Marked Changes in Biochar’s Ability to Directly Immobilize Cd in Soil: Implication for Biochar Remediation of Cd Contaminated Soil

To investigate the change in biochar’s ability to directly immobilize Cd in soil ，a successive wheat cultivation with experiment was conducted. Three biochar with different Cd adsorption mechanisms were added into soils and a mesh bag was used to separate the soil particles (> 1 μm) from biochar. The results showed that the ash contents and anionic contents (CO 3 2- and PO 4 3- ) of the biochar decreased with the cultivation time, while the oxygen-containing functional groups content and CEC of the biochar increased. Resultly, the Cd concentration on biochar decreased, highly decreased by 68.9% for WBC300, while unstable Cd species (acid soluble and reducible fraction of Cd) on biochar increased with successive cultivation, increasing from 3% to 17% for WBC300 in FS. Correspondingly, the ability of biochar to inhibit Cd accumulation in wheat decreased. The results of this study illustrated that the ability of biochar to directly immobilize Cd in soil is not permanent, it gradually decreases with aging in soil. The adsorption mechanism of Cd on biochar changed from precipitation to complexation and ion exchange processes could be the main reason.

Distribution of Geochemical Species of P, Fe and Mn in Surface Sediments in the Eutrophic Estuary, Northern Taiwan

The Danshuei River Estuary (DRE) in northern Taiwan is a seriously eutrophic estuary due to the domestic effluent discharge. Surface sediment samples were collected from the DRE to study the concentrations and spatial distributions of different fractions of phosphorus through the five-step sequential extraction method which chemically divides the sedimentary P into five fractions: PSORB, PCDB, PCFA, PDET, and PORG. The Fe and Mn contents in the extracted solution were also determined. The total organic carbon (TOC) and grain size in sediment samples were analyzed as well. The sedimentary total P (TP) concentrations ranged within 537–1310 mg/kg and mostly exceeded 800 mg/kg, suggesting that the DRE sediments were moderately polluted by phosphorus. The PCDB was the dominant fraction of P, averagely contributing 58% of TP, followed by PDET 31%. The contributions of the PSORB and PCFA fractions to the TP were relatively minor. Two fractions, FeCDB and FeORG, of sedimentary Fe equally shared approximately 70% of total Fe, followed by FeDET with 22%. The contribution of different fractions of sedimentary Mn followed the sequence: MnCDB (36%) > MnCFA (29%) > MnORG (14.7%) > MnDET (14.5%) > MnSORB (5.3%). The sedimentary P, Fe, and Mn within the DRE are easily mobilized because they were mainly present in the reducible fraction. The concentrations of sedimentary TP positively correlated with the TOC contents and inversely negatively correlated with grain size, suggesting that the TOC and grain size play the crucial roles in influencing the distribution of sedimentary P within the DRE. Finally, the Fe(III) (hydro)oxides seems to play an important carriers to adsorb dissolved P because PCDB positively correlated with FeCDB.

Complexation Of Amino Acid With Cadmium And Its Application To Remove Cadmium From Contaminated Soil

Low molecular organic acids, such as amino acid, play an important role in cadmium (Cd) mobility. However, its complexation ability with Cd was not well studied. The complexation structure of amino and cadmium was investigated by theory calculation based on B3ly/SDD and detecting by FTIR spectrum. The conformers were found to be [COc, COc] for fatty amino-cadmium and PheCd2+, [COc, COc, COs] for GluCd2+and ThrCd2+, respectively. The complex energy of these conformers was calculated in water phase by SMD model and the order of chelation energy was; PheCd2+> AlaCd2+ > LeuCd2+ > GluCd2+ > GlyCd2+ > ThrCd2+. All the dissolving energy of complexes was below zero, indicating these complexes was easily dissolved in water. In aqueous solution experiment, the Cd2+ concentration decreased with increasing amino acid concentration. The order of logβ (Complex stability constant) was: PheCd2+> AlaCd2+ > LeuCd2+ > GluCd2+ > GlyCd2+ > ThrCd2+, consisting with the order of calculated chelation energy. The Cd removal efficiency by Thr, Glu, Gly, Ala, Leu and Phe were 38.88%, 37.47%, 35.5%, 34.72%, 34.04% and 31.99%, respectively. From soil batch experiment, the total Cd in soil was decreased in present of amino acid with the concentration of Cd in water increased from 231.97 µg/L to 652.94-793.51 µg/L. The results of BCR sequential extraction showed that the Cd in acid soluble and reducible fraction sharply decreased. From all the results, the amino acid has potential to be used as a chelation to remedy the Cd contaminated soil.

An Assessment of Heavy Metal Contamination in the Nakdong River Around the Weir

In this study, the concentrations and characteristics of copper (Cu), zinc (Zn), and lead (Pb) contamination in sediment samples were investigated using aqua regia extraction and Tessier’s five-step sequential extraction. Based on the concentration of metals, the influence of the Hapcheon-Changnyeong weir on sediments in the Nakdong River was assessed. The origins of the contaminants, their bioavailability, and their mobility were determined using sequential extraction. Greater concentrations of heavy metals were found in samples collected closer to the weir. The largest proportion of Cu was identified in the residual fraction based on sequential extraction, whereas Zn was predominantly found in the reducible fraction. Iron-manganese in the reducible fraction of Zn has the potential to leach back to the water body. In addition, the combined concentration of fractions 1 and 2 of Cu comprised more than 20% of total amount that still has potential to affect the water quality. The results of this study were compared with existing sediment standards set out by the NIER (National Institute of Environmental Research), Canada, and US EPA (United States Environmental Protection Agency) guidelines, as well as the risk assessment code (RAC). The concentrations of heavy metals exceeded the standards set by the Canadian guideline by up to four times in particular samples, highlighting the need for continual monitoring.

Influence of thermal hydrolysis treatment on chemical speciation and bioleaching behavior of heavy metals in the sewage sludge

In this study, the transformation of chemical speciation of Cr, Mn, As and Cd in the sewage sludge before and after thermal hydrolysis treatment was investigated using modified BCR method. The effect of thermal hydrolysis treatment and chemical speciation change on the subsequent bioleaching behavior was also researched. The results showed that the concentrations of Cr, Mn, As and Cd in oxidizable fraction decreased in the sludge treated by thermal hydrolysis. Meanwhile, the proportions of Cr, Mn and As in the mobile fractions (acid-soluble/exchangeable and reducible fraction) all decreased, while Cd was concentrated in the sludge treated by thermal hydrolysis. The final pH value of bioleached sludge treated by thermal hydrolysis was lower than that in the bioleached raw sewage sludge. And faster increase of oxidation-reduction potential (ORP) was also found in the bioleaching process of the sludge treated by thermal hydrolysis. The removal percentage of Mn and Cd increased in the bioleached sludge treated by thermal hydrolysis. Thermal hydrolysis treatment can promote the bioleaching to some extent. Furthermore, the environmental risk of Cr, Mn, As and Cd in the bioleached sludge treated by thermal hydrolysis was all alleviated according to risk assessment analysis compared with the bioleached raw sewage sludge.

Investigating the Potential Impact of Louisiana Coastal Restoration on the Trace Metal Geochemistry of Constructed Marshlands

Coastal restoration through diversion of suspended sediments from the Lower Mississippi River (LMR) into hydrologically isolated marshlands of Mid-Barataria Bay and Mid-Breton Sounds in southern Louisiana has the potential to mobilize lead (Pb), and other trace elements. We investigate the potential impact(s) of the diversion on marsh porewater through analysis of modern riverbank and suspended sediments, compared to sediments from pre-industrial deltaic deposits of LMR. Sequential extraction methods were used to evaluate Pb, cobalt (Co), copper (Cu), nickel (Ni), and zinc (Zn) in the sediments. Our results show that metal contents are higher (e.g., 8- to 10-fold for Pb) in the modern sediments relative to pre-industrial deposits. Also, the reducible fraction, presumably iron/manganese (Fe/Mn) oxides/oxyhydroxides, is the chief reservoir of environmentally available metals. The substantially higher trace metal contents of the modern relative to pre-industrial sediments suggest that the modern sediments contain a sizeable amount of anthropogenic contributions. Furthermore, the concentration of the trace metals in the reducible fraction suggests bioavailability to marsh organisms upon reductive dissolution within the planned, constructed coastal marshes. Still, additional sediment samples from the marshlands during the diversion implementation phase will be necessary to support the preliminary findings in this contribution as it affects coastal marshes and vital local fisheries.

X-ray absorption analysis of Zn and Cu speciation in soils around the sediment ponds of chemical plants

<p>Study of Zn and Cu accumulation and transformation in highly contaminated technogenically transformed soils near the sediment pond of a chemical plant using a combination of direct nondestructive physical methods, including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) based on synchrotron radiation. The object of the study was technogenic soils (Technosol) subjected to long-term anthropogenic load. The object of research was a territory of sludge collectors region of the Atamanskoe Lake natural basin, the city of Kamensk-Shakhtinskii, Southern Russia. The contents of Zn and Cu were determined by the X-ray fluorescence method. The EXAFS and XANES experimental data were obtained at the Structural Material Science Station at the 1.3b beamline of the Kurchatov Center of Synchrotron Radiation ''Kurchatov Institute''. Soil samples were analysed with the sequential extraction procedure recommended by BCR. This procedure can be described as follows: first step (exchangeable fraction), second step (reducible fraction) and third step (oxidisable fraction). The studied Technosols are characterized by exceeding of the lithosphere clark for Zn in hundreds of times (26 000-66 000 mg/kg) and for Cu in tens of times (376-577 mg/kg). It has been found that in the oxidisable fraction of Zn is coordinated by four O atoms and only two Zn atoms. The Zn-Zn distance is 3.36 Å, and there are two different short Zn-O bonds (1.95 and 2.04 Å). In the reducible and exchangeable fractions, the main peaks of the EXAFS Fourier transform are shifted to the region of large values, which indicates the possible presence of Zn-S bonds of 2.34 Å. The simulation results have shown a high content of ZnS in the reducible fraction; ZnS with an admixture of ZnSO<sub>4</sub> and ZnO dominates in the exchangeable fraction. The oxidisable fraction is characterized by a high content of ZnSO<sub>4</sub> with the addition of ZnO. The significant difference in the position of the absorption edge and the values of the main features of the spectrum with Cu–S and Cu–O bonds has made it possible to reliably diagnose these types of Cu environments in Technosol. Peaks of the EXAFS Fourier transforms of Cu spectra indicate the predominance of Cu–O bonds in the oxidisable fraction and Cu–S bonds in the reducible and exchangeable fractions. The results of fitting Cu spectra by a linear combination indicate that the spectra of the reducible fraction coincide with high accuracy with the spectra of Cu<sub>2</sub>S. In the exchangeable fraction, the content of Cu<sub>2</sub>S is also high, although there are CuSO<sub>4 </sub>impurities. The oxidisable fraction is characterized by a high content of CuCO<sub>3</sub> and the presence of Cu<sub>2</sub>S and CuSO<sub>4</sub> as impurities as trace amounts. Thus, sequential chemical selective fractionation and subsequent X-ray spectral diagnostics based on synchrotron radiation and molecular calculations have made it possible to identify and evaluate the Zn and Cu phases in Technosol.</p><p>The reported study was funded by RFBR, projects no. 19-34-60041 and 19-05-50097.</p>

The content and solubility of lead in arable soils of the Podlasie Province (eastern Poland)

The aim of the study was the estimation of total content of lead and its fraction in arable soils and permanent grassland of Podlasie Province, eastern Poland. The research material included 104 soil samples from Podlasie Province, which were collected in years 2011–2013 from the topsoil (0–30 cm) after plant harvest. The following basic physicochemical properties of soil samples were determined: granulometric composition, organic carbon content and pH in 1 mol·dm−3KCl solution. Based on the granulometric composition soils were divided into three groups: very light and light, medium and organic soils. The total lead and its content in fractions was determined by means of GFAAS technique using Varian AA-100 apparatus. The fractions of lead were extracted by BCR method. In the case of very light and light soils the lowest percentage share of Pb on average was noted in exchangeable fraction (16.3% of total content) and the highest in fraction bound to Fe/Mn oxides (43.5%). Similarly in medium and organic soils the highest amount of Pb was stated in reducible fraction, 43.7 and 41.3% of total content, respectively, and the lowest in exchangeable fraction, 16.5 and 12.2%, respectively. It was found that content of total lead was typical for arable uncontaminated soils.

THE CONTENT OF TOTAL CADMIUM AND ITS FRACTIONS IN ARABLE LAND OF THE PODLASIE PROVINCE

<p>The aim of this study was estimation of total cadmium content and its fractional composition in arable soils, depending on their physicochemical properties. The research material consisted of samples taken from arable soil in 81 points within then Podlasie Province. The content of total cadmium in soils and its fractional composition was determined with the BCR method. It was found that the total content of cadmium was typical for uncontaminated soils and ranged from 0.11 to 1.59 mg kg-1. The percentage of acid in the soluble and exchangeable fraction fluctuated at around 10% on average. The reducible fraction comprised about 20% and oxidizable fraction 26%, on average. Most of the cadmium was in the residual fraction. The factors that influenced the fractional composition of cadmium were determined. For the very light and light soils it was mainly the content of magnesium and pH, while for medium soils it was the organic carbon and magnesium content, content of soil fraction &lt;0.02 mm, as well as the percentage of Cd in reducible fraction.</p><p> </p><p>Celem pracy było określenie zawartości ogólnej kadmu i jego składu frakcyjnego w glebach ornych w zależności od ich właściwości fizykochemicznych. Badania wykonano w oparciu o 81 próbek gleb uprawnych pobranych w woj. podlaskim. Określono w nich zawartość ogólną kadmu i jego skład frakcyjny metodą BCR. Zawartość ogólna kadmu była typowa dla gleb niezanieczyszczonych i wahała się w przedziale od 0,11 do 1,59 mg kg-1. Udział kadmu we frakcji rozpuszczalnej w kwasach i wymienialnej wynosił średnio około 10%, we frakcji redukowalnej średnio około 20% i we frakcji utlenialnej średnio 26%. Najwięcej kadmu zgromadziła frakcja rezydualna. Określono czynniki, które wpływały na dystrybucję kadmu pomiędzy frakcjami. W przypadku gleb bardzo lekkich i lekkich największy wpływ miała zawartość magnezu i pH, a w przypadku gleb średnich zawartość magnezu, węgla organicznego, frakcji spławianych i udział procentowy kadmu we frakcji redukowalnej.</p>