| 1. |
- Atsawawaranunt, Kamolphat, et al.
(author)
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The SISAL database : a global resource to document oxygen and carbon isotope records from speleothems
- 2018
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In: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 10:3, s. 1687-1713
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Journal article (peer-reviewed)abstract
- Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide "out-of-sample" evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (delta O-18, delta C-13) measurements are referenced by distance from the top or bottom of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information on the full range of measurements carried out on each speleothem and information on the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data.
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| 2. |
- Comas-Bru, Laia, et al.
(author)
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Evaluating model outputs using integrated global speleothem records of climate change since the last glacial
- 2019
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In: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:4, s. 1557-1579
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Journal article (peer-reviewed)abstract
- Although quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to using the speleothem data for data-model comparisons. Here, we illustrate this using 456 globally distributed speleothem delta O-18 records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates the process of procuring large numbers of records if data-model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotope values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model's ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotope data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on delta O-18 values, the optimum period for the modern observational baseline and the selection of an appropriate time window for creating means of the isotope data for palaeo-time-slices.
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| 3. |
- He, Yan, et al.
(author)
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Discovering Optimal Triplets for Assessing the Uncertainties of Satellite-Derived Evapotranspiration Products
- 2023
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In: Remote Sensing. - 2072-4292. ; 15:13
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Journal article (peer-reviewed)abstract
- Information relating to errors in evapotranspiration (ET) products, including satellite-derived ET products, is critical to their application but often challenging to obtain, with a limited number of flux towers available for the sufficient validation of measurements. Triple collocation (TC) methods can assess the inherent uncertainties of the above ET products using just three independent variables as a triplet input. However, both the severity with which the variables in the triplet violate the assumptions of zero error correlations and the corresponding impact on the error estimation are unknown. This study proposed a cross-correlation analysis approach to discover the optimal triplet of satellite-derived ET products with regard to providing the most reliable error estimation. All possible triple collocation solutions for the same product were first evaluated by the extended triple collocation (ETC), among which the optimum was selected based on the correlation between ETC-based and in-situ-based error metrics, and correspondingly, a statistic experiment based on ranked triplets demonstrated how the optimal triplet was valid for all pixels of the product. Six popular products (MOD16, PML_V2, GLASS, SSEBop, ERA5, and GLEAM) that were produced between 2003 to 2018 and which cover China’s mainland were chosen for the experiment, in which the error estimates were compared with measurements from 23 in-situ flux towers. The findings suggest that (1) there exists an optimal triplet in which a product as an input of TC with other collocating inputs together violate TC assumptions the least; (2) the error characteristics of the six ET products varied significantly across China, with GLASS performing the best (median error: 0.1 mm/day), followed by GLEAM, ERA5, and MOD16 (median errors below 0.2 mm/day), while PML_V2 and SSEBop had slightly higher median errors (0.24 mm/day and 0.27 mm/day, respectively); and (3) removing seasonal variations in ET signals has a substantial impact on enhancing the accuracy of error estimations.
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| 4. |
- Hu, Xianfeng, et al.
(author)
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A novel process on the recovery of zinc and manganese from spent alkaline and zinc-carbon batteries
- 2021
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In: Journal of Hazardous Materials. - : Elsevier B.V.. - 0304-3894 .- 1873-3336. ; 411
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Journal article (peer-reviewed)abstract
- Spent alkaline and zinc-carbon batteries contain valuable elements (notably, Zn and Mn), which need to be recovered to keep a circular economy. In this study, the black mass materials from those spent batteries are pyrometallurgically treated via a series of process steps in a pilot-scale KALDO furnace to produce an Mn–Zn product, a ZnO product, and an MnO (manganese monoxide) product, toward applications of Mn–Zn micronutrient fertilizer, zinc metal, and manganese alloy, respectively. After an oxidative roasting step, an Mn–Zn product, containing 43% Mn, 22% Zn, and negligible amounts of toxic elements (notably, Cd, Hg, and Pb), could be produced, being suitable for the micronutrient fertilizer application. After a reductive roasting step, a ZnO product and an MnO product are produced. The attained ZnO product, containing up to 84.6% ZnO, is suitable for zinc metal production when the leaching steps are taken to remove most of the Cl and F in the product. The attained MnO product, containing up to 91.7% MnO, is of premium quality for manganese alloy production, preferably for SiMn alloy production due to its low phosphorus content. The proposed application scenarios could substantially improve the recovery efficiency of those spent batteries.
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| 5. |
- Hu, Xianfeng, et al.
(author)
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Carbothermic reduction of synthetic chromite with/without the addition of iron powder
- 2016
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In: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 56:12, s. 2147-2155
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Journal article (peer-reviewed)abstract
- Carbothermic reduction of chromite is an important industrial process for extracting chromium from the chromite. To have a better understanding of the effect of iron on the carbothermic reduction of chromite, the reduction of synthetic chromite (FeCr2O4) by graphite with/without the addition of iron powder was investigated in this paper by Thermogravimetric Analysis (TGA) in argon atmosphere. The fractional reduced samples were examined by SEM/EDS and XRD analysis, and the reduction process was thermodynamically and kinetically evaluated. The experimental results show that the iron powder addition enhances the reduction of FeCr2O4 and this effect increases when increased amounts of iron powder are added. This phenomenon is attributed to the in situ dissolution of chromium into the iron and mixed carbide (Cr,Fe)7C3, which can decrease the activity of the nascent chromium formed by the reduction of the FeCr2O4. The experimental results indicate that the reduction of FeCr2O4 with up to 80 wt.% iron powder addition is likely to be a single-step process and the kinetic analysis suggests that the reduction reaction is likely to be either (a) chemical reaction at the surface of FeCr2O4 or (b) diffusional dissolution of the product (FeCr2) into the iron/alloy particles or the mixed control of (a) and (b).
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| 6. |
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| 7. |
- Hu, Xianfeng, et al.
(author)
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Direct Alloying Steel with Chromium by Briquettes Made from Chromite Ore, Mill Scale, and Petroleum Coke
- 2017
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In: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 88:5
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Journal article (peer-reviewed)abstract
- In this work, the effectiveness of using briquettes made from chromite ore, mill scale, and petroleum coke for direct chromium alloying is tested by induction furnace trials carried out in three different scales. The experimental results show that steel scrap can be alloyed with chromium by the chromite ore in the briquettes and the Cr yield from the chromite ore increases with the increase in mill scale addition to the briquettes: the more mill scale is added to the briquettes, the lower the mass ratio of Cr to (Cr + Fe) would be, leading to a higher Cr yield from the chromite ore. Specifically, the maximum Cr yield from the chromite ore is 99.9% when the mass ratio of Cr to (Cr + Fe) in the briquettes is 0.05, and being 93.0% when the ratio is 0.10. However, when the ratio of Cr to (Cr + Fe) in the briquettes reaches 0.20, the maximum Cr yield is only 67.1%. The reduction of chromite ore under the present experimental conditions is promoted by a solid-state reduction mechanism.
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| 8. |
- Hu, Xianfeng, et al.
(author)
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Direct chromium alloying by chromite ore with the presence of metallic iron
- 2013
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In: Journal of Mining and Metallurgy, Section B. - 1450-5339. ; 49:2, s. 207-215
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Journal article (peer-reviewed)abstract
- Direct chromium alloying by chromite ore in EAF operation is a promising process in stainless steel production, which has the advantage of resource-saving, energy-saving, and environment-friendly. In the present investigation, iron, carbon, and chromite ore mixture (Fe+C+FeCr2O4) were chosen as the precursor for direct chromium alloying. Thermogravimetric Analysis (TGA) experiments were carried out to investigate the effect of iron content on the reduction kinetics, and the results show that the presence of metallic iron in the precursor will increase the reduction rate of chromite. Up-scaling experiments (100 g and 500 g scale) have been carried out in the induction furnace to further test the effectiveness of using industrial chromite ore for direct chromium alloying. The induction furnace tests confirmed the necessity of adjusting composition of the slags to ensure high yield of chromium in the final products; and chromium yield can reach 90%.
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| 9. |
- Hu, Xianfeng, et al.
(author)
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Exploring the capability of muon scattering tomography for imaging the components in the blast furnace
- 2018
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In: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 58:1, s. 35-42
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Journal article (peer-reviewed)abstract
- Knowing the distribution of the materials in the blast furnace (BF) is believed to be of great interest for BF operation and process optimization. In this paper calibration samples (ferrous pellets and coke) and samples from LKAB’s experimental blast furnace (probe samples, excavation samples and core-drilling samples) were measured by the muon scattering tomography detector to explore the capability of using the muon scattering tomography to image the components in the blast furnace. The experimental results show that it is possible to use this technique to discriminate the ferrous pellets from the coke and it is also shown that the measured linear scattering densities (LSD) linearly correlate with the bulk densities of the measured materials. By applying the Stovall’s model a correlation among the LSD values, the bulk densities and the components of the materials in the probe samples and excavation samples was established. The theoretical analysis indicates that it is potential to use the present muon scattering tomography technique to image the components in various zones of the blast furnace.
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| 10. |
- Hu, Xianfeng
(author)
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Fundamental Studies on Direct Chromium Alloying by Chromite Ore with Designed Alloying Precursor
- 2014
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Licentiate thesis (other academic/artistic)abstract
- Chromium is an important alloying element for stainless steels and other Cr-bearing steels. During the steelmaking process chromium is added to the steels mainly in the form of ferrochrome, which is largely produced by the energy-intensive smelting reduction process of chromite ore in the submerged arc furnace. To reduce the overall energy consumption during the ferrochrome production process and the chromium alloying process, direct chromiumalloying by chromite ore has been proposed. The application of this process will integrate the processes for ferrochrome production and chromium alloying, and thus has the potential to cut the production costs of the Cr-bearing steels by avoiding, or at least partially avoiding, the usage of ferrochrome. Further, this new alloying process has the capacity to improve therecovery of chromium from chromite ore. This thesis presents fundamental studies on the carbothermic reduction of synthetic iron chromite (FeCr2O4) and chromite ore, which aim at designing a direct alloying precursor to be applied in the industrial process. Thermogravimetric Analysis (TGA) experiments have been carried out to investigate the carbothermic reduction processes of FeCr2O4 in the absence/presence of metallic iron, and of chromite ore in the absence/presence of mill scale. In the case of using the mixture ‘FeCr2O4 +iron powder + graphite’, it is found that the presence of metallic iron enhances the reduction of FeCr2O4, and this enhancing effect increases with increasing iron addition. The enhancing effect of iron addition on the reduction of FeCr2O4 is due to the fact that the reduction of component Cr2O3 in FeCr2O4 is enhanced, and this effect is attributed to the presence of solidiron which can decrease the activity of chromium by having chromium in situ dissolved in the iron. In the case of using the mixture ‘chromite ore + petcoke’, it is found that the reduction of iron ions in the chromite ore starts before that of chromium ions in the ore and the reduction of iron ions and chromium ions in the ore overlaps to some degree. (Cr,Fe)7C3 is found to bethe intermediate phase during the reduction and a chromium gradient is found in the spinel phase of the fractional reduced sample at 1673 K. A four-stage reduction process is proposed: one stage involving the reduction of iron ions in the chromite ore and three stages involving the reduction of chromium ions in the ore. The activity aspects of component FeCr2O4 and component MgCr2O4 in the chromite ore have been considered. The difficulty in the reductionof the chromite ore is attributed to the fact that, as the reduction proceeds, the activity of component MgCr2O4 in the fractional reduced ore will decrease to a very low level, which makes the further reduction very difficult. In the case of using the mixture ‘chromite ore + mill scale + petcoke’, it is found that mill scale is reduced to iron before 1573 K. The asreduced iron is disseminated around chromite ore particles and, at the same time, some carbonis dissolved in the iron via diffusion. Reduction of chromite ore is enhanced with the addition of mill scale at temperatures higher than 1623 K, and the enhancing effect increases with increasing mill scale addition. The enhancing effect, in this case, is attributed to the presence of molten Fe-Cr-C phase in the vicinity of chromite ore, which can decrease the activity of chromium by having chromium in situ dissolved into the melt. Induction furnace experiments have been carried out to investigate the effectiveness of some different alloying mixtures. The experimental results have confirmed the necessity ofadjusting the composition of the slag to ensure high chromium yield in the final product and the experimental results show that, by using iron scrap, chromium yield can reach 90%. The present findings have led to the proposal of using ‘chromite ore + mill scale + petcoke’ as alloying precursor for direct chromium alloying. The effectiveness of this alloying precursor needs to be further explored by induction furnace experiments, followed by full scale Electric Arc Furnace experiments.
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