Kinetic parameters and mechanisms of the batch biosorption of Cr(VI) and Cr(III) onto Leersia hexandra Swartz biomass

Distribution and migration of uranium, chromium, and accompanying metal(loid)s in soil-plants system around a uranium hydrometallurgical area

The extraction and utilization of uranium (U) ores have led to the release of significant amounts of potentially toxic metal(loid)s (PTMs) into the environment, constituting a grave threat to the ecosystem. However, research on the distribution and migration mechanism of U, chromium (Cr), and their accompanying PTMs in soil-plant system around U hydrometallurgical area remains insufficient and poorly understood. Herein, the distribution, migration, and risk level of PTMs were evaluated in soil and plant samples around U hydrometallurgical area, Northern Guangdong, China. The results demonstrated that the maximum content of U and Cr found in the analyzed soils were up to 84.2 and 238.9 mg/kg, respectively. These values far exceed the soil background values in China and other countries. The highest content of U (53.6 mg/kg) was detected in Colocasia antiquorum Schott, and the highest content of Cr (349.5 mg/kg) was observed in Pteridium aquilinum, both of which were enriched in their roots. The risk assessment of PTMs demonstrated that the study area suffered from severe pollution (PN > 3), especially from U, Cr, Th, and As, suggesting the non-negligible anthropogenic impacts. Hence, in light of the significant ecological hazard posed by the U hydrometallurgical area, it is imperative to implement appropriate restoration measures to ensure the human health and maintain the stability of the ecosystem.

Entrapment behaviours of trivalent and hexavalent chromium from aqueous medium using edible alkali-derived activated carbon of Eichhornia crassipes (water hyacinth)

The study examines the adsorption capabilities of an environmentally friendly activated carbon derived from a novel activating agent, i.e., an edible alkali prepared from black gram plant ash, for the removal of Cr(III) and Cr(VI) ions from an aqueous environment. The results of the systematic research show impressive removal efficiencies of 95.12% for Cr(III) ions and 99.6% for Cr(VI) ions. The kinetics and equilibrium data of the adsorption process confirm to the pseudo-second-order kinetics and Freundlich isotherm model. The thermodynamic analysis reveals the adsorption process as feasible and spontaneous across the temperature range of 298-313 K. The mechanism entails electrostatic attraction and adsorption of Cr(III) and Cr(VI) ions on oppositely charged surfaces and the participation of oxygen-containing functional groups on WHAC-BGA surface in the reduction of Cr(VI) to Cr(III). This study provides valuable insights for optimizing strategies to combat chromium contamination in water sources, offering a sustainable solution with the potential for real-world application.

Studying the Properties of Chromium-Contaminated Soil Solidified by Polyurethane

The solidification of chromium-contaminated soil using polyurethane (PU) was systematically investigated. The unconfined compression test was conducted to investigate the effects of the curing time, PU dosage and the content of chromium ions on the unconfined compressive strength (UCS) of chromium-contaminated soil. The effect of the PU dosage on the pore structure was investigated using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), and the mechanism of strength change was revealed by combining the strength law with the pore structure development law. In addition, the ability of the PU to solidify the chromium-contaminated soil was studied by the toxicity characteristic leaching procedure (TCLP). According to the above test results, the UCS and the ability of the PU to solidify the chromium ions increased with the increase in curing time. The NMR tests showed that with the increase in PU dosage, the porosity decreased and the soil became more compact, hence increasing the strength. When the chromium ion content was 2000 mg/kg and the PU dosage was 8%, the strength of the sample was 0.37 MPa after curing for 24 h, which met the requirement of 0.35 MPa set by the U.S. Environmental Protection Agency. Consequently, PU is a solidification agent with high-early strength.

Tea saponin enhanced bioleaching of Fusarium solani to remove hexavalent chromium from soil

Hexavalent chromium pollution is one of the most serious types of site pollution. In this study, a microorganism was screened to remove most hexavalent chromium from soil by leaching in 24 h. After ITS sequencing, the microorganism was identified as belonging to the genus Fusarium solani. The optimization experiment of leaching conditions determined that the removal rate reached the maximum 80% when the rotation speed was 200 rpm, the liquid-soil ratio was 15:1, the temperature was 35℃, and the pH was 7. The study has also shown that tea saponin can effectively strengthen the leaching of Fusarium solani to remove hexavalent chromium from the soil. Compared with tea saponin, the strengthening effect of glucose and rhamnolipid was relatively small. The removal rate of hexavalent chromium reached 85% when the added amount of tea saponin was 0.02 g/mL. The leaching solution destroyed part of the iron-manganese nodule structure of the soil, and its hydroxyl, carboxyl, and other groups complexed metal ions into the solution to achieve the purpose of removing hexavalent chromium. However, since the main crystal of the soil was SiO₂, there was no obvious change in the XRD of the soil. Toxicity test showed that after leaching, the content of hexavalent chromium leached was 0.28 mg/L (< 1.5 mg/L), which meet the entry standard of the landfill site.

Biosorptive ascendency of plant based biosorbents in removing hexavalent chromium from aqueous solutions - Insights into isotherm and kinetic studies

Chromium is a toxic heavy metal prevalent in higher levels in aqueous matrices owing to industrial applications. Whilst being a key player in industries, the environmental issues caused by Cr(VI) are highly deleterious. Adsorptive remediation is found to be an effective method adopted by researchers in the past decades for Cr(VI) removal from water streams in which variety of naturally available biosorbents have been explored for handling Cr(VI). This review article briefly sketches up the biosorptive potential of plant-based biosorbents used in raw and chemically modified form for the optimum exclusion of Cr(VI) from aqueous sources. Mechanisms and kinetic behavior of the removal process are also discussed. pH of the solution and initial Cr(VI) concentration were found to be the key parameters in Cr removal. The mechanism of Cr removal from aqueous systems was elucidated to be either adsorption or adsorption-coupled-reduction. After precise discussion on various plant-based biosorbents with their maximum adsorption capacities, desorption and regeneration potential, it is perceived that plant-based biosorbents are superior options for Cr(VI) elimination from aqueous streams.

Bioprocess development for biosorption of cobalt ions and Congo red from aquatic mixture using Enteromorpha intestinalis biomass as sustainable biosorbent

Because of the increased amount of cobalt and Congo red dye effluents attributable to the industrial operations, the capacity of Enteromorpha intestinalis biomass as a sustainable source to achieve significant biosorption percent for both pollutants from dual solution was assessed. A fifty batch FCCCD experiments for biosorption of cobalt ions and Congo red dye were performed. The complete removal of Congo red dye was obtained at 36th run using an initial pH value of 10, 1.0 g/L of Enteromorpha intestinalis biomass, 100 and 200 mg/L of Congo red and cobalt for a 20-min incubation time. Meanwhile, a cobalt removal percent of 85.22 was obtained at 35th run using a neutral pH of 7.0, 3.0 g/L of algal biomass, 150 and 120 mg/L of Congo red, and cobalt for a 60-min incubation time. For further illustration and to interpret how the biosorption mechanism was performed, FTIR analysis was conducted to inspect the role of each active group in the biosorption process, it can be inferred that -OH, C-H, C=O, O-SO3- and C-O-C groups were mainly responsible for Co2+ adsorption of from aqueous dual solution. Also, scan electron microscope revealed the appearance of new shiny particles biosorbed on E. intestinalis surface after the biosorption process. EDS analysis proved the presence of Co2+ on the algal surface after the biosorption process.

Designing of a nanoscale zerovalent iron@fly ash composite as efficient and sustainable adsorbents for hexavalent chromium (Cr(VI)) from water

The present study encompasses a unique concept involving the formation of core-shell particles with surface-activated fly ash (FA) as core and nanoscale zerovalent iron (nZVI) particles as shell, which not only imparts high adsorption efficiency for Cr(VI) but also contributes to fruitful utilization of FA while overcoming the drawbacks associated with ZVI nanoparticles (aggregation, rapid oxidation and less durability). The otherwise inert surface of FA has been modified and activated to achieve a uniform and stable layer of nZVI over FA. The functionalized particles were studied using FE-SEM/EDAX, HR-TEM, XRD and FT-IR studies for its physical, functional and morphological characteristics. The results indicate the strong adsorption ability of nZVI@FA particles, with 100% removal efficiency within 10 min at low initial concentrations of Cr(VI), which is appreciably higher than that of pure fly ash (26%) after 60 min of reaction. Besides, the so-formed structure of composite aids to improve its life, as the synthesized nZVI@FA particles could be efficiently regenerated and reused up to 5 subsequent adsorption-desorption cycles, which is in contrast with the ability of fly ash considering its low desorption potential. Hence, the composite material proves to be an effective and sustainable alternative for treatment of a waste using a waste.

Sonochemical synthesis of ZnS nanolayers on the surface of microbial cells and their application in the removal of heavy metals

In order to improve the adsorption performance of microorganisms, we synthesized a novel material - phanerochaete chrysosporium cells covered with a layer of ZnS nanoparticles (ZnS-cells). The preparation of the ZnS-cells is based on the Sonochemical method to synthesize the ZnS nanoparticle layer on the surface of the microbial cells. The ZnS-cells were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). Characterization results showed that wurtzite ZnS was coated on the cell surface in the form of nanoclusters by sonochemical reaction, and the formation of ZnS was related to the carboxyl group on the cell surface. Batch experiments showed that the ZnS-cells exhibited high adsorption efficiency for Pb²⁺and Cd²⁺, the removal rate of Pb²⁺ and Cd²⁺ by ZnS-cells was 140 % and 160 % higher than that of pure P. chrysosporium, respectively. Studies on the adsorption mechanism showed that the removal of heavy metals by ZnS-cells mainly depended on the complexation of surface functional groups on the surface of the cells and the ion exchange of ZnS nanofilms.

Eco-friendly approach for biosorption of Pb2+ and carcinogenic Congo red dye from binary solution onto sustainable Ulva lactuca biomass

Dyes constitute an important group of organic contaminants and are recognized for its harmful effects on the aquatic environments and humans. Heavy metals are also the largest group of inorganic pollutants due to their accumulation in the environment, contaminate food chains and cause adverse effects on the living organisms. Biosorption capacity of Ulva lactuca biomass was assessed in batch experiments for simultaneous removal of Pb2+ and Congo red dye from binary solution. The process variables effects on Congo red dye and Pb2+ removal percentages were explored by performing 50 experiments using Face-centered central composite design. The highest removal percentages of Congo red dye (97.89%) and Pb2+ (98.78%) were achieved in the run no. 24, using 100 mg/L Congo red dye, 200 mg/L Pb2+, 3 g/L algal biomass, initial pH 6 and contact time was 120 min at 30 °C. FTIR analysis of the algal biomass showed the existence of many functional groups responsible for the biosorption process. After the biosorption process, SEM analysis revealed obvious morphological changes including surface shrinkage and the presence of new glossy Pb2+ particles, and the EDS spectra reveals presence of additional Pb2+ peak confirming the capacity of Ulva lactuca biomass to remove Pb2+ from binary solution.

Fungal cell with artificial metal container for heavy metals biosorption: Equilibrium, kinetics study and mechanisms analysis

White-rot fungi show low-cost superiority as a promising biosorbent in heavy metal removal, but limited by its poor biosorption capacity. Herein, a novel biosorbent, functionalized Phanerochaete chrysosporium with intracellular mineral scaffold, was prepared for the biosorption of heavy metal ions. The functionalized fungi cells with intracellular mineral scaffold that serve as internal metal container exhibiting high biosorption efficiency for Pb(II) and Cd(II) ions. Adsorption isotherm models were employed to investigate the biosorption isotherm and determine the biosorption equilibrium. The Freundlich model shows better fit with the experimental data of both metal ions (R² = 0.9866 and 0.9897 for Pb(II) and Cd(II) respectively). Three kinetic models, pseudo-first-order, pseudo-second-order and intra-particle diffusion models, were used to determine the biosorption kinetics. The pseudo-second-order model shows the better fit with the experimental data, and we suggests the rate-limiting step of the biosorption could be a chemisorption step which involves sharing or exchanging of electrons between adsorbent and adsorbate. Intra-particle diffusion model study result shows the biosorption process could be divided into three steps: a fast surface adsorption stage, a slow transfer stage from external to internal, and a stage of andante reaching equilibrium. The biosorption mechanism was carefully analyzed by various characterization methods.

Influence of preparation method on structural, optical, magnetic, and adsorption properties of nano-NiFe2O4

Nickel ferrite (NiFe₂O₄) nanoparticles are prepared through different routes (microwave, co-precipitation, and pyrolysis) and tested for water purification applications through adsorption removal of an acid red dye B as a model organic pollutant. The characterizations of the prepared samples were done using XRD, FT-IR, SEM, TEM, BET, UV-Vis absorbance, Raman spectrum, and vibrating sample magnetometer (VSM). All samples showed an inverse spinel crystal structure. The obtained results pointed out to the effect of the synthetic route on the morphology, particle size, optical, and magnetic properties of the prepared ferrites. Magnetic measurements showed super-paramagnetic behavior for all samples. The magnetic saturation (M_s) of the sample prepared by pyrolysis, was found to possess the highest saturation value, 34.8 emu/g. Adsorption experiments were performed under the change in several parameters, such as pH, adsorbent dosage, and initial dye concentration. A dye removal percentage of 99% was reached under the optimum state. The isothermal adsorption of the acid red dye was investigated using several models, in which the experimental data could be best described by the Freundlich model. Several kinetic and equilibrium models were inspected by linear regression analysis and showed best fitting for the adsorption data through pseudo-second-order model. The calculated thermodynamic parameters indicated that the adsorption of acid red dye onto all the ferrite samples is a spontaneous and endothermic physical adsorption process.

Removal of aromatic and hydrophobic fractions of natural organic matter (NOM) using surfactant modified magnetic nanoadsorbents (MNPs)

The present study investigated the potential of surfactant modified magnetic nanoadsorbents (MNPs) for the removal of aromatic and hydrophobic fractions of natural organic matter (NOM), leading to the formation of trihalomethanes (THMs) in chlorinated drinking water. Co-precipitation method was used for the synthesis of MNPs. However, MNPs have a tendency to form an agglomeration. Therefore, polyethylene glycol (PEG) was used as a surface modifier to reduce the agglomeration. The PEG-coated MNPs were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), BET surface area, X-ray diffraction (XRD), Fourier transform spectrometer (FTIR), and zeta (ζ) potential. FESEM observation indicates that PEG-coated MNPs were spherical in shape and 25 nm in size. Zeta potential values (- 58.35 to - 74.9 mV) indicated excellent stability of PEG-MNPs. FTIR spectra indicated the presence of a -CH₂ group, responsible for the chemical interaction between aromatic and humic content. Batch experiments were conducted by studying the effect of pH, contact time, and adsorbent dosage on NOM removal. Excellent removal of DOC (94.49%) and UV₂₅₄ (89.32%) was observed at the optimum dose of adsorbent (0.75 g/L) and at pH 7.0. Adsorption kinetics followed pseudo-second-order reaction (R², 0.973) and occurs by multilayer chemisorption which is due to the chemical interaction between aromatic and humic compounds of NOM with MNPs. Thus, MNPs showed great potential as a novel adsorbent for the removal of aromatic and hydrophobic compounds of NOM and can significantly be used to curtail the problem of THMs in drinking water supplies.

Chromium removal from industrial wastewater using Phyllostachys pubescens biomass loaded Cu-S nanospheres

In this paper, a new surface modification method was reported for the preparation of Phyllostachys pubescens powder as an effective adsorbent for the removal of chromium. Complex copper sulfide (Cu-S)nanospheres were evenly dispersed and loaded into the internal surface of the adsorbent, which provided both the ion exchange and oxidative-reductive properties. The composite showed an excellent adsorption efficacy for Cr(III) and Cr(VI). The surface properties of the obtained materials were characterized by FTIR and SEM. Maximum adsorption for Cr(III) and Cr(VI) was observed at pH 6.1 and 1.9, respectively. The experimental sorption equilibrium data were modeled using Langmuir and Freundlich isotherm equations. It was found that the maximum adsorption capacities of Cr(III) and Cr(VI) were 52.30 mg g-1 and 94.25 mg g-1, respectively. The adsorption mechanism analysis inferred that the major adsorption mode of Cr(III) was ion exchange, and Cr(VI) was oxide-reduction.

Root-associated bacterial diversities of Oryza rufipogon and Oryza sativa and their influencing environmental factors

Oryza rufipogon is the ancestor of human-cultivated Oryza sativa. However, little is known about the difference between the root-associated microorganisms of O. rufipogon and O. sativa. In this study, the root-associated bacteria of O. rufipogon, Leersia hexandra, and O. sativa from different latitudes in China were studied by DGGE analysis. Their bacterial community structures were compared by principal component analysis. The relationship between root-associated bacteria and soil properties was explored by canonical correspondence analysis. The relationships of glomalin-related soil protein (GRSP) content, soluble sugar content, proline content of the plant, and bacterial diversity indices of their root-associated microorganisms were also investigated. We found both broad-spectrum and host-specific bacteria, and the similarity, diversity and abundance indices of O. rufipogon and L. hexandra were higher than O. sativa root-associated bacteria. However, even living in the same habitat, O. rufipogon and L. hexandra selected different root-associated bacteria. Microbial composition was primarily correlated with available N, P, and K and the annual precipitation. We also found a positive correlation between the soluble sugar content of the plant and GRSP content of the root soil. The above results indicated that the community structure of root-associated bacteria differs between wild rice and cultivated rice. Human activity and the natural selection of the host plants shaped the differences, consistent with our hypothesis.

High-capacity adsorption of dissolved hexavalent chromium using amine-functionalized magnetic corn stalk composites

Easily separable amine-functionalized magnetic corn stalk composites (AF-MCS) were employed for effective adsorption and reduction of toxic hexavalent chromium [Cr(VI)] to nontoxic Cr(III). The saturated magnetization of AF-MCS reached 6.2emu/g, and as a result, it could be separated from aqueous solution by a magnetic process for its superparamagnetism. The studies of various factors influencing the sorption behavior indicated that the optimum AF-MCS dosage for Cr(VI) adsorption was 1g/L, and the maximum adsorption capacity was observed at pH 3.0. The chromium adsorption perfectly fitted the Langmuir isotherm model and pseudo second order kinetic model. Furthermore, characterization of AF-MCS was investigated by means of XRD, SEM, TEM, FT-IR, BET, VSM and XPS analysis to discuss the uptake mechanism. Basically, these results demonstrated that AF-MCS prepared in this work has shown its merit in effective removal of Cr(VI) and rapid separation from effluents simultaneously.

Evaluation of Cr(VI) Exposed and Unexposed Plant Parts of Tradescantia pallida (Rose) D. R. Hunt. for Cr Removal from Wastewater by Biosorption

Phytoremediation is an efficient method for the removal of heavy metals from contaminated systems. A productive disposal of metal accumulating plants is a major concern in current scenario. In this work, Cr(VI) accumulating Tradescantia pallida plant parts were investigated for its reuse as a biosorbent for the removal of Cr(VI) ions. The effect of pH, contact time, sorbent dosage, Cr(VI) concentration and temperature was examined to optimize these process parameters. Results showed that Cr(VI) exposed/unexposed T. pallida leaf biomass could remove 94% of chromium with a sorption capacity of 64.672 mg g(-1). Whereas the kinetics of Cr(VI) biosorption was well explained by the pseudo second-order kinetic model, the Langmuir model better described the data on Cr(VI) sorption isotherm compared with the Freundlich model. The changes in the free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) were found to be -5.276 kJ mol(-1), 0.391 kJ mol(-1) K(-1) and 11.346 kJ mol(-1), respectively, which indicated the process to be spontaneous, feasible and endothermic in nature. FTIR spectra of T. pallida leaf biomass revealed the active participation of ligands, such as -NH, amide, hydroxyl and sulphonate groups present in the biomass for Cr(VI) binding, SEM analysis revealed a porous structure of the biosorbent for an easy uptake of Cr(VI).

Comparison of biosorption and phytoremediation of cadmium and methyl parathion, a case-study with live Lemna gibba and Lemna gibba powder

Heavy metals and pesticides can be adsorbed by several biomasses such as living or non-living aquatic plants. In this study adsorption properties of live Lemna gibba and Lemna gibba powder were investigated with regard to cadmium and methyl parathion (MP). Toxicity data (IC50) on live L. gibba indicated that the period of four days was adequate for phytoremediation. Initial adsorption studies showed that both adsorbents were capable of removing cadmium and methyl parathion. Cadmium and methyl parathion adsorption onto L. gibba powder was fast and equilibrium was attained within 120min. The adsorption data could be well interpreted by the Freundlich model. The KF were: 7.8963 (Cd(2+)/ live Lemna); 0.7300 (MP/live Lemna); 11.5813 (Cd(2+)/Lemna powder); 1.1852 (MP/Lemna powder) indicating that Cd(2+) was more efficiently removed by both biosorbents than MP. Adsorption kinetics for cadmium and methyl parathion in both systems and rate constants were determined for each contaminant. It was found that the overall adsorption process was best described by pseudo-second-order kinetics. Boyd model and external mass-transfer expression were tested. It was concluded that cadmium and methyl parathion sorption onto Lemna powder is governed by film diffusion.

Removing Cr(VI) from aqueous solutions using a functional ionic liquid-based cross-linked polymer

A novel functional ionic liquid-based cross-linked polymer was synthesized from 1-aminoethyl-3-vinylimidazolium chloride hydrochloride and divinylbenzene. The physicochemical properties of the adsorbent were investigated using scanning electron microscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The adsorption capacity of the novel cross-linked polymer with respect to Cr(VI) was investigated using a batch adsorption procedure and the kinetics and thermodynamics of the adsorption process were further investigated. It was found that the adsorption kinetics was well fitted by a pseudo-second-order model and the adsorption isotherms agreed well with the Langmuir model. The maximum adsorption capacity after 5 min at room temperature (25 °C) was found to be 391.4 mg/g, which was much better than the most of the previously reported adsorbents. The adsorption process was found to be dominated by electrostatic interactions. The introduction of functional ionic liquid moieties into cross-linked poly(divinylbenzene) polymer constitutes a new and efficient kind of adsorbent.

Dynamic behaviour of Cd2+ adsorption in equilibrium batch studies by CaCO3(-)-rich Corbicula fluminea shell

This work presents the structural and adsorption properties of the CaCO3(-)-rich Corbicula fluminea shell as a natural and economic adsorbent to remove Cd ions from aqueous solutions under batch studies. Experiments were conducted with different contact times, various initial concentrations, initial solution pH and serial biosorbent dosage to examine the dynamic characterization of the adsorption and its influence on Cd uptake capacity. The characterization of the C. fluminea shell using SEM/EDX revealed that the adsorbent surface is mostly impregnated by small particles of potentially calcium salts. The dominant Cd adsorption mechanism is strongly pH and concentration dependent. A maximum Cd removal efficiency of 96.20% was obtained at pH 7 while the optimum adsorbent dosage was observed as 5 g/L. The Langmuir isotherm was discovered to be more suitable to represent the experimental equilibrium isotherm results with higher correlation coefficients (R(2) > 0.98) than Freundlich (R(2) < 0.97).The correlation coefficient values (p < 0.01) indicated the superiority of the Langmuir isotherm over the Freundlich isotherm.

Isotherm and thermodynamic studies of Zn (II) adsorption on lignite and coconut shell-based activated carbon fiber

The Zn (II) adsorption capacity of lignite and coconut shell-based activated carbon fiber (ACF) was evaluated as a function of initial Zn (II) concentration, temperature and contact time in batch adsorption process in this study. Adsorption uptake increased with initial Zn (II) concentration and temperature. Optimal contact time for the adsorption of Zn (II) ions onto lignite and coconut shell-based ACF was found to be 50 min. Removal percentage decreased from 88.0% to 78.54% with the increment in initial Zn (II) concentration from 5 to 50 mg L(-1). Equilibrium data fit well with Langmuir-I isotherm indicating homogeneous monolayer coverage of Zn (II) ions on the adsorbent surface. Maximum monolayer adsorption capacity of Zn (II) ions on ACF was found to be 9.43 mg g(-1). Surface morphology and functionality of ACF prior to and after adsorption were characterized by electron microscopy and infrared spectroscopy. Various thermodynamic parameters such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were evaluated.

Preparation of bio-based porous carbon by microwave assisted phosphoric acid activation and its use for adsorption of Cr(VI)

Ficus carica fiber based activated carbon (FCAC) was used as a potential adsorbent for Cr(VI) removal from aqueous system. The adsorbent was prepared by carbonization of F. carica fiber followed by H3PO4 activation under microwave radiations. The activated carbon was characterized using scanning electron microscopy and Fourier transformer infrared spectroscopy. The adsorption data were well studied for adsorption isotherms, kinetics models, and thermodynamics. Adsorption of chromium ion followed the second-order kinetics and best fitted the Langmuir adsorption isotherms. The maximum adsorption capacity of Cr(VI) onto FCAC was 44.84 mg/g. The calculated values of thermodynamic parameters like enthalpy change (ΔH°), entropy change (ΔS°), and free energy change (ΔG°) were found to be 7.85 kJ/mol, 69.17 J/mol K, and -13.11 kJ/mol, respectively. Adsorption process was spontaneous and endothermic in nature.

Removal of Cr(VI) onto Ficus carica biosorbent from water

The utilization of sustainable and biodegradable lignocellulosic fiber to detoxify the noxious Cr(VI) from wastewater is considered a versatile approach to clean up a contaminated aquatic environment. The aim of the present research is to assess the proficiency and mechanism of biosorption on Ficus carica bast fiber via isotherm models (Langmuir, Freundlich, Temkin, Harkin's-Jura, and Dubinin-Radushkevich), kinetic models, and thermodynamic parameters. The biomass extracted from fig plant was characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and contact time were studied by batch method. The equilibrium data were best represented by the Langmuir isotherm model, and the maximum adsorption capacity of Cr(VI) onto biosorbent was found to be 19.68 mg/g. The pseudo-second-order kinetic model adequately described the kinetic data. The calculated values of thermodynamic parameters such as enthalpy change (∆H(0)), entropy change (∆S(0)), and free energy change (∆G(0)) were 21.55 kJ/mol, 76.24 J/mol K, and -1.55 kJ/mol, respectively, at 30 °C which accounted for spontaneous and endothermic processes. The study of adsorbent capacity for Cr(VI) removal in the presence of Na(+), Mg(2+), Ca(2+), SO 4 (2-) , HCO 3 (-) and Cl(-) illustrated that the removal of Cr(VI) increased in the presence of HCO(3-) ions; the presence of Na(+), SO 4 (2-) or Cl(-) showed no significant influence on Cr(VI) adsorption, while Ca(2+) and Mg(2+) ions led to an insignificant decrease in Cr(VI) adsorption. Further, the desorption studies illustrated that 31.10% of metal ions can be removed from an aqueous system, out of which 26.63% of metal ions can be recovered by desorption in first cycle and the adsorbent can be reused. The results of the scale-up study show that the ecofriendly detoxification of Cr(VI) from aqueous systems was technologically feasible.

Biosorption: a mechanistic approach

The ability of microbial cells to sequester solutes selectively from aquatic solutions, via nonmetabolically mediated pathways, has been termed biosorption. The mechanism of biosorption has been shown not to be simple and often specific to the biomass-solute pair. The understanding of the mechanism at play, in each biosorption system, is a prerequisite for the understanding of the stoichiometry, the equilibrium, the kinetics, the selectivity, and the engineering process application potential. Biosorption has been studied mostly for inorganic ionic solutes, but there is also reported work on the biosorption of organic molecules. Reference is also made to the biosorption engineering application issues.

Biosorption of Cr(III) and Fe(III) in single and binary systems onto pretreated orange peel

Trivalent chromium and iron are the products of the traditional reduction of hexavalent chromium by ferrous salts in industrial wastewater. Although there have been a few studies of Cr(III) adsorption, none have considered the effect of Fe(III) on Cr(III) adsorption in a binary system representing expected products of hexavalent chromium in industrial wastewater. The biosorption of Cr(III) and Fe(III) ions onto pretreated ground orange peel in single and binary systems was studied in batch experiments using a variety of techniques. The kinetic results showed a rapid rate of biosorption of Cr(III) and Fe(III) in single and binary systems and mutual interference effects in the competitive binary Cr(III)-Fe(III) system. Second order kinetic models showed the best fit for all systems. The behavior of competitive Cr(III)-Fe(III) biosorption were successfully described by the multicomponent Langmuir model, obtaining maximum capacities for Cr(III) and Fe(III) of 9.43 and 18.19 mg/g respectively. SEM/EDS results confirmed that the metals adsorb on the surface and FTIR identified the hydroxyl groups on the carboxylic acids as the active binding sites.

A spectroscopic study for understanding the speciation of Cr on palm shell based adsorbents and their application for the remediation of chrome plating effluents

Palm shell based adsorbents prepared under five different thermochemical conditions have been shown to be quite effective for removal of chromium (III and VI) from aqueous solutions. X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FT-IR) have been used to determine information about the speciation and binding of chromium on the adsorbents under study. X-ray photoelectron spectroscopy (XPS) studies indicate that oxidation of lignin moieties takes place concurrently to Cr(VI) reduction and leads to the formation of hydroxyl and carboxyl functions. The maximum adsorption capacity for hexavalent chromium was found to be about 313 mg/g in an acidic medium using PAPSP. This is comparable to other natural substrates and ordinary adsorbents. The efficacy of the adsorbents under study to remove chromium from plating waste water has been demonstrated.

Cd(II) biosorption using Lessonia kelps

Lessonia kelps (L. trabeculata and L. nigrescens) have been successfully used for the recovery of Cd(II) from near neutral solutions. The biomass was pre-treated with calcium chloride for stabilization of alginate-based compounds. SEM-EDAX analysis and FT-IR spectrometry analysis were used for identifying the modifications of the biomass. Sorption isotherms were performed at the optimum pH (i.e., pH 6) and the maximum sorption capacity reached up to 1 and 1.5 mmol Cd g(-1) for L. nigrescens (L.n.) and L. trabeculata (L.t.), respectively. The Langmuir equation fits well experimental data. The temperature (in the range 20-40 °C) had a more marked effect on affinity coefficient than on maximum sorption capacity. The influence of particle size, sorbent dosage, metal concentration and temperature was evaluated on uptake kinetics. The kinetic profiles that were modeled using the Crank equation (i.e., the resistance to intraparticle diffusion) were hardly affected by the temperature and the particle size contrary to the sorbent dosage and the metal concentration, which show greater impact. The pseudo-second order rate equation was also tested for the modeling of uptake kinetics.

Adsorption of chromium(VI) and Rhodamine B by surface modified tannery waste: kinetic, mechanistic and thermodynamic studies

In this study, various activation methods have been employed to examine the potential reuse of tannery residual biomass (TRB) obtained from vegetable tanning process for the removal of Cr(VI) and Rhodamine B (RB) from aqueous solution. The maximum BET surface area (10.42 m(2)/g), honey comb pore distribution and uptake of both Cr(VI) and RB were achieved when only 3-fold volume of HCl was used to activate the biomass. The pH and temperature experiment showed that they have considerable impact on the adsorption capacity of the used adsorbent. The presence of other ions (Na(+), Ca(2+) and NH(4)(+)) significantly reduces the metal uptake but marginal enhancement in the dye removal was observed when Na(+) and NH(4)(+) ions were present in the solution. The equilibrium data fitted satisfactorily with the Langmuir model and monolayer sorption capacity obtained as 177-217 and 213-250 mg/g for Cr(VI) and RB at 30-50°C, respectively. The sorption kinetics was found to follow the pseudo-second-order kinetic model. The increase in adsorption capacity for both metal and dye with increase in temperature indicates that the uptake was endothermic in nature. The results indicate that the HCl modified TRB (A-TRB) could be employed as a low cost adsorbent for the removal of both Cr(VI) and RB from the aqueous solution including industrial wastewater.

Biosorption of metal ions from aqueous solution and tannery effluent by Bacillus sp. FM1

The metal binding capacity of Bacillus sp. FM1 isolated from soil irrigated with tannery effluent was assessed using synthetic metal solutions and tannery wastewater. Biosorption of Cr(VI) and Cu(II) ions from aqueous solutions using Bacillus was investigated as a function of pH, initial metal ion concentration and contact time. The optimum adsorption pH value observed for Cr(VI) and Cu(II) ions was 2 and 5, respectively. Metal ion uptake increased with increasing initial metal concentration but no significant difference was observed by increasing the time after 60 min. Maximum uptake capacity of chromium was estimated as 64.102 mg g(-1), and of copper to 78.125 mg g(-1). Equilibrium data were well described by the Langmuir and Freundlich adsorption relations. The presence of functional groups on the cell wall surface of the biomass that may interact with the metal ion was confirmed by Fourier Transform Infrared (FTIR) spectroscopy. The application of Bacillus to remove Cr(VI) and Cu(II) in tannery effluent revealed that the biomass was capable of removing both the metal ions. However, the biosorption performance was slightly lower compared to that of synthetic metal solutions. Several factors may be responsible for this difference. However, the most important factor appears to be the presence of other contaminants such as anions, organics, and other trace metals in the effluent.

Mechanism of electron transfer in the bioadsorption of hexavalent chromium within Leersia hexandra Swartz granules by X-ray photoelectron spectroscopy

Leersia hexandra Swartz biogranules were used to adsorb Cr(VI) from aqueous solutions. Batch biosorption experiments showed that the Cr(VI) concentration sharply decreases in the first 15 min. The main functional groups that may be involved in chromium sorption were determined using Fourier transform infrared spectroscopy. The use of X-ray photoelectron spectroscopy confirmed the reduction of Cr(VI) to Cr(III) through L. hexandra Sw. Results indicate that Cr(III) is the dominant species on the surface of the biogranules and that the redox reaction can be accomplished within 40 min. The mechanism of electron transfer during Cr(VI) reduction to Cr(III) was investigated. Protonation of the oxygen-containing groups produces electrostatic-sorption power over Cr(VI). The nitrogen-containing groups serve as the electron-donor groups in the process of reduction-sorption. Moreover, after the complete reduction of Cr(VI), the pH of the suspension significantly increases.