A remediation approach to chromium-contaminated water and soil using engineered biochar derived from peanut shell.

Hexavalent chromium (Cr[VI]) is one of the major environmental concerns due to its excessive discharge through effluents from the leather tanning industry. Peanut production leads to the generation of residual shells as waste calling for sustainable disposal. In this study, we employed an innovative approach of applying peanut-shell-derived pristine and engineered biochar for the remediation of Cr-contaminated wastewater and soil. The peanut shell waste was converted to biochar, which was further engineered with cetyltrimethylammonium bromide (CTAB, a commonly used cationic surfactant). The biochars were then used for the adsorption and immobilization of Cr(VI) in water and soil, respectively. The adsorption experiments demonstrated high Cr(VI) removal efficiency for the engineered biochar (79.35%) compared with the pristine biochar (37.47%). The Langmuir model best described the Cr(VI) adsorption onto the biochars (R2 > 0.97), indicating monolayer adsorption. Meanwhile, the adsorption kinetics indicated that chemisorption was the dominant mechanism of interaction between the Cr(VI) and the biochars, as indicated by the best fitting to the pseudo-second-order model (R2 > 0.98). Adsorption through the fixed-bed column also presented higher Cr(VI) adsorption onto the engineered biochar (qeq = 22.93 mg g-1) than onto the pristine biochar (qeq = 18.54 mg g-1). In addition, the desorption rate was higher for the pristine biochar column (13.83 mg g-1) than the engineered biochar column (10.45 mg g-1), indicating that Cr(VI) was more strongly adsorbed onto the engineered biochar. A higher immobilization of Cr(VI) was observed in the soil with the engineered biochar than with the pristine biochar, as was confirmed by the significant decreases in the Cr(VI) bioavailability (92%), leachability (100%), and bioaccessibility (97%) compared with the control (soil without biochar). The CTAB-engineered biochar could thus potentially be used as an efficient adsorbent for the removal and the immobilization of Cr(VI) in water and soil, respectively.

Effects of long-term paddy rice cultivation on soil arsenic speciation.

Geochemical behavior of arsenic (As) in rice paddy soils determines the availability and mobility of As in the soils, but little is known about the long-term effects of paddy rice cultivation on As speciation in the soils. In this study, surface soil samples were collected from a rice paddy land and its adjacent dry land with similar soil properties and known cultivation histories. The soils of the paddy land and dry land contained 378 and 423 mg As kg-1, respectively. The predominant As species in the soils were investigated using As K-edge X-ray absorption spectroscopy (XAS) in combination with two sequential chemical fractionation methods. The XAS results showed that the predominant As species in the soils were As(III)- and As(V)-ferrihydrite, As(V)-goethite and scorodite. In comparison to the dry land soil, the paddy land soil contained a higher proportion of As(V)-ferrihydrite and a lower proportion of scorodite. The results of chemical fractionation revealed that As in the paddy land soil was more labile than that in the dry land soil. It is therefore suggested that long-term rice cultivation enhances the mobility and availability of As in paddy soils.

Speciation and Fractionation of Soil Arsenic from Natural and Anthropogenic Sources: Chemical Extraction, Scanning Electron Microscopy, and Micro-XRF/XAFS Investigation.

A large amount of excavated soils with low-level As contamination caused by civil construction projects is of great concern in Japan. This study investigated the chemical speciation and extractability of As in 24 soil samples from the sites affected and unaffected (naturally contaminated) by anthropogenic pollution. The results of As K-edge XANES demonstrated that naturally contaminated soils were grouped into two types: (i) soils containing FeAsS-like and As2S3-like species (ave. 53%, hereafter As-S species) and (ii) soils with no or minor As-S species (ave. 3%). Clear differences were found in As, Fe, and S fractionations by sequential extraction. From naturally contaminated soils enriched with As-S species, more than 50% of As was extracted in the oxidizable fraction. Arsenic was mainly recovered in the reducible fraction for naturally contaminated soils with no or minor As-S species and anthropogenically contaminated soils. The µ-XRF and µ-XAFS revealed that the naturally contaminated soils containing As-S species were abundant in pyrite framboids (∼20 µm in diameter) in which As occurred as multiple oxidation states. The results suggest that framboidal pyrite becomes a source of As in naturally contaminated soils after being excavated and exposed to the surface environment.

Speciation of Phosphorus Zinc and Copper in Soil and Water-Dispersible Colloid Affected by a Long-Term Application of Swine Manure Compost.

The objective of this study was to investigate the concentration and chemical species of Zn, Cu, and P in the bulk soil and water-dispersible colloid (WDC) fraction collected from a field where swine manure (SM) compost has been continually applied for 23 years. A filtration and ultracentrifugation process was used to separate and collect WDC (20-1000 nm) from the soil. The continual application of SM increased soil P from 1.6 to 4.5 g kg-1, Zn from 109 to 224 mg kg-1, and Cu from 87 to 95 mg kg-1 for 23 years. The continual SM compost application also enhanced the formation of soil WDC in which Zn (215 mg kg-1) and Cu (62 mg kg-1) were highly accumulated and P (25 g kg-1) was greater than in the bulk soil. According to the result of X-ray absorption spectroscopy (XAS), the continual application of SM compost increased P associated with Fe hydroxides in the soil and WDC fraction. Iron K-edge XAS revealed the dominance of goethite and ferrihydrite in the WDC fraction, suggesting that P was bound to these (oxy)hydroxides. Copper K-edge XAS determined the dominance of Cu(II) associated with humus in the soil and WDC fraction. For Zn species in the SM-compost-applied soil, hopeite and Zn associated with humus were accumulated in the bulk soil, whereas Zn associated with humus was the primary species in the WDC fraction. Our study suggests that the formation of organic complexes in the WDC fraction could enhance the mobility of Zn and Cu as the repeated application of SM compost continues.

Pollution potential leaching index as a tool to assess water leaching risk of arsenic in excavated urban soils.

Leaching of hazardous trace elements from excavated urban soils during construction of cities has received considerable attention in recent years in Japan. A new concept, the pollution potential leaching index (PPLI), was applied to assess the risk of arsenic (As) leaching from excavated soils. Sequential leaching tests (SLT) with two liquid-to-solid (L/S) ratios (10 and 20Lkg-1) were conducted to determine the PPLI values, which represent the critical cumulative L/S ratios at which the average As concentrations in the cumulative leachates are reduced to critical values (10 or 5µgL-1). Two models (a logarithmic function model and an empirical two-site first-order leaching model) were compared to estimate the PPLI values. The fractionations of As before and after SLT were extracted according to a five-step sequential extraction procedure. Ten alkaline excavated soils were obtained from different construction projects in Japan. Although their total As contents were low (from 6.75 to 79.4mgkg-1), the As leaching was not negligible. Different L/S ratios at each step of the SLT had little influence on the cumulative As release or PPLI values. Experimentally determined PPLI values were in agreement with those from model estimations. A five-step SLT with an L/S of 10Lkg-1 at each step, combined with a logarithmic function fitting was suggested for the easy estimation of PPLI. Results of the sequential extraction procedure showed that large portions of more labile As fractions (non-specifically and specifically sorbed fractions) were removed during long-term leaching and so were small, but non-negligible, portions of strongly bound As fractions.

Investigations of water-extractability of As in excavated urban soils using sequential leaching tests: Effect of testing parameters.

Excavated soils with low-level As contamination obtained from construction projects during city development have been of great concern in Japan. Water-extractable As represents the most easily mobilized and ecotoxicologically relevant fraction in the soil environment. In the present study, the water-extractability of As in excavated alkaline urban soils was assessed using sequential leaching tests (SLTs) with a focus on the effects of test parameters. In addition, the potentially water-leachable As over an extremely long period was assessed using the pollution potential leaching index (PPLI), from which one can estimate the number of extractions required to reduce the As in the cumulative leachates to below the Japanese environmental standard (10 µg L-1). Total As concentrations varied from 6.75 to 79.4 mg kg-1, and As was continuously detectable among replicate SLT experiments. The water-extractable As obtained in the first step of the SLT accounted for 0.41%-7.60% of total As (average: 2.36%), while the cumulative released As in the SLTs corresponded to 1.30%-21.6% of the total (average: 10.6%). The variability of the water-soluble fractions was sensitive to the test conditions. The shaking time at each SLT step had the largest effect on the As water-extractability; followed by sample storage, shaking speed and shaking interruption. A longer shaking time in the standard leaching test of excavated soils is suggested for regulatory purposes in Japan. The use of the PPLI concept for quick estimation of the potential As leachability from excavated soils was supported by the good reproducibility of PPLI results obtained from SLTs under different test parameters.

Chemical Species of Phosphorus and Zinc in Water-Dispersible Colloids from Swine Manure Compost.

The release of phosphorus (P) and zinc (Zn) from swine manure compost and from soils applied with swine manure compost can be accelerated by colloidal particles. This study investigated the concentrations and chemical species of P and Zn in water-dispersible colloids (WDCs) collected from swine manure compost by using X-ray absorption fine structure (XAFS) spectroscopy. A filtration and ultracentrifugation process was used to separate and collect WDCs (20-1000 nm) from the bulk swine manure compost (<2 mm). The swine manure compost contained 2.7 g kg WDC, in which P (140 g kg) was highly concentrated and Zn concentrations were greater than in the bulk compost (1.45 g kg). Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy determined the presence of struvite (NHMgPO·6HO) as a major P species (74%), followed by tricalcium phosphate as a secondary component (26%). In the WDC fraction, struvite was not found, but tricalcium phosphate (56%) occurred as a primary component. Zinc K-edge XAFS spectroscopy determined hopeite [Zn(PO)·4HO, 59%] and to a lesser extent smithsonite (ZnCO, 24%) and Zn adsorbed on ferrihydrite (17%). In the WDC fraction, hopeite (44%) and organically bound Zn (35%) were predominant. Our results demonstrate the notable difference in the concentration and chemical species of P and Zn between the WDC and bulk fractions of swine manure compost.

Impact of natural and calcined starfish (Asterina pectinifera) on the stabilization of Pb, Zn and As in contaminated agricultural soil.

Metal stabilization using soil amendments is an extensively applied, economically viable and environmentally friendly remediation technique. The stabilization of Pb, Zn and As in contaminated soils was evaluated using natural starfish (NSF) and calcined starfish (CSF) wastes at different application rates (0, 2.5, 5.0 and 10.0 wt%). An incubation study was conducted over 14 months, and the efficiency of stabilization for Pb, Zn and As in soil was evaluated by the toxicity characteristic leaching procedure (TCLP) test. The TCLP-extractable Pb was reduced by 76.3-100 and 91.2-100 % in soil treated with NSF and CSF, respectively. The TCLP-extractable Zn was also reduced by 89.8-100 and 93.2-100 % in soil treated with NSF and CSF, respectively. These reductions could be associated with the increased metal adsorption and the formation of insoluble metal precipitates due to increased soil pH following application of the amendments. However, the TCLP-extractable As was increased in the soil treated with NSF, possibly due to the competitive adsorption of phosphorous. In contrast, the TCLP-extractable As in the 10 % CSF treatment was not detectable because insoluble Ca-As compounds might be formed at high pH values. Thermodynamic modeling by visual MINTEQ predicted the formation of ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and portlandite (Ca(OH)2) in the 10 % CSF-treated soil, while SEM-EDS analysis confirmed the needle-like structure of ettringite in which Pb was incorporated and stabilized in the 10 % CSF treatment.

Formations of hydroxyapatite and inositol hexakisphosphate in poultry litter during the composting period: sequential fractionation, P K-edge XANES and solution (31)P NMR investigations.

Little is known about how the solubility and chemical speciation of phosphorus (P) in poultry litters are altered during the composting period. This study investigated the quantitative and qualitative changes in organic P (Po) and inorganic P (Pi) compositions in poultry litters during the seven-day composting period using sequential extraction in combination with P K-edge X-ray absorption near-edge structure (XANES) and solution (31)P nuclear magnetic resonance (NMR) spectroscopy. The result of sequential extraction illustrated that the significant decrease of H2O-P by 55% in poultry litters occurred concomitantly with the increase of HCl-Pi and HCl-Po during the composting period (p < 0.05). X-ray diffraction results for poultry litter samples showed three distinct peaks indicative of hydroxyapatite. Phosphorus K-edge XANES confirmed the increase of hydroxyapatite during the composting period, corresponding to the increase of HCl-Pi determined by the sequential extraction. The NaOH-EDTA extraction for solution (31)P NMR revealed that myo-inositol hexakisphosphate (IHP) constituted about 80% of phosphate monoesters and was increased from 16 to 28% in the poultry litter during the composting period. The combined applications of chemical extraction and molecular-spectroscopic techniques determined that water-soluble P in poultry litter was transformed into less soluble phases, primarily hydroxyapatite and IHP, during the composting period.

Characterization of trace elements in coal fly ash by extraction, micro-PIXE, TOF-SIMS, and XAFS.

Coal fly ash (CFA) contains considerable amounts of potentially hazardous trace elements. Characterization of trace elements in CFA is essential for the safe disposal and recycle of CFA. The objectives of this study were i) to determine and predict the solubility of trace elements in CFA in relation to their chemical and mineralogical properties, and ii) to characterize trace elements using the surface chemical analysis including time-of-flight secondary ion mass spectrometry (TOF-SIMS) and accelerator-based micro particle induced X-ray emission (PIXE) analysis, in combination with X-ray absorption fine structure (XAFS) spectroscopy with a primary focus on As and Cr. The CFA samples from 12 thermal power plants contained B (ave. 203 mg kg-1), F (90 mg kg-1), Cr (63 mg kg-1), As (21 mg kg-1), and Se (3.2 mg kg-1), in which the water soluble fraction relative to the total concentration decreased in the order B (24 %) > Se (23 %) > F (20 %) > As (1.7 %) > Cr(IV) (0.71 %). A regression model indicated that water extractable As and Cr(VI) from CFA increased linearly with increasing SiO2 and CaO in CFA, respectively. The SIMS images showed that B was finely and heterogeneously distributed on CFA, whereas F was distributed homogeneously on CFA. The combined results from micro-PIXE and XAFS revealed that i) As was distributed on about 50-µm particles in the form of As(V) associated with Al and Ca, and ii) Cr was co-located with Fe and Ca on about 50-µm particles and was present as Cr(III). This study demonstrated that the combined results from TOF-SIMS, micro-PIXE, and XAFS techniques enable trace elements in CFA to be better characterized in terms of spatial distribution and chemical speciation.

Soluble soil Pb minimized by thermal transformation to Pb-bearing feldspar.

Thermal transformation is an effective remediation measure to stabilize soil Pb and other heavy metals via transformation into less soluble compounds. This study aimed to determine the solubility of Pb in soils subjected to heating at a range of temperatures (100-900 °C) in relation to the changes in Pb speciation using XAFS spectroscopy. Lead solubility in the contaminated soils after thermal treatment corresponded well to the chemical species of Pb present. As the temperature was increased to 300 °C, cerussite and Pb associated with humus started to decompose in the soils. As the temperature was further increased to 900 °C, the amount of water and HCl extractable Pb decreased significantly from the soils, whereas Pb-bearing feldspar started to occur, accounting for nearly 70% of the soil Pb. During thermal treatment, Pb species in the soils were little affected by Fe oxides that showed a significant phase transformation into hematite. Our study proposes the following underlying mechanisms for Pb immobilization in thermally treated soils: i) thermally labile Pb species such as PbCO3 and Pb associated with humus start to decompose at temperatures around 300 °C, ii) aluminosilicates with crystalline and poorly ordered structures undergo thermal decomposition at temperatures around 400 °C, iii) liberating Pb in the soil is then associated with a Si and Al rich liquid derived from thermally decomposed aluminosilicates at higher temperatures, and iv) the formation of Pb-feldspar like minerals is enhanced at 900 °C.

Temporal transformation of indium speciation in rice paddy soils and spatial distribution of indium in rice rhizosphere.

Indium is a potentially toxic element that could enter human food chains, including soil-rice systems. The submerged environment in rice paddy soil results in temporal and spatial variations in the chemical properties of the rice rhizosphere and bulk soils, expected to cause changes in indium's chemical speciation and consequently affect its bioavailability. Therefore, this study aimed to investigate indium speciation and fractionation in soils at different periods of rice growth under continuous submergence using X-ray absorption spectroscopy and a sequential extraction method. The predominant indium species were identified as indium-associated Fe hydroxide, and indium hydroxide and phosphate precipitates. The reductive dissolution of indium-associated Fe hydroxides led to the release of indium into the soil solution under continuous submergence of soils, and the released indium concentration decreased with time due to re-sorption and re-precipitation. Meanwhile, indium hydroxide was found to be the predominant species in rice rhizosphere using µ-X-ray absorption spectroscopy. The relative depletion of indium-associated Fe hydroxides in the rice rhizosphere was attributed to the low mobility of indium from bulk soil to rice rhizosphere and the root uptake of indium associated with Fe hydroxide around rice roots. Consequently, indium uptake by rice roots was lower during the reproductive and grain-ripening stage of rice growth. Understanding the behavior of indium will help develop a strategy to minimize uptake into crops in indium-contaminated paddy soils.

Ruptured Hepatic Hemangioma in the Third Trimester of Pregnancy: A Rare Case Report.

Hepatic hemangiomas are considered the most common benign mesenchymal hepatic tumors. Most cases are asymptomatic. However, giant hemangiomas can present with a variety of clinical presentations, with a rupture being the most catastrophic outcome. Only a few cases of ruptured perinatal hepatic hemangiomas have been reported. Accelerated growth of hepatic hemangiomas caused by increased estrogen in pregnancy, increased intra-abdominal pressure, and direct contact with a gravid uterus are possible mechanisms for increased risk of rupture during pregnancy. The safety of either non-operative or surgical treatment of symptomatic giant hemangioma during pregnancy has not been adequately investigated. We present a rare case of a 28-year-old G1P0 female at 33 weeks gestation that presented with a ruptured hepatic hemangioma treated with damage control surgery followed by nonanatomic surgical resection.

Zero valent iron or Fe3O4-loaded biochar for remediation of Pb contaminated sandy soil: Sequential extraction, magnetic separation, XAFS and ryegrass growth.

In this study, the feasibility of using zero-valent iron (ZVI) and Fe3O4-loaded biochar for Pb immobilization in contaminated sandy soil was investigated. A 180-day incubation study, combined with dry magnetic separation, chemical extraction, mineralogical characterization, and model plant (ryegrass, namely the Lilium perenne L.) growth experiment was conducted to verify the performance of these two materials. The results showed that both amendments significantly transferred the available Pb (the exchangeable and carbonates fraction) into more stable fractions (mainly Fe/Mn oxides-bound Pb), and ZVI alone showed a better performance than the magnetic biochar alone. The magnetic separation and extended X-ray absorption fine structure (EXAFS) analysis proved that Fe (oxyhydr)oxides on aged ZVI particles were the major scavengers of Pb in ZVI-amended soils. In comparison, the reduced Pb availability in magnetic biochar-amended soil could be explained by the association of Pb with Fe/Mn (oxyhydr)oxides in aged magnetic biochar, also the possible precipitation of soil Pb with soluble anions (e.g. OH-, PO43-, and SO42-) released from magnetic biochar. ZVI increased ryegrass production while Fe3O4-loaded biochar had a negative effect on the ryegrass growth. Moreover, both markedly decreased the Pb accumulation in aboveground and root tissues. The simple dry magnetic separation presents opportunities for the removal of Pb from soils, even though the efficiencies were not high (17.5% and 12.9% of total Pb from ZVI and biochar-treated soils, respectively). However, it should be noted that the ageing process easily result in the loss of magnetism of ZVI while the magnetic biochar tends to be more stable and has high retrievability during the dry magnetic separation application.

Enhanced transformation of lead speciation in rhizosphere soils using phosphorus amendments and phytostabilization: an x-ray absorption fine structure spectroscopy investigation.

To formulate successful phytostabilization strategies in a shooting range soil, understanding how heavy metals are immobilized at the molecular level in the rhizosphere soil is critical. Lead (Pb) speciation and solubility in rhizosphere soils of five different plant species were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. The EXAFS analysis indicated that Pb occurred as PbCO (37%), Pb sorbed to organic matter (Pb-org: 15%), and Pb sorbed to pedogenic birnessite and/or ferrihydrite (Pb-ox: 36%) in the bulk soil. Comparison of the EXAFS spectra between bulk and rhizosphere soils demonstrated notable differences in fine structure, indicating that Pb species had been modified by rhizosphere processes. The estimated proportion of PbCO (25%) in the buckwheat soil was smaller than the other rhizosphere soils (35-39%). The addition of P significantly reduced Pb solubility in the bulk and rhizosphere soil except in the rhizosphere of buckwheat, for which the Pb solubility was 10-fold greater than in the other P-amended soils. This larger solubility in the buckwheat rhizosphere could not be explained by the total Pb speciation in the soil but was presumably related to the acidifying effect of buckwheat, resulting in a decrease of the soil pH by 0.4 units. The reduced Pb solubility by P amendment resulted from the transformation of preexisting PbCO (37%) into Pb(PO)Cl (26-32%) in the bulk and rhizosphere soils. In the P-amended rhizosphere soils, Pb-org species were no longer detected, and the Pb-ox pool increased (51-57%). The present study demonstrated that rhizosphere processes modify Pb solubility and speciation in P-amended soils and that some plant species, like buckwheat, may impair the efficiency of Pb immobilization by P amendments.

Arsenic immobilization and removal in contaminated soil using zero-valent iron or magnetic biochar amendment followed by dry magnetic separation.

The potential of using zero-valent iron (ZVI) or a Fe3O4-loaded magnetic biochar to stabilize arsenic (As) in contaminated soil was investigated in the processes of incubation trial, chemical extraction, pot experiments with ryegrass growth. Additionally, a dry magnetic separation technique was applied to verify the possible permanent removal of As from the bulk soil. Results showed the ZVI amendment greatly reduced the As leaching, and the leached concentration became much lower than the Japanese environment standard (10 µg/L) after 180 days of incubation. Contrarily, the magnetic biochar amendment readily increased the As leachability due to the changes in pH, dissolved organic carbon, and soluble P and Si. The ZVI had a greater effect over the magnetic biochar, supported by the significantly reduced As leachability in the combined amendments. Furthermore, results from sequential extraction analysis indicate that both amendments significantly decreased the available As in (NH4)2SO4 and NH4H2PO4 extraction and increased the As bound to amorphous Fe oxides. But ZVI amendment alone performed better than magnetic biochar amendment alone. Plant growth experiment showed that the ZVI amendment enhanced ryegrass growth and significantly increased the ryegrass biomass. However, the magnetic biochar amendment resulted in an adverse effect on the ryegrass root growth, probably due to a marked enhancement of salinity. Meanwhile, the As uptake by ryegrass was significantly reduced in both ZVI and magnetic biochar-amended soils. Results of dry magnetic separation showed that averaged 20% and 25% of total As could be retrieved from ZVI and magnetic biochar amended soil, respectively; and the As bound to amorphous Fe oxides was the main retrieved fraction. This study indicated that ZVI or magnetic biochar could be applied as a promising amendment for reducing (phyto)availability of As in soil, and dry magnetic separation could be served as an alternative option for permanently removing As.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water.

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N2 (BC-N) and CO2 (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Boron incorporation into precipitated calcium carbonates affected by aqueous pH and boron concentration.

The objectives of this study were to investigate the amount of B incorporation into precipitated calcium carbonate (PCC) in the coprecipitation process, and to determine specific mineral phases (calcite or vaterite) and the mode of B coordination (trigonal or tetrahedral) in PCC under different pH and B concentrations. The amount of B incorporation into PCC increased in general with increasing aqueous B (Baq) concentrations in the pH range from 8 to 12. The B removal by PCC reached maximum (∼200 mmol kg-1) at pH 10 with Baq concentrations between 30 and 50 mM. The transformation of vaterite to calcite was promoted with increasing Baq at pH 8 and 10, whereas an excess concentration of aqueous (poly)borate anions (100 mM) inhibited crystal growth of calcite. As determined by B K-edge X-ray absorption fine structure spectroscopy, the coordination of B incorporated in PCC was preferentially tetrahedral (IVB, 55-70%) over trigonal (IIIB, 30-45%) at Baq <75 mM. In contrast, the preferential incorporation of IVB into PCC was not observed in the solution with a high B concentration (i.e., 100 mM). The amount of B incorporation, the morphology of PCC and B coordination in PCC were remarkably changed in high Baq concentrations.

Reducing geogenic arsenic leaching from excavated sedimentary soil using zero-valent iron amendment followed by dry magnetic separation: A case study.

Although the deep-layer sedimentary soils excavated from construction sites contain low level of geogenic arsenic (As), remediation is necessary when the As leachability exceeds the environmental standard (10 µg/L) in Japan. In this study, the zero-valent iron (ZVI) amendment followed by dry magnetic separation (ZVI-DMS) was implemented for the treatment of a geogenic As-contaminated alkaline sedimentary soil (pH 8.9; 7.5 mg/kg of total As; 0.33 mg/kg of water-extractable As). This technology involves pH adjustment (adding H2SO4), ZVI addition, water content reduction (adding water adsorbent CaSO4·0.5H2O), and dry magnetic separation. The short-term and long-term As leachability before and after treatment was compared using sequential water leaching tests (SWLT). The results illustrated that As could be removed from the bulk soil through the magnetic separation of As-ZVI complexes, although the amount was limited (about 2% of total As). Moreover, immobilization played a dominant role in suppressing As leaching. The H2SO4 addition decreased pH to a circumneutral range and thereby suppress As release. The CaSO4·0.5H2O addition also contributed to the pH decrease and reduced As leachability. Besides, CaSO4·0.5H2O-dissolution released Ca2+ that favored As adsorption, and enhanced dissolved organic carbon (DOC) coagulation that decelerated As dissolution. SWLT results indicated that As leachability from remediated soil satisfied the environmental standard (10 µg/L) in both short-term and long-term perspective. However, the secular stability of treated soil deserves more attention due to the easy re-release of As caused by As-bearing framboidal pyrite oxidation. Additionally, during ZVI-DMS process, there is a need to scientifically decide the dosage of ZVI to avoid excessive addition. Our results demonstrated that ZVI-DMS technology could be a promising remediation strategy for geogenic As contaminated sedimentary soils/rocks.

Evolution of As speciation with depth in a soil profile with a geothermal As origin.

High contents of arsenic were detected in soils in Guandu plain, northwest Taiwan. To determine the sources and speciation of As in the soils, the depth profiles of soil properties, elemental composition and As speciation were investigated. The As concentrations in the soil profile ranged from 152 to 1222 mg kg-1, with the highest concentration at the depth of 70-80 cm. The As distribution was found to be positively correlated to Fe, Pb, and Ba. The As(V)-adsorbed ferrihydrite and scorodite were the predominant phases in the top layers (<50 cm), while beudantite was the predominant phase below 50 cm along with As(III)- and As(V)-adsorbed ferrihydrite as the minor components. The results of sequential extraction showed that As-associated with noncrystalline and crystalline Fe/Al hydrous oxides and residual phases were predominant at the depths of 0-60, 60-100 and 100-140 cm, respectively, indicating an increasing As recalcitrance with soil depth. Based on the soil properties, and elemental and mineral compositions at different soil depths, the origin of beudantite in the soils was likely allogenic rather than authigenic or anthropogenic. The formation of scorodite in the surface soils was suggested to be transformed from beudantite. As-associated Fe hydrous oxides may be contributed by the progressive dissolution of beudantite and scorodite, and the continuous influxes of As and Fe. While Fe hydrous oxides were able to immobilize As during the dissolution of As-bearing minerals, the increase of As mobility in soils may imply an increase in the environmental risk of As over time.