Simultaneous stabilization of arsenic, lead, and copper in contaminated soil using mixed waste resources

In the present study, stabilization treatment using waste resource stabilizers was performed for soil contaminated with As and heavy metals (Pb and Cu). Calcined oyster shell (COS) and coal mine drainage sludge (CMDS) were used as a mixed stabilizing agent for a wet-curing duration of 28 days. After the stabilization treatment, the treatment process efficiency was evaluated by the results of various batch- and column-leaching tests. Neutral and weak acid extraction methods, such as water-soluble extraction and SPLP, did not exhibit satisfactory results for heavy metal stabilization, even if they showed very low leachability. On the other hand, TCLP and 0.1 M HCl extraction showed that the stabilizers significantly reduced the amount of heavy metals leached from the soil, which strongly supports the thesis that the stabilization treatment is efficient in the acidic leaching conditions that were explored. Specifically, in the 0.1 M HCl extraction, the reduction efficiencies of As, Pb, and Cu leachings were more than 90 %, compared with control experiments. This study demonstrates that the application of waste resources for the stabilization of As and heavy metals is feasible. However, some limitations observed in the experiments should be considered in future studies, such as the mobilization of alkali-soluble elements, and in particular, exchangeable fractions of Cu. In addition, the treatment efficiency can be evaluated by different leaching methods, which suggests that multidirectional approaches are required for the proper evaluation of stabilization treatment.     

Stabilization of arsenic-contaminated mine tailings using natural and calcined oyster shells

Natural oyster shells (NOS) and calcined oyster shells (COS) were used to immobilize arsenic (As) from contaminated mine tailings. In addition, a blend of Portland cement (PC)/cement kiln dust (CKD) was used as a stabilizing agent. The Korean Standard Test (KST) method (1 N HCl extraction) was used to evaluate the effectiveness of the treatment. The experimental results showed that COS effectively immobilized As in treated mine tailings. Specifically, an As concentration less than 1 mg L⁻¹ was obtained following COS treatment at 25 and 30 wt%. However, all the samples subjected to NOS treatments failed the Korean warning standard of 1.2 mg L⁻¹ after 28 days of curing. All of the COS-PC treatments were successful meeting the Korean warning standard after 7 days of curing. However, the PC-only treatment failed to meet the Korean warning standard. Similarly, the CKD-only treatment was failed to meet the Korean warning standard after 7 days of curing. However, the COS-CKD treatment showed that when the COS content was greater than 20 wt%, less than 1 mg L⁻¹ of As leachability was obtained. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) showed needle-like and torpedo-like Ca–As phases in the COS-treated samples suggesting that As was strongly associated with Ca and O. X-ray absorption near edge structure (XANES) analyses confirmed that As(V) was prevalent in the tailings and that there were no changes in As speciation following NOS or COS treatment.     

Effects of natural and calcined poultry waste on Cd, Pb and As mobility in contaminated soil

The reuse of waste materials as soil additives could be a welcome development in soil remediation. The mobility of Cd, Pb and As in a contaminated soil was investigated using natural and calcined poultry wastes (eggshell and chicken bone), CaCO₃ and CaO at different application rates (0, 1, 3 and 5 %). The chemical composition accompanied with mineralogical composition indicated that CaCO₃ and CaO were the major components in natural and calcined eggshells, respectively, while hydroxyapatite (HAP) dominated the natural and calcined chicken bones. The results showed that soil pH tended to increase in response to increasing application rates of all soil additives. The effectiveness of the additives in reducing Cd, Pb and As mobility was assessed by means of chemical extractions with 0.1 N HCl for Cd and Pb or 1 N HCl for As, according to Korean Standard Test (KST) method. Both calcined eggshell and chicken bone were equally effective with CaO or CaCO₃ in reducing the concentration of 0.1 N HCl-extractable Cd from 6.17 mg kg^?1 to below warning level of 1.5 mg kg^?1, especially at the highest application rate. The application of calcined eggshell, CaO and CaCO₃ also decreased the concentration of 0.1 N HCl-extractable Pb from 1,012 mg kg^?1 to below warning level of 100 mg kg^?1. The Pb concentration decreased significantly with an increasing application rate of chicken bone, but remained above warning level even at the highest application rate. On the contrary, natural and calcined chicken bones led to a significant increase in the mobility of As when compared with the control soil. These findings illustrate that calcined eggshell in particular is equally effective as pure chemical additives in stabilizing Cd and Pb in a contaminated agricultural soil. The presence of As in metal-contaminated soils should be taken into consideration when applying phosphate-containing materials as soil additives, because phosphate can compete with arsenate on adsorption sites and result in As mobilization.     

Heavy metal contamination in surface sediments of Gökçekaya Dam Lake,Eskişehir,Turkey

The present study to find seasonal (September 2010–June 2011) heavy metal (Cd, Pb, Cr, Co, Ni, Zn, Cu, Fe, As) contamination and the origins thereof in surface sediments of Gökçekaya Dam Lake, as constructed on Sakarya River, the third-longest river in Turkey and the largest river of the Northwestern Anatolia. Upon analyses for the purpose thereof, heavy metal contamination in annual average concentrations in the lake sediment varied, respectively, as Fe > Zn > Cr > Ni > Cu > Pb > Co > As > Cd. Statistical assessments performed in order to see whether the average values of the heavy metal contamination as measured at stations placed in the lake changed by seasonal periods. There found statistically significant differences especially in Cd, Zn, and Pb between seasonal periods. In accordance with the Sediment Quality Index, Gökçekaya Dam Lake sediment was classified as “highly polluted” in terms of the amount of anthropogenic contaminants of As, Cr, Cu, Ni, Pb, and Zn. Enrichment factor and geoaccumulation index values (I _geo) were calculated in order to geochemically interpret the source of contamination due to heavy metal concentration in the lake sediment and the level of pollution. The As, Co, Cr, Cu, Ni Pb, and Zn values demonstrated that the sediment was rich for anthropogenic contaminants. The lake was found especially rich for arsenic (14.97–34.70 mg/kg) and lead (68.75–98.65 mg/kg) in accordance with annual average values. In general the lake was geochemically characterized as “moderately contaminated” in terms of As, Co, Cr, Cu, Ni, Pb, and Zn content.     

Evaluation of ability of Rock Check Dam to prevent the transportation of Pb-contaminated sediment in Khli Ti Creek, Thailand

Discharge of wastewater from the retaining pond of a Pb ore-flotation plant since 1967 and breaching of the retaining pond in April 1998 contaminated 17540 cbm of river bank sediment with 833 ton Pb, nearly 19 km along the Khli Ti Creek. High blood Pb concentration was detected in many inhabitants. Prohibition of water and aquatic biota consumption has caused difficulties for rural people to make their ends meet. The governmental agency closed the ore-floatation plant and built 2 rock check dams downstream. The dam was designed to slow down water velocity and precipitate particulate matter. Contaminated sediments that have been trapped in front of the dam were planned to be dredged and disposed in landfill. Until now, no dredging is performed because some experts claim that dredging will resuspend the contaminated sediment into the water column, and fresh sediment deposited during periods of high flow will cover the contaminated sediment. The aim of this study was to evaluate the ability of the rock check dam to prevent the transportation of Pb-contaminated sediment in the Khli Ti Creek. Sediment located before and after the rock check dam and 2 km downstream were collected in September 2003 and May 2005. During September 2003, Pb concentrations in sediment deposited before and after the rock check dam and 2 km downstream were 48840, 53741 and 36020 mg/kg, respectively. These results showed that Pb-contaminated sediment was transported over the first rock check dam but still remained after the rock check dam. Result of May 2005 sampling also showed the same trend, although with different ranges due to seasonal variation, types of collected sediment, sample preparation and analytical techniques. Pb concentrations in sediment were 209684, 306775 and 33760 mg/kg, respectively.     

Characterization and low-cost treatment of an industrial arid soil polluted with lead sulfide in northern Chile

Lead (Pb) dust exposure can have detrimental environmental and human health effects. Improperly enclosed stockpiles of Pb concentrates can cause dust emissions, subsequent pollution of the soil and environmental risk. The aim of this work was to study Pb form, distribution and immobilization (by using eggshell and seashell) in an industrial arid soil near a storage area of Pb mineral concentrates in northern Chile. High amounts of sulfur (S; 9900 mg kg^?1) and Pb (6530 mg kg^?1) were found in the polluted soil. The energy-dispersive X-ray spectroscopy analysis revealed a lead sulfide (PbS: galena). Metallic Pb particles, which were between 41 and 46 µm, were identified in the soil. After eggshell and seashell (20%) were applied, the soil pH increased from 6.0 to 7.84 and 8.07, respectively. In the studied soil, the leaching test showed a 59 mg L^?1 average Pb extractable concentration. After 240 days, extractable Pb by toxicity characteristics leaching procedure decreased to 4.79 mg L^?1 (93.3%) with the application of seashell at 20% compared with a decrease of 33.33 mg L^?1 (53.6%) using eggshell. Pb in the polluted soil was mainly found in the exchangeable fraction (66%), followed by the reducible (24%), residual (7%) and oxidizable (6%) fractions. According to the risk assessment code, the contaminated soil before treatment was classified as very high risk. Adding eggshell (20%) and seashell (20%) decreased the exchangeable fractions to 39 and 35%, respectively. Applying these liming materials achieved Pb immobilization in the soil, but the soil remained in the high environmental risk category. We conclude that the application of seashell waste, resulting from high aquaculture activity, opens an interesting window to the treatment of contaminated arid soils.     

Changes of biochemical properties and heavy metal bioavailability in soil treated with natural liming materials

This study evaluated the efficiency of naturally occurring lime-based waste materials (oyster shells, eggshells, and mussel shells) on immobilization of selected heavy metals (Cd and Pb) and a metalloid (As) in a contaminated agricultural soil. A 30-day incubation experiment was performed using soil mixture with natural liming materials or calcite (CaCO₃) at 0, 1, 3, 5, and 10 wt %. Soil biochemical properties including pH, electrical conductivity (EC), exchangeable cations, organic matter (OM), total nitrogen (TN), microbial populations, and enzyme activities were determined to ensure the changes in soil quality during incubation. The results showed that the application of natural liming materials led to an increase in soil pH similar to that of CaCO₃. Soil concentrations of Cd, Pb, and As extracted with 0.1 or 1 M HCl, and diethylene triamine pentacetic acid (DTPA) were decreased significantly after adding liming materials, accompanied by increased microbial population and enzyme activities of dehydrogenase, phosphatase, β-glucosidase, and arylsulfatase. Additionally, eggshells and mussel shells induced significant increases in OM and TN in the soil. Application of natural liming materials offers a cost-effective way to immobilize heavy metals and metalloids in soils.     

Distribution and contamination assessment of toxic trace elements in sediment of the Daliao River System, China

The Daliao River System (DRS) is one of the major river systems in the northeastern China and receives substantial discharges from industrial, municipal, and agricultural effluents. In this study, the contents and partition of toxic trace elements in the DRS sediments were evaluated in terms of contamination levels and ecological risks using geoaccumulation index (Igeo), relative enrichment factor (REF), sediment pollution index (SPI), and potential effect concentration quotient (PECQ). Fourteen samples were collected and measured for trace and major elements and sediment properties. The following concentration ranges (mg kg^?1) of toxic trace elements were found: As, 1.6–18.0; Cd 0.1–0.9; Co 3.8–23.4; Cr 12.9–151.6; Cu 4.6–86.1; Hg 0.01–0.35; Ni 8.4–64.4; Pb 11.6–67.1; Sb 0.13–1.77; V 18.5–153.3; and Zn 20.4–211.3. The proportions of soluble and exchangeable trace metals were less than 1 %, while the proportions of trace metals bound to carbonate, amorphous oxides, organic matter, and crystalline oxides were usually each <10 %. However, 28.8 % of Cd, on average, was associated with carbonate. The average proportions of trace metals in the residual fraction ranged 57.3 % for Cd to 85.4 % for Cr, indicating low mobility and bioavailability. Cr, Ni, V, and Co in the sediments mainly originated from natural sources, while Cd, As, Pb, Sb, and Hg partially originated from anthropogenic sources. The Igeo, REF, SPI, and PECQ values of the heavy metals in the sediment were not in agreement with each another. The average REF values of Cd and As were higher than those of the other metals. However, the average PECQ value was higher for Cr and Ni than for the other metals, indicating that these two metals would cause higher adverse biological effects than the other metals. In addition, the sediments located adjacent to cities were more contaminated. Therefore, it is suggested that future management and pollution control within the DRS might focus on As, Cd, Cr, and Ni in the sediments, particularly in the sediments adjacent to cities.     

Heavy-metal loadings related to urban contamination in the Kooloonbung Creek catchment,Port Macquarie,New South Wales

Urbanisation and industrial development lead to contamination of estuaries and streams with dispersed loadings of heavy metals and metalloids. Contributions of these elements also occur from natural sources. This study provides baseline geochemical data on the respective natural and anthropogenic inputs of Cu, Pb, Zn, Cd, As, Sb, Cr, Ni, Mn and S to estuarine, fluvial and wetland sediments, and adjacent soils, in the Kooloonbung Creek catchment that drains the Port Macquarie urban area in north coastal New South Wales. There have been anthropogenic additions of Cu, Pb, Zn and As from dispersed urban sources at Port Macquarie, but they are restricted to the local catchment and do not impact on the adjacent Hastings River estuary. The most contaminated sediments display enrichment factors up to 20 × for Cu and Pb, 9 × for Zn and 5 × for As relative to local background values. However, only one value (for Pb) exceeds National Water Quality Management Strategy interim sediment quality guideline (high) values. On the other hand, sediments and local soils are commonly strongly enriched in Cr, Ni and Mn, reflecting adjacent ultramafic and mafic rock substrate and lateritic regolith. Concentrations of Cr and Ni are commonly well above interim sediment quality guideline (high) values for sediments, but are in mineralogical forms that are not readily bioavailable. Sediment and soil quality guideline values consequently need to recognise natural enrichments and the mineralogical siting of heavy metals. Although dissolved concentrations of heavy metals in stream waters are commonly low, there is evidence for mobility of Cu, Zn, Fe and Al. Parts of the Kooloonbung Creek wetland area lie on sulfidic estuarine sediments (potential acid sulfate soils). Experimental oxidation of uncontaminated and contaminated sulfidic sediments leads to substantial dissolution of heavy metals under acid conditions, with subsequent aquatic mobility. The results warn about disturbance and oxidation of potential acid sulfate soils that have been contaminated by urban and natural heavy-metal sources.     

Water lily (<Emphasis Type="Italic">Nymphaea</Emphasis> sp.): an alternative organic amendment for treatment of hydrocarbon-contaminated soil by chemical–biological stabilization

The chemical–biological stabilization technology has been employed in several successful studies using sugarcane cachasse as the organic amendment. However, in some petroleum-producing areas, there are no sugar mills nearby (which is the source of this material), and the cost of transport to the contaminated site is prohibitive. Therefore, water lily, which is considered a weedy plant in many tropical and subtropical areas, was evaluated as an alternative. In 3-month experiment, water lily was compared (with and without addition of molasses) with cachasse for the treatment of clayey sediment contaminated with > 6% extra-heavy crude oil. All treatments resulted in a reduction in the hydrocarbon concentration of 15–23%, without significant differences (P > 0.05). During this process, the pH was reduced to the 7–7.5 range and water repellency (molarity ethanol drop) to 3.5–3.6 M. Also, field capacity increased to 36.3–38.5% humidity, establishing adequate conditions for the development of vegetation at this site. Likewise, toxicity was reduced to practically null (Vibrio fischeri bioassay), and hydrocarbons in leachates were reduced to 3.4–4.3 mg/l, conditions adequate for the protection of groundwater and human health in rural areas. This study confirms that water lily is an adequate substitute for the application of this treatment method for hydrocarbon-contaminated sites that are far from sugar production areas.     

Comparison of the effectiveness of different binders in solidification/stabilization of a contaminated soil

In the current research, solidification/stabilization (S/S) treatment of the contaminated soil using hydraulic binders and additives was used to (1) reduce the mobility of organic and inorganic contaminants and (2) compare the ability of various binders in fixing contaminants. The samples were collected from Franco-Tunisian Petroleum Company, located in Sidi Litayem, Sfax (Southern Tunisia). Leaching tests were performed on contaminated soil, containing metallic elements, and hydrocarbons. Calcium aluminate cement (CAC), ordinary Portland cement (OPC), and ground-granulated blast-furnace slag (GGBFS), additives especially the bentonite and water, were used for S/S treatment. The obtained standard specimens were subjected for treating after treatment the leachability of pollutants, compressive strength (CS), and XRD analysis. The results of analysis conducted on contaminated soils showed that concentrations of metallic elements were in the range of 9.08–427 mg/kg and 15,520 mg/kg of organic compound. Next, 10% of the used binder improved the immobilization of pollutants and gave a satisfactory CS exceeding 1 MPa. Thus, the CAC is more effective in reducing the leachability of metal contaminants than OPC + GGBFS and produces much higher strength, which was of the order of 2.41 MPa. The mechanical characterization was confirmed by XRD analysis. The lowest values of organic compounds are presented in mixtures treated by 10% of used binder, indicating the effectiveness of those with the presence of 10% of bentonite. This work shows that 10% (OPC + GGBFS) +?10% bentonite improved the immobilization of metallic elements and hydrocarbons, thus proving its efficiency due to its low cost.     

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin,East Cameroon: a tool for contamination assessment

The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (<?150 µm) was subjected to total digestion (HClO₄?+?HF?+?HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As?=?99.40 µg/kg, Zn?=?573.24 µg/kg, V?=?963.14 µg/kg and Cr?=?763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended.     

Assessment of heavy metals in sediments near Hazira industrial zone at Tapti River estuary, Surat, India

Heavy metal accumulation due to industrial activities has become a very sensitive issue for the survival of the aquatic life. Therefore, distributions of several heavy metals have been studied in the surface sediments of Tapti–Hazira estuary, Surat, to assess the impact of anthropogenic and industrial activities near estuary. Totally 60 sediment samples were collected from four different sites at Tapti–Hazira estuary, Surat from January 2011 to May 2011 and examined for metal contents. The average heavy metal load in the study area are found to be 43.28–77.74 mg/kg for Pb, 48.26–72.40 mg/kg for Cr, 117.47–178.80 mg/kg for Zn, 71.13–107.82 mg/kg for Ni, 123.17–170.52 mg/kg for Cu, 0.74–1.25 mg/kg for Cd, 14.73–21.69 mg/kg for Co. Calculated enrichment factors (EF) reveal that enrichment of Pb and Cd is moderate at all sites, whereas other metals Cr, Ni, Zn, Co, and Cu show significant to very high enrichment. Geo-accumulation index (I _geo) results revealed that the study area is nil to moderately contaminated with respect to Cd, moderately to highly polluted with respect to Pb, Zn, and Cu and high to very highly polluted with respect to Co and Cr.     

An assessment of Portland cement,cement kiln dust and Class C fly ash for the immobilization of Zn in contaminated soils

Zn-contaminated soils obtained from a steel company in the Republic of Korea were stabilized using Portland cement (PC), cement kiln dust (CKD) and Class C fly ash (FA). The effectiveness of the treatment was evaluated by the United States Environmental Protection Agency toxicity characteristic leaching procedure (TCLP) and the Universal Treatment Standard (UTS) of 4.3 mg/L. X-ray powder diffraction (XRPD) analyses were performed to investigate the crystalline phases associated with Zn immobilization. Scanning electron microscopy (SEM)–energy dispersive X-ray (EDX) analyses were utilized to support the XRPD results. The treatment results showed that the TCLP-Zn concentrations obtained from the 10 wt% PC and 15 wt% CKD treated samples were less than the UTS, after 7 days curing. However, the FA treatment (up to 30 wt%) was not effective in meeting the UTS even after 28 days curing. All PC–CKD treatment combinations were effective in reducing the TCLP-Zn concentrations below the UTS criteria. Moreover, a 20 wt% dose of a PC-FA treatment combination (75/25 PC-FA) was successful in reducing the TCLP-Zn concentrations below 4.3 mg/L after 1 day. The XRPD results showed that ettringite and Zn₆Al₂(OH)₁₆CO₃·4H₂O were the possible phases associated with Zn immobilization upon PC and CKD treatment. The SEM–EDX results confirmed the presence of ettringite, while Zn₆Al₂(OH)₁₆CO₃·4H₂O was not identified.     

溶解性有机质对冻融作用下污染土壤中重金属Pb的溶出释放规律

采用室内模拟实验方法研究了溶解性有机质（DOM）对冻融作用下污染土壤中重金属Pb的溶出规律。结果表明：冻融作用明显改变了土壤基本理化性质和重金属Pb的化学形态;与未冻融土壤相比,DOM明显促进了冻融土壤中Pb的溶出释放。DOM对污染土壤中Pb的溶出释放作用与土壤类型、土壤污染时间和污染程度有关：DOM对棕壤中Pb的溶出释放作用大于对黑土中Pb的溶出释放作用;而且随着土壤Pb污染时间越长和污染程度越重,DOM对土壤中Pb的溶出释放作用越大。DOM对土壤中Pb的溶出释放还与DOM质量浓度、性质和组成密切相关：DOM质量浓度的增加提高了污染土壤中Pb的溶出释放;DOM的低pH和小分子量亲水性组分利于土壤中Pb的溶出释放。     

U–Pb detrital zircon evidence of transcontinental sediment dispersal: provenance of Late Mississippian Wedington Sandstone member,NW Arkansas

ABSTRACT

U–Pb ages of detrital zircons from the Wedington Sandstone member in northwest Arkansas provide evidence for Late Mississippian westward transcontinental sediment transport from the Appalachian foreland. The Late Mississippian Wedington Sandstone member of the Fayetteville Shale is a fine- to medium-grained quartzarenite. It separates the Fayetteville Shale into informal lower and upper intervals, and was deposited as a small constructive delta complex that prograded towards the south and southeast during the Late Mississippian. As a major influx of clastic sediments, the Wedington Sandstone member records the sediment source and dispersal in the mid-continent during the Late Mississippian. A total of 559 detrital zircon grains from six Wedington samples were recovered for U–Pb detrital zircon geochronological analysis. Results show that age distributions can be subdivided into six groups: ~350–500, ~900–1350, ~1360–1500, ~1600–1800, ~1800–2300, and > ~2500 Ma, and are characterized by a prominent peak for the age group of ~900–1350 Ma, a major peak at ~1600–1800 Ma, and a few other minor age clusters. Regional correlation and geological evidence from surrounding areas suggest that the transcontinental sediment dispersal started as early as the Late Mississippian. U–Pb detrital zircon age distribution suggests that the Wedington Sandstone member was likely derived from the Appalachian foreland with contributions from the Nemaha Ridge to the west where the Yavapai–Mazatzal sources were exposed during the Late Mississippian. Sediment was likely transported westward through or around the Illinois Basin, merged with mid-continent sediment, and then entered into its current location in northwest Arkansas. Transportation of this sediment from mixed sources continued along its course to the south, forming a delta on the Northern Arkansas Structural Platform.     

Advantage of almond green hull over its resultant ash for chromium(VI) removal from aqueous solutions

The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.     

Zircon SHRIMP U–Pb age of Late Jurassic OIB-type volcanic rocks from the Tethyan Himalaya: constraints on the initial activity time of the Kerguelen mantle plume

This work presents zircon U–Pb age and whole-rock geochemical data for the volcanic rocks from the Lakang Formation in the southeastern Tethyan Himalaya and represents the initial activity of the Kerguelen mantle plume. SHRIMP U–Pb dating of zircons from the volcanic rocks yielded a ²⁰⁶Pb/²³⁸U age of 147 ± 2 Ma that reflects the time of Late Jurassic magmatism. Whole rock analyses of major and trace elements show that the volcanic rocks are characterized by high content of TiO₂ (2.62 wt%–4.25 wt%) and P₂O₅ (0.38 wt%–0.68 wt%), highly fractionated in LREE/HREE [(La/Yb)_N = 5.35–8.31] with no obvious anomaly of Eu, and HFSE enrichment with no obvious anomaly of Nb and Ta, which are similar to those of ocean island basalts and tholeiitic basaltic andesites indicating a mantle plume origin. The Kerguelen mantle plume produced a massive amount of magmatic rocks from Early Cretaceous to the present, which widely dispersed from their original localities of emplacement due to the changing motions of the Antarctic, Australian, and Indian plates. However, our new geochronological and geochemical results indicate that the Kerguelen mantle plume started from the Late Jurassic. Furthermore, we suggest that the Kerguelen mantle plume may played a significant role in the breakup of eastern Gondwanaland according to the available geochronological, geochemical and paleomagnetic data.     

Geochemical mobility of arsenic in the surficial waters from Argentina

The presence of arsenic (As) in surface water constitutes an important environmental risk, where mobility and adsorption processes are responsible for its behavior in the sediment–water interface. Therefore, the assessment of adsorption, mobility and water availability of arsenic in freshwater sediments, with agricultural, livestock and urban soil uses was performed. Arsenic concentrations in sediments ranged from 5.4 to 15.9 mg kg^?1 (total) and 2.8 to 6.5 mg kg^?1 (labile), and those of iron and manganese were 11,563–23,500 and 140.6–662.1 mg kg^?1, respectively. The As levels in water were significantly lower than those of sediments. Results would suggest that As co-precipitation and adsorption on Fe oxides are probably the major route of immobilization, determining its low lability. Manganese did not present an outstanding contribution to the retention, and cation-exchange capacity, pH and organic matter of sediments did not show an influence on the mobility of As.     

Reclamation of mine-degraded agricultural soils from metal mining: lessons from 4 years of monitoring activity in Korea

The environmental issues associated with mining have damaged the industry’s substantial global economic value. In particular, the mining industry has a negative legacy of contaminated land. The effective reclamation of contaminated soil is therefore required before former mining land can be further developed for residential and commercial purposes. The objective of this study was to technically evaluate the feasibility of reclamation techniques for agricultural soils contaminated with toxic elements (As, Cd, Cu, Pb, and Zn) associated with metal mining. The reclamation methods investigated were covering without stabilization, covering with stabilization, and exchange with stabilization. The thickness of the soil layer used in covering and exchange was in the range of 30–50 cm. Limestone, furnace slag, and a mixture of limestone and furnace slag were applied as soil amendments. After reclamation, the contamination level in surface tillage soils and crops was monitored regularly. Four years of monitoring data revealed that surface soil contamination levels could be maintained at acceptable levels, although at some sites, the metal levels in crops exceeded legislative limits. Soil reclamation at former mining sites in Korea has not yet been perfected, but the results of this study show that there is potential for safe agricultural operations on large sites in a cost-effective manner, as long as the appropriate control of surface soil contamination and adequate agronomic management is undertaken.