Effects of Calcium on Arsenate Adsorption and Arsenate/Iron Bioreduction of Ferrihydrite in Stimulated Groundwater

Prediction and verification of arsenic phytoavailability in paddy soil based on CD-MUSIC model in the Xiangjiang River Basin

Arsenic (As) accumulation in rice grains is primarily governed by its phytoavailability, which is major influenced by soil physicochemical properties and the surface activity of iron oxides, particularly goethite and ferrihydrite. Soil pH and the ionic strength of the soil solution are determinants of surface activity on iron oxides, which controlled the As adsorption and desorption dynamics. However, As activity is highly variable during the rice reproductive cycle, there is still a lack of approach to accurately predict and to the phytoavailability of As due to the paddy soil heterogeneity and complexity. The Charge Distribution-Multisite Complexation (CD-MUSIC) is a promising method to simulate ion adsorption behavior on iron oxide surfaces. This study applied the CD-MUSIC model to optimize soil pH and ionic strength parameters based on different scenario simulation. Subsequent linear regression analysis revealed a strong correlation (R² = 0.7664) between model-predicted dissolved As concentrations and As accumulation in rice grains. The R2 between predicted rice As with pot rice As increasing to 0.9208 after BCF (Bioconcentration Factor) corrected, demonstrating high homology between model-predicted dissolved As and bioavailable As assimilated by rice plants. To evaluate regional applicability, the model was simplified and validated across 293 sampling sites spanning the upper, middle, and lower reaches of the Xiangjiang River Basin, achieving a robust regional-scale prediction accuracy (R² = 0.6958). These results provide a feasible model for predicting rice As accumulation, which supports the safe development of regional agriculture and risk management.

Geochemistry of arsenic in soils with a focus on calcareous soils: control strategies and perspectives

Arsenic (As) contamination has become a significant environmental challenge due to the global expansion of industrial, agricultural, and mining activities, which contribute to the contamination of water, air, soils, and biota with As and other metals and metalloids. This review elucidates the geochemical behavior of As in soils, focusing on the factors influencing its dynamics and the effectiveness of various remediation techniques, particularly in calcareous soils. Calcareous soils, characterized by their unique properties, exhibit intricate interactions with As, necessitating a deeper understanding of the mechanisms driving these processes. Compared to other soil types, the bioavailability of As in calcareous soils is generally lower, largely due to their elevated pH and the presence of calcium carbonate (CaCO3). These factors contribute to the enhanced adsorption of As by soil organic and mineral components, forming less soluble As-CaCO3 complexes and decreasing As solubility. Despite this, research on As geochemistry in calcareous soils and the development of effective removal techniques still needs to be completed, emphasizing the need for further study. Additionally, this review explores future research directions in the context of As contamination and remediation, integrating case studies and advanced technologies to highlight innovative approaches for mitigating As contamination in calcareous soils.

Removal of Arsenic(V) from wastewater using calcined eggshells as a cost-effective adsorbent

This study investigates calcined eggshells (CES) as an effective adsorbent for the remediation of As(V). Characterization of CES was performed using zeta potential analysis, FTIR, XRD and SEM-EDX. Batch studies were conducted to examine the effects of pH, adsorption kinetics, and adsorption isotherms to assess efficacy. The adsorption of As(V) followed the Langmuir isotherm and pseudo-second-order kinetics, with a maximum capacity of 91.05 mg g⁻1 at pH 6.0 and 298 K. The presence of additional anions such as chloride, sulfate, or nitrate had no significant impact on the biosorption of arsenate. However, the introduction of phosphate ions notably decreased the rate of arsenic adsorption. CES was easily regenerated with an alkaline solution and showed excellent reusability over four cycles. Thermodynamic studies confirmed the spontaneity and feasibility of the biosorption process. This study highlights that CES is a promising adsorbent for As(V) removal from contaminated water.

Optimizing the dual role of biochar for phosphorus availability and arsenic immobilization in soils

Soil Phosphorus (P) fixation and Arsenic (As) contamination pose significant challenges to agriculture and environmental health. Biochar has emerged as a promising soil amendment capable of enhancing P availability while immobilizing As. This review explored the mechanisms by which biochar influences P dynamics and As sequestration. Biochar enhances P availability by reducing fixation, stimulating P-solubilizing microorganisms, and gradually releasing the adsorbed P. Specific biochars, such as Mg-modified and La-modified types, demonstrate high P adsorption capacities, reaching up to 263 mg/g, while cerium and iron-modified biochars show As adsorption efficiencies up to 99 % under certain conditions. Biochar's surface functional groups are essential for P and As adsorption through mechanisms such as surface adsorption, ligand exchange, and inner-sphere complexation. The competitive adsorption between P and As is influenced by pH, biochar modification, and co-existing anions. Under acidic conditions, As shows a higher affinity for biochar, forming stable complexes with metal oxides like iron and aluminum. Biochars modified with calcium, magnesium, lanthanum, zinc, cerium, and iron demonstrate enhanced adsorption capacities. In neutral to alkaline conditions, calcium- and magnesium-modified biochars benefit P retention, while iron-modified biochar is preferable for As adsorption. Additionally, biochar promotes microbial activity and enzymatic processes that facilitate As transformation and P mineralization, enhancing overall soil health. These findings underscore biochar's dual role in increasing nutrient availability and reducing contaminant risks, making it a valuable tool for sustainable agriculture. Field-scale applications should be prioritized in future research to optimize biochar's impact on soil fertility and environmental remediation.

Polycaprolactone-Modified Biochar Supported Nanoscale Zero-Valent Iron Coupling with Shewanella putrefaciens CN32 for 1,1,1-Trichloroethane Removal from Simulated Groundwater: Synthesis, Optimization, and Mechanism

1,1,1-Trichloroethane (1,1,1-TCA) is a typical organochloride solvent in groundwater that poses threats to human health and the environment due to its carcinogenesis and bioaccumulation. In this study, a novel composite with nanoscale zero-valent iron (nZVI) supported by polycaprolac-tone (PCL)-modified biochar (nZVI@PBC) was synthesized via solution intercalation and liquid-phase reduction to address the 1,1,1-TCA pollution problem in groundwater. The synergy effect and improvement mechanism of 1,1,1-TCA removal from simulated groundwater in the presence of nZVI@PBC coupling with Shewanella putrefaciens CN32 were investigated. The results were as follows: (1) The composite surface was rough and porous, and PCL and nZVI were loaded uniformly onto the biochar surface as micro-particles and nanoparticles, respectively; (2) the optimal mass ratio of PCL, biochar, and nZVI was 1:7:2, and the optimal composite dosage was 1.0% (w/v); (3) under the optimal conditions, nZVI@PBC + CN32 exhibited excellent removal performance for 1,1,1-TCA, with a removal rate of 82.98% within 360 h, while the maximum removal rate was only 41.44% in the nZVI + CN32 treatment; (4) the abundance of CN32 and the concentration of adsorbed Fe(II) in the nZVI@PBC + CN32 treatment were significantly higher than that in control treatments, while the total organic carbon (TOC) concentration first increased and then decreased during the culture process; (5) the major improvement mechanisms include the nZVI-mediated chemical reductive dechlorination and the CN32-mediated microbial dissimilatory iron reduction. In conclusion, the nZVI@PBC composite coupling with CN32 can be a potential technique to apply for 1,1,1-TCA removal in groundwater.

Adsorption of Arsenic, Lead, Cadmium, and Chromium Ions from Aqueous Solution Using a Protonated Chabazite: Preparation, Characterization, and Removal Mechanism

The adsorption of As(V), Pb(II), Cd(II), and Cr(III) ions from aqueous solutions on natural and modified chabazite was studied. The functionalization of chabazite was performed via a protonation and calcination with the aim of generating Lewis acid sites to improve its anion exchange properties. The surface and physicochemical properties of both adsorbents were studied and compared. The adsorption isotherms of tested heavy metal ions were quantified and modeled to identify the best isotherm equation. Steric parameters for the adsorption of these ions were also calculated with a monolayer statistical physics model. Natural chabazite showed the maximum adsorption capacity for Pb(II), while the modified zeolite improved its As(V) properties in 79%. These results showed that the modified zeolite was able to remove both cations and anions from aqueous solution. The application of this functionalized chabazite can be extended for the removal of other anionic pollutants from water, thus opening the possibility of preparing new adsorbents with tailored properties for water treatment.

Phytoremediation of arsenic contaminated soil based on drip irrigation and intercropping

A directional leaching in drip irrigation along with intercropping was developed for enhanced phytoremediation of soils contaminated with arsenic (As). Spatiotemporal variations of As levels in soil and effects of irrigation eluents on As migration were analyzed in drip irrigation. Moreover, accumulated levels of As in Zea mays L. and Brassica rapa L. ssp. chinensis (the intercropping species) under drip irrigation and flood irrigation were compared to evaluate the enhancement on phytoremediation by drip irrigation. Results showed that As exhibited a directional migration in soil under drip irrigation, in which the solution of potassium dihydrogen phosphate (PDP) as the eluent significantly promoted As directional migration in soil. Compared to the flood-irrigated intercropping treatments, the As levels in crops (Brassica rapa L. ssp. chinensis) decreased significantly and that of remediating plants (Zea mays L. seedlings) increased significantly under the drip-irrigated intercropping condition. Drip irrigation coupled with intercropping dramatically reduced the risk of As contamination in crops and improved the phytoremediation of As-contaminated soil. PDP further enhanced the disparate effect of drip irrigation on As accumulation by crops and remediation plants.