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Mineralogical and morphological factors affecting the separation of copper and arsenic in flash copper smelting slag flotation beneficiation process
No full textSeparating 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
Prediction of the confirmed cases and deaths of global COVID-19 using artificial intelligence
No full textThe outbreak of coronavirus disease 2019 (COVID-19) has seriously affected the environment, ecology, economy, society, and human health. With the global epidemic dynamics becoming more and more serious, the prediction and analysis of the confirmed cases and deaths of COVID-19 has become an important task. We develop an artificial neural network (ANN) for modeling of the confirmed cases and deaths of COVID-19. The confirmed cases and deaths data are collected from January 20 to November 11, 2020 by the World Health Organization (WHO). By introducing root mean square error (RMSE), correlation coefficient (R), and mean absolute error (MAE), statistical indicators of the prediction model are verified and evaluated. The size of training and test confirmed cases and death base employed in the model is optimized. The best simulating performance with RMSE, R, and MAE is realized using the 7 past days' cases as input variables in the training and test dataset. And the estimated R are 0.9948 and 0.9683, respectively. Compared with different algorithms, experimental simulation shows that trainbr algorithm has better performance than other algorithms in reproducing the amount of the confirmed cases and deaths. This study shows that the ANN model is suitable for predicting the confirmed cases and deaths of COVID-19 in the future. Using the ANN model, we also predict the confirmed cases and deaths of COVID-19 from June 5, 2020 to November 11, 2020. During the predicting period, the R, RMSE, and MAE for new infected confirmed cases of COVID-19 are 0.9848, 17,554, and 12,229, respectively; the R, RMSE, and MAE for new confirmed deaths of COVID-19 are 0.8593, 631.8, and 463.7, respectively. The predicted confirmed cases and deaths of COVID-19 are very close to the actual confirmed cases and deaths. The results show that continuous and strict control measures should be taken to prevent the further spread of the epidemic
Indian summer monsoon variability in northeastern India during the last two millennia
No full textHigh-resolution proxy records help to understand natural forcing of climate variability and improving our capability to predict climate variability on decadal to centennial time scales. Present study from the Mawmluh cave, northeastern India shows sudden shifts in speleothem oxygen isotope values, indicating several abrupt changes in the Indian summer monsoon (ISM) during-212 BCE to 1986 CE. Moderate ISM conditions prevailed during-212 BCE to 400 CE punctuated with weak intervals, strong ISM during 400 and 500 CE and from 640 to 1060 CE, whereas weak ISM conditions prevailed during 520-540 CE, 820-850 CE and 940-980 CE and after 1060 CE. The interval from 1060 to 1986 CE witnessed decreased precipitation than the previous millennium. The latter phase of the Medieval Climate Anomaly (MCA; 1060 to 1200 CE) was quite drier in contrast to the earlier intervals. The ISM was generally weak during the Little Ice Age (LIA; 1350 to 1850 CE) with short-term pulses of high precipitation when sun-spot activity was high. The data shows the weakest ISM condition during 1640-1740 CE (Maunder Minimum) of the last two millennia. Variations in extra-tropical northern hemisphere temperatures due to volcanic activity and solar insolation, and accompanying northward/southward shifting of the Inter-Tropical Convergence Zone played a pivotal role in modulating the strength of the ISM during the past two millennia
A long-term chemical characteristics and source apportionment of atmospheric rainfall in a northwest megacity of Xi'an, China
No full textA long-term measurement on rainfall was conducted in urban Xi'an, China, from 2009 to 2016. The seasonal and annual variations of major inorganic components and their chemical properties in the rainfall were studied. The annual rainfall ranged from 165.3 to 916.3 mm. The pH value of the rainfall ranged from 6.36 to 7.19, with an average value of 6.70. The electric conductivity (EC) in the rainfall was in a range of 55.91 to 227.44 mu S center dot cm(-1). Ammonium (NH4+), calcium (Ca2+), nitrate (NO3-), and sulfate (SO42-) were the four major components, accounting for 88.5% of the total quantified inorganic ion concentration. Neutralization factors were determined for Ca2+ (1.03), NH4+ (0.57), Mg2+ (0.10), Na+ (0.06), and K+ (0.04). The high abundance of NH4+ that formed from its precursor of ammonia gas (NH3) suggested the contribution of agricultural fertilization. Ca2+ in the rainfall was mainly from natural sources such as soil dust, while anions of NO3- and SO42- originated from fossil fuel combustion. Source apportionment was conducted with positive matrix factorization (PMF) which identified that secondary inorganic formation, crustal dust, coal combustion, and biomass burning are the contributors to the rainfall. In between, secondary inorganic formation was the largest contributor, which accounted for 27.8-58.1% of the total sources, followed by crustal dust of 0.4-42.6%. The results of this long-term study demonstrated the decreasing trends of contributions from coal combustion and biomass burning under a series of air pollution control measures implemented by the government. However, continuous urbanization and development of the city caused substantial increases of the construction activities, inducing more crustal dusts to the environment in urban Xi'an
Timing and forcing mechanism of the final Neotethys seawater retreat from Central Iran in response to the Arabia-Asia collision in the late early Miocene
No full textThe Iranian Plateau lies in the middle of the Neotethys tectonic domain; to the east it connects with the Tibetan Plateau, and to the west with the Anatolian Plateau and the Alpine orogenic belts. In the Cenozoic it underwent land/sea changes and tectonic uplift in response to the Arabia-Asia plate collision. One of the most prominent geological consequences of the collision was the disappearance of an epicontinental sea in Central Iran, which was a northeastern branch of the Neotethys seaway in the Oligocene-early Miocene. The timing of the final seawater retreat from Central Iran and its forcing mechanism are important for understanding the effects of Arabia-Asia plate collision as well as global eustatic sea-level changes. In this paper we present new magnetostratigraphy, U-Pb ages of one tuffaceous bed, and stable isotopic records of carbonates. The results of this multidisciplinary study indicate that a shallow open sea in the Qom back-arc basin ended at 17 Ma, but the final seawater retreat from a restricted marine environment was at 16.8 Ma. The final regression was just before the Middle Miocene Optimum, implying that it was not related to a climatic factor, but driven by the Arabia-Asia plate collision. Moreover, the delta O-18 record of fine-grained lacustrine carbonates indicates an isotopic shift towards more positive isotopes after 13 Ma, suggesting an enhanced aridification in Central Iran. This climatic deterioration was a response to reduced transport of moisture by westerlies from a retreating Neotethys Sea driven by a global eustatic sea-level drop in response to the East Antarctica ice-sheet expansion after the middle Miocene Optimum
Quantitative estimates of Holocene glacier meltwater variations on the Western Tibetan Plateau
No full textKnowledge of the alpine glacier meltwater variations is fundamental prerequisite for understanding glacier dynamics and assessing the availability of freshwater resources. Glaciers on the Tibetan Plateau (TP) are sources of water for most major Asian rivers, but their melting history remains unclear, preventing in-depth understanding of their mechanisms. Here, we propose the authigenic carbonate delta O-18 from glacial lakes as a quantitative proxy to estimate variations of glacier meltwater. In the Western Kunlun Mountain, 6 18 0 record at Guozha Co indicates that maximum glacier meltwater (-28.62 +/- 25.76 Gt) occurred at 9.5-8.5 ka BP, and minimum glacier meltwater (24.53 +/- 25.02 Gt) at 1.3-0.5 ka BP. Nearly 20% of regional glaciers melted from the Early to Late Holocene, likely controlled by the summer temperature and accumulation of melting potential estimated by positive degree-day. Based on the projected temperature, this study suggests the TP glaciers likely face severe threats at the current rates of global warming. (C) 2021 Elsevier B.V. All rights reserved
Responses of soil ammonia-oxidizing bacteria and archaea to short-term warming and nitrogen input in a semi-arid grassland on the Loess Plateau
No full textAmmonia-oxidizing archaea (AOA) and bacteria (AOB) predominantly control ammonia oxidation, the first and rate-limiting step of nitrification, and critically affect plant utilization and the fate of reactive nitrogen (N) input to soil. Both AOA and AOB are often sensitive to environmental changes, but their responses to the concurrent climate warming and N input remain poorly understood, particularly in semi-arid grassland ecosystems where nitrification dominates soil N transformations. We examined the interactive effects of short-term (2-yr) warming and N input (12 g N m(-2) y(-1)) on the abundance and community structure of AOA and AOB in a semi-arid grassland on China's Loess Plateau. Results showed that AOA abundance was significantly higher than AOB in all treatments. N input significantly increased the abundance of AOA and AOB by 32% and 521%, respectively, and induced a significant shift in the AOB community composition. Warming significantly increased the abundance of AOB by 94%, but had no impact on the AOA abundance. Warming (alone or combined with N input) did not significantly affect the community structure of AOA or AOB. These results indicated that AOB was more sensitive to N input and climate warming than AOA in semi-arid Loess grasslands. Our findings suggest that understanding the responses of AOB abundance and composition may be key to predict the N dynamics under future global change scenarios
Rapid warming has resulted in more wildfires in northeastern Australia
No full textWildfires, or bushfires, are one of the most destructive natural disasters in Australia, which can cause many deaths of stock, native animals, sometimes humans, and huge impacts on infrastructure. Reconstructing past wildfires and exploring the links between wildfires and climate are essential for understanding the dynamics of wildfires and for predicting future risks. In this study, the frequency of wildfires in northeastern Australia over the past 25,000 years was reconstructed from the charcoal records preserved in peat and lake sediments. The results showed that the frequency of wildfires were relatively low during the cool last glacial period and the warm mid Holocene, indicating that the stable mean climate conditions, whether cool or warm, would not independently initiate increased wildfires in northeastern Australia. The most frequent wildfires occurred during the last deglaciation period, when Earth's climate warmed and the warming rate was the highest over the last 25,000 years, before recent anthropogenic warming. It suggested that the rapid global warming may greatly increase the likelihood of dangerous wildfires in northeastern Australia during the last deglaciation. The wildfires reactivated over the most recent 4000 years, coinciding with amplified climate variability and probably an expansion of human activity. The rapid warming of global climate during the last deglaciation period is an ideal analogue for current anthropogenic global warming. The comparison between fire count and temperature changes in Australia since 2003 also showed that the fire frequency in Australia in recent years is more closely correlated with the warming amplitude, rather than mean temperature. Our results implied that the wildfire risk in northeastern Australia may increase further under the expected accelerating global warming, if human management systems does not intrude. Wildfire modeling could benefit greatly by considering the relationship of fires with dimate variability rather than only with stable climate scenarios. (C) 2021 Elsevier B.V. All rights reserved
Holocene variability of East Asian summer monsoon as viewed from the speleothem delta O-18 records in central China
No full textMonsoon precipitation in East China shows distinct spatial distribution and its variability is closely linked with the changes of the East Asian summer monsoon (EASM). Located in the transition zone between the southern subtropical humid climate and the northern warm temperate semi-humid climate, central China is a core region for recognizing and understanding the spatio-temporal variability of the EASM. Using U-series dating and stable isotope analysis on five stalagmites (MG-1, MG-2, MG-7, MG-40 and MG-64) from Magou Cave, Henan Province, Central China, we construct a high-resolution and precisely dated composite stalagmite delta O-18 time series covering most of the Holocene. This composite record reveals variations in precipitation delta O-18 between 11.7 and 1.1 ka BP with average resolution of similar to 4 yrs. The Magou composite record demonstrates that EASM intensity dominates long-term changes in precipitation delta O-18, which generally follows the northern hemisphere summer insolation (NHSI) trend. Both, Ensemble Empirical Mode Decomposition (EEMD) and wavelet filtering analyses real that the amplitudes of long-term (100-500 and 500-3000 yrs) components were slightly reduced between 8.5 and 4.9 ka BP, implying a weakened influence of climatic forcings on centennial and even millennial timescales during this warm period. Variance on 1-30-yr timescales is relatively low and ascribed to sampling resolution. Fourteen weak EASM intervals, including the 8.2 ka event, were identified within the period corresponding broadly with the Holocene Megathermal. Since no cold excursions other than the 8.2 ka event are found in the Greenland ice core records, we tentatively propose that oscillations in tropical sea surface temperature (SST) likely play an important role in steering other weak monsoon events. Aligning the Magou composite record and other moisture records with archaeological records from the study region, it seems that climate change influenced both the spatial distribution and agricultural practices of ancient cultures. However, overall moderate climatic changes in this region, most likely characterized by shifts between subtropical humid climate and warm temperate semi-humid climate, supported a generally consecutive development of ancient cultures without major hiatuses. (C) 2021 Elsevier B.V. All rights reserved
High light absorption and radiative forcing contributions of primary brown carbon and black carbon to urban aerosol
No full textTo investigate the seasonal variation of black carbon (BC) and brown carbon (BrC) light absorption at an urban site in Xi'an, China, an annual measurement was conducted by using a 7-wavelengths Aethalometer (model AE33). The results showed the aerosol absorptions were observed approximately 5-8 times greater in winter (395 Mm(-1) at 370 nm and 99 Mm(-1) at 880 nm, respectively) than those in autumn (49 Mm(-1) at 370 nm and 18 Mm(-1) at 880 nm, respectively). BC was the dominant light absorbing carbonaceous component at all wavelengths (from 370 nm to 950 nm). BrC absorption (370 nm) maximized during winter with 41% of the total aerosol absorption, and was lower in autumn (16%). The light absorption contributions of primary BrC (BrCpri) were higher than that of secondary BrC (BrCsec) in four seasons, with more than 67% of total BrC light absorption. The seasonal absorption Angstrom exponents (AAEs) of BrC, BrCpri, and BrCsec were directly derived with the highest values (3.91, 3.69, and 4.94, respectively) in wintertime. The BrCpri contributed much higher solar absorptions percentage to BC than BrCsec. The results underlined the primary emissions of urban BrCpri and BC, implying that the strategies of energy efficiency enhancement and energy structure reformation will be very important in reducing primary emissions in China. Such investigations should be conducted in other developing countries with severe air pollution.
(c) 2020 Published by Elsevier B.V. on behalf of International Association for Gondwana Research