Cd Initial Concentration Research Articles

Cadmium-resistant phosphate-solubilizing bacteria immobilized on phosphoric acid-ball milling modified biochar enhances soil cadmium passivation and phosphorus bioavailability

Cadmium (Cd) can accumulate in agriculture soil from the regular application of phosphorus (P) fertilizer. Microbiological method is considered as a potentially effective strategy that can not only remediate the Cd-contaminated soil but also provide the phosphorus needed for crop growth. However, the toxicity of Cd may affect the activity of microorganisms. To solve this problem, Klebsiella variicola with excellent phosphate solubilization ability (155.30 mg L−1 at 48 h) and Cd adsorption rate (90.84 % with 10 mg L−1 Cd initial concentration) was firstly isolated and identified in this study. Then, a phosphoric acid and ball milling co-modified biochar (PBC) was selected as the carrier to promote the activities of K. variicola under Cd pollution. Surface characterization revealed that the promotion of K. variicola by PBC was mainly attributed to the large specific surface area and diverse functional groups. Compared to contaminated soil, microbial PBC (MPBC) significantly increased the pakchoi biomass and phosphorus (P) content, while the Cd content in leave and root of pakchoi (Brassica chinensis L.) decreased by 25.90–43.46 % (P < 0.05). The combined application also favored the transformation of the resistant P fractions to bioavailable P, and facilitated the immobilization of 20.12 % exchangeable Cd to reducible, oxidizable, and residual Cd in the treated soil. High-throughput sequencing revealed that the response of the soil microbial community to the MPBC was more beneficial than K. variicola or PBC alone. Therefore, the application of MPBC has the potential to act as an efficient, stable, and environmentally friendly sustainable product for Cd remediation and enhanced P bioavailability in agricultural production.

Synthesis of fungal chitosan-polystyrene modified by nanoparticles of binary metals for the removal of heavy metals from waste aqueous media.

The objective of this study was to assess the efficacy of fungal chitosan-polystyrene-Co-nanocomposites (FCPNC) as a material for the adsorptive removal of cadmium (Cd) ions from aqueous solutions. The synthesis and characterization of FCPNC were accomplished using various analytical techniques, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and dynamic light scattering (DLS). The effectiveness of this adsorbent in removing Cd(ii) species from solution matrices was systematically investigated, resulting in the achievement of a maximum adsorption capacity of approximately 112.36 mg g-1. This high adsorption capacity was detected using the following operational parameters: solution pH equals 5.0, 60 min as a contact time between the adsorbent and Cd(ii) solution, Cd initial concentration of 50 ppm, adsorbent dosage of 0.5 g L-1 and room temperature. The process of cadmium adsorption by FCPNC was found to follow the Langmuir isotherm model, suggesting that a chemical reaction occurs on the biosorbent surface. Kinetic studies have demonstrated that the cadmium removal process aligns well with the pseudo-second-order model. The thermodynamic analysis revealed the following values: ΔH° = 25.89 kJ mol-1, ΔG° = -21.58 kJ mol-1, and ΔS° = 159.30 J mol-1 K-1. These values indicate that the sorption process is endothermic, spontaneous, and feasible. These findings suggest the potential of FCPNC as an exceptionally effective biosorbent for the removal of water contaminants.

Cadmium and zinc uptake by dried activated sludge: Equilibrium and experimental design study

Removal of Cd2+ and Zn2+ ions from single and binary solutions by dried activated sludge was studied in batch experiments. It was shown that the metal removal is a rapid process significantly influenced by solution pH. Maximum uptake of both Cd and Zn was reached at pH 6.0 and negligible uptake was observed at pH 2.0. The Langmuir isotherm was found to well represent the measured equilibrium sorption data in single metal systems and the maximum sorption capacities Qmax of the activated sludge (d.w.), calculated from Langmuir model were 540 ± 16 μmol/g for Zn2+ and 510 ± 17 μmol/g for Cd2+ ions. The Response surface methodology (RSM) was used for investigation of interaction and competitive effects in binary metal system. It was found that dried activated sludge in binary system Cd-Zn has slightly higher affinity for Cd2+ comparing with Zn2+ ions. Competitive effect of Cd on Zn uptake increased with increasing solution pH and Cd initial concentration. Maximum sorption capacities of the activated sludge were 321 μmol Cd2+/g and 312 μmol Zn2+/g. RSM appears to be a better tool for the evaluation of interaction and competitive effects in binary systems than both the simple extrapolation from single-component systems and experimentally difficult study of multi-component systems.

Removal of cadmium from aqueous solution using sonochemically modified clinoptilolite: Optimization and modeling

Abstract Clinoptilolite (CL) has been sonochemically modified by using NaCl solution and applying a 35 kHz ultrasound in 30 min and at 60 o C. The modified clinoptlolite (SNa–CL) has been characterized by X-ray diffraction (XRD), laser scattering, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and nitrogen adsorption/desorption isotherms. Results showed that the sonochemical modification process could reduce particle size, enhance effective cation exchange capacity from 0.10 to 1.58 meq/g, and enlarge the surface area of CL from 31.14 to 37.25 m2/g The cadmium removal efficiency of the modified CL was optimized using response surface methodology (RSM) with central composite design (CCD). Under the optimal condition with pH of 6.3, the contact time of 309 min, Cd initial concentration of 79.41 mg/L, and SNa–CL dosage of 7.02 g/L, the removal efficiency reached 99%. The adsorption kinetics was obeyed the second-order model and controlled by multiple steps. The adsorption isotherms were well fitted to the Langmuir model and the maximum adsorption capacity at different temperatures was more than 20 mg/L. The thermodynamic study showed that the adsorption of Cd onto SNa–CL was a spontaneous, endothermic, and physical–chemical process. The results in this work suggested that the sonochemical modification is a potential method for fabricating effective and low-cost adsorbents from natural resources.

The removal of Cd by sulfidated nanoscale zero-valent iron: The structural, chemical bonding evolution and the reaction kinetics

In this study, the microstructure of sulfidated nanoscale zero-valent iron (S-nZVI), and the reaction mechanism with cadmium (Cd) were investigated. Combining with spherical aberration-corrected scanning transmission electron microscope (Cs-STEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transformed infrared (FTIR), it was found that the one-step synthesized S-nZVI with Na2S as the sulfidation reagent is irregular in shape and consisted of heterogeneous mixtures of Fe0, amorphous FeS, and Fe3O4. The dominant reaction mechanism between S-nZVI and Cd is displacement of Fe in FeS and the formation of CdS. The effects of Cd initial concentration, Mg2+, NO3−, and humic acid (HA) on the reaction kinetics were also studied. The removal capacity of Cd by S-nZVI can reach up to 495 mg/g, which is significantly higher than other S-nZVI and adsorbents. The reactions follow pseudo-second-order adsorption model, with chemisorption as the rate limiting step during the displacement reaction. Low concentration of Mg2+ (<30 mg/L), NO3− (<60 mg/L), and HA (<10 mg/L) slightly decreases the removal of Cd due to the competition. Moreover, S-nZVI shows high efficiency and stability towards the removal of both free Cd ions and EDTA-chelated Cd during the concentration investigated. Overall, the study shows that sulfur plays a critical role in the particle microstructure and transformation of Cd in the environment.

Remediation of cadmium contaminated water and soil using vinegar residue biochar.

This study investigated a new biochar produced from vinegar residue that could be used to remediate cadmium (Cd)-contaminated water and soil. Aqueous solution adsorption and soil incubation experiments were performed to investigate whether a biochar prepared at 700°C from vinegar residue could efficiently adsorb and/or stabilize Cd in water and soil. In the aqueous solution adsorption experiment, the Cd adsorption process was best fitted by the pseudo-second-order kinetic and Freundlich isotherm models. If the optimum parameters were used, i.e., pH5 or higher, a biochar dosage of 12gL-1, a 10mgL-1 Cd initial concentration, and 15-min equilibrium time, at 25°C, then Cd removal could reach about 100%. The soil incubation experiment evaluated the biochar effects at four different application rates (1, 2, 5, and 10% w/w) and three Cd contamination rates (0.5, 1, and 2.5mgkg-1) on soil properties and Cd fractionation. Soil pH and organic matter increased after adding biochar, especially at the 10% application rate. At Cd pollution levels of 1.0 or 2.5mgkg-1, a 10% biochar application rate was most effective. At 0.5mg Cdkg-1 soil, a 5% biochar application rate was most efficient at transforming the acid extractable and easily reducible Cd fractions to oxidizable and residual Cd. The results from this study demonstrated that biochar made from vinegar residue could be a new and promising alternative biomass-derived material for Cd remediation in water and soil.