowledge on the origins and atmospheric processes of atmospheric proteinaceous compounds

Hydrothermal synthesis of mesoporous tobermorite from fly ash with enhanced removal performance towards Pb2+ from wastewater

The mesoporous tobermorite with high removal efficiency of Pb2+ was hydrothermally synthesized from fly ash (FA). The physicochemical characteristics of the synthesized tobermorite were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller specific surface area analyzer, and Fourier transform infrared spectroscopy (FTIR). It was found that the specific surface area and pore volume of the mesoporous tobermorite were 29.98 m2/g and 0.1325 cm3/g, respectively, which were much higher than those of FA. The tobermorite showed high removal efficiency for Pb2+ of 99.93%, and the adsorption kinetic data for Pb2+ adsorption on tobermorite were better fitted with the pseudo-second-order model. Besides, the Langmuir isotherm model provided better description of the Pb2+ adsorption isotherm, and the maximum adsorption capacity for Pb2+ adsorption on tobermorite was 266.67 mg/g, which was much higher than that on FA (86.13 mg/ g). What's more, the adsorption mechanisms of the tobermorite towards Pb2+ were analyzed by XRD, SEMenergy dispersive spectroscopy, and FTIR. It was found that the high adsorption capacity of the tobermorite towards Pb2+ was ascribed to its mesoporous structure, a mass of -OH, the ion-exchange of Ca2+ with Pb2+, and the precipitation of 2PbCO3.Pb(OH)2. This work presents the tobermorite synthesized from FA as an effective and low-cost adsorbent towards Pb2+, and provides a potential application method of FA in treatment of industrial wastewater containing Pb2+

Effective removal of Pb2+ and Cd2+ from wastewater by mesoporous tobermorite synthesized from alumina-extracted fly ash

In this study, for the first time, the effective removal of Pb2+ and Cd2+ from wastewater by mesoporous tobermorite synthesized from alumina-extracted fly ash (AEFA) was reported. The results of characterization of the synthesized tobermorite indicated that it showed mesoporous structure, with a high specific surface area of 68.4 m(2) g(-1). The tobermorite particles were aggregates of plate-like particles resulting in slit-shaped pores. The mesoporous tobermorite showed high removal efficiency for Pb2+ and Cd2+ of 99.97% and 78.64%, respectively, and the adsorption kinetic data for Pb2+ and Cd2+ on tobermorite were better fitted to the pseudo-second-order kinetic model. The Pb2+ and Cd2+ adsorption isotherms were better described by the Langmuir isotherm model, and the maximum adsorption capacities of the tobermorite towards Pb2+ and Cd2+ were 338.98 and 105.37 mg g(-1), respectively. The high adsorption capacities of the tobermorite towards Pb2+ and Cd2+ were due to its high specific surface area, the ion exchange of Ca2+ with Pb2+ and Cd2+, and the precipitation. This study shows the mesoporous tobermorite synthesized from AEFA as a low-cost and effective adsorbent for Pb2+ and Cd2+ and broadens the potential application of AEFA in wastewater treatment

Removal of methyl orange from aqueous solutions through adsorption by calcium aluminate hydrates

Methyl orange (MO) is a kind of anionic dye and widely used in industry. In this study, tricalcium aluminate hydrates (Ca-Al-LDHs) are used as an adsorbent to remove methyl orange (MO) from aqueous solutions. The resulting products were studied by X-ray diffraction (XRD), infrared spectroscopy (MIR), thermal analysis (TG-DTA) and scanning electron microscope (SEM). The XRD results indicated that the MO molecules were successfully intercalated into the tricalcium aluminate hydrates, with the basal spacing of Ca-Al-LDH expanding to 2.48 nm. The MIR spectrum for CaAl-MO-LDH shows obvious bands assigned to the N@N, N@H stretching vibrations and S@O, SO_ 3 group respectively, which are considered as marks to assess MO_ ion intercalation into the interlayers of LDH. The overall morphology of CaAl-MOLDH displayed a ‘‘honey-comb’’ like structure, with the adjacent layers expanded