Initial Cd Concentration Research Articles

Synergistic passivation performance of cadmium pollution by biochar combined with sulfate reducing bacteria

The use of sulfate-reducing bacteria (SRB) for the remediation of Cd-contaminated soil is an attractive option. However, there are various factors that limit the activity of free SRB in soil, which hinders the rapid reduction of sulfate. The immobilized SRB technology has been proposed as a possible solution to overcome this barrier. This study aimed to isolate an Enterobacter sp. strain (SRB15-3-2) with high resistance to Cd2+ from a tailing. Wheat, maize, and rice straws were selected to prepare biochar for inoculating the screened bacteria. The results showed that wheat straw biochar pyrolyzed at 700 °C (WS700) had the highest performance in carrying SRB for Cd2+ immobilization. Furthermore, the WS700 was found to promote SRB15-3-2 for offering S2− and functional groups (C-S, C=O, C=C, C-C=O, and C-O-C, etc.) during the immobilization process. The immobilized SRB with WS700 (ISRBWS700) agglomerated and reacted with Cd2+ to form metal precipitations, predominantly CdS and CdCO3. Which lead to a significant decrease of exchangeable-Cd in contaminated soil (with initial Cd concentrations of 1, 5, and 20 mg/kg) by 18.5%–31.6% after applying the ISRBWS700, indicating that the indigenous soil microbes were been protected from Cd toxicity. Additionally, ISRBWS700 exhibited a synergistic effect in enhancing SRB15-3-2 propagation and the activities of saccharase, urease, and acid phosphatase, compared to the separate treatment of SRB15-3-2 and WS700. Overall, ISRBWS700 prepared in this study represented an accessible way to resolve Cd-contaminated soil, which provided new theoretical insights into eco-friendly technologies for Cd-polluted soil remediation both in development and sustainable aspects.

Rapid and efficient removal of Cd(II) from aqueous solution in a wide range pH by sodalite type sorbents using cellulose superfine fiber as a template agent

Sodalite is a common zeolite, which is often discarded or ignored due to its small pore size and poor adsorption capacity. In this study, two sodalite type materials, CSF-S and N-CSF-S, were synthesized using cellulose superfine fiber (CSF) as template. Its unique scaly structure not only enhances its adsorption capacity for Cd (II), but also improves its adsorption efficiency. At 298 K and the initial Cd (II) concentration of 100 mg/L, the adsorption equilibrium of CSF-S was achieved within 30 min, which is 98% shorter than that of traditional sodalite. The adsorption of Cd (II) by CSF-S and N-CSF-S is an endothermic process and at 298 K the adsorption capacity could be as high as 260.1 and 284.1 mg/L, respectively, which were 1.9 and 2.0 times of the original sodalite, far higher than the reported similar adsorbents, and competitive to over other types of adsorbents. In addition, with low zero points of charge CSF-S (pHzpc around 1) and N-CSF-S (pHzpc around 3) can effectively remove Cd(II) over a wide pH range, superior to most zeolitic sorbent materials. Therefore, this work proposes a simple and cost-effective synthesis method for the sodalite type sorbents with high Cd(II) adsorption capacity and rapid adsorption rate, and also provides some basis for the study of heavy metal adsorption materials in aqueous systems.

Use of thermally activated Fenton sludge for Cd removal in zinc smelter wastewater: Mechanism and feasibility of Cd removal

Fenton sludge is a byproduct of the Fenton process that contains large amounts of Fe and Ca. Because of the secondary contamination generated during the disposal of this byproduct, ecofriendly treatment methods are needed. In this study, we used Fenton sludge to remove the Cd discharged from a zinc smelter factory, using thermal activation to enhance the Cd adsorption capacity. Among the various temperatures considered (300–900 °C), the Fenton sludge that was thermally activated at 900 °C (TA–FS–900) adsorbed the highest amount of Cd because of its high specific surface area and high Fe content. Cd was adsorbed onto TA–FS–900 via complexation with C–OH, C–COOH, FeO−, and FeOH and cation exchange with Ca2+. The maximum adsorption of TA–FS–900 was 260.2 mg/g, indicating that TA–FS–900 is an efficient adsorbent, comparable to those reported in the literature. The initial Cd concentration in the zinc smelter wastewater discharged was 105.7 mg/L, 98.4% of which was removed by applying TA–FS–900, suggesting the applicability of TA–FS–900 for real wastewater containing high concentrations of various cations and anions. The leaching of heavy metals from TA–FS–900 was within the EPA standard limits. We concluded that the environmental impact of Fenton sludge disposal can be reduced, and the use of Fenton sludge can add value to the treatment of industrial wastewater in terms of the circular economy and environment.

Enhanced photocatalytic removal of Cd(II) from aqueous solution using Bi/S co-doped carbon quantum dots

In this study, S and Bi Co-doped carbon quantum dots were synthesized and their application for Cd(II) removal was investigated. All the experiments were performed in batch mode and effect Bi/S ratio on pH was investigated. It was observed that 12 pH is most suitable for fast removal of Cd2+. The optimized Bi/S ratio was further investigated for effect of adsorbent dosage, initial concentration of Cd(II). Addition of four scavenger solvent namely formaldehyde, acetic acid, ethanediamine and methanol was investigated for enhancement in the photocatalytic activity. Maximum removal efficiency was observed with ethandiamine ∼94% at 300 ppm as compared to formaldehyde (∼90.3%), methanol (∼86.7%) and acetic acid(∼86.3%) indicating that amine group is more suitable as scavenger molecule. Adsorption isotherms of Cd(II) on Bi/S doped on CQD were fitted for different adsorption isotherm model namely Langmuir, Freundlich and Temkin isotherms. Both Lanmguir and Temkin isotherm were observed to fit well with R2 value above 98% as compared to Freundlich with lower R2 value (∼95.3%), indicating that a combination of chemisorption phenomenon as well as availability of energy of electron could be responsible for the Cd(II) removal. Thermodynamic parameters both enthalpy change and entropy change were estimated as −10.76 kJ/mol and −11.2 kJ/mol K. All three parameters were negative indicating that the process was spontaneous and exothermic.

First principal observation documenting the three-dimensional uptake of cadmium and spatial distribution of cadmium hydroxyapatite mineral in bone char

The 3-D matrix scale ion-exchange mechanism was explored for high-capacity cadmium (Cd) removal using bone chars (BC) chunks (1–2 mm) made at 500 °C (500BC) and 700 °C (700BC) in aqueous solutions. The Cd incorporation into the carbonated hydroxyapatite (CHAp) mineral of BC was examined using a set of synchrotron-based techniques. The Cd removal from solution and incorporation into mineral lattice were higher in 500BC than 700BC, and the diffusion depth was modulated by the initial Cd concentration and charring temperature. A higher carbonate level of BC, more pre-leached Ca sites, and external phosphorus input enhanced Cd removal. The 500BC showed a higher CO32-/PO43- ratio and specific surface area (SSA) than the 700BC, providing more vacant sites by dissolution of Ca2+. In situ observations revealed the refilling of sub-micron pore space in the mineral matrix because of Cd incorporation.The X-ray nanodiffraction (XND) analyses revealed that Cd was mainly removed from water by incorporation into the mineral lattice of 500BC via ion exchange, rather than surface sorption and precipitation, and the mineral phase was transformed from hydroxyapatite (HAp) to cadmium hydroxyapatite (Cd-HAp). The Rietveld's refinement of X-ray diffraction (XRD) data resolved up to 91% of the crystal displacement of Ca2+ by Cd2+. The specific phase and stoichiometry of the new Cd-HAp mineral was dependent on the level of ion exchange. This mechanistic study confirmed that 3-D ion exchange was the most important path for heavy metal removal from aqueous solution and immobilization in BC mineral matrix, and put forward a novel and sustainable remediation strategy for Cd removal in wastewater and soil clean-up.

Adsorption of cadmium (II) from aqueous solutions by coconut dregs residue: Kinetic and thermodynamic studies

ABSTRACT In this study, the potential of coconut dregs residue (CDR) as a low-cost biosorbent for the removal of cadmium (II) from aqueous solutions was investigated. The removal efficiency of Cd (II) by CDR was tested through batch adsorption experiments under different conditions including contact time, initial pH, initial Cd (II) concentration, adsorbent dose, and temperature. The optimal pH for removal was found to be 7.0 where an 87.6% removal was achieved with a metal concentration of 25 ppm, a 0.5 g/100.00 cm3 adsorbent dosage, and a 250–500 µm particle size within 120 minutes at 303 K. The Freundlich isotherm model was employed to explain the adsorption process, while the pseudo-second-order model proved to be the best-fit kinetic model. Results showed that the Gibbs free energy change in Cd (II) adsorption was −5.4 kJ mol−1 indicating a spontaneous process. The raw CDR exhibited an adsorption capacity of 4.31 mg/g. Scanning electron microscopic (SEM) analysis revealed the presence of tubular voids which contributed to the adsorption process. Additionally, activated carbon prepared from CDR showed a higher removal efficiency of 95.6% for Cd (II) as compared to the raw CDR biosorbent.

Adsorption of Cd (II) by a novel living and non-living Cupriavidus necator GX_5: optimization, equilibrium and kinetic studies

Biosorbents have been extensively studied for heavy metal adsorption due to their advantages of low cost and high efficiency. In the study, the living and non-living biomass of Cupriavidus necator GX_5 previously isolated were evaluated for their adsorption capacity and/or removal efficiency for Cd (II) through batch experiments, SEM and FT-IR investigations. The maximum removal efficiency rates for the live and dead biomass were 60.51% and 78.53%, respectively, at an optimum pH of 6, a dosage of 1 g/L and an initial Cd (II) concentration of 5 mg/L. The pseudo-second-order kinetic model was more suitable for fitting the experimental data, indicating that the rate-limiting step might be chemisorption. The Freundlich isotherm model fit better than the Langmuir isotherm model, implying that the adsorption process of both biosorbents was heterogeneous. FT-IR observation reflected that various functional groups were involved in Cd (II) adsorption: –OH, –NH, C=O, C–O and C–C groups for the living biomass and –OH, –NH, C–H, C = O, C–N and N–H groups for the dead biomass. Our results imply that non-living biosorbents have a higher capacity and stronger strength for absorbing Cd (II) than living biomass. Therefore, we suggest that dead GX_5 is a promising adsorbent and can be used in Cd (II)-contaminated environments.

Development and Characterization of Biosorbent Film from Eggshell/Orange Waste Enriched with Banana Starch.

The conversion of waste into a valuable product is regarded as a promising alternative to relieving the burden of solid waste management and could be beneficial to the environment and humans. This study is focused on utilizing eggshell and orange peel enriched with banana starch to fabricate biofilm via the casting technique. The developed film is further characterized by field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The physical properties of films, including thickness, density, color, porosity, moisture content, water solubility, water absorption, and water vapor permeability, were also characterized. The removal efficiency of the metal ions onto film at different contact times, pH, biosorbent dosages, and initial concentration of Cd(II) were analyzed using atomic absorption spectroscopy (AAS). The film's surface was found to have a porous and rough structure with no cracks, which can enhance the target analytes interactions. EDX and XRD analyses confirmed that eggshell particles were made of calcium carbonate (CaCO3), and the appearance of the main peak at 2θ = 29.65° and 2θ = 29.49° proves the presence of calcite in eggshells. The FTIR indicated that the films contain various functional groups, such as alkane (C-H), hydroxyl (-OH), carbonyl (C=O), carbonate (CO32-), and carboxylic acid (-COOH) that can act as biosorption materials. According to the findings, the developed film exhibits a notable enhancement in its water barrier properties, thereby leading to improved adsorption capacity. The batch experiments showed that the film obtained the maximum removal percentage at pH = 8 and 6 g of biosorbent dose. Notably, the developed film could reach sorption equilibrium within 120 min at the initial concentration of 80 mg/L and remove 99.95% of Cd(II) in the aqueous solutions. This outcome presents potential opportunities for the application of these films in the food industry as both biosorbents and packaging materials. Such utilization can significantly enhance the overall quality of food products.

Removal of cadmium from aqueous solution using nano Prosopis cineraria leaf ash (NPCLA)

Background: Heavy metal pollution has become one of the most severe environmental problems, therefore, the present study was conducted to investigate removal of cadmium (Cd) from aqueous solution. Methods: In the present study, nano Prosopis cineraria leaf ash (NPCLA) was used as an adsorbent for removing Cd from aqueous solution. Contact time, initial pH of the solutions, sorbent dosages, and initial Cd (II) concentration were considered as parameters affecting Cd removal efficiency. The experiments were designed by Design of Expert (DOE) software. Results: It was revealed that an NPCLA dosage of 2.45 gL-1, pH of 6.3, and initial Cd (II) concentration of 20.7 mgL-1 in contact time of 60 min was the optimum condition for removal of Cd (II) in the domain of experiments and at this optimum condition, the prediction value of removal efficiency was found 99.9%. Based on the results of kinetics experiments, the sorption system and experiment data of Cd (II) adsorption on the NPCLA followed the pseudo-second-order kinetic model. Freundlich, Langmuir, Brunauer-Emmett-Teller (BET), and Temkin isotherm models were investigated. The equilibrium adsorption data were fitted well with linearly transformed Langmuir isotherm with a correlation coefficient of R2=0.9877, and the maximum sorption capacity of NPCLA was obtained to be 25.25 mgg-1. Conclusion: In laboratory conditions, NPCLA can remove Cd from aqueous solution with a high efficiency. Therefore, due to this plant’s availability and cheapness, NPCLA can be considered a suitable option for producing adsorbents on industrial scales.

Partitioning and transformation behavior of Cd(II) and As(V) during As(V)-Cd(II)-Fe(III) coprecipitation: Effect of aging under aerobic conditions at pH 5 and 11 relevant to tailings and acid waste

Aerobic coprecipitation and subsequent aging of the As(V)-Cd(II)-Fe(III) system are ubiquitous processes in engineered settings, natural shallow water, surficial soils, and mine tailings. Herein, we have investigated the partitioning of As(V) and Cd(II) coupled with the solid evolution during As(V)-Cd(II)-Fe(III) coprecipitation and subsequent aging process under aerobic conditions at different pH (5 and 11) and Fe(III)/As(V) ratios (10 and 40) with various Cd(II) concentrations at 90 °C. X-ray diffraction and transmission electron microscopy results reveal that ferrihydrite is the dominant phase in the initial coprecipitates, regardless of pH and the coexisting As(V) and Cd(II). Low pH and high Fe(III)/As(V) ratios favor the transformation of initial ferrihydrite to hematite during the aging process, which can further promote the incorporation of ferrihydrite-bound As(V) and Cd(II) into stable hematite. Chemical analyses indicate that the partitioning fractions of adsorbed/extractable and solid-incorporated As(V) and Cd(II) are controlled by pH, Fe(III)/As(V) ratio, and aging time during ferrihydrite transformation. High Fe(III)/As(V) ratios facilitate the incorporation of the extractable Cd(II) into the aging intermediates, whereas the As(V) partitioning is less affected by the initial Cd(II) concentration. The crystallization rates of ferrihydrite at high Fe(III)/As(V) ratios or low pH are higher than those at low Fe(III)/As(V) ratios or high pH. Furthermore, increased Cd(II) concentrations significantly reduce the crystallization rates of the initial ferrihydrite. These findings have shed new light on the mobility and transformation behavior of toxic As(V) and Cd(II) in the As(V)-Cd(II)-Fe(III) coexisting environment under aerobic conditions and are useful for developing novel As(V)-Cd(II)-compound contaminant management strategies for metallurgical waste residues and water treatment sludges.

Novel and sustainable green sulfur-doped carbon nanospheres via hydrothermal process for Cd (II) ion removal

Herein, the synthesis, characterization, and adsorption performance of a novel green sulfur-doped carbon nanosphere (S-CNs) is studied to eliminate Cd (II) ions from water effectively. S-CNs were characterized using different techniques including Raman spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), , Brunauer–Emmett–Teller (BET) specific surface area analysis and Fourier transform infrared spectrophotometry (FT-IR), were performed. The efficient adsorption of the Cd (II) ions onto S-CNs strongly depended on pH, initial concentration of Cd (II) ions, S-CNs dosage, and temperature. Four isotherm models (Langmuir, Freundlich, Temkin & Redlich Peterson) were tested for modeling. Out of four, Langmuir showed more applicability than the other three models, with a Qmax value of 242.72 mg/g. Kinetic modeling studies suggest a superior fit of the obtained experimental data with the Elovich equation (linear) and pseudo-second-order (non-linear) rather than other linear and non-linear models. Data obtained from thermodynamic modeling indicates that using S-CNs for Cd (II) ions adsorption is a spontaneous and endothermic . The current work recommends using better and recyclable S-CNs to uptake excess Cd (II) ions.

A Novel Chitosan/Nano-Hydroxyapatite Composite for the Adsorptive Removal of Cd(II) from Aqueous Solution.

A novel polymer bio-composite based on nano-hydroxyapatite (n-Hap) and chitosan (CS) (CS/n-Hap) was synthesized to effectively address toxic cadmium ions removal from water. The composition and structure of CS/n-Hap bio-composite were analyzed through different characterization techniques. XRD patterns affirmed that the crystalline structure of n-Hap remained unaltered during CS/n-Hap synthesis, while FT-IR spectrum sustained all the characteristic peaks of both CS and n-Hap, affirming the successful synthesis of CS/n-Hap. Adsorption studies, including pH, adsorbent dosage, contact time, initial Cd(II) concentration, and temperature, were carried out to explain and understand the adsorption mechanism. Comparatively, CS/n-Hap bio-composite exhibited better Cd(II) adsorption capacity than pristine CS, with an experimental maximum uptake of 126.65 mg/g under optimized conditions. In addition, the kinetic data were well fitted to the pseudo-second-order model, indicating the formation of chemical bonds between Cd(II) and CS/n-Hap during adsorption. Furthermore, the thermodynamic study suggested that Cd(II) adsorption onto CS/n-Hap was endothermic and spontaneous. The regeneration study showed only about a 3% loss in Cd(II) uptake by CS/n-Hap after five consecutive cycles. Thus, a simple and facile approach was here developed to synthesize an eco-friendly and cost-effective material that can be successfully employed for the removal of toxic heavy metal ions from water.

Effect of salinity on the potential cadmium phytoremediation from the polluted soil by carpobrotus rossii

Nowadays, toxic metals accumulation in soil texture due to anthropogenic activities is a major form of pollution, which can lead to worldwide concerns; however, there are many treatment methods to remove them from soil such as phytoremediation. The carpobrotus rossii, has shown great potential to tolerate high salinity and accumulate Cd from contaminated soils. The experiments, in this study, are analyzed and optimized by Central Composite Design (CCD) as method and using Response Surface Methodology (RSM) package in R software. The Cd removal by root and the whole plant followed the quadratic model and the R2 values were 94.95 and 94.81, respectively. The results showed that a decrease in NaCl concentration in Cd-containing solution can increase the phytoremediation process of Cd by carpobrotus rossii, significantly. The optimum conditions for 58% Cd removal by the whole plant, predicted through a CCD response surface methodology model were as follows: initial Cd concentration of 49 mgKg−1,NaCl concentration of 16 dSm−1, time of 17 days, and pH of 6.5. C. rossii's potential in removing 58% of Cd under the obtained optimum condition from the modelling was evaluated in real condition in the laboratory. The results revealed that around 56% of the initial added Cd concentration was removed by carpobrotus rossii. As a take home message, carpobrotus rossii can be recommended as an efficient plant to remove heavy metals especially cadmium from soil and sediments in arid area which have a salty soil.

Succinylated Salvia spinosa hydrogel: Modification, characterization, cadmium-uptake from spiked high-hardness groundwater and statistical analysis of sorption data

Herein, we synthesized sodium salt of succinylated Salvia spinosa hydrogel (NaS-SSH), a novel and green polysaccharide-based ion-exchanger for cadmium uptake from deionized water (DW) and spiked high-hard ground water (HGW). The S. spinosa hydrogel (SSH), succinylated SSH (S-SSH) and its sodic form (NaS-SSH) were characterized through Fourier transform infrared spectroscopy, solid-state CP/MAS 13C-NMR spectroscopy, scanning electron microscopy-energy dispersive spectroscopy, and thermogravimetric analysis. The surface charge on NaS-SSH was calculated by performing point of zero charge pH, i.e., pHZPC analysis and it was found to be 4.77 ± 0.35. Cd(II) uptake efficiency of NaS-SSH was accessed on pH (1–7), sorbent dosage (10–90 mg/100 mL), initial concentration of Cd(II) ions (10–250 mg L−1), contact time (5–150 min), and temperature (298–338 K). Sorption data fitted well to Langmuir isothermal model and sorption maxima (Qmax) was calculated as 344.83 mg g−1 for DW and 312.5 mg g−1 for HGW and found comparable with the experimental sorption capacities. The sorption kinetics followed the pseudo-second-order kinetic model and occurred through the exchange of ions via chemisorption. Thermodynamics of the sorption process was judged through negative values of thermodynamic triplets (ΔG°, ΔH°, and ΔS°) and revealed spontaneous and exothermic in nature. Competitive studies indicated the potential of NaS-SSH for metal removal from a binary mixture of Ni(II)-Cd(II). Moreover, NaS-SSH was regenerated and could be used over several repetitive cycles. Comparing the sorption efficiency of NaS-SSH with already reported succinylated biosorbents having similar structural features, it was noted that our developed biosorpbent is more effective for Cd(II) uptake.

The Effect of Metals of the 2nd and 12th Groups on the Productivity and Selectivity of Cumene Oxidation—The First Stage of the Technological Chain for the Production of Polymer Composites

The effect of the process temperature and the initial concentration of Mg, Ca, Sr, Ba, Zn, Cd, and Hg 2-ethylhexanoates as catalysts on the productivity and selectivity of the oxidation stage of cumene is studied in the technological chain for the production of polymer composites from cumene; “production of phenol by cumene method (stage 1 is cumene oxidation to cumene hydroperoxide, stage 2 is decomposition of cumene hydroperoxide into phenol and acetone) → production of precursors from phenol → production of polymers from precursors → production of composites from polymers”. A criterion has been introduced that reflects the productivity of cumene oxidation at the moment of reaching the maximum concentration of cumene hydroperoxide, which takes into account the cumene conversion and selectivity achieved in this case in the shortest possible time using the selectivity comparable with the selectivity of a non-catalytic process. It has been shown that the achievement of the maximum value of this criterion, among all the considered catalysts, is ensured by Mg 2-ethylhexanoate at its relatively low initial concentration (1 mmol/L) under conditions of moderately-high process temperatures (393–413 K).

Recyclable magnetic nanocomposites for efficient removal of cadmium ions from water: performance, mechanism and isotherm studies

ABSTRACT Herein, succinic acid functionalized Fe3O4@AMPA nanocomposite was synthesized as an effective adsorbent and used for the efficient removal of Cd(II) ions from aqueous media. Zeta potential, BET, TEM, TGA, and FTIR spectra were applied to characterize the Fe3O4@AMPA@SA nanocomposite. According to the BET analysis, the surface area of Fe3O4@AMPA@SA was found to be 43 m2/g. The influence of pH value, initial Cd(II) concentration, adsorbent dosage, temperature, and contact time on the adsorption process was achieved via the batch experiment method. The result showed that the optimal parameters were 6, 250 mg/L, 0.03 g/50 mL, 150 min, and 25°C, respectively. The experimental data fitted well to the Langmuir isotherm and the pseudo-first-order models. The maximum monolayer adsorption capacity of Cd(II) ions was 265 mg g−1. The adsorption mechanism of Cd(II) on magnetic nanocomposite is physical adsorption. The Fe3O4@AMPA@SA nanocomposite shows excellent reusability with a removal efficiency of 81.4% after three cycles.

Anaerobic syntrophic system composed of phosphate solubilizing bacteria and dissimilatory iron reducing bacteria induces cadmium immobilization via secondary mineralization

Secondary mineralization is a promising method for remediating cadmium (Cd) pollution in sediments, but the poor stability of Cd-containing secondary minerals is a bottleneck that limits the development of this approach. The existence of phosphate can enhance the formation of stable secondary minerals and points a new direction for Cd immobilization. In this research, a novel syntrophic system composed of phosphate solubilizing bacteria (PSB) and dissimilatory iron reducing bacteria (DIRB) was established and the effect and mechanism of Cd immobilization in the system were also explored. The results showed that under the conditions of DIRB:PSB (V:V)= 3:1, syntrophic bacteria dosage of 5% and glucose dosage of 5 g/L, Cd incorporated in the secondary minerals could account for about 60% of the total Cd. In the pH range of 5–9, alkaline environment was conducive to the immobilization of Cd and the percentage of combined Cd was up to 58%, while the combined Cd in secondary minerals decreased from 62% to 56% with the increase of initial Cd concentration from 0.1 to 0.3 mmol/L. In addition, XRD, XPS, Mössbauer and other characterization results showed that secondary minerals, such as Cd exchange hydroxyapatite (Cd-HAP) and kryzhanovskite (Fe3(PO4)2(OH)3) were formed in this new system. The established syntrophic system of PSB and DIRB is thus a prospective bioremediation technology for Cd immobilization in sediments and can avoid the potential risk might be caused by the addition of phosphorus-containing materials.

Highly efficient preferential adsorption of Pb(II) and Cd(II) from aqueous solution using sodium lignosulfonate modified illite.

In this study, sodium lignosulfonate modified illite (LS-ILT), an environmentally friendly adsorbent, was prepared by hydrothermal modification. An extensive study of Pb(II) and Cd(II) adsorption behavior and the mechanisms were conducted by evaluating the effects of initial pH value, sorbents dosage, and initial concentration of Pb(II) and Cd(II). Results showed that the adsorption characteristics of Pb(II) and Cd(II) by LS-ILT were well described by quasi-second-order kinetics and the Freundlich model, and the maximum adsorption capacity of Pb(II) and Cd(II) was 42.3mg/g and 17.0mg/g, respectively. The optimal application conditions for adsorption equilibrium were the dosage of 4g/L and reaction pH = 5.5-5.8. The adsorption stability of Pb(II) by LS-ILT was better than that of Cd(II), and most of the existence of coexisting cations had no obvious inhibitory effect on the removal of Pb(II) and Cd(II). Furthermore, the dynamic adsorption results showed that LS-ILT can meet the ultra-low emission standard, and the adsorption capacity could maintain over 50% after four cycles, further providing certain guiding significance for the treatment of wastewater with ultra-low concentrations of heavy metals Pb(II) and Cd(II).

Efficiency, mechanism and microbial community of Cd(II) removal by mixed bacteria enriched from heavy metals mine soil

Mixed bacteria were enriched from heavy metals mine soil for cadmium (Cd(II))-containing wastewater treatment. Batch adsorption experiment results showed that the optimal pH, temperature, initial Cd(II) concentration, and biomass dosage were 6.0, 30 °C, 20 mg/L, and 1 g/L, respectively. Living biomass exhibited better Cd(II) removal efficiency (91.97%) than autoclaved biomass (79.54%) under optimal conditions. The isotherms and kinetics of living biomass conformed to the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. FTIR results implied that amine groups, hydroxyl groups and phosphoric acid play an important role in the Cd(II) adsorption process, while XRD results showed that crystalline Cd(OH)2 and CdO were obtained. After Cd(II)-containing wastewater treatment exposure, the dominant bacteria genera included Comamonas (39.94%), unclassified_f__Enterobacteriaceae (34.96%), Ochrobactrum (14.07%), Alcaligenes (4.84%), Bordetella (2.07%), Serratia (1.04%), and Bacillus (1.01%). Function prediction showed that the abundance of metabolic genes changed significantly. This study proposes the potential application of mixed bacteria for Cd(II)-containing wastewater treatment.

Adsorption of cadmium(II) in wastewater by magnesium oxide modified biochar

A new MgO-AC (magnesium oxide modified activated carbon) adsorbent was successfully synthesized under microwave irradiation. XRD, FT-IR, XPS, SEM and N2 adsorption were used to characterize the properties of MgO-AC. It was found that MgO-AC was highly crystalline under the preparation process, and the doping of MgO (Magnesium oxide) did not cause the gap blockage of AC (activated carbon), but the micropore area and average pore size of modified AC increased significantly. Multiple conditional parameters were studied to determine the optimal adsorption effect, such as roasting temperature, holding time, MgO doping amount, contact time, adsorption temperature, system pH, and initial concentration of Cd(II) (divalent cadmium ion). The results show that the optimal parameter conditions are as follows: the insulation temperature is 800 °C, holding time of 40 min, the doping amount of MgO is 1/20 of AC, and the maximum adsorption capacity is 649.9 mg·g−1 at pH = 7. In addition, thermodynamic studies show that the adsorption process is spontaneous and endothermic, and kinetic and adsorption isotherm models show that the pseudo-second-order kinetic model and Langmuir model are well fitted for the adsorption process.