Ion-exchangeable Fractions Research Articles

Physicochemical analysis and sequential extraction of rare earth elements from Malaysian ion-adsorption clays

Abstract The growing demand for Rare Earth Elements (REEs) has spurred the search for new sources, including ion adsorption clays. This research focused on characterizing ion-adsorption clay minerals and sequentially extracting samples from Kelantan, Malaysia, to assess their potential for REE extraction. Techniques such as XRF, XRD, and ICP-MS were used to analyze the samples, which primarily consisted of Si, Al and Na. XRD results indicated that kaolinite and quartz were the main components of ion adsorption clay. Sequential extraction revealed that most REEs were in the ion exchangeable fraction, with lanthanum, cerium, and neodymium showing higher concentrations. This study advances REE extraction methods and lays the groundwork for future research

An assessment of Rare Earth Elements in borehole cores from the Ermelo, Witbank and Waterberg Coalfields, South Africa: Focus on mode of occurrence

There is currently limited knowledge concerning South African coal deposits as hosts for rare earth elements (REE). This project aims to determine the concentration of REE, including yttrium and scandium (REY+Sc) in various coal seams and adjacent sediments in borehole cores from the Ermelo, Witbank, and Waterberg coalfields in South Africa. Coal petrography (maceral count and vitrinite reflectance), XRD, XRF, sequential chemical extraction procedure (SCEP) before ICP-MS, and mineral liberation analysis (MLA) were conducted on the coal and associated sediment samples. The coals were inertinite-rich, medium-rank bituminous coal, with moderate to high ash content. The two dominant minerals in all the coalfields are kaolinite and quartz, except for sample ZBS2M, where dolomite was dominant. The dominant major oxides are Al2O3, SiO2, Fe2O3, and CaO, which concur with the XRD results. The ICP-MS results following SCEP indicated that both coal and the associated sediments were light REY+Sc dominant. There was also an elevation of medium REY+Sc in the Witbank coal's associated sediment samples. Notably, the samples with the highest REY+Sc results were the sediment samples. The Waterberg samples had the lowest REY+Sc from both the coal (less than 2 μg/g to 7 μg/g) and associated sediments (2 μg/g to 15 μg/g). While the highest REY+Sc was yielded from the Witbank-associated sediments (500 μg/g to 2,500 μg/g). The carbonate fraction step proved to be the most successful leaching step, as most REY+Sc was recovered in that step for all coalfields. In addition to the carbonate fraction, the silicates and sulfide fraction in the Witbank samples, and the ion-exchangeable fraction for the Waterberg-associated sediments samples proved successful in leaching out the REY+Sc. MLA determined that monazite and xenotime in all the coal samples were the REY+Sc-bearing minerals.

Investigation of sorption behavior of 137Cs in a river–sea system boundary area after the Fukushima Dai-ichi nuclear power plant accident

The radiocesium (137Cs) distribution between dissolved and particulate phases was examined in river water and coastal seawater as a function of the 137Cs sorption behavior on suspended particles. Dissolved 137Cs activity concentrations in the Tomioka River (salinity <0.1), about 10 km south of Fukushima Dai-ichi Nuclear Power Plant, and in coastal seawater at Tomioka fishery port (salinity >30), Fukushima Prefecture, from June 2019 to October 2021 were 3.6–20 Bq/m3 (geometric mean 11 Bq/m3) and 2.4–86 Bq/m3 (13 Bq/m3), respectively. Although the suspended particle concentration was lower in the river than in seawater, the mean 137Cs activity on suspended particles was 11,000 Bq/kg-dry in the river versus 3200 Bq/kg-dry in seawater. Proportions of ion-exchangeable, organically bound, and refractory fractions of 137Cs on suspended particles were determined by sequential extraction. The ion-exchangeable fraction accounted for 0.3–2.0% (average: 1.2%) and 0.4–1.3% (0.8%) at the river and port sites, respectively. The organically bound fraction accounted for 0.3–4.8% (1.8%) and 0.1–5.5% (2.1%) at the river and port sites, respectively. In both areas, the refractory fraction accounted for >90% of 137Cs. Therefore, the small labile 137Cs fraction on suspended particles in coastal seawater indicates that the mobility of 137Cs to marine biota is quite low. SynopsisThis study is the first to examine radiocesium sorption forms on suspended particles in coastal seawater near the Fukushima Dai-ichi Nuclear Power Plant. It suggests immobility of 137Cs in suspended particles being incorporated to marine biota.

Effects of flooding and warming on soil nitrogen fraction transformation under low‐molecular‐weight organic acid inputs

AbstractFlooding and climate warming lead to the increase of low‐molecular‐weight organic acid (LMWOA) inputs to soil. However, it is unclear what the effects of flooding and climate warming on soil nitrogen fraction transformation under LMWOA input are. Fluvisol was collected in the riparian zone of the Three Gorges Reservoir to conduct an incubation experiment with the treatments of three LMWOAs at five contents, two hydrological environments and two temperatures. Compared with LMWOA input of 0 mg kg−1, the soil nitrogen in ion exchangeable fraction (IEF‐N), strong oxidant extractable fraction (SOEF‐N) and non‐transformable nitrogen (NTF‐N) were increased by 35.77, 54.71 and 25.49 mg kg−1, respectively, under LMWOA input of 40 mmol kg−1. Soil nitrogen in the weak acid extractable fraction (WAEF‐N) was decreased by 117.41 mg kg−1. Microbial biomass nitrogen (MBN) was increased by 25.29 mg kg−1, and calcium carbonate (CaCO3) was decreased by 8.03 g kg−1. The contents of IEF‐N, NTF‐N and amorphous iron oxides were higher under the flooding environment than under the drying environment. In contrast, opposite results were observed for soil nitrogen in the strong alkali extractable fraction (SAEF‐N), SOEF‐N and MBN. IEF‐N and NTF‐N contents were higher at 20°C than at 30°C, and the contents of SOEF‐N and MBN were higher at 30°C than at 20°C. WAEF‐N was dissolved by LMWOA through CaCO3 dissolution. The dissolved WAEF‐N was partly transformed into SOEF‐N and NTF‐N by microbial assimilation and humification. Flooding desorbed SAEF‐N through the crystalline transformation of iron oxides. Flooding inhibited the transformation of IEF‐N to SOEF‐N and promoted the formation of NTF‐N, while warming did the opposite. The results provide a perspective of the bound state between soil and nitrogen for understanding the soil nitrogen cycling and help to assess the impacts of climate warming and flooding on soil nitrogen loss from soil to the surrounding water.

Determination of metal fractions and rare earth anomalies in red mud: the case of bauxite mining district of Seydişehir (Turkey)

A three-step sequential extraction was carried out by modified BCR approach for fractionation of metals, including rare earths in red mud. Acetic acid leaching, hydroxylamine hydrochloride + nitric acid leaching, hydrogen peroxide + acid ammonium acetate leaching, and orthophosphoric + nitric acid digestion in microwave were performed to determine ion exchangeable (F1), reducible (F2), oxidizable (F3), and residual (F4) fractions of metals, respectively. Accordingly, the highest readily soluble phases were obtained for Ca, Na, and K, while the reducible were Al, Zn, Cu, and Li. Rare earth elements (REEs) except for Eu were mostly identified in residual fraction. Most of Eu (88.7%) was detected in the reducible fraction, while the negligible part in residual. Chondrite normalization was implemented for obtaining REE anomalies. The remarkable Eu and Gd negative anomaly differences were determined between the red mud and its origin, Mortaş bauxite. The LREE to HREE ratio and LaN/YbN scores of 8.42 and 7.82, respectively indicated the LREE enrichment to HREE. By performing multivariate analysis, six and five-group clusters were obtained for REEs and non-REE metals in terms of fractional distribution, proving the easier release potential of Eu, La, Gd, K, Na, and Ca.

Accumulation and Pollution Risks of Heavy Metals in Soils and Agricultural Products from a Typical Black Shale Region with High Geological Background

Soil polluted by heavy metals (HMs) is an important environmental issue in China, and regional geological background is a vital factor that influences the enrichment of HMs in soils. Previous studies have shown that soils derived from black shales are commonly enriched in HMs and present high potential eco-environmental risks. However, few studies have investigated the HMs in different agricultural products, which inhibit the safe use of land and safe production of food crops in black shale regions. This study investigated the concentrations, pollution risks, and speciation of HMs in soils and agricultural products from a typical black shale region in Chongqing. The results showed that the study soils were enriched in Cd, Cr, Cu, Zn, and Se but not in Pb. Approximately 98.7% of total soils exceeded the risk screening values, and 47.3% of total soils exceeded the risk intervention values. Cd had the highest pollution level and potential ecological risks and was the primary pollutant in soils of the study area. Most of the Cd resided in ion-exchangeable fractions (40.6%), followed by residual fractions (19.1%) and weak organic matter combined fractions (16.6%), whereas Cr, Cu, Pb, Se, and Zn were dominated by residual fractions. Additionally, organic combined fractions contributed to Se and Cu, and Fe-Mn oxide combined fractions contributed to Pb. These results indicated that Cd had higher mobility and availability than those of other metals. The agricultural products presented a weak ability to accumulate HMs. Approximately 18.7% of the collected samples with Cd exceeded the safety limit, but the enrichment factor was relatively low, indicating low pollution risks of the heavy metals. The findings of this study could provide guidelines for safe use of land and safe production of food crops in black shale regions with high geological background.

Characterization and Leaching Kinetics of Rare Earth Elements from Phosphogypsum in Hydrochloric Acid

The characterization and leaching mechanism of REEs from phosphogypsum (PG) in HCl was studied in-depth. REEs contained in the PG were 208 ppm, of which Y, La, Ce, and Nd were the four most abundant elements. The modes of occurrence of rare earth elements (REEs) in the PG were quantified using the sequential chemical extraction (SCE) method. Among the five REE occurrence species, the metal oxide form accounted for the largest proportion, followed by the residual, organic matter, and ion-exchangeable fractions, and REEs bound to carbonates were the least. From the comparison of the distributions of REEs and calcium in different occurrence states, it can be determined that REEs contained in the PG were mainly present in the residue state (existed in the gypsum lattice) and the metal oxide state (easily leached). The leaching results show that the suitable leaching conditions were acid concentration of 1.65 mol/L, S/L ratio of 1/10, and reaction temperature of 60 °C. At the condition, the maximum leaching efficiency for ∑REE was 65.6%, of which the yttrium leaching rate was the highest and reached 73.8%. Importantly, A new kinetic equation based on the cylindrical shrinking core model (SCM) was deduced and could well describe REE leaching process from PG. The apparent activation energy for ∑REE leaching was determined to be 20.65 kJ·mol−1.

Heavy metal mobility, bioavailability, and potential toxicity in sediments of the Korle lagoon in Ghana

ABSTRACT This study aimed to identify the mobility, bioavailability, and potential toxicity of heavy metals (HM) in sediments of the Korle lagoon using metal partition. Sediments were analysed using the BCR (Bureau of reference) method. As (60%), Pb (50%), Zn (57%) and Fe (40%) were found in high concentration in the ion exchangeable fraction. The oxidisable fraction was dominated by Cu (51%), Cd (95%), Cr (61%), Ni (63%), As (35%), Fe (21%), Hg (30%), Pb (19%) and Zn (11%). The reducible fraction was dominated by Zn (29%), Pb (24%) and Hg (19%). The residual fraction was dominated by Hg (49%) and Fe (34%). PCA was used to identify pH and organic matter as the most important factors controlling the mobility and bioavailability of HM in the sediments. Arsenic, Pb, Zn and Fe were found to have the highest mobility. Chromium, Cu and Ni have medium mobility. Hg has low mobility. Most of the HM show potential bioavailability and toxicity.

REE fractionation controlled by REE speciation during formation of the Renju regolith-hosted REE deposits in Guangdong Province, South China

• A 78 m long weathering profile developed in quartz diorite of the Huangshe regolith-hosted LREE deposit was investigated. • LREE-rich minerals, e.g., titanite and allanite , were dissolved preferentially during the breakdown of rocks during weathering. • The activated REEs are immobilised, occurring mainly as ion exchangeable and Fe-Mn (hydr)oxide fractions, with a few amounts of the organic and carbonate binding fractions. • Most HREEs were preferentially scavenged in the Fe-Mn (hydr)oxide fraction, which leads to LREE enrichment in the ion exchangeable fraction. Regolith-hosted rare earth element (REE) resources in South China are the dominant global source of heavy REEs (HREEs), which are critical for high technology and military industries. Most previous studies focused on the proportion of ion exchangeable REE fractions, but other speciations thereof and their effects on REE fractionation are still poorly understood. Therefore, to address this issue, this study focused on a systematic analysis of the geochemistry and mineralogy of a complete weathering 78 m profile in the Renju regolith-hosted REE deposit in northeast Guangdong Province, China. In the quartz diorite bedrock, the main REE minerals were titanite, allanite, and REE fluorocarbonates abundant in REEs (332–338 ppm). During the breakdown of rocks due to weathering, the light REE (LREE)-rich minerals, e.g., titanite and allanite, were dissolved preferentially, resulting in the release of the REEs. Thus, the HREE-rich minerals, including xenotime and zircon, are preserved with progressive weathering. The results of sequential extraction show that the activated REEs are immobilised, occurring mainly as ion exchangeable and Fe-Mn (hydr)oxide fractions, with a few amounts of the organic and carbonate binding fractions. Fe (hydr)oxides, as seen via transmission electron microscopy, usually occur in the form of goethite and hematite in the lower and upper parts of regoliths, respectively, while Mn is present as a trace element in Fe (hydr)oxides. The lower La/Yb ratios in the Fe-Mn (hydr)oxide fraction indicate that HREEs are preferably bonded on Fe-Mn (hydr)oxides, causing LREEs to exist mainly as ion exchangeable fractions. In addition, positive Ce anomalies exist in both the lateritic horizon with strong oxidation of weak acid and in the Fe-Mn (hydr)oxide fraction as a co-precipitate with Fe oxides. The results obtained advance our understanding of the mechanisms of REE fractionation and the mutual effect of REE speciation on the formation of regolith-hosted REE deposits in South China.

Long-term acid generation and heavy metal leaching from the tailings of Shimokawa mine, Hokkaido, Japan: Column study under natural condition

The leaching from mine tailings results in contamination of nearby groundwaters and rivers by hazardous metals like copper (Cu), zinc (Zn), and iron (Fe). In this study, unweathered tailings samples at depths of 1 to 3 m were collected from a tailings dam of an abandoned mine located in the north of Hokkaido, Japan. The mechanisms of long-term tailings weathering were assessed through leaching of hazardous metals by three column experiments. Measurements of mineralogical and chemical constituents, observation by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), sequential extraction of the tailings, and chemical analyses of the leachates were carried out to determine the processes responsible for the leaching of Cu, Zn, Fe, and sulfate ion (SO42−). The contents of Cu, Zn, and Fe in the tailings were mainly associated with ion exchangeable and sulfide fractions. The pH values of the effluents from the columns were 3.0–3.7 throughout the experiments over 84 weeks, and approximately 15–23% of Cu, 35–45% of Zn, 2.5–4% of Fe and 15–20% of S were leached. Higher concentrations of Cu, Zn, Fe, and SO42− at the beginning of the experiments were observed, which could be attributed to the dissolution of soluble sulfate minerals present in the tailings. This indicates that the formation and dissolution of secondary soluble sulfate minerals contributed to Cu and Zn leaching. The continuous leaching of Cu, Zn, Fe, and SO42− suggests the oxidation of pyrite and other sulfide minerals. During these processes, ferrihydrite, goethite, lepidocrocite, and maghemite were formed and these minerals also acted as a sink for Cu and Zn by adsorption, and/or co-precipitation. These results mean the significance of the long-term behavior of hazardous metals released from mine tailings dams, which could provide helpful information on the management of tailings dams after mine closure.

Enhanced characterisation for the management of industrial steel processing by products: potential of sequential chemical extraction

There is a pressing need for innovative waste management approaches as environmental regulations become more stringent worldwide alongside increasing demand for a more circular economy. Sequential chemical extraction (SE) analysis, which has previously been applied to environmental media such as soils and sediments, offers the potential to provide an understanding of the composition of solid steel processing by products, aiding the waste classification process and improving environmental protection. The definition of seven-phase associations through a SE method evaluated in this study were for (1) water soluble, (2) ion exchangeable, (3) carbonate, (4) amorphous Fe–Mn oxides, (5) crystalline Fe–Mn oxides, (6) sulphides and (7) silicate residues. Steel waste by-products (flue dust and filter cake) were evaluated for both extracted components (ICP analysis) and residual phases (using powder X-ray diffraction, SEM and FTIR), to model the transformations taking place during extraction. The presence and removal of important potentially toxic element (PTE) host solid phases were confirmed during extraction. The SE protocol provides key information, particularly for the association of potentially toxic elements with the first three extracts, which are most sensitive in waste management processes. The water-soluble phase is the most available followed by ion-exchangeable and carbonate fractions, all representing phases more sensitive to environmental change, in particular to pH. This study demonstrates that the distribution of potentially toxic elements such as zinc, lead and copper between sensitive and immobile phases can be reliably obtained in technological process by-products. We demonstrate that despite heterogeneity as a major variable, even for fine particulate matter, SE can provide more refined classification with information to identify reuse potential and ultimately minimise hazardous waste streams.

Bioremediation of strontium and technetium contaminated groundwater using glycerol phosphate

Groundwater at legacy nuclear facilities around the world is contaminated with radionuclides including strontium-90 and technetium-99, which are often present as co-contaminants. Here we investigated whether biostimulation of indigenous microbial communities by glycerol phosphate can co-treat 90Sr through incorporation into phosphate biominerals, and 99Tc through microbially-induced reduction of the sediment to form less mobile Tc(IV) phases via reaction with reduced species (e.g. Fe(II)). Results showed that 95% of Sr was removed from solution in sediment microcosms treated with glycerol phosphate, and sequential extraction showed that ~18% of the Sr in the resulting solid phase was associated with the pH 5 Na-acetate fraction and 75% was in the ion exchangeable fraction. This removal and partitioning to recalcitrant phases during glycerol phosphate treatment was greater than in the untreated controls, where only 60% of Sr was removed from solution, and of the solid-associated Sr, 95% was present in the exchangeable fraction. Fitting of Sr K-edge EXAFS spectra confirmed these findings, with shell by shell fitting suggesting ~30% of sediment-associated Sr was present in a coordination environment consistent with phosphate biominerals following glycerol phosphate treatment, whilst Sr was present only as outer-sphere complexes in the controls. In addition,16S rRNA sequencing of sediments stimulated with glycerol phosphate demonstrated the growth of potential phosphate-solubilising species such as Chryseobacterium and Serratia spp. Finally, glycerol phosphate treatment stimulated bioreduction via addition of electron donor in the form of glycerol to the system, in turn this stimulated the removal of 99Tc from solution concomitant with microbial Fe(III) reduction to form poorly soluble hydrous Tc(IV)O2 like phases. In sediments amended with an electron donor, the microbial community also reflected the onset of bioreduction with an increased relative abundance of Fe(III) and sulfate-reducing bacteria such as Geothrix, Geobacter and Desulfobulbus spp. Overall these results suggest application of glycerol phosphate offers a promising bioremediation strategy to co-treat both 90Sr and 99Tc contaminated groundwaters, and promotes the formation of Sr-phosphate and Tc(IV) bearing biominerals when reducing conditions are maintained. Combined with past work which shows the scavenging of uranium from solution following addition of glycerol phosphate, this extends the scope for glycerol phosphate as a treatment for radioactive contamination in groundwaters.

Modes of Occurrence of Cr, Co, Ni, Cu, Cd, and Pb in the Main Coal Seams of Southwestern China’s Nantong Coalfield

The modes of occurrence of trace elements in coal reveal essential information about environmental impact during coal exploitation and utilization. Utilizing improvements on a recently published sequential leaching protocol, this study investigated the modes of occurrence of Cr, Co, Ni, Cu, Cd, and Pb (water-soluble, ion-exchangeable, carbonate-bound, sulfide-bound, organic-bound, and silicate-bound) in coal samples collected from the Nantong coalfield in southwestern China. Results suggest the improved method favorably affected the sequential leaching experiment. The ashing temperature did not exceed 390°C and did not damage the structure of the silicate minerals, facilitating the effective extraction of trace elements within the organic matter. The case study in the Nantong coalfield demonstrated that the water-soluble and ion-exchangeable fractions account for only a small portion of the six elements. Specifically, chromium exhibited affinities with carbonates and silicates. The percentages of different target fractions for cobalt varied significantly in different samples. Nickel was almost evenly distributed in the fractions of carbonates, sulfides, organic matter, and silicates. For cadmium, silicate was the main fraction, followed by sulfides. Lead predominantly appeared in carbonates and sulfides. The correlativity of different elements in the corresponding fractions revealed carbonates and sulfides as the primary carriers for all six elements, followed by silicates and organic matter. Overall, Cr, Co, Ni, and Cu exhibited very close relationships and similar distribution patterns in different coal samples. Organic-bound Cr, Co, and Ni were noticeable in the No. 4 and 6 coal seams, though they were not the dominant fractions. The affinity between Pb and Cd indicated they have similar modes of occurrence.

Mercury fractions in gypsum and estimation of mercury emission from coal-fired power plants

With continuing improvements in the efficiencies of the flue gas pollution control devices, a greater proportion of mercury emitted from coal fired power plants is in the recovered byproducts, such as fly ash and desulfurization gypsum. The leaching ability and bioavailability of mercury are related with its speciation and finally determine the total emission of mercury from power plants. Therefore, it is important to understand the speciation of mercury in the byproducts. In this study, mercury in the gypsum samples from eleven power plants in Hebei Province, China was determined in five sequential extracts representing fractionation of mercury species, namely water soluble fraction (WS, F1), ion-exchangeable fraction (IE, F2), acid soluble fraction (AS, F3), elemental fraction (EF, F4) and sulfide fraction (SF, F5). The leaching ability and the distribution of mercury in the various fractions from different power plants were examined. The results showed that mercury was dominantly in elemental fraction, and the leaching ability as well as the fraction distribution of mercury varied with samples from different power plants. The rapid release and releasable mercury in gypsum which shouldn’t be overlooked were taken into account for the estimation of mercury emission from coal fired power plants. Three models, including Mass Balance model (MB), Emission modification factors model (EMF) and Flue calculation model (FC), were also employed to estimate the possible mercury emission from flue gas in these studied power plants. A comparison of the results from the different models indicated variability among the different models. The mercury re-emission from gypsum to the environment is needed to address the important issue of further improvement of these models for estimation of mercury emission.

Mercury release and fraction transformation during desulfurization gypsum aging process (UV irradiation)

The transformation of mercury fractions under both natural environmental conditions and ultraviolet irradiation (UV) conditions was studied in this work. Mercury in desulfurization gypsum was divided into five fractions by sequential extraction procedure depending on its bioavailability. The five fractions were named as water soluble fraction (F1), ion-exchangeable fraction (F2), acid soluble fraction (F3), elemental fraction (F4), and sulfide fraction (F5). The results from our study demonstrated that the proportion of different fraction was in the following order: elemental fraction > water soluble fraction > acid soluble fraction > ion-exchangeable fraction > sulfide fraction. The results indicated that mercury could be released from desulfurization gypsum during aging process and the release process could be promoted via ultraviolet irradiation. The release amount increased with the irradiation time and intensity (up to 25.1% of the total initial amount). The percentage of mercury in F1 decreased gradually with aging time, while the percentage of mercury in elemental and residual fractions increased gradually. Our research will be helpful for the survey and understand of mercury emission from desulfurization gypsum.

The content of selected heavy metals and their bioavailable fraction in sediments of Solina Reservoir (Poland)

Research on sediments of Solina Reservoir, Poland, were characterized by a content of copper higher than other heavy metals (Cr, Ni, Cd and Zn). The strongest correlations between pairs of heavy metals were Zn–Cu and Ni–Cr, were revealed while there was also a correlation between total contents of chromium and nickel, and between pH value and sediment percentage of organic matter. The content of copper at levels exceeding the geochemical background (more than 20–fold), sediments could only by classified as of the 3rd purity class (according to the PIG criterion) or the 5th purity class (according to Müller’s classification). Ecotoxicological criteria indicate that levels of chromium, copper, nickel and cadmium are all high enough to affect aquatic life. However, the heavy metals analyzed differ in their mobility and bioavailability. The highest percentage value for the ion–exchangeable fraction was noted for cadmium, the lowest for chromium. This means that sediments have a greater capacity to release cadmium into the water column, with the consequence being secondary pollution source for the aquatic ecosystem.

Sorption and mobility of Co(II) in relation to soil properties

The kinetic and equilibrium sorption data of Co(II) ions were obtained from batch sorption experiments, using soils samples with a wide range of texture, carbonate and organic content. Sequential extraction protocol was applied to evaluate Co(II) interactions with soil fractions. The parameters, obtained from kinetic and isotherm data modeling, as well as the results of Co(II) distribution and desorption studies, were correlated with soil properties. Kinetics of Co(II) sorption was fast and obeyed the pseudo-second order kinetic model at the contact time ranged from 30min to 30days, using Co(II) concentration of 1.5×10−3molL−1. Maximum sorption capacities were highly correlated with soil pH. The sorbed Co(II) was associated with Fe,Mn-oxide and carbonate phase of calcareous soil, whereas in other soil types ion-exchangeable fraction was dominant. The effect of aging on Co(II) stabilization in soil was more pronounced for lower contamination levels and soils with higher pH. For non-calcareous soils, the desorption of Co(II) could be achieved by EDTA and HCl solutions.

Trace and Major Elements in Ash of “Nikola Tesla A” Power Plant (III)—Associations of Elements in Passive Cassette Ash

Statistical analysis of concentrations of trace and major elements obtained by five-step sequential extraction of samples of dump ash taken from a passive, previously filled cassette of “Nikola Tesla A” power plant dump located near Belgrade, Serbia, revealed the existence of magnesium alumosilicates, mixed silicates of potassium and magnesium, alumosilicates not containing magnesium, and compounds of aluminium, not containing silicon or magnesium that were dissolved in the fifth phase of extraction. Intraphase associations of major elements dissolved in the third phase were not established. Preferential intraphase and interphase binding of matrix and adsorbed and ion-exchangeable fractions of elements were established and discussed.

Study on bromine release from bituminous coal during combustion

Abstract Modes of occurrence of Br in bituminous coal from China were extracted using sequential chemical extraction; coal combustion was simulated with a tube furnace, and the effects and mechanisms of combustion temperature, combustion time, O 2 flow rate and water vapor access on the Br release from bituminous coal were investigated. The results showed that the Br release rate increased with the increase of temperature, and 500–900 °C was the main stage of Br release. The Br occurred as water-soluble, ion exchangeable and organic fraction may be completely emitted before 700 °C, bound to carbonate and Fe–Mn oxide may be mainly emitted in 700–900 °C, and occurred in residual fraction which cannot be extracted using sequential chemical extraction can be largely emitted during combustion. Moreover, the Br release rate in bituminous coal increased with the increase of combustion time and O 2 flow rate, and more than 97% Br may be emitted at the given experimental condition of combustion temperature of 1000 °C, water vapor access, O 2 flow rate of 90 mL min −1 and combustion time of 20 min. During combustion, the Br in bituminous coal was transformed into HBr and easily taken out of the furnace with the help of water vapor, which indicated water vapor can obviously promote the Br release. The additive of SiO 2 can capture the Br effectively in the process of the coal combustion.

Associations and Pollution Potential of Selected Trace and Major Elements in Filter Lignite Ash—Statistical Analysis

Six combined samples of filter ash obtained by lignite combustion in the “Nikola Tesla A” Power Plant were subjected to a five-phase sequential extraction. In order to establish associations of extracted trace and major elements, obtained concentrations were subjected to intraphase and interphase correlation analysis. Statistical analysis revealed the pollution potential, association forms of trace and major elements with the inorganic matrix, binding pattern of adsorbed and ion-exchangeable fractions to the inorganic matrix, and changes in association forms occurred during and after lignite combustion.