Mobility Of Chromium Research Articles

Fe (hydr)oxides and organic colloids mediate colloid-bound chromium mobilization in Cr(VI) contaminated paddy soil

The association of chromium (Cr) with colloidal particles transport in contaminated sites can affect hexavalent chromium (Cr(VI)) migration and transformation, which is an important mechanism for Cr pollutants in soil and groundwater systems. Here, we investigated colloid and particle-bound Cr migration and transformation effects on rice Cr accumulation during different rice growth stages and different redox conditions in Cr(VI) contaminated soil by pot experiment. Results showed that 13–29% of soil Cr was water dispersible colloid-bound (100–1000 nm) form during rice growth. Using transmission electron microscopy - energy dispersion spectroscopy and asymmetric flow field - flow separation, we identified colloid-bound organic matter (OM) and iron (Fe), most likely in the form of Fe (hydr)oxides - clay composites, as the primary Cr carrier. Specifically, colloid-bound Cr was mainly associated with 125–350 nm soil particle size. Under different redox conditions, colloid- and nanoparticle-bound Cr concentration decreased with increasing nanoparticles zero-valent iron (nZVI) dose. Soil reoxidation promoted the colloid- and nanoparticle-bound Cr release due to the weakly crystalline Fe-(hydr)oxides reprecipitation. Further quantitative analysis showed that colloid-bound Cr concentrations were positively correlated with colloid-bound Mn concentrations during the whole rice growth soils. Most important of all, Cr content in rice grain was positively correlated with colloid-bound Cr significantly. This study provides a quantitative and size-resolved understanding of particle-bound Cr in paddy soils, highlighting the importance of colloid-bound Cr and Fe interactions in Cr geochemical cycle of paddy soil.

Binding mechanisms of trivalent chromium on colloidal phases from ultramafic systems: Insights from batch experiments and XAS analysis

Understanding the availability and mobility of chromium is a key factor in gaining insight into the fate of chromium and thus essential for assessing the risk of contamination and developing effective remediation strategies. In the natural environment, such as ultramafic systems, which are natural pools of chromium, chromium occurs mostly in the trivalent state (Cr(III)), which is known to have a high affinity for the solid phases such as particles and colloids. However, since Cr(VI) is more toxic, the vast majority of experimental studies focus on its reduction to Cr(III), which is often considered to form (hydr)oxide precipitates due to its poor solubility. Furthermore, while the oxidation state of Cr dictates its geochemical behavior, its interaction with particles and colloids is rarely controlled or monitored. Therefore, the interaction mechanisms between Cr(III) and particles or colloids require further attention. In this study, ten mineral phases (goethite, hematite, pyrolusite, kaolinite, montmorillonite, chlorite, serpentine, fuchsite, amphibole, and chromite) and one organic phase (humic acid), relevant to chromium bearing and carrier phases in ultramafic soils, were investigated to explore their interaction with Cr(III) species. These phases were first characterized by various techniques (including XRD, XRF, SEM, and BET). Adsorption and desorption experiments of Cr(III) on these phases were then carried out, and the distribution of Cr oxidation states in both the aqueous and solid phases was carefully monitored using UV–vis spectroscopy, geochemical speciation modeling, and Cr K-edge XAS spectroscopy. With the exception of pyrolusite, where partial oxidation of Cr(III) to Cr(VI) occurred, Cr(III) was shown to persist as a single oxidation state in all experiments. Desorption analyses showed significantly low desorbed rates, which further confirmed the prevalence of Cr(III). Experimental sorption isotherm data were interpreted using the Langmuir model and its linearized form, which provides important thermodynamic characteristics of adsorbents related to their structural and surface features. This study will provide better constraints for the understanding and prediction of Cr behavior and fate in the environment, especially in ultramafic systems.

Effect of straw decomposition on hexavalent chromium removal by straw: Significant roles of surface potential and dissolved organic matter

Mobility and bioavailability of hexavalent chromium (Cr(VI)) in agricultural soils are affected by interactions between Cr(VI) and returned crop straws. However, the effect of straw decomposition on Cr(VI) removal and underlying mechanisms remain unclear. In this study, Cr(VI) removal by pristine and decomposed rice/rape straws was investigated by batch experiments and a series of spectroscopies. The results showed that straw decomposition inhibited Cr(VI) removal, regardless of straw types. However, the potential mechanisms of the inhibition were distinct for the two straws. For the rice straw, a lower zeta potential after decomposition suppressed Cr(VI) sorption and subsequent reduction. In addition, less Cr(VI) was reduced by the decomposed rice straw-derived dissolved organic matter (DOM) than the pristine one. In contrast, for the rape straw, due to the increased zeta potential after decomposition, the decreased Cr(VI) removal was mainly ascribed to less Cr(VI) reduction by the rape straw-derived DOM. These results emphasized the significant roles of straw surface potential and DOM in Cr(VI) removal, depending on straw types and decomposition, which facilitate the fundamental understanding of Cr(VI) removal by straws and are helpful for predicting the environmental risk of Cr and rational straw return in Cr(VI)-contaminated fields.

Effect of biochar-derived DOM on contrasting redistribution of chromate during Schwertmannite dissolution and recrystallization

Biochar-derived dissolved organic matter (BDOM), is extensively involved in the recrystallization of minerals and the speciation alteration of associated toxic metals. This study investigates how BDOM extracted from tobacco petiole (TP) or tobacco stalk (TS) biochar influences the speciation repartitioning of Cr(VI) in environments impacted by acid mine drainage (AMD), focusing on interactions with secondary minerals during Schwertmannite (Sch) dissolution and recrystallization. TP-BDOM, rich in lignin-like substances, slowed down the Cr-Sch dissolution and Cr release under acidic conditions compared to TS-BDOM. TP-BDOM's higher O/C component exerts a delayed impact on Cr-Sch stability and Cr(VI) reduction. In-situ ATR-FTIR and 2D-COS analysis showed that carboxylic and aromatic N-OH groups in BDOM could interact with Cr-Sch surfaces, affecting sulfate and Cr(VI) release. It was also observed that slight recrystallization occurred from Cr-Sch to goethite, along with increased Cr incorporation into secondary minerals within TS-BDOM. This enhances our understanding of BDOM's role in Cr(VI) speciation changes in AMD-contaminated sites.

Highly alkaline electrokinetic extraction: Characteristics of chromium mobilization, conversion and transport in high alkalinity soil

In site chromium (Cr) contaminated soil characterized by high alkalinity and carbonate content, protons are not effectively targeted for Cr(III) mobilization but rather accelerate the reduction of easily transportable Cr(VI) within the acidification electrokinetic (EK) system. As an alternative, the highly alkaline extraction conditions (HAECs) maintained by anolyte regulation are explored owing to the ability to desorb strong binding Cr(VI) and form anionic Cr(III)-hydroxides (Cr(OH)4−, Cr(OH)52−). The results demonstrate that HAECs were more efficient in mobilizing ions in severe alkalinity and electrical conductivity soil compared to organic acid acidifying extraction conditions (OAECs). Simultaneously, a limited amount of soluble Cr(III) was produced; however, its transportation was hindered and more noticeable in the case of Cr(VI), displaying a distinct retention phase within the intermediate soil chamber. The antagonistic interplay between electromigration and electroosmotic flow was considered the main responsible factor. The conversion intensity of Cr(VI) to Cr(III) was inhibited at HAECs. The promising mobilization and low conversion intensity contributed to total Cr removal. At HAECs, enhanced electromigration and electroosmotic flow combined with a favorable oxidation environment may facilitate in situ delivery of oxidants, offering practical implications for the EK detoxification of high alkalinity site soil contaminated with Cr. The practicability of HAECs is likely to be enhanced when the cost-benefit balance of providing a simultaneous energy supply during site treatment is resolved.

Partitioning and Mobility of Chromium in Iron-Rich Laterites from an Optimized Sequential Extraction Procedure.

Chromium (Cr) leached from iron (Fe) (oxyhydr)oxide-rich tropical laterites can substantially impact downstream groundwater, ecosystems, and human health. However, its partitioning into mineral hosts, its binding, oxidation state, and potential release are poorly defined. This is in part due to the current lack of well-designed and validated Cr-specific sequential extraction procedures (SEPs) for laterites. To fill this gap, we have (i) first optimized a Cr SEP for Fe (oxyhydr)oxide-rich laterites using synthetic and natural Cr-bearing minerals and laterite references, (ii) used a complementary suite of techniques and critically evaluated existing non-laterite and non-Cr-optimized SEPs, compared to our optimized SEP, and (iii) confirmed the efficiency of our new SEP through analyses of laterites from the Philippines. Our results show that other SEPs inadequately leach Cr host phases and underestimate the Cr fractions. Our SEP recovered up to seven times higher Cr contents because it (a) more efficiently dissolves metal-substituted Fe phases, (b) quantitatively extracts adsorbed Cr, and (c) prevents overestimation of organic Cr in laterites. With this new SEP, we can estimate the mineral-specific Cr fractionation in Fe-rich tropical soils more quantitatively and thus improve our knowledge of the potential environmental impacts of Cr from lateritic areas.

Combined effects of biochar and biodegradable mulch film on chromium bioavailability and the agronomic characteristics of tobacco

Biochar (BC) and biodegradable mulch film (BMF) are both commonly used means of production in agriculture. In recent years, most studies have focused on the effects of BC or BMF on soil heavy metal pollution, while they have neglected the combined effects. In this study, a pot experiment was conducted to examine the impacts of BMF, BC, and combined BMF and BC (CMB) on the mobility of chromium (Cr) and the agronomic characteristics of flue-cured tobacco. Compared with the control, BMF, BC, and CMB significantly reduced the concentrations of diethylenetriamine pentaacetic acid (DTPA) extractable Cr in soils by 29.07–29.75%, 45.35–48.54%, and 34.21–37.92%, respectively. In comparison to the application of BMF and BC alone, co-application reduced the availability of Cr in soil via increasing the adsorption of soil Cr and soil enzyme activity, which resulted in the decrease of Cr content and bioconcentration factor and in plants. Moreover, the combined application increased the plant height, stem diameter, leaf area, total root area, root tip number, and root activity of tobacco, which leaded to increase in leaf and root biomass by 11.40–67.01% and 23.91–50.74%, respectively. Therefore, the application of CMB can reduce the heavy metal residues in tobacco leaves and improve tobacco yield and quality.

Redox control of chromium in the red soils from China evidenced by Cr stable isotopes

With chromium isotopes, we study the intricate dynamics of adsorption and redox processes in soil ecosystems, focusing on chromium's behaviour, in red soil profiles enriched with iron-manganese nodules (FMNs) in South China. Key findings reveal that the primary geological source of chromium in the red soil profiles is the weathering of colluvium parent minerals. FMNs have higher chromium concentrations (325–1451 µg/g) compared to surrounding soils (95–247 µg/g) and display stable δ53Cr values (0.78 ± 0.17‰), indicating their role as stable chromium repositories, reflecting historical processes. Furthermore, by isolating chromium associated with iron oxides (FeO) and silicate minerals (ReS) within FMNs and surrounding soils using CBD extractions, we show that FeO predominantly carry chromium, particularly in FMNs. The δ53Cr values of FeO fractions consistently exhibit heavier signatures than ReS fractions, suggesting the sequestration of isotopically heavy chromium (VI) during Fe oxide precipitation. Fluctuations in soil’s redox, rather than land use, play a pivotal role in controlling the precipitation of Fe oxides in surrounding soils and the formation of FMNs, thus influencing chromium mobility. This highlights the significance of these factors when utilizing chromium isotopic techniques for source tracking in soil systems, contributing to our understanding of chromium's behaviour in soil environments.

Study of the Removal Efficiency of Chromium Ions Using a Membrane by Electro-Kinetic Technique from Sludge.

Recently, electro-kinetic (EK) remediation has become more popular as a novel method for removing chromium contamination from soil. This approach, however, is ineffective since it uses both cationic and anionic forms of chromium. In this study, a membrane-based technique was employed to increase the efficiency of the electro-kinetic removal of chromium. Chromium removal from polluted sludge was studied using four bench-scale experiments. Two of these experiments employed distilled water (EK-1 and EK-2 and membrane), whereas the other used acetic acid as the catholyte (EK-3 and EK-4 and membrane). The pH, total chromium, and fractionation of chromium in the sludge were measured after remediation. In the EK-1, EK-2 and membrane, and EK-3 and EK-4 and membrane trials, the average removal efficiencies of total chromium were 47.6%, 58.6%, and 74.4%, 79.6%, respectively. In contrast to the electro-kinetic remediation strategy, which left approximately 80% of the sludge neutral or alkaline after treatment, the membrane created acidic soil conditions throughout the sludge. For example, the high field intensity used in the membrane tests may have helped to facilitate chromium desorption, dissolution, and separation from the sludge and enhanced chromium mobility. The findings show that the membrane can improve the effectiveness of chromium removal from sludge when utilized in the EK remediation process.

Environmental impact of solution pH on the formation and migration of iron colloids in deep subsurface energy systems

Deep subsurface stimulation processes often promote fluid-rock interactions that can lead to the formation of small colloidal particles that are suspected to migrate through the rock matrix, partially or fully clog pores and microfractures, and promote the mobilization of contaminants. Thus, the goal of this work is to understand the geochemical changes of the host rock in response to reservoir stimulation that promote the formation and migration of colloids. Two different carbonate-rich shales were exposed to different solution pHs (pH = 2 and 7). Iron and other mineral transformations at the shale-fluid interface were first characterized by synchrotron-based XRF mapping. Then, colloids that were able to migrate from the shale into the bulk fluid were characterized by synchrotron-based extended X-ray absorption structure (EXAFS), scanning electron microscopy (SEM), and single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS). When exposed to the pH = 2 solution, extensive mineral dissolution and secondary precipitation was observed; iron-(oxyhydr)oxide colloids colocated with silicates were observed by SEM at the fluid-shale interfaces, and the mobilization of chromium and nickel with these iron colloids into the bulk fluid was detected by sp-icpTOF-MS. Iron EXAFS spectra of the solution at the shale-fluid interface suggests the rapid (within minutes) formation of ferrihydrite-like nanoparticles. Thus, we demonstrate that the pH neutralization promotes the mobilization of existing silicate minerals and the rapid formation of new iron colloids. These Fe colloids have the potential to migrate through the shale matrix and mobilize other heavy metals (such as Cr and Ni, in this study) and impacting groundwater quality, as well produced waters from these hydraulic fracturing operations.

Release and mobility of hexavalent chromium in contaminated soil with chemical factory waste: Experiments, Cr isotope analysis and reactive transport modeling

Our study focused on the leaching processes in soil contaminated with hexavalent chromium (Cr(VI)), traced to industrial waste from a disused site and resulting in groundwater contamination. Mineral and geochemical characterization of the soil by means of XRD, SEM-EDS, total digestion and sequential extractions revealed that the main Cr content was from solid waste located in the upper meter of the soil profile. Flow-through and column experiments were carried out to investigate the processes responsible for Cr(VI) release. Cr(VI) mobility along the soil profile was also assessed. Moreover, Cr isotope signatures were used to evaluate a potential Cr(VI) reduction process, which preferably could immobilize toxic Cr(VI) complexes. One-dimensional (1D) numerical simulations reproduced the Cr(VI) release from the flow-through experiment containing the Cr(VI) rich-solid waste and also the Cr(VI) mobility along the column experiment. These results enabled us to interpret quantitatively the processes resulting in Cr(VI) contamination and mobility along the soil profile. Cr(VI) was released from dissolving Cr(VI)-rich phases (e.g., sodium chromate, Cr(VI)-hydrocalumite and Cr(VI)-ettringite) of the solid waste layer. Cr(VI) reduction and Cr(VI) adsorption did not take place along the column. Such accurate characterization of these processes is necessary for the mitigation of Cr(VI) mobility in contaminated soils.

Changes in the agrochemical parameters of sod-podzolic soils under the influence of chromium pollution and recultivation measures

In the conditions of the Udmurt Republic, field experiments (2017-2021) were carried out on the remediation of agro-podzolic loamy soil (albeluvisoils) with a high level of chromium contamination (application of 500 mg a.i./kg of soil). Both chemical and physicochemical mechanisms have been used to reduce the degree of mobility of this heavy metal in soil. Ameliorants and fertilizers (limestone and phosphate rock, superphosphate, potassium humate, peat, zeolite) in various doses were studied as ameliorative additives. Various doses of ameliorants and fertilizers were studied as ameliorative additives: limestone and phospharite meal, superphosphate, potassium humate, peat and zeolite. As a result of the research, it was found that all ameliorative additives not only caused a sharp decrease in the mobility of chromium by 40-65 %, but also had a positive effect on the agrochemical parameters of the contaminated soil. The nature and parameters of this influence were determined by their chemical composition, the rate of application, and the period that passed after the application. Limestone flour statistically significantly reduced soil acidity in contaminated soil (by 1.21-3.03 pHKCl units) and increased the total of absorbed bases by 1.7-6.5 times. Phospharite meal (by 2.1-9.1 times) and superphosphate (by 13-43 %) increased the mobile phosphorus content in the soil; peat increased the organic matter content (by 0.28-1.47 abs.%); zeolite increased the total exchangeable bases by 1.4-9.8 mmol/100g or by 12-239 %. The positive effect of these ameliorative additives, especially their increased doses, was traced during all five years of observation, what allows them to be recommended as promising ameliorants for restoring the fertility of soddy-podzolic soils contaminated with chromium.

Long-distance mobilization of chromium(III) in soil associated with submicron Cr2O3

Trivalent chromium is generally assumed to form insoluble species, resulting in low mobility of Cr(III) in soils. Here, we report continuous distributions (0–19 m) of a high concentration of Cr(III) in the alkaline soils of a historically industrial site for producing Na2Cr2O7, CrO3, and Cr2O3, which challenges this abovementioned conventional wisdom. The thermodynamic equilibrium model showed the low possibility of Cr(III) originating from Cr(VI) reduction under the redox conditions of this study. The AF4-MALLS-ICP-MS and μ-XRF-XANES were used to identify the particle size distribution of Cr(III)-containing colloids and Cr(III) species in mobile colloids. In any soil layer, Cr(III) accounts for 71.1–94.3% of the total Cr in submicron soil colloids and is composed of submicron intrinsic Cr2O3 (55.2%−63.8%), Cr(OH)3 (0–33.0%), and Cr(III) adsorbed by ferrihydrite (0–19.0%) and clay montmorillonite (11.1%−21.1%) colloid. On the contrary, Cr(VI) was mainly distributed in bulk soil (> 2 µm) except for the topsoil, accounting for 62.6–90.0% of total Cr(VI). Organic matter content and soil texture are the most critical factors driving the mobilization of submicron colloids in soils by principal component analysis. Humic acid (HA) formed HA-corona on Cr2O3 surface and enhanced colloidal dispersion, thereby accelerating the long-distance mobilization of submicron Cr2O3 colloids in alkaline soil layers, whereas the heteroaggregation of clay colloid with Cr2O3 was only favorable for short-distance mobilization. Our findings help to re-recognize the potential migration risks of insoluble heavy metals in soils.

Thermal Transformation of Natural Schwertmannite in the Presence of Chromium

Schwertmannite is a metastable mineral playing a crucial role in the immobilization of metal(oid)s in acid mine drainage (AMD) systems. High temperatures associated with wildfires could lead to a sudden schwertmannite transformation, changing the mobility of metal(oid)s. The objective of the present study was to examine the thermal transformation from schwertmannite to hematite, and the subsequent effect on the chromium partitioning. The immobilization of arsenate after thermal transformation and its implications on chromium mobility was also evaluated. Natural schwertmannite, with increasing contents of chromium, was thermally treated between 200 to 800 °C. Transformation products were characterized by solid-phase techniques and selective chemical extractions. Results indicated a transformation to hematite at temperatures above 400 °C. The presence of chromium barely affected the temperature at which the transformation occurred, although partitioning of chromium in the mineral changed with temperature. As the temperature increased from 25 °C to 400 °C, chromium was less mobile and less outcompeted by arsenic adsorption, suggesting a larger contribution of inner-sphere complexes with increasing temperature. At temperatures above 600 °C, non-mobile forms strongly associated with neo-formed hematite were found. Finally, neo-formation of hematite led to a decrease in arsenic adsorption, implying a potentially enhanced arsenic mobility in AMD systems upon wildfires.

Dual diffusive gradients in the thin films (DGT) probes provide insights into speciation and mobility of sediment chromium (Cr) from the Xizhi River basin, South China

Investigation of the speciation and remobilization mechanisms of chromium (Cr) in sediment is essential for accurate estimation of its ecological risks in aquatic systems. In this work, a three-step chemical extraction procedure and diffusive gradient in thin films (DGT) technique were combined to investigate the geochemical speciation, mobility potentials, and release characteristics of sediment Cr. The geochemical speciation of sediment Cr decreased in the following order: oxidizable > reducible > residual > acid-soluble fraction. Dissociation of OM-bound Cr(III) and oxidation by Mn oxides contributed to higher labile Cr(III) and Cr(VI) levels in winter, with the labile Cr(III) being the dominant species and accounting for 48.1%65.5% of the total concentration of labile Cr; whereas, reductive dissolution of Mn oxides was responsible for the remobilization of labile Cr(VI) in summer, leading to a shift in dominant Cr species to Cr(VI) (48.9%65.7%) due to rapid precipitation of Cr(III). Sediment acted as a major sink for labile Cr(VI) in two sampling campaigns. For labile Cr(III), sediment converted from source in winter to sink in summer. The diffusive release of labile Cr(III) deserves preferential concern due to its potential to be re-oxidized to more toxic Cr(VI) under the oxic conditions of river water in winter.

Simultaneous measurements of Cr, Cd, Hg and Pb species in ng L−1 levels by interfacing high performance liquid chromatography and inductively coupled plasma mass spectrometry

Toxicity, mobility, bioavailability and biofunctions of chromium, cadmium, mercury and lead are heavily dependent upon their specific chemical forms, leading to a high demand to metal speciation analysis rather than total quantification. Simultaneous speciation analysis of multiple metal(loid)s is attractive to a large sample capacity containing unstable analytes due to its economic and environmental advantages over the conventional single elemental strategies. In this work, an analytical method integrating online solid phase extraction into high performance liquid chromatography interfaced with inductively coupled plasma mass spectrometry (ICP-MS) to simultaneously preconcentrate and quantify Cr, Cd, Hg and Pb forms in pg L−1 levels in water was developed. Cr(III + VI), Cd(II), Hg(II), Pb(II), methylmercury (MeHg), ethylmercury (EtHg), and trimethyl (TML) and triethyl lead (TEL) were captured by the C18 adsorbent (equilibrated with 10 mL of 1.0 mM 2-hydroxyethanethiol at 10 mL min−1) and eluted by mobile phase (5.0 mM Cys at pH 2.0), then completely separated on the C18 column within 8.0 min and eventually determined by ICP-MS. Low limits of detection (0.001–0.007 ng L−1) and quantification (0.003–0.023 ng L−1), good relative standard deviations (<4%) and high enrichment factors (827–2656 folds) were obtained with good linearities. Three reference materials of total cadmium (GBW08602), total mercury (GBW08603) and total lead (GBW08601) in water were analyzed by the developed method to validate the accuracy with good agreement with certified values and satisfactory recoveries (92–100%). This method was proved feasible by the determination of Cr, Cd, Hg and Pb compounds in drinking water, river water, pond water and tap water.

Effects of tannic acid on the transport behavior of trivalent chromium in soils and its mechanism

Trivalent chromium [Cr(III)] and tannins serve as necessary substances in leather processing and coexist in tannery site, which lead to the chromium contamination in site soil when disposed improperly. However, coexisting tannins are very likely to complex with Cr(III) and affect its properties, ultimately changing the mobility of chromium in soil. In this study, tannic acid (TA) was selected to investigate the complexation with Cr(III) and the influence on the solubility and sorption of Cr(III) in soils. Then, the transport behavior and mechanism of Cr(III)-TA complexes in soil was clarified. Dialysis results showed that the increase of TA concentration and solution pH promoted the formation of complexed Cr(III). The results of UV–Vis absorption spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations indicated that the adjacent ionized phenolic hydroxyls in TA functioned as the binding sites with Cr(III) to form the Cr–O bonds and the degree of complexation increased with pH. The Cr(III)-TA complexes had higher solubility than free Cr(III) at pH ≥ 6.0. Batch sorption experiments demonstrated that the sorption capacity of Cr(III)-TA to soils with different pH was always lower than that of free Cr(III). These reasons led to the stronger mobility of Cr(III)-TA in soil columns than Cr(III). Our research reveals that the enhanced mobility of Cr(III) in soils coexisting with TA.

Effects of Alkali on Water Soluble Hexavalent Chromium in Ordinary Portland Cement.

Due to the toxicity and mobility of chromium, the disposal of chromium-containing waste is a pressing issue. Co-processing of chromium-containing waste in a cement kiln is currently one of the most effective methods. However, the presence of water-soluble hexavalent chromium (Cr(VI)) in cement limits the use of this method. In this study, Na2CO3 was used to simulate alkali in industrial raw materials to investigate the pattern of influence of alkali content on water-soluble hexavalent chromium. The mechanisms associated with the oxidation and dissolution of chromium were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma emission spectrometry (ICP-OES). The proportion of Cr(VI) in the clinker detected by XPS increased rapidly with increasing alkali content. In the cement slurry system, alkali promotes more hexavalent chromium leaching by influencing pH and other ion concentrations (Ca2+, SO42−). Therefore, the addition of alkali to either the raw meal or to the cement slurry system will favour an increase in the water-soluble Cr(VI) content. This study may provide theoretical guidance for the preparation and use of clinkers containing chromium.

Hexavalent Chromium Mobility and Distribution Behavior in Riparian Agricultural Tropical Soils: A Column Experiment

Hexavalent Chromium Mobility and Distribution Behavior in Riparian Agricultural Tropical Soils: A Column Experiment

Comparison of chromium mobility at naturally enriched and anthropogenically polluted sites: A column leaching experiment

This study aims to compare the chromium (Cr) mobility in two soils with different Cr sources. The first one is an anthropogenically contaminated soil from an area of a piston ring production factory, and the second one is a serpentine soil with a naturally increased Cr level from the National Nature Reserve Mohelno serpentine steppe in the Czech Republic. To assess the influence of naturally occurring environmental factors on the Cr mobility, two sets of column leaching experiments were constructed, namely an acidified water treatment (AW) and a simulated root exudate treatment (SRE). It was found that the anthropogenically contaminated soil leached out many times more Cr for both (the AW and SRE) treatments in comparison with the serpentine soil. Generally, all the samples showed enhanced leaching from the bottom layer, respectively the horizon, for both treatments. Only the anthropogenic soil showed some differences in the bottom layer, which was more susceptible to the AW treatment than to the SRE one. These findings show the high dependence of the leachability of Cr on the Cr content origin. It has been proven that naturally enriched sites where elevated levels of Cr originate from the bedrock are more resistant to Cr leaching than anthropogenically contaminated soils. Feasible causes of these differences are discussed in this study.