Sequential Extraction Scheme Research Articles

Antimony(V) sorption and coprecipitation with ferrihydrite: An examination of retention mechanisms and the selectivity of commonly-applied extraction procedures

We investigated the mechanisms that control Sb(V) sorption and coprecipitation with ferrihydrite across a range of Sb(V) loadings, and examined the associated effects on Sb(V) extractability during the commonly-applied 1M HCl extraction scheme and the BCR and Wenzel sequential extraction schemes. EXAFS spectroscopy reveals that Sb(V) sorption and coprecipitation mainly involved Sb(V) incorporation into the ferrihydrite structure via edge sharing and double-corner sharing between SbO6 and FeO6 octahedra. Large amounts of these linkages partially stabilized ferrihydrite against extraction with 1M HCl. Negligible (<0.5%) ferrihydrite-bound Sb(V) was recovered in the “acid extractable” and “reducible” fractions of the BCR scheme, while 1-16% was recovered in the “oxidizable” fraction. As such, the BCR scheme risks ferrihydrite-bound Sb(V) being misidentified as Sb residing mainly in “residual” phases. In contrast, in the Wenzel scheme, almost all sorbed- and coprecipitated-Sb(V) was recovered in the “amorphous hydrous oxide-bound” fraction, with only 0.6-3.3% in the “specifically-bound” fraction (consistent with our finding of Sb(V) retention via incorporation into ferrihydrite, as opposed to adsorption by the ferrihydrite surface). Collectively, the results provide new insights into the retention mechanisms and extraction behaviour of ferrihydrite-bound Sb(V), enhancing our ability to assess Sb contamination in soils, sediments and geogenic wastes.

Comparative study of the sequential extraction methodologies for fractionation analysis of mercury in coal of Thar coalfield.

The primary objective of this study was to evaluate the bound fractions of mercury (Hg), physicochemical parameters, and mineral composition of coal. Coal samples were collected from various depths within Block-VII of the Thar coalfield in Pakistan. The Hg associated with different chemical fractions of coal was extracted using a sequential extraction scheme as per the community bureau of reference (BCR) protocol. This study utilized both the BCR-sequential extraction method (BCR-SEM) and a single-step sequential extraction based on an ultrasonic-assisted method (SSE-UAM) for the fractionation analysis of Hg in coal. The extraction methodologies, BCR-SEM and SSE-UAM, were specifically designed for analyzing Hg fractionation in coal samples. The SSE-UAM offers an operational advantage, requiring only 2h compared to the 51h needed for BCR-SEM. The analyses were validated using standard reference material (SRM-1635a) and the spiking addition method, achieving a recovery percentage of 97.1% for total Hg concentrations using the pseudo-extraction method in SRM-1635A. Total Hg content in the coal samples ranged from 0.60 to 2.34µgg-1 across four different coal seams from Block-VII of the Thar coalfield. Additionally, Hg concentration was observed to decrease with increasing depth, attributed to changes in mineralogical composition. The highest concentration of Hg was detected at a depth of 200-203m, while the lowest concentration was at a depth of 152-154m. The concentration of Hg in various fractions was 32-60% in the acid-soluble fraction, 1.72-4.92% in the reducible fraction, and 9.58-50.8% in the oxidizable fractions. The coal sample characteristics were analyzed using an elemental analyzer and scanning electron microscopy with energy-dispersive spectroscopy. Cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the extracted fractional concentration of Hg in coal.

The use of organophosphorus extractants as a component of hydrophobic deep eutectic solvents (HDES) for the processing of spent lithium‑iron phosphate batteries

Hydrometallurgical processes for managing industrial waste have attracted significant attention due to tightening global standards on toxic emissions. Among these processes, the use of non-volatile hydrophobic deep eutectic solvents (HDESs) has emerged as a promising approach to optimising extraction processes. In this study, HDESs incorporating tributyl phosphate (TBP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) were investigated in the context of the extraction and separation of elements found in lithium‑iron phosphate batteries, including lithium, aluminium, iron and copper. The physical properties of the HDESs, such as density, viscosity and refractive index, were characterized and the interactions between their components were analysed using infrared spectroscopy. Considering the different classes of extractants represented by D2EHPA and TBP, extraction efficiency for target metals was evaluated across a range of hydrochloric acid concentrations (1–10 mol/L). Optimal conditions for re-extraction (stripping) were identified for extractant regeneration and the production of individual metal ion solutions. Results demonstrated that Fe3+ ions could be extracted with an efficiency exceeding 99% across the majority of acidity levels, while Al3+ ions exhibited similar efficiency from a pH of 1.4. In contrast, Cu2+ ions showed limited extraction (<5%) at lower pH values but the level of extraction increased to 50% at pH 1.9 and above. Leveraging these findings, a sequential extraction scheme is proposed for Al3+, Cu2+, Fe3+ and Li+ from their mixture, based on a gradual reduction in solution acidity.

Green solvent selection and extractin protocol for selective recovery of anti-diabetic components from T. crispa

This study systematically explores a green extraction process of T. crispa stems to selectively isolate therapeutic compounds, borapetoside C (BPC) and magnoflorine (MGF), recognized for their anti-diabetic properties. In agreement with Hansen solubility parameters prediction, H2O and EtOH were found to be suitable solvents for extraction of BPC and MGF, respectively, resulting in 33 % and 45 % extractabilities after 60 min. Further investigations demonstrated considerable increase in BPC extractability using 20 % EtOH:H2O mixture at 40 °C, with complete extraction achieved after 60 min. While for MGF, pure-EtOH at 40 °C, was the most suitable solvent, showing the highest selectivity and complete extraction after 100 min. The BPC-rich extract from 20 % EtOH:H2O exhibited higher anti-diabatic activity (IC50 = 0.63 ± 0.03 and 0.72 ± 0.04 mg/mL, respectively, for α-glucosidase and α-amylase enzymes inhibition activity), and considerably lower cytotoxicity to L6 and HepG2 cells, with IC50 = 0.26 ± 0.16 and 0.24 ± 0.02 mg/mL, respectively, compared with the MGF-rich extract obtained with pure-EtOH. Based on these results, a sequential extraction scheme was proposed involving initial pure-EtOH extraction to selectively and completely remove MGF, followed by extraction with a 20 % EtOH:H2O mixture to recover the remaining BPC, which was approximately 80 % of the BPC originally present. The obtained MGF-free BPC-rich extract showed significantly lower cytotoxicity (IC50 = 0.31 ± 0.06 mg/mL against L6 cell) and higher enzyme inhibition activities (IC50 = 0.53 ± 0.32 and 0.52 ± 0.02 mg/mL for α-glucosidase and α-glucosidase enzymes inhibition activity), comparable to acarbose (IC50 = 0.43 ± 0.02 and 0.83 ± 0.03 mg/mL for α-glucosidase and α-glucosidase enzymes inhibition activity), the result that potentially leads to the development of a promising industrial process to harness T. crispa for diabetes prevention and treatment.

Microbial features with uranium pollution in artificial reservoir sediments at different depths under drought stress

The uranium (U) containing leachate from uranium tailings dam into the natural settings, may greatly affect the downstream environment. To reveal such relationship between uranium contamination and microbial communities in the most affected downstream environment under drought stress, a 180 cm downstream artificial reservoir depth sediment profile was collected, and the microbial communities and related genes were analyzed by 16S rDNA and metagenomics. Besides, the sequential extraction scheme was employed to shed light on the distinct role of U geochemical speciations in shaping microbial community structures. The results showed that U content ranged from 28.1 to 70.1 mg/kg, with an average content of 44.9 mg/kg, significantly exceeding the value of background sediments. Further, U in all the studied sediments was related to remarkably high portions of mobile fractions, and U was likely deposited layer by layer depending on the discharge/leachate inputs from uranium-involving anthoropogenic facilities/activities upstream. The nexus between U speciation, physico-chemical indicators and microbial composition showed that Fe, S, and N metabolism played a vital role in microbial adaptation to U-enriched environment; meanwhile, the fraction of Ureducible and the Fe and S contents had the most significant effects on microbial community composition in the sediments under drought stress.

Comparison of sedimentary iron speciation obtained by sequential extraction and X-ray absorption spectroscopy

Iron (Fe) speciation in marine sediments and suspended particulate matter (SPM) are widely used to investigate the role of Fe minerals in marine biogeochemical cycling and to reconstruct paleo-redox conditions. A traditional method for the determination of Fe speciation are sequential extractions, in which operationally defined Fe pools are dissolved by specific extraction solutions. More recently, many studies make use of synchrotron radiation-based X-ray absorption near edge spectroscopy (XANES), especially if little sample material is available or a high spatial resolution is required. However, few studies have systematically compared Fe speciation obtained by the two methods. Here, we report Fe speciation for marine sediments (both wet and freeze-dried) and SPM from contrasting marine environments (western Baltic Sea and Amazon shelf) obtained by sequential extraction and XANES. The two methods yield comparable results regarding the approximate proportion of reactive Fe ((oxyhydr)oxide, carbonate and sulfide minerals) in the total Fe pool and the extent to which reactive Fe minerals have been converted to pyrite. However, methodological issues associated with both approaches complicate a direct comparison of specific mineral groups. Pyrite concentrations obtained by XANES are lower than those obtained by extraction, which is attributed to an underestimation by XANES due to self-absorption effects and an overestimation by the chromium reduction method due to dissolution of reduced sulfur phases that are not associated with Fe. As substantial amounts of pyrite are oxidized during freeze-drying and sample storage, we recommend to analyze wet sediments in modern marine environments. The XANES spectra of Fe (oxyhydr)oxide and Fe(III)-containing (ferric) clay minerals are similar, which is why these components cannot be differentiated by XANES. Similarly, sequential extraction schemes are known to dissolve a variable proportion of ferric clay minerals along with Fe carbonates and Fe (oxyhydr)oxides. Further investigating the role of ferric clay minerals in the low-temperature marine Fe cycle may therefore require the use of additional methods. Our findings may help to assess the transferability of XANES-based Fe speciation for small sediment and SPM samples to those reported in more traditional studies on Fe biogeochemical cycling and paleo-redox conditions.

Sequential extraction of labile and recalcitrant fractions of soil organic matter: A case study focusing on antimony (Sb) in humic acids, fulvic acids and humin fractions of long-term aged contaminated soils

Soil organic matter (SOM) plays a key role in environmental chemistry of macro and micro nutrients as well as heavy metal (loids). In this research, a modified sequential extraction scheme was used to isolate labile and recalcitrant SOM from organic rich soils after 18 months of ageing with antimony. Humic substances were extracted with a mixture of 0.5 M sodium hydroxide +0.1 M sodium pyrophosphate solution from soils. Then soils deprived of humic substances were sequentially subjected to extraction with glycerol, citric acid, pre-treated with acid and extracted with boiling alkali mixture. The humic acids (HA) and fulvic acids (FA) of isolated SOM fractions were separated and HAs been characterized using FTIR, 1H NMR, and UV-VIS. Acid-alkali treatment of the most recalcitrant SOM fraction (A1-ROM) led to the extraction of sparingly soluble, highly aromatic compound with considerable amounts of N (44% of the extractable N), possibly due to the breakdown of bounds between aromatic rings and amine functional groups. Nevertheless, the highest content of C and TOC was associated with the glycerol extractable SOM. Substantial amounts of Fe and Al were extracted with glycerol, resulting in a dramatic rise of Sb in SOM extracts. The largest increase (60%) in Sb concentrations was observed after the removal of Fe with citric acid. The humic substances (HS) were responsible for 63% of extractable Sb, whereas even after exhaustive alkali extractions 22% of the total Sb remained in the residual humin fraction. Within the HS fraction, 95% of antimony was associated with the low molecular weight FAs. Antimony concentrations in organic fractions correlated significantly with TOC and N contents, possibly due to the role of amine functional groups in Sb complexation. The results of this research highlight the importance of Fe–Al-SOM bridging and humin fraction in sequestration of Sb in recalcitrant SOM pools.

Chemical association and combustion behaviour of cadmium in coal of different mining fields using sequential and single step extraction methods

ABSTRACT This work sought to conduct the chemical association of a toxic metal (cadmium) in coal samples of various origins in Pakistan. For that purpose, a sequential extraction scheme recommended by the Community Bureau of Reference (BCR) has been carried out to know the chemical fractionation of Cd in different coal samples. Simultaneously a time saving vortex-assisted single-step extraction (VA-SSE) via the same experimental parameters conditions used in each fraction steps of BCR sequential extraction procedure (BCR-SE). The coal samples were collected from Thar coal (TCF) and Lakhra coal fields (LCF) of Sindh, Pakistan. The validity of BCR-SE and VA-SSE were checked by applying spiking standard addition procedure on real coal samples. The BCR-SE and VA-SSE were completed in 51 h and 1.0–2.0 min, respectively. In second phase determined the combustion behaviour of Cd or/amount of Cd in coal samples volatilise after heating in an electric furnace in laboratory at three temperature interim (200°C, 400°C and 900°C). The coal ash obtained at 900°C was put to three step sequential extraction method. The evaluated result showed that the total values of Cd in coal samples of block II of Thar coal field (TCF), Site I and Site II of Lakhra coal field (LCF) were found in the range of 3.42–4.43, 2.02–2.82 and 2.91–3.92 mg/kg, correspondingly. The final result indicated that the major chemical fraction of Cd was bound with organic phase of coal samples of both origins (about 40%). The evaluated data showed that 60–71% of Cd in coal samples was found in first three fractions, whilst about 29–40% of Cd was observed in residual. The extracted Cd concentrations in various chemical fractions of coal samples obtained through VA-SSE were 1.6–2.6%, higher than those values gained via BCR-SE (p < 0.04). The resulted data indicated that, after burning of coal samples at 900°C, about 63–69% of total Cd in coal samples of both mining areas was found in residual ash, while 31–34% was vaporised/volatilised out into the atmosphere.

Determination of occurrence and leaching toxicity of arsenic in copper flash smelting slags

The efficient and safe disposition of arsenic (As)-containing copper slag depends on the accurate understanding of the As species and their corresponding leaching toxicity. The As species in copper smelting slag were investigated by X-ray fluorescence spectrometry, X-ray diffractometry, electron probe microanalyzer, scanning electron microscopy equipped with energy dispersive spectroscopy, and selectively sequential extraction scheme. Based on the accurate fractionation of As species, the potential source of As toxicity of copper slag was investigated. The results show that As can be associated with smelting slag in the forms of water-soluble As, Cu−As intermetallics, Cu−As sulfides, as well as the As incorporated in fayalite and glassy silicates. The removal of readily soluble As and Cu−As intermetallics from smelting slag by flotation can reduce the As leaching toxicity of slag tailings, making them conform to the USEPA and SEPA regulatory thresholds for As.

Chemical association of copper and selenium in coals of Sindh by time saving single step strategy and their impact on groundwater.

The aim of the present study is to estimate the different chemical fractionations of copper (Cu) and selenium (Se) in coal samples of different coal mining areas. The Cu and Se bound to various chemical fractions of coal collected from two mining fields of Sindh, Pakistan, have been determined by BCR sequential extraction scheme (BCR-SES). The long duration of the BCR sequential scheme (51h) was reduced by a time-saving shaking device (ultrasonic bath) termed as ultrasonic-assisted extraction (USE) depending on the same operating conditions and extracting solutions used for BCR sequential extraction scheme. The both trace elements were determined in aquifer water, sampled from different depth of both coal mining fields. In addition, the groundwater of dug well in the vicinity of coal mining areas were also analyzed for Cu and Se using reported extraction methodologies. The partitioning of Cu and Se bound with different chemical fractions of coal was successfully made by proposed USE, within 2h as compared to long duration of BCR-SES (51h). The Cu and Se concentrations in acid-soluble fractions of coal samples were > 10%, enhanced by USE extraction procedure than those values gained via BCR-SES (p < 0.01). About 67 to 69% of Cu were found in the first three fractions, whereas their remaining amount corresponding to 31 to 33%, respectively bound with crystalline/residual fraction, while up to 66.1 to 71.1% of total Se contents extracted in three extractable phases, followed up to 28.9 to 33.8% of it was bound with residual phase. The concentrations of Cu and Se in groundwater of different aquifers were found in decreasing order as AQ1 > AQII > AQIII; the same trend was observed for two aquifers of Lakhra coal mining, whereas the groundwater samples have two to three folds higher levels of Se than WHO limit. The Cu levels in water samples were significantly lower than the recommended limit of WHO for drinking water (p < 0.01).

Cereal grain mineral micronutrient and soil chemistry data from GeoNutrition surveys in Ethiopia and Malawi

The dataset comprises primary data for the concentration of 29 mineral micronutrients in cereal grains and up to 84 soil chemistry properties from GeoNutrition project surveys in Ethiopia and Malawi. The work provided insights on geospatial variation in the micronutrient concentration in staple crops, and the potential influencing soil factors. In Ethiopia, sampling was conducted in Amhara, Oromia, and Tigray regions, during the late-2017 and late-2018 harvest seasons. In Malawi, national-scale sampling was conducted during the April–June 2018 harvest season. The concentrations of micronutrients in grain were measured using inductively coupled plasma mass spectrometry (ICP-MS). Soil chemistry properties reported include soil pH; total soil nitrogen; total soil carbon (C); soil organic C; effective cation exchange capacity and exchangeable cations; a three-step sequential extraction scheme for the fractionation of sulfur and selenium; available phosphate; diethylenetriaminepentaacetic acid (DTPA)-extractable trace elements; extractable trace elements using 0.01 M Ca(NO3)2 and 0.01 M CaCl2; and isotopically exchangeable Zn. These data are reported here according to FAIR data principles to enable users to further explore agriculture-nutrition linkages.

Enhanced As, Pb and Zn Uptake by Helianthus annuus from a Heavily Contaminated Mining Soil Amended with EDTA and Olive Mill Wastewater Due to Increased Element Mobilization, as Verified by Sequential Extraction Schemes

Soils close to former mines or metallurgical facilities often contain extreme concentrations of potentially toxic elements (PTEs), and among soil remediation actions needed, enhanced phytoextraction techniques using chelating agents could be a very promising option. In this context, a pot experiment was conducted to evaluate the effect of Na2-EDTA, olive mill wastewater (OMW), and their combination (EDTA + OMW) on As, Pb and Zn uptake by Helianthus annuus (sunflower), grown in a heavily contaminated soil from Lavrio, Greece. After harvest, aboveground and belowground biomass and the concentrations of As, Pb and Zn were determined. Additionally, composite soil samples of all treatments were subjected to appropriate sequential extraction procedures for each PTE. Results showed that although nonstatistically significant effects on plant growth and As concentration were observed, Pb and Zn plant concentrations increased by the EDTA addition, alone or combined with OMW. When the total bioavailability parameter was assessed, EDTA treatment was also found to significantly enhance As uptake (50% increase, p ≤ 0.05). These results were further supported by the respective sequential extraction schemes in which both Pb and As showed increased concentration in the corresponding more soluble soil fractions, probably as an outcome of partial Fe–Mn amorphous oxide dissolution. Our study thus suggests that the applied treatments of EDTA, OMW or their combined application could play a key role as reductive agents in enhancing the mobility of these PTEs in the soil environment, triggering their increased uptake by H. annuus.

Identification of Heavy Metal Compounds in Technogenically Transformed Soils Using Sequential Fractionation, XAFS Spectroscopy, and XRD Powder Diffraction

The transformation of technogenic Cu and Zn compounds in technogenically transformed soils (Spolic Technosols) with high and very high concentrations of metals formed at the site of a natural tailings pond in the floodplain of the Seversky Donets River, the main tributary of the Don River (Rostov oblast, Russia) has been studied. The Technosols are compared to an unpolluted meadow-chernozemic soil (Fluvisol) outside the impact zone. The state of Cu and Zn is assessed using three sequential extraction schemes—Miller’s, Tessier’s, and BCR, as well as synchrotron X-ray powder diffraction (XRD) and analysis of synchrotron X-ray absorption spectrometry (XAFS) spectra. It is shown that the distribution of metals in soil is largely related to their properties, such as electronegativity, hydrolyzability, and softness parameter. As is observed, Cu mainly concentrates in the residual fraction (to 42%) and in the fraction associated with organic matter (up to 27%). The mobility of Zn in the studied soils is higher than that of Cu. Its main part (up to 56%) is in the residual fraction and the fraction associated with Fe and Mn oxides (up to 48%), especially with Fe(III) crystalline compounds. The combination of a three-stage BCR scheme with XAFS and XRD techniques is used for the first time. Most of the peaks in diffraction patterns of soil samples after the first and second extraction stages correspond to the authigenic sulfur-containing minerals, namely, wurtzite (ZnS with a hexagonal structure), sphalerite (cubic ZnS), covellite (CuS), and bornite (Cu5FeS4). Wurtzite is present in the exchangeable and reducible fractions. These fractions also contain chalcocite (Cu2S). Sulfides are most abundant in soil sample after extraction of the oxidizable fraction, while phyllosilicates are prevalent in the sample after extraction of the reducible fraction. X-ray absorption spectroscopy demonstrates molecular structural changes in the Zn and Cu compounds in heavily polluted soils, suggesting the transformation of metals under different environmental conditions, which is important for assessment of the soil protective function.

Volatilisation of selenium from coals by heating at different temperature: application of sequential extraction scheme on ash

ABSTRACT An important issue to the earth’s atmosphere is the volatilisation of elements such as selenium, from the burning of coal at different temperatures. In the current work, the volatilisation of selenium (Se) during combustion of coal samples at different control temperature range in an electrically controlled furnace was carried out. The coal samples were obtained from various coal fields of Sindh, Pakistan. The duplicate coal samples were combusted in controlled furnace by applying three temperature rounds (200°C, 400°C and 900°C). The ash formed following each temperature round was examined to know the volatilisation contents of Se after burning of coal samples at different temperature. The fractionation of Se in coal ash gained after combustion at 900°C was subjected to three-stage sequential extraction scheme (SES). The obtained data indicated that the total contents of Se in coal samples of block II of Thar coal field (TCF), and Site I and Site II of Lakhra coal field (LCF) were observed in the range of 7.72–14.3, 9.02–16.3 and 8.92–14.2 mg/kg, respectively. It was observed that after the burning of coal samples at 900°C, about 75–81.8% of the total Se was volatised out into atmosphere.

Chemical Fractionation in Environmental Studies of Potentially Toxic Particulate-Bound Elements in Urban Air: A Critical Review.

In recent years, studies of heavy metal air pollution have increasingly gone beyond determining total concentrations of individual toxic metals. Chemical fractionation of potentially toxic elements in airborne particles is becoming an important part of these studies. This review covers the articles that have been published over the last three decades. Attention was paid to the issue of atmospheric aerosol sampling, sample pretreatment, sequential extraction schemes and conditions of individual extractions. Geochemical forms of metals occurring in the air in urban areas were considered in detail. Based on the data sets from chemical fractionation of particulate matter samples by three sequential extraction procedures (SEPs)—Fernández Espinosa, BCR and Chester’s—the compilation of the chemical distribution patterns of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn was prepared. The human health risk posed by these toxic and/or carcinogenic elements via inhalation of atmospheric particles was estimated for two categories of polluted urban areas: the commonly encountered pollution level and the high pollution level.

Fractionation of Metal(loid)s in Three European Mine Wastes by Sequential Extraction

Mine waste can constitute an environmental hazard, especially when poorly managed. Environmental assessment is essential for estimating potential threats and optimizing mine waste management. This study evaluated the potential environmental risk of sulfidic mine waste samples originating from the Neves Corvo Mine, Portugal, and the closed Freiberg mining district, Germany. Metal(loid)s in the waste samples were partitioned into seven operationally defined fractions using the Zeien and Brummer sequential extraction scheme. The results showed similar partitioning patterns for the elements in the waste rock and tailing samples from Neves Corvo Mine; most metal(loid)s showed lower mobility, as they were mainly residual-bound. On the contrary, the Freiberg tailing sample had considerably elevated (24–37%) mobile fractions of Zn, Co, Cd, and Mn. The majority of Fe (83–96%) in all samples was retained in the residual fractions, while Ca was highly mobile. Overall, Pb was the most mobile toxic element in the three samples. A large portion of Pb (32–57%) was predominantly found in the most mobilizable fractions of the studied waste samples. This study revealed that the three mine wastes have contamination potential for Pb and Zn, which can be easily released into the environment from these waste sources.

Impacts of wet thermal treatment on heavy metals speciation in contaminated waste activated sludge using a modified sequential extraction scheme

The mobility and the bioavailability of heavy metals in waste activated sludge were determined according to their total content and chemical speciation. A modified three-step sequential extraction procedure was used to determine the total content and metal speciation distribution pattern of various heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) pretreated at a temperature of 100 °C to 200 °C. It was found that the organics solubilization was enhanced at higher temperature, increased by 1.75, 183 and 3.03 folds over the soluble chemical oxygen demand (SCOD) at 100 °C. The total contents of Cd, Pb and Zn exceeded the threshold value established in GB/T standard 23486 (2009), as a function of pH, due to the pollution from the local nonferrous metals industry. For most cases, the impacts of thermal pretreatment on the species distribution were limited and obscure. Cr was the only element showing a potential risk of metal mobilization, such that its residual fraction shifted towards oxidizable fraction at higher treatment temperature. The speciation distribution pattern of Ni, Cr, Cu, and Zn showed potential risks of contamination due to their bioavailability, mobility, or toxicity.

The impact of climate change and eutrophication on phosphorus forms in sediment: Results from a long-term lake mesocosm experiment

Characteristics of bottom sediments in lake mesocosms 11 years after starting the experiment were studied in order to determine the effects of nutrient loading, temperature increase and vegetation type on concentration and vertical distribution of phosphorus (P) forms. The experimental setup consisted of 24 outdoor flow-through mesocosms with two nutrient treatments – low (L) and high (H) and 3 temperature levels – ambient (T0), heated by 2–4 °C (T1) and 3–6 °C (T2) in four replicates. Thickness of the organic sediment was measured and the sediment analysed for dry weight, organic matter, and P fractions (according to a sequential extraction scheme) and organic P compounds (by 31P nuclear magnetic resonance spectroscopy). Higher nutrient loading led to increased sediment accumulation and higher concentration of total P and most P fractions, except P bound to aluminium and humic matter. The dominant vegetation type covaried with nutrient levels. Vertical gradients in Ca bound P and mobile P in low nutrient mesocosms was perhaps a result of P coprecipitation with calcite on macrophytes and P uptake by roots indicating that in macrophyte-rich lakes, plants can be important modifiers of early P diagenesis. Temperature alone did not significantly affect sediment accumulation rate but the interaction effect between nutrient and temperature treatments was significant. At high nutrient loading, sediment thickness decreased with increasing temperature, but at low nutrient loading, it increased with warming. The effect of warming on sediment composition became obvious only in nutrient enriched mesocosms showing that eutrophication makes shallow lake ecosystems more susceptible to climate change.

Evaluation of arsenic mineralogy and geochemistry in gold mine-impacted matrices: Speciation, transformation, and potential associated risks

The risk of arsenic (As) contamination from gold mining is a long-term environmental concern for mines worldwide. Researchers have mainly focused on As contamination induced by tailings, however, less attention has been paid mineralogically to differentiate the fate of As among different As-bearing matrices. This paper presents a detailed study of the mineralogical and morphological features of three typical As-bearing matrices (waste rock, ores, and tailings) using bulk chemical, microscopic and spectroscopic analyses, and reveals the geochemical behavior of As in those matrices. Results from mineral composition identified by RoqSCAN revealed that the matrices were dominated by quartz, k-feldspar, albite, muscovite, and clay minerals, with subordinate ankerite, chlorite, smectite, hematite, arsenopyrite, pyrrhotite, apatite, pyrite, halite, and calcite. The sequential extraction scheme indicated that As in waste rock, ores and tailings was mainly hosted in arsenopyrite. Microscopic analysis observed that waste rock was significantly different from the ores and tailings in terms of mineralogical and morphological characteristics. For waste rock, from arsenopyrite to hematite, As content decreased from 46.12 wt% to 3.54 wt%. However, arsenopyrite presented as unweathered euhedral crystals or slight fragmentation in ores and tailings and a narrower oxidation rims than that of waste rock. The leaching test of SPLP showed that the highest As leaching was found in waste rock (0.246 mg/L) which was significantly higher than those in ores (0.080 mg/L) and tailings (0.148 mg/L). The As in waste rock displayed weaker geochemical stability than in ores and tailings, as supported by mineralogy analysis. Health risk assessment suggested waste rock had a higher health risk for both adults and children compared with ores and tailings. These findings reaffirm that understanding of As fate among different source materials is paramount for securing humans from As hazards. More must be done to decelerate the continuous oxidation of waste rock, thus mitigating As release into nature.

The Effect of Compost and Apatite on Pb Distribution in the Pb- Contaminated Soil

There are various techniques for rehabilitating soils contaminated by heavy metals, such as physical treatment, chemical treatment, and phytoremediation. Pb-contaminated soils are mostly treated with soil mixing, soil dressing, or soil washing. In this study, hydroxyapatite powder and organic compost of different mix ratios were added to two kinds of high-concentration synthesized Pb-contaminated soils (1000 mg/kg), which were processed with sequential extraction schemes after different incubation periods in order to examine the distribution of Pb forms in them. The form distributions analyzed included the exchangeable form Pb (PbE), Fe-Mn oxidation form Pb (PbFe-Mn), organic bonded form Pb (PbO), and residual form Pb (PbR). The findings indicated that after stabilization for one month, the alkaline Tk series soil was less susceptible to Pb contamination when no hydroxyapatite and compost was applied, which made it more difficult for Pb in the soil to interact with cations and trigger exchange reactions. Next, the PbR concentrations of the two soils tested were higher after hydroxyapatite was added. This result suggested that hydroxyapatite helped to stabilize the Pb in the soil samples and prevented it from precipitating, thereby controlling the Pb concentration at a certain level to avoid contamination. Lastly, when hydroxyapatite and compost of different mix ratios were applied to the two kinds of Pb-contaminated soils, we found that the PbE concentration of the Tk series soil declined as the concentration of compost increased, suggesting that increasing the compost concentration raised the pH value of the soil and enhanced its fertility. On the other hand, the PbE concentration of the Lp series soil increased as the compost concentration rose, indicating that an increase in compost concentration hampered plants from absorbing soluble nutrients in the soil, thereby making it easier for Pb to precipitate via cation exchange and resulting in Pb contamination.