Sequential Chemical Extraction Research Articles

Release and Transformation of Sodium during Pyrolysis of Zhundong Coals

Zhundong coalfield is one of the superhuge coalfields newly discovered in Xinjiang Autonomous Region of China. While many studies on alkali metals in coal/biomass have been reported previously, few efforts were conducted on Zhundong coals which are characterized by a high content of sodium. It is challenging to explore the ash deposition problems related to Zhundong coals directly using existing findings on the behavior of alkali metals. The occurrence mode and transformation of alkali metals during thermal conversion of Zhundong coals could be quite different. Specific investigation on sodium transformation during pyrolysis of Zhundong coals will make a contribution to our understanding on the fate and behavior of alkali metals involved in high-sodium coals. Here, the release and transformation fundamentals of sodium during pyrolysis of two Zhundong bituminous coals were investigated using an experimental approach of sequential chemical extraction. The sodium volatilization and evolution of occurrence modes in chars of Zhundong coal were probed in a laboratory-scale reactor. The occurrence of alkali metals in Zhundong coals greatly differs from those in other coals of China. Water-soluble sodium is the predominant chemical form in Zhundong coals. Most of the water-soluble sodium is released into gas phase as a volatile during pyrolysis and part of the remainder is converted into an insoluble form, but the release of sodium is not always synchronous with volatility. The release behavior of sodium demonstrates a nonmonotonic variation with the particle size of the coal while the effect of particle size includes many factors resulting in the challenge of demonstrating its individual contribution to sodium release. The duration time has an insignificant effect on volatile release and sodium transformation at low temperature, while it has an obvious influence at high temperature or in the initial stage of pyrolysis. With the extension of duration time at high temperature, no more sodium is obviously released from the residual chars of Zhundong coal but more water-soluble sodium will still transform into insoluble form. During the devolatilization of Zhundong coals under CO2 atmosphere, the release of sodium and its conversion into insoluble form will be inhibited compared to that under N2 condition.

Ecological risk assessment of metals contamination in the sediment of the Bamdezh wetland, Iran

Present survey investigates the intensity of heavy metals pollution (Ca, Fe, Ni, Cd, Pb, Zn, AS, Hg) in the sediments of Bamdezh wetland, Iran . The main objective of the study is quantification of heavy metal pollution intensity in this wetland. Bamdezh wetland is located in about 40 km northwest of Ahvaz, Iran. This wetland is a habitat and food source for aquatic ecosystem and migratory birds, also a significant resource of income for the locals. Anthropogenic portion of the metals was determined through five-step chemical sequential extraction. The results of partition studies revealed the arrangement of anthropogenic portions for the metals as follows: Cd (86 %) > Pb (80 %) > Ni (46 %) > Zn (44 %) > Fe (24 %). The mean enrichment factor values for various metals were between minimal enrichment and extremely enrichment. The values obtained from I poll index are indicative of a broad range from unpolluted to moderately polluted to moderately to strongly polluted. All stations can be interpreted as a very high degree of contamination using C d and high degree of contamination using mCd classification. PLI ranged from 1.22 at station 3 to 1.55 at station 4. Result of cluster analysis for Zn and LOI shows that these two elements are related together by high similarity coefficient. As LOI in the environment is the index of biological activity, then Zn should have biological origin. The dendrogram also showed that a part of Ca and Ni is derived from lithogenous source as they are linked to Fe.

Assessment of mobility and bio-availability of heavy metals in dry depositions of Asian dust and implications for environmental risk

We assess the potential mobility and bio-availability of selected metals (As, Cd, Co, Cr, Cu, Ni, Mo, Pb, S, Zn, and Zr) in the dry depositions of Asian and non-Asian dust from the city of Daejeon, Korea. For this study, we applied Pb isotopes, total extraction and chemical sequential extraction methods to the dry depositions. In addition, microscopic analysis was performed using X-ray diffraction (XRD) and focused ion beam (FIB)-scanning electron microscopy (SEM-EDS). FIB–SEM cross-section observations and Pb isotope data showed a black carbon is an important carrier of associated heavy metals originating from China. A five-step sequential extraction performed on the dry depositions showed that S and Cd are the most abundant elements in the water-soluble and cation-exchangeable fraction. In addition, Zn and Pb appeared predominantly in the carbonate and reducible fractions. On the other hand, Cu, Mo and, to a lesser degree, As were significantly associated with the organic fraction, while Co, Ni, Cr and Zr were bound to the residual fraction. These results showed that S, Cd, Zn and Pb, which were highly concentrated in potentially mobile fractions, have potential environmental risk because potential changes in redox state and pH may remobilize these metals. In addition, the estimated remobilization concentrations of these metals were significant. Thus, this study shows that frequent and careful monitoring of S, Cd, Z, Pb and, to a lesser degree, Cu, Mo and As is very important for assessing environmental risk in Korea.

Characterization of phosphorus species in sediments from the Arabian Sea oxygen minimum zone: Combining sequential extractions and X-ray spectroscopy

The bulk phosphorus (P) distribution in sediment samples from the oxygen minimum zone of the northern Arabian Sea was determined using two methods: sequential chemical extraction (the ‘SEDEX’ procedure) and X-ray absorption near-edge structure (XANES) spectroscopy of the phosphorus K-edge. Our results show good agreement between iron (Fe-)associated P and calcium phosphate minerals (Ca-P) determined by both methods. Furthermore, we find that SEDEX exchangeable P likely represents loosely Fe-bound P, and that the SEDEX detrital fraction may consist partly of polyphosphate, i.e. microbially synthesized intracellular phosphate. Below productive waters with relatively high sedimentary organic matter and P contents, polyphosphates may represent an important P sink that is not easily identified by chemical sequential extraction. This study highlights the value of SEDEX as a generally accurate and fast P speciation technique (especially for Fe- and Ca-P) and, for the first time, demonstrates the possibilities of P K-edge XANES as a bulk P speciation tool for marine sediments.

Cadmium accumulation in six common plant species associated with soils containing high geogenic cadmium concentrations at Le Gurnigel, Swiss Jura Mountains

The uptake of cadmium (Cd) was analyzed for six different perennial plant species growing in a wooded pasture of the Swiss Jura Mountains, where the soils are geogenically enriched in Cd (4.58mg·kg−1 on average (n=36); maximal value: 16.3mg·kg−1). The six selected plants — Hypericum maculatum (Hypericaceae), Alchemilla xanthochlora (Rosaceae), Cynosurus cristatus (Poaceae), Ranunculus acris (Ranunculaceae), Dactylis glomerata (Poaceae) and Acer pseudoplatanus (Sapindaceae) — show variable Cd contents among the species and among individuals from the same family (Poaceae). Average Cd concentrations in the selected plants are in the 2–6mg·kg−1 range and exceed the maximal Cd concentration tolerated in vegetal feed for animals, which is established at 1mg·kg−1. High Cd concentrations in the soil result in a reduction of Cd accumulation in the shoots and a corresponding increase in the roots. This implies that Cd transfer coefficients from the soil/rhizosphere to the plant are inversely proportional to the total Cd concentrations in soils and do not depend on plant species but instead on soil type. Sequential chemical extractions reveal that variations in Cd distribution between the bulk soil and the corresponding rhizospheric soil occur mainly in the Cd-bearing phases, which are exchangeable, bound to carbonates, and associated with organic matter. This is principally due to the incorporation of root exudates, which modify pH and redox conditions of the rhizosphere. Elevated Cd concentrations in the shoots of A. xanthochlora (up to 8mg·kg−1), C. cristatus (9mg·kg−1) and H. maculatum (3mg·kg−1) may represent a long-term hazard for livestock and human health since these plants are used either by grazing cattle or for medicinal purposes. On the contrary, R. acris, A. pseudoplatanus, and especially D. glomerata show lower Cd concentrations and are of minor concern with regards to their environmental impact.

The Impact of Combustion Technology of Sewage Sludge on Mobility of Heavy Metals in Sewage Sludge Ash/Wpływ Technologii Spalania Komunalnych Osadów Ściekowych Na Mobilność Metali Ciężkich Z Popiołów

Abstract Sewage sludge ashes from grate furnace and fluidized bed furnace were used in this research. This research was carried out to investigate the impact of combustion technology on sewage sludge speciation of heavy metals from sewage sludge ash. This was achieved by conducting a sequential chemical extraction procedure Community Bureau Reference (BCR). This study indicated that heavy metals in sewage sludge ash were dominant in immobile fractions. Moreover, it was stated that the combustion technology of sewage sludge did not have a significant influence on the mobility of heavy metals in ashes

Fe(II)-catalyzed recrystallization of goethite revisited.

Results from enriched (57)Fe isotope tracer experiments have shown that atom exchange can occur between structural Fe in Fe(III) oxides and aqueous Fe(II) with no formation of secondary minerals or change in particle size or shape. Here we derive a mass balance model to quantify the extent of Fe atom exchange between goethite and aqueous Fe(II) that accounts for different Fe pool sizes. We use this model to reinterpret our previous work and to quantify the influence of particle size and pH on extent of goethite exchange with aqueous Fe(II). Consistent with our previous interpretation, substantial exchange of goethite occurred at pH 7.5 (≈ 90%) and we observed little effect of particle size between nanogoethite (average size of 81 × 11 nm; ≈ 110 m(2)/g) and microgoethite (average size of 590 × 42 nm; ≈ 40 m(2)/g). Despite ≈ 90% of the bulk goethite exchanging at pH 7.5, we found no change in mineral phase, average particle size, crystallinity, or reactivity after reaction with aqueous Fe(II). At a lower pH of 5.0, no net sorption of Fe(II) was observed and significantly less exchange occurred accounting for less than the estimated proportion of surface Fe atoms in the particles. Particle size appears to influence the amount of exchange at pH 5.0 and we suggest that aggregation and surface area may play a role. Results from sequential chemical extractions indicate that (57)Fe accumulates in extracted Fe(III) goethite components. Isotopic compositions of the extracts indicate that a gradient of (57)Fe develops within the goethite with more accumulation of (57)Fe occurring in the more easily extracted Fe(III) that may be nearer to the surface.

Combining chemical sequential extractions with 3D fluorescence spectroscopy to characterize sludge organic matter

The design and management of anaerobic digestion of sewage sludge (SS) require a relevant characterisation of the sludge organic matter (OM). Methods currently used are time-consuming and often insufficiently informative. A new method combining chemical sequential extractions (CSE) with 3D fluorescence spectroscopy was developed to provide a relevant SS characterisation to assess both OM bioaccessibility and complexity which govern SS biodegradability. CSE fractionates the sludge OM into 5 compartments of decreasing accessibility. First applied on three SS samples with different OM stability, fractionation profiles obtained were in accordance with the latter. 3D fluorescence spectroscopy revealed that the bioaccessible compartments were mainly constituted of simple and easily biodegradable OM while the unaccessible ones were largely made of complex and refractory OM. Then, primary, secondary and anaerobically digested sludge with different biodegradabilities were tested. Complexity revealed by 3D fluorescence spectroscopy was linked with biodegradability and chemical accessibility was correlated with sludge bioaccessibility.

Copper, zinc and lead biogeochemistry in aquatic and land plants from the Iberian Pyrite Belt (Portugal) and north of Morocco mining areas.

The ability of aquatic (Juncus effusus L., Scirpus holoschoenus L., Thypha latifolia L. and Juncus sp.) and land (Cistus ladanifer L., Erica andevalensis C.-R., Nerium oleander L., Isatis tinctoria L., Rosmarinus officinalis L., Cynodon dactylon L. and Hordeum murinum L.) plants from Portugal (Aljustrel, Lousal and São Domingos) and Morocco (Tighza and Zeida) mining areas to uptake, translocate and tolerate heavy metals (Cu, Zn and Pb) was evaluated. The soils (rhizosphere) of the first mining area are characterized by high acidity conditions (pH 2-5), whereas from the second area, by alkaline conditions (pH 7.0-8.5). Physicochemical parameters and mineralogy of the rhizosphere were determined from both areas. Chemical analysis of plants and the rhizosphere was carried out by inductively coupled plasma emission spectrometry. The sequential chemical extraction procedure was applied for rhizosphere samples collected from both mining areas. In the acid conditions, the aquatic plants show a high capacity for Zn bioaccumulation and translocation and less for Pb, reflecting the following metal mobility sequence: Zn > Cu > Pb. Kaolinite detected in the roots by infrared spectroscopy (IR) contributed to metal fixation (i.e. Cu), reducing its translocation to the aerial parts. Lead identified in the roots of land plants (e.g. E. andevalensis) was probably adsorbed by C-H functional groups identified by IR, being easily translocated to the aerial parts. It was found that aquatic plants are more efficient for phytostabilization than bioaccumulation. Lead is more bioavailable in the rhizosphere from Morocco mining areas due to scarcity of minerals with high adsorption ability, being absorbed and translocated by both aquatic and land plants.

Research on the Improvement and Application of Chemical Sequential Extraction of Phosphorus in Sediments

By the chemical sequential extraction method, various chemical speciation of phosphorus were extracted from shallow sediments of Nansi Lake. Aiming at the existing problems of lower concentration of phosphorus, the method combined the original sequential extraction and Mo-Sb Anti spectrophotometric method was improved to reduce the interference caused by stratification and chromogenic reaction. In addition, due to the presence of excess sodium dithionite, the extracting solution need to be diluted during occlude phosphorus (Oc-P) extraction process.

Role of micrometer sediment particles (SPLITT fractionation) in phosphorus speciation and its recycling in lakes

To study the potential of phosphorus (P) release from sediments in the lakes: Chelmzynskie and Wieczno Pld. was the aim of this study. The task was realized by carrying chemical sequential extractions. The novelty of our approach consists in adopting the SPLITT (split-flow lateral-transport thin) method of particles separation, which was used supplementary to sieving. Sieving provides following sediment fractions: 0.25–0.5, 0.125–0.25, 0.09–0.125 mm, whereas the SPLITT allows separation of particles which smaller than 30 μm, and which constituted >30 % of total sediment mass. The mass distribution of size fractions in sediments from both the lakes was very similar. P content, as the sum of HCl-P, NaOH-P, NH4Cl-P, was by ca. 20 % lower in the particle size fractions 0.25–0.5, 0.125–25 mm, whereas total P content in SPLIT sediment was much higher in all size fractions (<5, 5–10, 10–30 μm) in the Wieczno Pld. Lake. Although the ecological status is stated to be good in the Wieczno Pld. and moderate in the Chelmzynskie, the Wieczno Pld. experiences very extensive and frequent algal blooms which form scum on the lake’s surface. Based on our findings, we are of the opinion that shallowness of the Lake Wieczno Pld. favors water mixing causing resuspension of fine particles, which results in enhanced P internal cycling and thus P availability for primary producers. Much higher content of phosphorus in the fractions below 30 μm in the Wieczno Pld. than the Chelmzynskie Lake supports our statement.

Impact of Mining Dump on the Accumulation and Mobility of Metals in the Bytomka River Sediments

Abstract The research aim was to determine the long-term impact of the mine waste stored at the coal waste dump Hałda Ruda on the content of heavy metals in the bottom sediments of the Bytomka River. It is a watercourse flowing along this coal waste dump and has been under its influence for over fifty years. The research also attempted to determine the seasonality of changes (2 years) and mobility of selected elements. The article presents total contents of Cr, Mn, Ni, Cu, Zn, As, Cd and Pb in the bottom sediments collected from the Bytomka River. It also focuses on the distribution of these elements in particular geochemical fractions determined with the Tessier's sequential chemical extraction procedure. Total element contents were determined with an EDPXRF (Energy Dispersive X-ray Fluorescence) technique. The extractants of particular Tessier's fractions were determined quantitatively with an ICP-MS (Inductively Coupled Plasma Mass Spectrometry) spectrometer. The research results show that the stored waste significantly influences the contents of heavy metals in the Bytomka River bottom sediments. The lowest concentration of heavy metals was observed at the B1 spot (above the dump), while the highest one was measured at the B3 spot (below the dump). Sequential chemical extraction of the bottom sediments indicates that the Zn content in the ion-exchange and carbonate fractions diminished within a year. Nevertheless, Zn bound to Fe and Mn oxides acted in the opposite way. Mn, Zn and Pb are the most dangerous elements from the viewpoint of environmental hazards, as their total concentrations were high. Moreover, their high contents were observed in the most mobile (ion-exchange and carbonate) fractions. Extremely toxic Cd was bound to the oxide fraction to the largest extent. Cu was mainly bound to the organic fraction while environmentally hazardous Cr was bound to the residual fraction.

Partitioning and transformation behavior of toxic elements during circulated fluidized bed combustion of coal gangue

A study on toxic elements behaviors from a 330MW coal gangue circulated fluidized bed co-combustion power plant equipped with electrostatic precipitators (ESPs) was performed. Simultaneous sampling of feed coal, bottom ash, fly ash and flue gas were implemented. Sequential chemical extraction was taken to investigate the transformation behaviors of toxic elements. The relative distribution and partitioning behavior of toxic elements in the power plants were analyzed systemically. The toxic elements can be divided into two groups, Cluster one, whereby high volatile tendencies are represented by As, Cd, Cu, Pb, Se and Sn which have a volatilization ratio more than 20% and are mainly enriched in fly ash. These elements are primarily associated with sulfide minerals. Cluster two, represented by Co, Cr, Mn and V, have low volatilization rate (⩽5%) and are equally distributed between bottom ash and fly ash. In addition, Bi, Ni and Zn may be located between Cluster one and Cluster two. The variation of modes of occurrence of toxic elements could lead to the difference of transformation behaviors during the combustion of feed coal. Most toxic elements transformed and partitioned into other fractions from Fe–Mn oxides during combustion.

Iron and manganese speciation and cycling in glacially influenced high-latitude fjord sediments (West Spitsbergen, Svalbard): Evidence for a benthic recycling-transport mechanism

Glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese phases to the coastal ocean in high-latitude regions. Little is known about the fate and biogeochemical cycling of glacially derived iron and manganese in the coastal marine realm. Sediment and porewater samples were collected along transects from the fjord mouths to the tidewater glaciers at the fjord heads in Smeerenburgfjorden, Kongsfjorden, and Van Keulenfjorden along Western Svalbard. Solid-phase iron and manganese speciation, determined by sequential chemical extraction, could be linked to the compositions of the local bedrock and hydrological/weathering conditions below the local glaciers. The concentration and sulfur isotope composition of chromium reducible sulfur (CRS) in Kongs- and Van Keulenfjorden sediments largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers. The varying input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the pathways of organic carbon mineralization in the sediments of the three fjords. High reducible iron and manganese oxide concentrations and elevated metal accumulation rates coupled to low input of “fresh” organic matter lead to a strong expression of dissimilatory metal oxide reduction evidenced in very high porewater iron (up to 800μM) and manganese (up to 210μM) concentrations in Kongsfjorden and Van Keulenfjorden. Sediment reworking by the benthic macrofauna and physical sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese cycling in these fjords. On-going benthic recycling of glacially derived dissolved iron into overlying seawater, where partial re-oxidation and deposition occurs, facilitates the transport of iron across the fjords and potentially into adjacent continental shelf waters. Such iron-dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond. By contrast, low delivery of reducible iron (oxyhydr)oxide phases and elevated organic carbon mineralization rates driven by elevated input of “fresh” marine organic matter allow organoclastic sulfate reduction to dominate carbon remineralization at the outer Smeerenburgfjorden sites, which may limit iron fluxes to the water column.

Chemical Speciations of Uranium of a Sandstone Uranium Deposit and their Effects to &lt;i&gt;In Situ&lt;/i&gt; Leaching, Northwest China

The chemical speciations of uranium of a sandstone uranium deposit in the Yili Basin were quantitative analyzed using the method of sequential chemical extraction, and the implications of which for in-situ leaching of uranium were discussed. The proportion of chemical speciations of uranium shows that the bound to carbonates&gt;the bound to Fe-Mn oxides&gt;the exchangeable&gt;the residual&gt;the bound to sulfide-organic matter speciation, which is beneficial to cost reduction on in-situ leaching of uranium and environmental protection. The active uranium includes 4 chemical speciations except for the residual speciation is principal, which suggests that the leaching rate of uranium of the sandstone uranium deposit is high. The inert uranium is the residual speciation, with low proportion. The sample with high proportion of active uranium is of high grade, and vice versa, which indicates that the ratio of total uranium extracted/reserves should be relatively high. Hence, based on the chemical speciations of uranium, the sandstone uranium deposit can be exploited suitably using the technique of in-situ leaching with dilute sulfuric acid, integrated considering that cost control of in-situ leaching of uranium, environmental protection, leaching rate of uranium and the ratio of total uranium extracted/reserves of uranium.

In-situ determination of metallic variation and multi-association in single particles by combining synchrotron microprobe, sequential chemical extraction and multivariate statistical analysis

Due to the heterogeneity of metal distribution, it is challenging to identify the speciation, source and fate of metals in solid samples at micro scales. To overcome these challenges single particles of air pollution control residues were detected in situ by synchrotron microprobe after each step of chemical extraction and analyzed by multivariate statistical analysis. Results showed that Pb, Cu and Zn co-existed as acid soluble fractions during chemical extraction, regardless of their individual distribution as chlorides or oxides in the raw particles. Besides the forms of Fe2O3, MnO2 and FeCr2O4, Fe, Mn, Cr and Ni were closely associated with each other, mainly as reducible fractions. In addition, the two groups of metals had interrelations with the Si-containing insoluble matrix. The binding could not be directly detected by micro-X-ray diffraction (μ-XRD) and XRD, suggesting their partial existence as amorphous forms or in the solid solution. The combined method on single particles can effectively determine metallic multi-associations and various extraction behaviors that could not be identified by XRD, μ-XRD or X-ray absorption spectroscopy. The results are useful for further source identification and migration tracing of heavy metals.

Mercury speciation in the Mt. Amiata mining district (Italy): Interplay between urban activities and mercury contamination

A fundamental step to evaluate the biogeochemical and eco-toxicological significance of Hg dispersion in the environment is to determine speciation of Hg in solid matrices. In this study, several analytical techniques such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), sequential chemical extractions (SCEs), and X-ray absorption spectroscopy (XANES) were used to identify Hg compounds and Hg speciation in samples collected from the Mt. Amiata Hg mining district, southern Tuscany, Italy. Different geological materials, such as mine waste calcine (retorted ore), soil, stream sediment, and stream water suspended particulate matter were analyzed. Results show that the samples were generally composed of highly insoluble Hg compounds such as sulphides (HgS, cinnabar and metacinnabar), and more soluble Hg halides such as those associated with the mosesite group. Other moderately soluble Hg compounds, HgCl2, HgO and Hg0, were also identified in stream sediments draining the mining area. The presence of these minerals suggests active and continuous runoff of soluble Hg compounds from calcines, where such Hg compounds form during retorting, or later in secondary processes. Specifically, we suggest that, due to the proximity of Hg mines to the urban center of Abbadia San Salvatore, the influence of other anthropogenic activities was a key factor for Hg speciation, resulting in the formation of unusual Hg-minerals such as mosesite.

Sequential extraction of heavy metals in soils from a copper mine: Distribution in geochemical fractions

We evaluated heavy metal contamination (Cr, Cu, Mn, Ni, Pb, and Zn) in soils from the copper mine in Touro, NW Spain. Their total content and geochemical phase distribution were determined using sequential chemical extraction. Representative soils from the area were selected and the objectives were to analyse the total content of heavy metals and their distribution in the different geochemical soil phases, and to determine their association with the soil components using XRD, FE-SEM/EDS and TOF-SIMS. Results show that the Cu total contents (104–2924mgkg−1) exceed the intervention limits. Most of the heavy metal content is in the residual fraction, Cr (82–95%), Cu (30–70%), Mn (60–96%), Ni (77–95%), Pb (47–68%) and Zn (85–97%). Fe-oxides play an important role in the fixation of metals, especially Cu. The amounts associated with soil organic matter and in the exchangeable form are very low (>10%). TOF-SIMS and FE-SEM/EDS techniques confirm the fractionation results, showing that only a very small part of the studied metals are sorbed, mainly in the iron oxides and interacting with several soil mineral components. FE-SEM/EDS combined with TOF-SIMS, sequential extraction assays and statistical analyses are an effective tool to check the affinity of the soil components for heavy metal cations.

Geological and Geochemical Characteristics of Chang 7 Uranium-Enriched Hydrocarbon Source Rocks in Ordos Basin and the Possible Reasons for its Formation

The Ordos basin Chang 7 hydrocarbon source rocks are the most important rock strata of premium oil source formed during the largest lake flood period of the terrestrial lacustrine. Our study found that the bottom of the rocks are rich in radioactive uranium. Element geochemical studies showed that the rocks are also rich in C, S, P, Cu, V, Mo and other pro-life elements but not rock-forming minerals-related lithophile elements Li, Zr, Sr, etc. Their uranium content has obvious positive correlation with phosphorus, sulfur, iron, organic carbon content, but not with major rock-forming elements. Petrography and scanning electron microscopy revealed the rocks are rich in pyrite, phosphate rock and striped organic matters. These features indicate that uranium enrichment and the presence of these minerals are closely related. The significantly positive correlation of the ratio of uranium to trace elements such as U/ (U+Ni) and U/Sc indicates that anoxic environment played an important role in uranium enrichment. Electron microprobe analysis found for the first time uranium ore and independent titanium-containing uranium minerals in phosphate rocks in the area. α radiation photography and sequential chemical extraction found that 50% of uranium present as independent uranium and its isomorphic minerals in the phosphate rocks, 20% is absorbed to pyrite and organic matter, and less than 10% is absorbed on clay minerals.

The impacts of different long-term fertilization regimes on the bioavailability of arsenic in soil: integrating chemical approach with Escherichia coli arsRp::luc-based biosensor

An Escherichia coli arsRp::luc-based biosensor was constructed to measure the bioavailability of arsenic (As) in soil. In previous induction experiments, it produced a linear response (R (2) = 0.96, P < 0.01) to As from 0.05 to 5μmol/L after a 2-h incubation. Then, both chemical sequential extraction, Community Bureau of Reference recommended sequential extraction procedures (BCR-SEPs) and E. coli biosensor, were employed to assess the impact of different long-term fertilization regimes containing N, NP, NPK, M (manure), and NPK + M treatments on the bioavailability of arsenic (As) in soil. Per the BCR-SEPs analysis, the application of M and M + NPK led to a significant (P < 0.01) increase of exchangeable As (2-7 times and 2-5 times, respectively) and reducible As (1.5-2.5 times and 1.5-2.3 times, respectively) compared with the no fertilization treated soil (CK). In addition, direct contact assay of E. coli biosensor with soil particles also supported that bioavailable As in manure-fertilized (M and M + NPK) soil was significantly higher (P < 0.01) than that in CK soil (7 and 9 times, respectively). Organic carbon may be the major factor governing the increase of bioavailable As. More significantly, E. coli biosensor-determined As was only 18.46-85.17% of exchangeable As and 20.68-90.1% of reducible As based on BCR-SEPs. In conclusion, NKP fertilization was recommended as a more suitable regime in As-polluted soil especially with high As concentration, and this E. coli arsRp::luc-based biosensor was a more realistic approach in assessing the bioavailability of As in soil since it would not overrate the risk of As to the environment.