Crystalline Fe Oxide Fractions Research Articles

Chemical speciation and release kinetics of Ni in a Ni-contaminated calcareous soil as affected by organic waste biochars and soil moisture regime.

Biochars vary widely in properties and have been shown to have variable effects on potentially toxic element(s) stabilization in soil. This is the first study to examine the interaction effects of biochar and soil moisture regime on Ni stabilization in a Ni-contaminated calcareous soil. Three different organic waste (cow manure, municipal compost and licorice root pulp) biochars produced at two temperatures (300 and 600°C) were applied (3% wt.) to a Ni-contaminated calcareous soil and incubated at field capacity and saturated conditions for 70 d. Sequential chemical fractionation and Ni release kinetics were then performed. All applied biochars, especially the high-temperature biochars, were significantly able to enhance Ni stabilization in the studied soil. In particular, the biochars significantly decreased Ni content in the water-soluble and exchangeable fractions (10-42% decrease), while increasing the immobile residual fraction (13-38% increase). The biochars also significantly decreased the rate and cumulative amount of EDTA-extractable Ni from the calcareous soil. Among the studied biochars, the cow manure and municipal compost biochars produced at 600 °C were the most effective at reducing Ni mobility factor (27-28% decrease) and initial release rate (42-49% decrease), likely due to their high ash content and pH, which promotes Ni sorption in soil. Soil moisture regime was not found to significantly affect the Ni mobility factor or rates of Ni release from the calcareous soil but did, however, affect certain soil Ni chemical fractions. Soil water saturation significantly decreased Ni in the Mn (4%) and non-crystalline Fe oxides (17%) fractions, while increased the crystalline Fe oxide fraction (3%), attributed to reductive dissolution of Mn and Fe oxide crystallinity enhancement. Saturation also significantly enhanced Ni in the residual fraction (4%), attributed to the associated pH increase and potential sulfide formation. The results of this study demonstrate that high temperature, ash-rich, and alkaline biochars are most effective at Ni immobilization, and that soil water saturation can further enhance Ni in the residual fraction.

Seasonal impacts on arsenic mobility and geochemistry in streams surrounding a gold mineralization area, Paracatu, Brazil

Arsenic (As) is a trace element in the Earth's crust that often occurs with gold mineralization, where it is found in association with sulfide-bearing minerals such as pyrite (FeS2). Our study evaluated the mobility of As in creeks that traverse a gold mineralization area in Paracatu, Brazil. The results relate As mobility in water draining actively mined areas to season, wet and dry, and to the impact of in-stream channels lined with limestone that are used to neutralize acid mine drainage. Passage of the creek water through channels lined with limestone decreased soluble As to concentrations below the drinking water threshold in 13 out of 31 samples (10 μg.L−1). The soluble As concentrations were generally higher during the wet season. Arsenic speciation in water was mainly influenced by the season and by the proximity to mineralization zones in the areas that are actively mined. The organic arsenic species DMA (dimethylarsinate) was detected near the mineralized area during the wet season. Sediment-associated As varied with season and with sampling site, but was consistently high at one headwater spring; the highest observed value was 8750 mg As kg−1. We applied selective sequential extraction techniques to assess the portioning of As in the creek sediments. Two of the most mobile fractions of sediment-associated As, the adsorbed and very poorly crystalline fractions, showed a strong seasonal dependence which supported mobilization of As during the wet season. The amorphous Fe oxide fraction followed the same trend but contributed less As, and As associated with the crystalline Fe oxide fraction showed little fluctuation with season.

Effect of Oxidation-Reduction Fluctuations on Metal Mobility of Speciated Metals and Arsenic in Bottom Sediments of Middleton River, Bayelsa State, Nigeria

Speciation and chemical mobility of heavy metals were assessed with a view to provide information on bioavailability of metals in a sediment matrix in order to account for the vulnerability of sediment dwelling fauna within the Middleton river ecosystem. Sediment was collected in triplicate from seven locations (five reflecting activities of oil installations in the study area and two controls). Sediments were collected in the months of March and August 2017 to reflect the dry and wet seasons respectively. Concentration of metals in each fraction was determined using a GBC Avanta Atomic Absorption Spectrophotometer. The residual fraction was the most important for Cr with average levels of (49.4%) and (41.1%) for the dry and wet seasons respectively. Also, the most prevalent fractions of Zn were the residual fractions which revealed (31.7%) and (42.6%) during the dry and wet seasons respectively. The metalloid (As) had (14.7%) and (13.8%) of its total concentration bound to the residual and crystalline Fe-oxide fractions during the dry and wet seasons respectively. The oxidation-reduction potential (ORP) was measured electrometrically using a redox potential meter; ORP ranged from (+288.67 to +351.33 mV) and (+331.00 to +465.67 mV) for the dry and wet seasons respectively, hence, depicting a fairly oxidizing sediment environment. Mobility factor of metals depicted (As > Cu > Cr) and (As > Cr > Cu) for the dry and wet seasons respectively. The effect of oxidation-reduction potential on metal mobility revealed the transportability of chromium with increasing redox potential while arsenic was barely mobile with increasing oxidation level. Also, zinc mobility diminished strongly with increasing oxidation-reduction potential. Keywords : Speciation, chemical mobility, bioavailability, Middleton River

Assessment of selected sequential extraction and the toxicity characteristic leaching test as indices of metal mobility in serpentinite soils

Serpentinite soils are characterised by high concentrations of chromium, nickel, and cobalt. The accumulation of heavy metals as non-degradable inorganic contaminants is of great concern. Under normal circumstances the form in which a metal exists governs its transport in the environment and thus, its hazards. In this study, a specific developed speciation analysis for tropical soils was applied to determine the mobility of Cr, Ni and Co in two serpentinitic soil outcrops in Malaysia. The combination of selective sequential extraction analysis (SEE) and X-ray diffraction of soil powders showed that Cr and Ni are primarily associated with the residual fraction of soil which is inherited from resistant silicates. The crystalline Fe-oxide fraction of soil is the second substanial scavenger of Cr and Ni, whilst the dynamics of Co are mostly controlled by Mn-oxide and the poor crystalline Fe-oxide. The more easily mobilised forms of the studied metals carried on soluble-exchangeable, surface adsorbed and organic matter fractions are of minimal compartments. Therefore these metals are basically not available in the environment. On the other hand, corroborating information on the mobility of the metals was gained by applying the toxicity characteristic leaching procedure test (TCLP). The consistent results of the TCLP with the SSE revealed the non-toxic effects of Cr, Ni and Co in the environment despite their overload accumulation in the analysed serpentinite soils.

Assessment of trace and heavy metal distribution by four sequential extraction procedures in a contaminated soil

Four sequential extraction procedures (Sposito, Tessier, Silveira and Bureau Communautaire de Reference (BCR)) were used to evaluate the distribution of some metals (Fe, Cu, Cd and Zn) in a contaminated soil around a mining area. The results showed that Fe and Zn were mainly recovered in the recalcitrant soil fractions, while Cd was primarily localized in the exchangeable fraction. Soil Cu was highly associated with organic matter fraction. The amorphous Fe fraction in Silveira could be recognized as part of the Fe-Mn oxide fraction in Tessier and BCR procedures, while the crystalline Fe oxide fraction was classified into the residual fraction in Sposito, BCR and Tessier schemes. Although the same reagent was used to extract target fraction, less carbonate-bound Cu, Cu and Zn were extracted in Tessier procedure as compared to Silveira method, while Tessier scheme yielded a higher proportion of Fe, Cu and Zn in the Fe-Mn oxide fraction than BCR method. Due to the lack of uniformity of experimental conditions and the differences in extraction reagents, the extraction efficiency of metal species varied with the sequential extraction schemes. Therefore, care should be taken when comparing the results obtained by different sequential extraction procedures.

Speciation of Fe, Mn and Zn in surficial sediments from the Egyptian Red Sea coasts

The use of two schemes (I and II) was compared for the fractionation of Fe, Mn and Zn in surficial sediments of the coastal regions of Egyptian Red Sea coasts. Scheme I measured the total oxide fraction. Scheme II, a detailed sequential extraction protocol, was used to distinguish oxide forms of the metal (Mn, poor crystalline Fe and crystalline Fe oxides). The data revealed that high percentage of Zn was concentrated in the residual fraction (lithogenic origin) in all sectors of the study. A high percentage of Mn was concentrated in the residual fraction in both of the Gulf of Aqaba and Red Sea proper samples. However, a high percentage of Mn was recorded in the non-residual form; 60.53% (anthropogenic origin) in the Suez Gulf samples. The recovery of Fe was efficient at most stations using Scheme II, and it was shown that most of the Fe was concentrated among residual, poor crystalline Fe oxide and crystalline Fe oxide fractions. Both Schemes I and II are recommended for speciation of Mn and Zn, but Scheme I is preferred since it has fewer analytical steps. However, Scheme 2 is strongly recommended for the determination of the Fe fractionation pattern. Principal component analysis was applied to the multivariate data derived from the geochemical analysis of 24 stations in the study area and the fractionation patterns of Fe, Mn and Zn associated with physico-chemical characteristics of the sediment are discussed.

Distribution Of Cadmium And Nickel Among Various Forms In Natural And Contaminated Soils Amended With Edta

Because of its strong chelating capacity, application of ethylenediaminetetraacetic acid (EDTA) to soils may change the amount and distribution of heavy metals among their various chemical forms. Therefore, a greenhouse experiment was conducted using two cultivars of Brassica species (Brassica juncea and Brassica carinata) as hyper accumulator test crops on natural and artificially Cd and Ni contaminated soils. Both natural and metal amended soils were treated with disodium salt of EDTA at 0 and 1 g kg−1 soil. After harvest of crops, soil samples were fractionated into water soluble plus exchangeable (WE), carbonate (CARB), organic matter (OM), Mn oxide (MnOX), amorphous Fe oxide (AFeOX), crystalline Fe oxide (CFeOX) and residual (RES) fractions. In metal amended soils, Cd and Ni were found predominantly in the AFeOX fraction in the absence of EDTA application and in the WE fraction in EDTA treated soil. Application of EDTA resulted in the redistribution of Cd among different forms and increased significantly Cd in the WE fraction with a concomitant significant decrease in the OM fraction. In natural soils, more than 40% of the total Cd was present in the RES fraction while in contaminated soil it was only 5%. Nickel in the WE fraction increased significantly while it considerably decreased in the CARB, OM, MnOX, AFeOX and CFeOX fractions with EDTA addition. This indicated that applied EDTA is capable to move Cd and Ni from the less soluble or more stable forms (CARB, OM, MnOX, AFeOX and CFeOX) to the most soluble form (WE). N natural soils, Ni in the RES fraction was found upto 49%, whereas only 10% of the total Ni was observed in contaminated soil, irrespective of EDTA treatment. In general, the amount of Cd recovered after harvest of both the Brassica cultivars did not differ significantly in any fraction except the WE fraction. The amount of Ni recovered in the AFeOX fraction was significantly higher after harvest of B. juncea as compared to B. carinata.

Fractionation of trace elements in some non-agricultural Australian soils

The fractionation of Ag, Ba, Co, Cr, Cu, Ni, Pb, V, and Zn in highly weathered soils was investigated using 5 operationally defined fractions: exchangeable, organic, amorphous Fe oxides, crystalline Fe oxides, and residual fraction. Crystalline Fe oxide and residual phases were the dominant hosts of Ag in the original soils, but for soils to which soluble Ag was added, much Ag was in the crystalline Fe oxide fractions and only a relatively small proportion of Ag was in the residual fraction. Crystalline Fe oxides and the residual fraction were also the major hosts to Co, Cr, Cu, Ni, Pb, V, and Zn.

Redistribution of forms of zinc, cadmium and nickel in soils treated with EDTA

Organic amendments are often added to soils in the form of waste materials which increase the soluble organic ligands in soil. To study the interaction of these soluble organics with metals in soil, Ethylenediaminetetraacetic acid (EDTA) can be used as a model compound for natural organics. The addition of EDTA to soil may alter the physicochemical forms of metals in soil because of its strong chelating capacity. In this work, samples of eight agricultural soils collected in Georgia were spiked with soluble salts of Zn, Cd, and Ni in proportions of 75.9, 1.62, and 4.30 mg kg−1, respectively. Both natural and metal-amended soils were treated with Na2-EDTA (disodium ethylenediamine tetraacetate) solution at amounts of 0, 1.0 and 2.0 g kg−1. After five months incubation in a greenhouse, the soil samples were fractionated into exchangeable (EXC), organic matter (OM), Mn oxide (MNO), amorphous Fe oxide (AFEO), crystalline Fe oxide (CFEO), and residual (RES) fractions. The added Zn was distributed among all fractions in the soils, and added Cd and Ni were found predominantly in the EXC and OM fractions with some of the added Ni occurring in the RES fraction. Increasing the amounts of EDTA significantly raised Zn concentrations in the EXC fraction in both natural and metal-amended soils, and the EDTA also increased Ni and Cd concentrations in the EXC fraction of the metal-amended soils. The results suggested that added EDTA enhanced the solubility of these metals in these soils. The OM-fraction metals decreased with increasing amounts of EDTA, except for Ni in the natural soils. The increase in Zn and Cd associated with the EXC fraction may have been related to solubilization of metals from the OM fraction by EDTA. In the metal-amended soils, EDTA not only removed Ni from the OM fraction, but also from the MNO, AFEO and CFEO fractions, and redistributed it into the EXC fraction. Based on relative percent, Cd in the EXC fraction was higher than Zn, while Ni in this fraction was lowest. This suggests that the order of solubility was: Cd>Zn>Ni for metals added to soils, but when EDTA was present, added Ni may be more vulnerable to solubilization than added Zn and Cd.

Distribution of zinc, cadmium, and copper forms in soils as influenced by phosphorus application

Abstract High P levels can alter the surface properties of soil colloids, possibly resulting in a redistribution of trace metals among various forms in soils. Therefore, the effect of P levels (0, 60, and 120 mg P kg‐1 soil) was studied on the various chemical pools—water soluble plus exchangeable (WE), carbonates (CARB), organic (OM), Mn oxide (MnOX), amorphous Fe oxide (AFeOX), crystalline Fe oxide (CFeOX), and residual (RES) of Zn, Cd, and Cu—in three soils. Increasing P levels resulted in lowering Zn and Cd in the CFeOX, OM, and CARB fractions, with a concomitant increase in the AFeOX and WE fractions, and had no effect on the RES fraction. Phosphorus application influenced AFeOX‐Zn fraction more than any other fraction. The depressive effect of P levels was more pronounced on the CFeOX fraction than on the OM or CARB fraction of Zn and Cd. Applied P moved Cu from the less soluble or most stable forms (CFeOX, CARB and OM) to the intermediately soluble forms (AFeOX and MnOX) and the most soluble form (...

Fractionation of micronutrient cations in a selected Saudi Arabian soil subjected to different tillage practices

Abstract Sustaining or increasing soil micronutient availability depends in part on soil tillage practices that alter soil properties, such as soil organic matter, pH, and cation exchange capacity. The main objective of this study was to determine the effect of various tillage systems on the distribution of the species of micronutrient cations in soil. Soils were sampled from the 0‐ to 20‐cm depth from three conservation practices (no‐tillage (NT), harrowing (HR), and chisel (CH)) and two conventional tillage systems (moldboard (MB) and disking (DS)). Soil samples were fractionated sequentially to determine Zn, Cu, Mn, and Fe in the following species: exchangeable, organic, occulted (Mn oxide, amorphus Fe oxide, crystalline Fe oxide), and residual forms. Conservation tillage systems (HR, CH, and NT), had a significant effect on the distribution of Zn, Cu, Mn, and Fe in exchangeable and organic forms compared to the conventional tillage systems (DS and MB). The conservation systems increased Zn and Fe in the exchangeable and organic form, and decreased Zn in the occulted form (amorphous Fe oxide fraction). Copper in the organic form was higher but its occulted form was lower (in the amorphous Fe oxide fraction) for conservation tillage systems compared to conventional systems. Manganese was higher in the organic fraction but lower in its occulted (amorphous Fe oxide) and residual fractions for conservation versus conventional tillage. Iron in the exchangeable and organic forms was higher, whereas Mn oxide and crystalline Fe oxide fractions were lower in conservation tillage than in conventional tillage systems. It appears that conservation tillage practices transformed Zn, Cu, Mn, and Fe from residual and occulted forms (amorphous Fe oxide, Mn oxide, and crystalline Fe oxide) to species of the exchangeable, organic, or Mn oxide fractions.

Effect of Phosphorus Level on Extractable Micronutrients and Their Distribution Among Soil Fractions

AbstractReduced tillage can cause high P levels at the soil surface which may influence soil properties so as to redistribute micronutrient metals among soil fractions and alter their plant availability. The objective was to determine the effect of P levels on the distribution of Mn, Cu, Fe, and Zn among soil fractions and on their extractability by commonly used soil extractants. Eight topsoils were treated with 0, 30 and 60 mg P kg−1 soil and none or one level of a blend of Mn, Cu, and Zn. After 22 wks, the soils were sequentially extracted to separate the exchangeable, organic, Mn oxide, amorphous Fe oxide, crystalline Fe oxide, and residual fractions. Mehlich‐1, Mehlich‐3, and DTPA (diethylenetriamine‐pentaacetic acid) extractable metals and Mehlich‐3 P were also determined. Increasing P moved Mn from the less‐soluble fractions (crystalline Fe oxide and residual) to the intermediately‐soluble fractions (Mn oxide and amorphous Fe oxide) and had little effect on the plant‐available fractions (exchangeable and organic). Copper moved to the exchangeable from the residual fraction for the fine‐textured soils. Zinc moved from the Mn oxide and crystalline Fe oxide fractions to the exchangeable fraction for all soils. Added Cu and Zn were evident in the more plant‐available fractions for most soils. Increased P increased extractable Mn and Fe for Mehlich‐1 and −3 and DTPA. Phosphorus treatments increased soil pH probably because of reactions with Fe and Al oxides producing hydroxyl ions. However, initial reactions may have lowered soil pH causing metals to be more soluble.

FRACTIONATION METHOD FOR SOIL MICROELEMENTS

To evaluate a sequential extraction procedure to separate chemical forms of soil microelements, I fractionated 16 soils, both surface and subsoils. The purpose of the sequential extractions was to solubilize the Mn, Cu, Fe, and Zn in the exchangeable, organic matter, Mn oxide, amorphous Fe oxide, and crystalline Fe oxide fractions. The solid portion remaining was separated into sand, silt, and clay sizes, and each was dissolved and analyzed for the above elements. Soil properties were determined, and whole soils were analyzed for total microelement content. Manganese was primarily in the organic and Mn oxide fractions, whereas Cu and Zn were found mainly in the crystalline Fe oxide, silt, and clay fractions for the fine-textured soils. In sandy soils the Mn was predominantly in the sand, and Cu was in the Fe oxide fractions. Iron was relatively higher in the organic matter, and Zn was relatively higher in the exchangeable and organic fractions in the sandy soils, compared with the fine-textured soils. High correlation coefficients were found among such soil properties as CEC, organic matter, and clay versus metals removed from the various fractions. The sums of the fractions versus whole soil digestion values compared favorably. The fractionation scheme presented was found to be satisfactory for a wide range of soils.