Estimated Solid Phase Distribution of Metals Released in the Acid Extractable and Reducible Steps of a Sequential Extraction

1996 ◽  
Vol 64 (3) ◽  
pp. 171-177 ◽  
Author(s):  
F. M. G. Tack ◽  
M. G. Verloo
Keyword(s):  
Sequential Extraction ◽  
Phase Distribution ◽  
Solid Phase

scholarly journals Influence of Sodium Sulfate Addition on Iron Grain Growth during Carbothermic Roasting of Red Mud Samples with Different Basicity

Metals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1571
Author(s):  
Pavel Grudinsky ◽  
Dmitry Zinoveev ◽  
Denis Pankratov ◽  
Artem Semenov ◽  
Maria Panova ◽  
...  
Keyword(s):  
Magnetic Separation ◽  
Grain Growth ◽  
Red Mud ◽  
Sodium Sulfate ◽  
Phase Distribution ◽  
Solid Phase ◽  
Alumina Production ◽  
Metallic Particles ◽  
Iron Phase ◽  
High Alkalinity

Red mud is an iron-containing waste of alumina production with high alkalinity. A promising approach for its recycling is solid-phase carbothermic roasting in the presence of special additives followed by magnetic separation. The crucial factor of the separation of the obtained iron metallic particles from gangue is sufficiently large iron grains. This study focuses on the influence of Na2SO4 addition on iron grain growth during carbothermic roasting of two red mud samples with different (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21, respectively. Iron phase distribution in the red mud and roasted samples were investigated in detail by Mössbauer spectroscopy method. Based on thermodynamic calculations and results of multifactorial experiments, the optimal conditions for the roasting of the red mud samples with (CaO + MgO)/(SiO2 + Al2O3) ratio of 0.46 and 1.21 were duration of 180 min with the addition of 13.65% Na2SO4 at 1150 °C and 1350 °C followed by magnetic separation that led to 97% and 83.91% of iron recovery, as well as 51.6% and 83.7% of iron grade, respectively. The mechanism of sodium sulfate effect on iron grain growth was proposed. The results pointed out that Na2SO4 addition is unfavorable for the red mud carbothermic roasting compared with other alkaline sulfur-free additives.

scholarly journals Sequential extraction and thermal desorption of mercury from contaminated soil and tailings from Mongolia

2012 ◽  
Vol 10 (5) ◽  
pp. 1565-1573 ◽  
Author(s):  
Pavel Coufalík ◽  
Pavel Krásenský ◽  
Marek Dosbaba ◽  
Josef Komárek
Keyword(s):  
Sequential Extraction ◽  
Thermal Desorption ◽  
Solid Phase ◽  
Extraction Procedure ◽  
Speciation Analysis ◽  
Water Soluble ◽  
Mercury Species ◽  
Different Temperatures ◽  
Acidic Conditions ◽  
Desorption Method

AbstractMercury forms in contaminated environmental samples were studied by means of sequential extraction and thermal desorption from the solid phase. The sequential extraction procedure involved the following fractions: water soluble mercury, mercury extracted in acidic conditions, mercury bound to humic substances, elemental Hg and mercury bound to complexes, HgS, and residual mercury. In addition to sequential extraction, the distribution of mercury species as a function of soil particles size was studied. The thermal desorption method is based on the thermal decomposition or desorption of Hg compounds at different temperatures. The following four species were observed: Hg0, HgCl2, HgS and Hg(II) bound to humic acids. The Hg release curves from artificial soils and real samples were obtained and their applicability to the speciation analysis was considered.

Application of Support Vector Machine Modeling on Phase Distribution in the Riser of an LSCFB Reactor

2014 ◽  
Vol 12 (1) ◽  
pp. 123-134 ◽  
Author(s):  
Shaikh A. Razzak ◽  
Muhammad I. Hossain ◽  
Syed M. Rahman ◽  
Mohammad M. Hossain
Keyword(s):  
Support Vector Machine ◽  
Circulating Fluidized Bed ◽  
Phase Distribution ◽  
Solid Phase ◽  
Correlation Coefficients ◽  
Absolute Error ◽  
Pilot Scale ◽  
Support Vector ◽  
Cross Sectional ◽  
Machine Modeling

Abstract Support vector machine (SVM) modeling approach is applied to predict the solids holdups distribution of a liquid–solid circulating fluidized bed (LSCFB) riser. The SVM model is developed/trained using experimental data collected from a pilot-scale LSCFB reactor. Two different size glass bead particles (500 μm (GB-500) and 1,290 μm (GB-1290)) are used as solid phase, and water is used as liquid phase. The trained model successfully predicted the experimental solids holdups of the LSCFB riser under different operating parameters. It is observed that the model predicted cross-sectional average of solids holdups in the axial directions and radial flow structure are well agreement with the experimental values. The goodness of the model prediction is verified by using different statistical performance indicators. For the both sizes of particles, the mean absolute error is found to be less than 5%. The correlation coefficients (0.998 for GB-500 and 0.994 for GB-1290) also show favorable indications of the suitability of SVM approach in predicting the solids holdup of the LSCFB system.

scholarly journals Investigating the Geochemical Controls on Pb Bioaccessibility in Urban Agricultural Soils to Inform Sustainable Site Management

Geosciences ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 398
Author(s):  
Jane Entwistle ◽  
Lindsay Bramwell ◽  
Joanna Wragg ◽  
Mark Cave ◽  
Elliott Hamilton ◽  
...  
Keyword(s):  
Sequential Extraction ◽  
Agricultural Soils ◽  
Solid Phase ◽  
Human Health Risk ◽  
Evidence Base ◽  
Natural Soil ◽  
Site Management ◽  
Relevant Evidence ◽  
Management Plans ◽  
Al Oxide

The solid-phase speciation of contaminants in soil plays a major role in regulating both the environmental mobility of contaminants and their bioavailability in biological receptors such as humans. With the increasing prevalence of urban agriculture, in tandem with growing evidence of the negative health impacts of even low levels of exposure to Pb, there is a pressing need to provide regulators with a relevant evidence base on which to build human health risk assessments and construct sustainable site management plans. We detail how the solid-phase fractionation of Pb from selected urban agricultural soil samples, using sequential extraction, can be utilised to interpret the bioaccessible fraction of Pb and ultimately inform sustainable site management plans. Our sequential extraction data shows that the Pb in our urban soils is primarily associated with Al oxide phases, with the second most important phase associated with either Fe oxyhydroxide or crystalline FeO, and only to a limited extent with Ca carbonates. We interpret the co-presence of a P component with the Al oxide cluster to indicate the soils contain Pb phosphate type minerals, such as plumbogummite (PbAl3(PO4)2(OH)5·H2O), as a consequence of natural “soil aging” processes. The presence of Pb phosphates, in conjunction with our biomonitoring data, which indicates the lack of elevated blood Pb levels in our gardeners compared to their non-gardening neighbours, suggests the (legacy) Pb in these soils has been rendered relatively immobile. This study has given confidence to the local authority regulators, and the gardeners, that these urban gardens can be safe to use, even where soil Pb levels are up to ten times above the UK’s recommended lead screening level. The advice to our urban gardeners, based on our findings, is to carry on gardening but follow recommended good land management and hygiene practices.

Bending theory for laminated composite cantilever beams with multiple embedded shape memory alloy layers

2019 ◽  
Vol 30 (10) ◽  
pp. 1549-1568 ◽  
Author(s):  
Nguyen Van Viet ◽  
Wael Zaki ◽  
Rehan Umer
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Numerical Solutions ◽  
Phase Distribution ◽  
Solid Phase ◽  
Axial Stress ◽  
Laminated Composite ◽  
Beam Theory ◽  
Cantilever Beams ◽  
Element Analysis

In this article, a new analytical model is proposed for laminated composite cantilever beams consisting of multiple alternating superelastic shape memory alloy and elastic layers. The model is based on the Zaki–Moumni model for shape memory alloys combined with Timoshenko’s beam theory. The Zaki–Moumni model accounts for solid phase transformation as well as detwinning and reorientation of martensite under multiaxial thermomechanical loading conditions. Mathematical formulas are first derived to characterize the evolution of the solid phase structure within the beam with a prescribed load at the tip during loading and unloading. Analytical moment–curvature and shear force–shear strain relations are then obtained following the strength of materials approach. The present work is the first to fully develop the nonlinear expressions of the axial stress in terms of the distance from the neutral plane and to allow the description of the phase distribution in both the longitudinal and the transverse directions in the beam as the load evolves. The proposed model is validated against finite element analysis and high-accuracy numerical solutions. The influence of temperature and the number of shape memory alloy layers on the superelastic behavior of the laminate is also investigated.

scholarly journals Investigation of the Primary Phase Segregation during the Filling of an Industrial Mold with Semi-Solid A357 Aluminum

2008 ◽  
Vol 141-143 ◽  
pp. 635-640 ◽  
Author(s):  
Frédéric Pineau ◽  
Geneviève Simard
Keyword(s):  
Phase Distribution ◽  
Solid Phase ◽  
Numerical Models ◽  
Phase Segregation ◽  
Homogeneous Distribution ◽  
Phase Interaction ◽  
Two Phase ◽  
Cast Part ◽  
Α Phase ◽  
Semi Solid

Casting metal alloys in the semi-solid state is now becoming a well established manufacturing technique. But, the success of this technology necessitates a good understanding of the feedstock material behaviour. To obtain high quality components with semi-solid metal processing, a homogeneous distribution of phases must be maintained in the material during the die filling stage. Many parameters affect the process such as temperature, time and stress history, which influence the shape, size and connectivity of the particles that make up the slurry. The subsequent phase interaction mechanisms are quite complex and have direct effects on the flow and final micro-structure distribution of the cast part and thus, without any doubt, on its mechanical properties. Two-phase numerical models have been developed to account for the liquid-solid phase separation e.g. [1,2]. Several two-phase models have been elaborated on the basis of soil mechanics and consider that the phase interaction term is mainly due to the flow through a porous medium. Because of the difficulties of making direct measurements in an extremely hostile environment, there has been very little work done to validate these models. In order to fill this gap, a better understanding of the phase distribution and phase segregation mechanisms during the filling step is required. In this work, the post-solidification primary α-phase distribution inside an industrial semi-solid cast part has thus been investigated. A thorough metallographic analysis has been performed using an upright microscope coupled to a Clemex image-analysis software. The results were then processed to produce a map of the final α-phase distribution. Many different grain scales have been observed in the solidified part and their distributions seem to be closely associated to the velocity field. Contacts between moving particles seem to play an important role in the phase distribution and show many similarities to granular materials. This latter aspect should be considered in the development of new constitutive models for semi-solid slurries.

Metals adsorbed to charcoal are not identifiable by sequential extraction

2007 ◽  
Vol 4 (1) ◽  
pp. 26 ◽  
Author(s):  
Yamin Ma ◽  
Andrew W. Rate
Keyword(s):  
Trace Elements ◽  
Metal Ions ◽  
Sequential Extraction ◽  
Trace Element ◽  
Manganese Oxides ◽  
Solid Phase ◽  
Ammonium Oxalate ◽  
Natural Soil ◽  
Trace Metal Ions ◽  
Iron Manganese

Environmental context. Charcoal is widespread in soils and may be a major component of soil organic matter. Trace metal ions in soils are predominantly associated with solid phase materials, including charcoal, and the identity of the solid phase and the mechanisms of association influence the geochemical behaviour of metals. Metals associated with soil mineral phases are estimated using techniques such as selective sequential extraction, and the sorption reactions of metal ions are well understood. Much less is known about the associations of trace metals with natural charcoal, and metals associated with charcoal in soils are likely to be misidentified in sequential extraction procedures. Abstract. Given that up to 50% of the soil carbon store can consist of charcoal, it is possible that trace elements can become immobilised through their interaction with natural charcoal. Hence, natural charcoal may be a significant sink that has yet to be accounted for in trace element biogeochemical cycles. Testing this hypothesis becomes problematic considering the typically small size (<53 µm) of charcoal particles that occur naturally in Australian soils, making isolation and analysis of natural soil charcoal difficult. Therefore, in this study, we test the robustness of a typical sequential extraction technique by applying it to naturally occurring charcoal that had been spiked with five different concentrations of metal ions (Al3+, Cr3+, Cu2+, Ni2+, Zn2+, Cd2+, Ag+, Pb2+). The method was then applied to contrasting soils mixed with this spiked charcoal. The sequential extraction scheme consisted of the following five extractions the in order: (1) sodium acetate (targeting the adsorbed-exchangeable-carbonate fraction), (2) sodium pyrophosphate (organic fraction), (3) ammonium oxalate (amorphous iron/manganese oxides), (4) hydroxylamine hydrochloride (crystalline iron/manganese oxides) and (5) residual (aqua regia digest). The majority of metals added to the charcoal were extracted in the fractions targeting both the amorphous and crystalline iron and manganese oxides, at low additions of metal ions. At higher additions of metals, the metals were mostly extracted from charcoal in the adsorbed-exchangeable-carbonate fraction. When the spiked charcoal was added to soils, a trend similar to the charcoal-only experiment was observed in the sequential extraction data. Higher concentrations of metals (compared with the control) were extracted for the charcoal-amended soils, in the same fractions as in the charcoal-only extractions. Since the concentration of metals extracted in the various extractants changed with increasing metal loads on charcoal, sequential extractions cannot be used to identify the contribution of metals from the charcoal pool. Therefore, a potentially large pool of trace elements could be misrepresented when sequential extraction techniques are applied, particularly for soils in which there is a large concentration of charcoal. Hence, there is still a large gap in knowledge with regard to the significance of charcoal in ‘real’ soils, particularly with respect to the role of charcoal as a trace element sink.

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