Initial Cd Concentration Research Articles

Optimization and statistical modelling of cadmium biosorption process in aqueous medium by Aspergillus niger using response surface methodology and principal component analysis

Biosorption is an efficient technology for the decontamination of metals from industrial wastewater. In present study, cadmium resistant fungal strain Aspergillus niger was isolated from the effluent of electroplating industry. The effect of five independent variables i.e. pH (2–8), initial Cd(II) ion concentration (20–180 mg/L), biomass dosage (0.5–2.5 g/mL), temperature (10–60 °C) and contact time (10–80 min) was studied on Cd(II) biosorption by employing Aspergillus niger using batch mode. Optimum conditions were selected for maximum biosorption. The experimental design i.e. Box– Behnken design (BBD) was aimed at distinguishing the optimum levels of the above selected process variables. Maximum biosorption was achieved at pH 5.0, initial Cd(II) concentration (100 mg/L), biomass dosage (1.5 g/mL), temperature (35 °C) and contact time (45 min). At optimum conditions, 93% removal of cadmium ions was achieved. The Principal component analysis (PCA) was performed to spot the correlation between the various parameters.

Synthesis and characterization of egg-albumen-formaldehyde based magnetic polymeric resin (MPR): Highly efficient adsorbent for Cd(II) ion removal from aqueous medium

In this study, egg-albumen-formaldehyde based magnetic polymeric resin (MPR) was synthesized and used for the removal of Cd(II) ion from aqueous solution. Different variables affecting the adsorption of Cd(II) ion such as sorption time, pH of the solution, initial concentration of Cd(II) ion and temperature were also examined. The percentage removal of Cd(II) ion was increased with increasing contact time and temperature. The highest removal of Cd(II) ion was observed at pH 7 and the equilibrium was achieved within 4 h. Thermodynamic factors such as ΔG°, ΔH° and ΔS° were also evaluated from graphical interpretation of the experimental results. Thermodynamic and kinetic analyses showed that the adsorption process was spontaneous and endothermic, which fitted well with the pseudo-first-order kinetic model and Langmuir isotherm model. The maximum adsorption capacity which was obtained using Langmuir equation was found to be 149.3 mg g−1 at 298 K which was increased with increasing temperature. Regeneration studies were also performed using 0.1 M HCl solution to examine the reusability characteristics of MPR. Consequently, it was concluded that the MPR could be successfully used for the removal of the Cd(II) ion from aqueous medium.

Adsorption behavior of PAMAM dendrimers functionalized silica for Cd(II) from aqueous solution: Experimental and theoretical calculation

Abstract The adsorption behavior of polyamidoamine (PAMAM) dendrimers functionalized silica (SG-G0∼SG-G4.0) for Cd(II) from aqueous solution was investigated by combining experimental and theoretical method. The influences of dendrimer generation, terminal functional group, solution pH, contact time, temperature, as well as the initial concentration of Cd(II) on the adsorption behavior were explored. Static adsorption indicates that the adsorption capacity increases first and then decreases with the increase of dendrimer generation, SG-G2.0 and SG-G2.5 possess the highest adsorption capacity for amino- and ester-terminated PAMAM functionalized silica, respectively. The optimal adsorption pH value is 6 for all the adsorbents. Kinetic adsorption implicates that the adsorption can approach equilibrium at about 200 min. The kinetic adsorption follows pseudo-second-order kinetic model and is dominated by film diffusion. The isotherm adsorption demonstrates that the adsorption favors high concentration and the adsorption capacity first increases and then decreases with the increase of temperature. Adsorption isotherm process can be well described by Langmuir model. FTIR technique and DFT calculation reveal that the involvement primary and secondary nitrogen atoms, as well as carbonyl oxygen atoms dominate the adsorption. As SG-G0∼SG-G4.0 displays excellent adsorption performance for Cd(II), they could be potentially used as effective adsorbents for the decontamination of aqueous Cd(II).

A highly porous nanocomposite (Fe3O4@BFR) for the removal of toxic Cd(II) ions from aqueous environment: Adsorption modelling and regeneration study

Adsorption is a commonly used technique for the removal of pollutants from wastewaters. In this study, a magnetic adsorbent (Fe3O4@BFR) was prepared using biuret-formaldehyde pre polymeric resin (BFR) and Fe3O4 nanoparticles. The adsorption ability of Fe3O4@BFR was investigated using Cd(II) metal ion as a typical pollutant. Adsorption of Cd(II) was studied as a function of temperature (25–45 °C), pH (2–7), time (5–300 min) and initial Cd(II) concentration (25–75 mg L−1). The morphology, structure and magnetic character of Fe3O4@BFR nanocomposite were explored using X-ray powder diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption isotherm, scanning electron microscopy and VSM analyses. Adsorption kinetics, isotherms and thermodynamics studies were also carried out. The experimental adsorption data followed the pseudo-first-order kinetic model and Langmuir isotherm with a maximum adsorption capacity of 92.6 mg g−1. The reusability of Fe3O4@BFR was tested and still over 70% Cd(II) was removed after three cycles. In conclusion, Fe3O4@BFR nanocomposite showed enormous potential for remediating industrial wastewater polluted by toxic Cd(II) metal ion.

Investigation of a combined continuous flow system for the removal of Pb and Cd from heavily contaminated soil

In this study, a combined continuous flow system was designed to remove Pb and Cd from heavily contaminated mine tailing soils. 0.05 M Na2EDTA was used as a chelating agent to remove Pb and Cd from polluted soil, taken from the vicinity of Kayseri ÇİNKUR, Turkey. The initial concentrations of Pb and Cd were 16381 ± 643 and 34347 ± 1310 mg kg-1, respectively. The electrochemical treatment process was applied to the waste washing solution, which emerged after being extracted from soil column and contained Pb and Cd. Metal ions were transformed to the metallic form by applying the electrochemical treatment process to the washing solution, containing Pb2+ and Cd2+.At the end of the leaching experiment, which was done with a 50 g soil sample in the soil column system, Pb and Cd removal efficiencies from soil were 59.72% and 58.01%, respectively. Then, the soil column solution was subjected to electrolysis through a 48 h period at 10 V. The electrochemical removal efficiency of ions, which moved from column to solution, was 84.46% for Pb and 59.21% for Cd.

Adsorption of Cd(II) from aqueous solutions via meso structured adsorbent based on Ni/Mo-LDH: kinetics, thermodynamics, and adsorption mechanism

ABSTRACT This paper deals with cadmium ions removal from aqueous solutions by Ni/Mo-layered double hydroxide with kinetics and thermodynamics studies. At temperature of 318 K, pH = 5.5, adsorbent mass of 0.5 g/L, time of 105 min, and initial Cd(II) concentration of 175 mgL–1, the maximum adsorption capacity reached to 68.4 mg/g. The adsorption processes followed pseudo-second-order model and Langmuir isotherm and the calculated thermodynamic parameters concluded that the adsorption process was spontaneous, thermally dependent, and endothermic in nature. Therefore, the adsorption mechanism was proposed through multilayer surface adsorption by coordination of cadmium ions with hexavalent molybdenum (Mo6+) and also the coexisting ions effect on removal was detected.

Biosorption of Cadmium from Aqueous Solution by Free and Immobilized Dry Biomass of Chlorella vulgaris

Biosorption by algae is an effective process for the removal of heavy metals from the aqueous solutions. The present work deals with the biosorption of Cd(II) by Chlorella vulgaris in a batch system. The biosorption efficiency of Cd(II) removal was studied at different pH (3–8), initial metal concentrations (20–100 ppm), agitation time (5–120 min.), agitation speed (50–250 rpm), and biomass dosage (0.01–0.1 g/50 ml of metal solution). The optimum conditions for maximum biosorption capacity for C. vulgaris were at pH 6, initial Cd(II) concentration 75 mg/l, biomass dosage 0.08 g/50 ml metal solution, temperature 25 °C, agitation speed 250 rpm, and agitation time 30 min. The cadmium removal efficiency of the raw and pretreated algal biomass was studied under the optimum conditions. The results showed that pretreatment with acetic acid gave 99.346% as compared with raw biomass. Different algal weights (0.2, 0.15, 0.1, 0.05, and 0.025 g) were immobilized with 10 ml of 4% calcium alginate. The results showed that the highest cadmium biosorption efficiency was 76.448% for 0.025 g as compared with the control. The biosorption mechanisms were examined by Fourier-transform infrared analysis and scanning electron microscopy for raw and pretreated algal biomasses before and after cadmium biosorption. It was found that hydroxyl, amide with hydrogen bond, and carbonyl stretching in carboxyl groups played an important role in biosorption.

"Removal comparative study for Cd(II) ions from polluted solutions by adsorption and coagulation techniques using Moringa Oleifera seeds".

The Moringa oleifera seed (MOS) was characterized by pHzpc, Fourier transform infrared spectroscopy (FT-IR), X-ray and scanning electron microscopy (SEM) in order to get an insight of the surface charge, functional groups, and morphology of the biosorbent, respectively. The MOS studies were conducted on Cd (II) with different parameters, such as solution pH, contact time, initial concentration of the pollutant and temperature were examined. Experimental results revealed an increase of the removal percentage of Cd (II) using adsorption compared with coagulation technique with increases of the initial Cd (II) concentration and contact time. However, an opposite trend was observed with an increase of the solution temperature and solution pHs value. The Freundlich isotherm linear equation are better described for the adsorption process and coagulation process for the removal of Cd (II) ions. By Comparing the thermodynamic parameters of Cd (II) removal, such as ∆H, ∆S and ∆G, distinct behaviours were observed, where adsorption process is positive values along all temperatures while coagulation process showed negative values (with exception of -∆G at 277 K). According to S* value, the adsorbent system are very high while the coagulation system are very low Keywords; Moringa Oleifera seeds, Cd (II), Adsorption, Thermodynamics.

Cadmium retention and distribution in contaminated soil: effects and interactions of soil properties, contamination level, aging time and in situ immobilization agents

As soil cadmium (Cd) contamination becomes a serious concern and one of the significant environmental pollution issues all over the world, knowledge of the basic chemistry, origin, inputs, sources, quantity, chemical forms, reactions, as well as the fate and transport of Cd in different types of soil is crucial for better understanding Cd bioavailability, health risks and remedial options. This study aimed to increase the current knowledge on the complex interdependence between the factors affecting behavior, transport and fate of Cd in the soil and to test and compare the performance of the stabilization agents in different soil types. Soils demonstrated various sorption affinity and capacity for Cd accumulation, which proved to be positively correlated with soil pH and the cation exchange capacity (CEC). With increasing levels of contamination, sequential extraction analysis showed the highest increase of relative Cd amounts in the exchangeable fraction regardless of the soil properties, suggesting that added Cd is principally associated with the easily accessible and mobile fraction. For different initial Cd concentrations and soil types, Cd sorption reached the quasi-equilibrium within 24 h of contact. Prolonged aging (two months) influenced the natural stabilization of Cd in all types of soil, but only at low contamination level. The application of both, conventional (slaked lime Ca(OH)2) and alternative phosphate-rich (annealed bovine bones B400) amendments, resulted in Cd relocation and reduction of exchangeable Cd content. Although the effect was smaller when apatite amendment was utilized, observed re-distribution of Cd to more stable soil fractions is preferable for achieving long-term stabilization. Cd concentrations extracted in exchangeable and acid soluble fractions after the treatments of contaminated soil samples suggest that the practical applicability of in situ immobilization depends on the soil properties and the level of contamination, as well as that effect, should be monitored for the possible re-mobilization of Cd.

Novel Magnetic Nanostructured Beads for Cadmium(II) Removal.

This study presents an effective magnetic separation method for cadmium removal, based on the use of a novel nanostructured material as an adsorbent. This adsorbent involves the incorporation of magnetite nanoparticles (Fe3O4-NPs), synthesized by the reverse coprecipitation method, into sodium alginate and activated carbon to form spherical structures by crosslinking Ca2+ ions with the charged alginate chains, referred to as magnetic alginate activated carbon (MAAC) beads. The effect of the experimental parameters, such as pH, contacting time, adsorbent dosage, agitation type, and rotating speed were investigated and optimized for an efficient removal of Cd(II) ions at an initial concentration of 250 mg/L. The amount of adsorbed Cd(II) by MAAC beads increased at a pH of 6 with a removal efficiency over 90%. The maximum adsorption capacity reached was 70 mg/g of adsorbent at an initial Cd(II) concentration of 150 mg/L, whereas at 250 mg/L the adsorption capacity lowered until 60 mg/g. Sorption isotherms were calculated using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich equations, and were better described by the Freundlich and Temkin models. These results proved the removal efficiency and the potential use under real environmental conditions of the MAAC beads, due to their easy recovery from contaminated aqueous solutions.

Sorption mechanism and distribution of cadmium by different microbial species

Bioremediation programs of cadmium (Cd) by microorganisms have being proposed, but the underlying mechanism of the remediation ion remains unexplored. Here, the sorption efficiency and subcellular fraction distribution of Cd in three selected microbial species were investigated. Our results showed that both species of the microorganisms and initial Cd concentrations strongly affected the Cd sorption capacity. In the three microbial species, the Cd removal efficiency increased with decreased Cd concentrations. Specifically, Hansenula anomala removed the highest Cd ions in low concentration of 0.05 mg L−1; while in medium concentration of 0.5 mg L−1 and high concentration of 5 mg L−1, Bacillus subtilis removed the highest Cd ions. The subcellular fractionation allocation showed that Cd was mainly allocated on cell wall (mantle and inner wall) in Pseudomonas stutzeri and B. subtilis, while cell cytomembrane accumulated similar amount of Cd compared to the cell wall of H. anomala at concentration of 0.5 mg L−1. Meanwhile, the Cd distributions on cell subcellular fractionation of the three species changed along the contact times, suggesting varied migration models during the biosorption process. Moreover, the functional groups involved in biosorption differed among the species based on Fourier Transform Infrared (FTIR) analysis. Our results have important implications for developing and improving Cd remediation by microorganisms, which is a low-cost and environmentally friendly bioremediation strategy of Cd pollution in environments.

Phytoextraction of Ni, Pb and, Cd by duckweeds

Heavy metals phytoextraction potential of swollen duckweed (Lemna gibba Linn.) and lesser duckweed (Lemna aequinoctialis Welw.) was determined under greenhouse conditions by exposing to untreated industrial/municipal effluent for a period of 21 days. The nickel (Ni), lead (Pb), and cadmium (Cd) concentrations in water samples were measured weekly and in plant biomass at the termination of experiments. Significant differences (p < 0.05) between initial and final physicochemical parameters and in heavy metal concentrations of plant and water samples were observed. Periodically measured metal concentrations in mediums revealed that removal percentage was dependent on initial Ni (2.15 mg L−1), Pb (1.51 mg L−1), and Cd (0.74 mg L−1) concentrations. The final metal removal percentages were in the sequence of Ni (97%) > Pb (94%) > Cd (90%) when treated with Lemna gibba L. as compared to control (9–12% reduction). High biomass production of Lemna gibba L. resulted in a large metal reduction in the growth medium and the total plant metal contents were in the sequence of Ni (427 µg) > Pb (293 µg) > Cd (105 µg). The lesser duckweed did not survive under experimental conditions. Based on these results, we concluded that Lemna gibba L. is a good candidate for phytoremediation of wastewater.

BP-ANN Approach for Modeling Cd(II) Bio-Sorption from Aqueous Solutions Using Cajanus cajan Husk

This work aims at the modeling of bio-sorption of cadmium(II) onto physically and chemically activated Cajanus cajan (Pigeon pea) husks. Experimental data obtained were fitted to a number of isotherm and kinetic models, and the results interpreted. The monolayer Cd(II) bio-sorption capacities of the husk were found to considerably increase by 2.82 times due to chemical activation, for bio-sorption from a solution containing an initial Cd(II) concentration of 100 mg/L and by about 1.78 times for a solution containing an initial Cd(II) concentration of 150 mg/L. Further, the BackPropagation Artificial Neural Network (BP-ANN) was applied to understand the accuracy and prediction of isotherm and kinetic data. The tangent sigmoid transfer function was used at the input to hidden layer whereas a linear function was used at output layer. The isotherm and kinetic data were distributed into training (65%) and testing (35%) phase. The training, testing, and prediction by BP-ANN were found to be adequate, with an absolute relative percentage error of 2.1827 and correlation coefficient R2of 0.9967 and 0.9863 at prediction for isotherm and kinetic studies, respectively. Comparison of BP-ANN and experimental results indicated that the prediction model is capable of predicting the bio-sorption effectiveness with good accuracy.

Removal of Cadmium (II) from Aqueous Solutions onto Dodonaeae Viscose Leg Powder Using a Green Process: Isotherms, Kinetics and Thermodynamics

In the present study, batch adsorption experiments of hazardous cadmium ions, Cd(II), onto low-cost Dodonaeae Viscose Legs (DVLs) surface were conducted with respect to contact time, solution pH, adsorbent dosage, initial Cd concentration and temperature. Sorption isotherm, kinetic and thermodynamic models were used to describe the equilibrium stage and their constants were determined. The DVLs were used without chemical or physical activation processes. The results showed that the optimum adsorption capacity of DVLs for Cd(II) ions was found to be 25.29 mg/g at solution pH 5.26, 50 min and 303K. DVL adsorption data was fitted well with Langmuir isotherm. The mean free energy was found to be 1.82E-02 using Dubinin-Radushkevich (DRK) isotherm, which indicates that the adsorption of Cd(II) ions onto DVL surface is physical adsorption. The activation energy (Ea) was 3.06 kJ/mol, which confirms that Cd(II)-DVL adsorption process is physical sorption. Pseudo-first-order, pseudo-second-order, Elovich, intra-particle and extra-particle diffusion models were used to describe the adsorption kinetics. The results show strong correspondence to a pseudo-second-order kinetics. Thermodynamic parameters suggested that the adsorption of Cd(II) ions onto DVL surface is an exothermic process.

Effects of Pretreatment Methods of Wheat Straw on Adsorption of Cd(II) from Waterlogged Paddy Soil.

Two types of pretreatment categories, namely microwave-assisted alkalization and microwave-assisted acid oxidation, were used to synthesize novel wheat straw adsorbents for the effective removal of Cd(II) in simulated waterlogged paddy soil. A systematic adsorption behavior study, including adsorption kinetics and adsorption isotherms was conducted. Results showed that wheat straw pretreated by microwave-assisted soaking of NaOH and ethanol solution obtained the highest Cd(II) removal efficiency of 96.4% at a reaction temperature of 25 ℃, pH of 7.0, initial Cd(II) concentration of 50 mg/L, and adsorbent/adsorbate ratio of 10 g/L. Sequential extraction experiment was carried out to analyze the changes of different of Cd(II) in soil, the aim of which was to study the mobility of Cd(II) and then evaluate the toxicity that Cd(II) might bring to plants. A 60-day incubation was performed to investigate the dynamic variations of soil pH and dissolved organic carbon content over incubation time. Characterization analyses revealed the morphological changes of wheat straw adsorbents, which suggested that those pretreatment methods were of significance. This study provided an environmentally friendly way to reuse agricultural wastes and remedy Cd(II) contaminated soil.

Optimization of adsorption of metal ions from a ternary aqueous solution with activated carbon from Acacia senegal (L.) Willd pods using Central Composite Design

Activated carbon was prepared from Acacia senegal using H3PO4, it was characterized using FTIR, SEM and BET. Optimization of adsorption of Cadmium, Chromium and Lead from ternary solution with the adsorbent was carried out using Design Expert software and the model validated. FTIR analyses showed the presence of some functional groups such as OH and CC which usually aid adsorption. SEM micrograph showed presence of pores of various sizes on the carbon surface, also responsible for adsorption of molecules of various sizes. BET analyses reported the carbon to have surface area of 427.5 m2/g, width of 5.839 nm signifying a mesopore responsible for various degrees of adsorption. The optimum factors which were responsible for 98.54%, 100.00% and 99.96% adsorption of Cd, Cr and Pb respectively predicted by the model were 145.06 mg/L, 144.15 mg/L, 63.83 mg/L, 8.0, 0.17 g and 8.46 min as initial concentrations of Cd, Cr, Pb, pH, dosage and contact time respectively. The optimum factors were further validated with coefficient of determination R2 ranging from 0.8267 to 0.9775. These models were also used to predict maximum adsorption of Cd, Cr and Pb from tannery water and ABU dam water, 73%, 82.54% and 87.23% were obtained as the experimental percentage removal of Cd, Cr and Pb respectively from ABU water, while removal from tannery wastewater stood at 62.75%, 85.2% and 77.83% for Cd, Cr and Pb respectively. Acacia senegal pod has been demonstrated to be an efficient precursor in activated carbon production for water treatment.

Facile and simple synthesis of triethylenetetramine-modified mesoporous silica adsorbent for removal of Cd(II)

Monodispersed porous silica microspheres (SM) were synthesized and further functionalized with amine moieties using triethylenetetramine (TETA) in order to obtain a novel adsorbent for Cd(II) elimination from aqueous media. The morphology, texture and structure of samples were characterized with the aid of Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), energy dispersive spectroscopy (EDS), and N2 adsorption-desorption. The adsorption efficiency was investigated based on the effect of operational parameters including pH of the solution, the dose of adsorbent, adsorption time, initial concentration of Cd(II) ions and temperature. The equilibrium, kinetics and thermodynamics of Cd(II) adsorption were also studied. The maximum adsorption capacity of amine functionalized silica microspheres (AMSM) for Cd(II) was 35.6 mg g-1. Cd(II) adsorption onto AMSM had highest consistency with Sips and Langmuir isotherms, while adsorption kinetics was best fitted with pseudo-second order model. Thermodynamics of adsorption revealed that Cd(II) adsorption on AMSM was spontaneous, feasible and exothermic with physical interactions and pore diffusion being the dominant mechanisms in the adsorption process. Results confirmed that AMSM adsorbent has the potential to be a suitable candidate for Cd(II) removal from aqueous solutions.

Creation of Hollow Calcite Single Crystals with CQDs: Synthesis, Characterization, and Fast and Efficient Decontamination of Cd(II)

In this work, carbon quantum dots were first prepared through one-pot hydrothermal route of the propyl aldehyde and sodium hydroxide via an aldol condensation reaction, and a novel solid-phase extraction adsorbent of hollow calcite single crystals was prepared via the precipitation of metal nitrates by the CO2 diffusion method in the presence of CQDs and further applied for excessive Cd(II) ions removal from water. The spectra and morphologies of the etched calcite were investigated by X-ray diffraction, Fourier transform infrared spectrometry, Scanning electron microscope, and Transmission electron microscopy. The results show that the CQDs etching technique successfully furnish a strategy for manufacturing interface defects onto the calcite crystal. Bath studies were done to evaluate the effects of the major parameters onto Cd(II) adsorption by the etched calcite, such as pH, contact time, and initial Cd(II) concentration. The Cd(II) adsorption onto the new adsorbent could reach a maximum adsorption amount of 66.68 mg/g at 120 min due to the abundant exterior adsorption sites on the adsorbent. The adsorption kinetics and adsorption isotherms of Cd(II) on the etched calcite were also investigated. The experimental datum showed that the adsorption kinetics and isotherms of Cd(II) on the etched calcite were well-fitted by the pseudo-second-order kinetic model and the Freundlich isotherm model respectively. The adsorption mechanisms could be primarily explained as the formation of Cd(OH)2 and CaxCd1−xCO3 solid solution on the adsorbent surface with the help of X-ray photoelectron spectroscopy.

Response surface methodological approach for optimizing the removal of cadmium from aqueous solutions using pistachio residues biochar supported/non-supported by nanoscalezero-valent iron

Abstract A three-level Box–Behnken model (BBM) under response surface methodology (RSM) was used to optimize the removal of cadmium (Cd) ion by pistachio residues biochar (PRB) and PRB supported by nanoscale zero-valent iron (PRB-nZVI) from aqueous solutions. Optimization experiments were carried out by evaluation of the effect of four variables (initial Cd concentration, initial solution pH, adsorbent dosage, and contact time) at three levels (high, medium, and low), and one category contained two variables (PRB and PRB-nZVI). For this purpose, a total of 58 experimental runs were set and the experimental data were fitted to the empirical second-order polynomial model of a suitable degree. The physical and chemical structure results of the adsorbents confirmed the formation of nZVI (with diameters ~35 nm) on the PRB surface. The results showed that the new composite of biochar (PRB-nZVI) exhibited higher Cd removal efficiency compared with PRB from aqueous solutions. The existence of functional groups and nZVI on the surface of PRB-nZVI could be better than PRB for Cd removal in aqueous solutions by the processes of sorption, precipitation, and co-precipitation. Numerical optimization revealed that the optimum removal (96.58%) was obtained at an initial Cd concentration of 25.99 mg L−1 (pH 6.58), adsorbent dose (PRB-nZVI) of 0.55 g L−1, and contact time of 34.11 min, with desirability of 1. Based on the results, it is recommended that PRB-nZVI can be effectively used for the removal of Cd from a contaminated aqueous solution with varying chemical and physical conditions.

Adsorption Properties and Mechanism of Cd2+ in Water by Zr-containing Silica Residue Purification.

Zirconium (Zr)-containing silica residue purification (ZSR-P) discharged from industrial production of ZrOCl2 was used as an adsorbent, and CdCl2 solution was used as the simulated wastewater containing cadmium ions (Cd2+). The properties and mechanisms of ZSR-P absorbing Cd2+ were studied. The results showed that ZSR-P had a good effect on the adsorption and removal of Cd2+ in water. The adsorption time, initial concentration of Cd2+, and pH of the solution had a significant effect on the adsorption behavior, whilst the pH value had the greatest effect amongst them. Under optimal conditions, the amount of Cd2+ adsorbed by ZSR-P was 43.1 mg/g. The isothermal adsorption conformed to the Langmuir adsorption model, and the adsorption kinetics conformed to the secondary adsorption rate model. In ZSR-P-Cd, Cd2+ was uniformly distributed on the surface of SiO2 particles and in the pores formed by the accumulation of particles. Adsorption of Cd2+ by ZSR-P was achieved through the reaction between Si-OH on the surface of SiO2 and Cd2+ hydroxyl compounds.