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Rice husk is one of the abundant wastes, especially in agricultural countries. Rice husk waste has a silica content of 95.80%, where the silica content can be utilized to make an adsorbent. One of the adsorbents that can be made is Mobil Composition of Matter 41 (MCM-41), a material with a hexagonal structure with a surface area to adsorb ibuprofen. Based on the results of the research that has been done, MCM-41 synthesized with rice husk has the same characterization results as MCM-41 synthesized with commercial materials tetraethyl orthosilicate (TEOS). Fourier Transform Infrared Spectroscopy (FTIR) characterization results show the absorption peak is at wave number 1068.58 cm1 which shows asymmetric Si-O-Si stretching vibrations and at 799.60 cm-1 region is symmetric Si-OSi stretching vibrations. X-ray diffraction (XRD) characterization results show an hexagonal crystal form at 2θ = 20o -30o . Scanning Electron Microscope (SEM) characterization results show particle of 2,664 μm. Based on the results of the research that has been done MCM-41 synthesized from rice husk can adsorb ibuprofen with Langmuir isotherm approach and Pseudo Second Order kinetics, and the maximum adsorbing capacity is 34.48 mg/g.

Since few researches were conducted regarding adsorption kinetics of lead (Pb) especially in calcareous soil therefore, this study has been conducted to determine the Pb adsorption, desorption, and kinetics in two types of calcareous soils. Pseudo-first-order, pseudo-second-order, elovich kinetic models used to determine Pb adsorption. To examine Pb adsorption isotherm, Freundlich, Langmuir, Temkin, and Elovich models were applied at three temperatures (298°, 308°, and 318°K). At three levels of temperatures (298°, 308°, and 318°K), thermodynamic parameters were studied. Desorption was also determined. Pseudo-second-order was the best model for describing the adsorption. Pb adsorption data of all samples were better fitted by Langmuir isotherm. Correlation between Pb adsorption and shaking periods was significantly correlated with soil pH, CCE, clay content, OM, and CEC. ΔGθ<0 shows Pb adsorption in our samples is thermodynamically possible and spontaneous. ΔSθ indicated that samples have a high affinity for Pb. Clay with the highest Pb adsorption capacity also has the lowest Pb desorption. Desorption percentage (Pdes) were 75% and 93.6% for clay and sandy clay loam, respectively. In other words, over time, sandy clay loam desorbed more Pb. [ABSTRACT FROM AUTHOR]

Nitrate is the main form of nitrogen species in natural waters. Excessive nitrate concentration in water is highly undesirable, so that removal of the excessive nitrates in waters is very important. However, the challenge is purposed to remove the excessive nitrates in sea waters by considering anions-rich sea water. Adsorption is a favorable method for the nitrate removal process. Therefore, this research was aimed to study the kinetics and isotherm of nitrates adsorption in salt water. The adsorbent preparation was done by modifying natural zeolite with iron oxide. The adsorbent characterization was carried out by FT-IR spectroscopy and Gas Sorption Analyis methods. The results showed that the modified zeolite have Fe−O group vibrations as indicated by a peak at a wave number of 1404.18 cm−1 and an increased specific surface area. The modified zeolite is capable of adsorbing nitrate ions. The adsorption isotherms studies indicated that the modified zeolite is appropriate to the Dubinin-Radushkevich model. The average adsorption energy value (ED), obtained based on the Dubinin-Radushkevich isotherm

This study reported the accumulation of Methylene Blue (MB) by sulphonated Solanum virginianum carbon (SSVC) using batch technique. Adsorption studies are conducted in altered initial dye concentrations, adsorbent doses, pH, contact time and temperature. The removal of MB increases with decrease in concentration of dye. The experimental data was analysed by Langmuir, Freundlich and Temkin models. The adsorption capacity (Qo) of SSVC was found to be 24.12 mg/g. The process of dye accumulation follows second order kinetics. From the effect of temperature, thermodynamic parameters such as the free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were determined. [ABSTRACT FROM AUTHOR]

The focus of this study was to modify the low cost, environment friendly and abundantly available dull pink clay (DPC) with cetyltrimethylammonium bromide (CTAB, a cationic surfactant) in order to increase its adsorption capacity. Surfactant-modified clays are known to enhance the adsorption capacity of hydrophobic organic contaminants from aqueous solution owing to their increased organic content. Herein, we described the modification of DPC with CTAB to produce modified adsorbent (CTAB-DPC) and its application for adsorptive removal of amaranth (AM) dye from water. The surface morphology of CTAB-DPC was revealed using scanning electron microscopy (SEM). The Brunauer–Emmett–Teller (BET) surface area, pore volume and pore diameter of CTAB-DPC was found to be 271.85 m2/g, 0.464 cm3/g and 10.068 nm, respectively. The adsorption of AM on CTAB-DPC strongly followed the Langmuir and Dubinin-Radushkevich isothermal models; whereas the kinetics studies revealed that the adsorption process was better explained by pseudo second order. At all temperatures the values of ΔG° are negative (−14.06 to −14.98 KJ/mol and −20.654 to −21.997 KJ/mol for DPC and CTAB-DPC, respectively), which shows that adsorption of AM onto DPC and CTAB-DPC is feasible and spontaneous at all temperatures. The CTAB-DPC displayed remarkable efficiency towards the removal of widely used AM from aqueous system. The results revealed that the maximum removal efficiency (~97%, 73 mg/g) was achieved at 0.5 g/L of CTAB-DPC dose, 50 ppm AM concentration, pH 2 and temperature 55°C, which suggests that CTAB-DPC could be an effective adsorbent that could easily be scaled-up into adsorption applications. [ABSTRACT FROM AUTHOR]

An activated carbon was prepared from Cassia fistula (L) Epicarps using phosphoric acid as an activating agent and designated as Cassia fistula Phosphoric acid Activated Carbon (CFPAC). Adsorption kinetics of copper (II) ion from aqueous solution onto the adsorbent CFPAC was investigated by taking different initial concentrations 10,20,30 and 40 mg/L at the temperature 303K. Kinetic data were fitted with Lagergren, Ho and Webber-Morris equations for pseudo first order and pseudo second order and intra particle diffusion models respectively. According to Mean of Sum of Squired Error (MSSE) tool, the adsorption followed pseudo second order kinetic equation. Intra particle diffusion was the rate determining step as per Webber Morris plot constant values. [ABSTRACT FROM AUTHOR]

Abstract The emergence of the aluminium recycling industry has led to an increase in aluminium-containing wastewater discharge to the environment. Biological treatment of metal is one of the solutions that can be provided as green technology. Screening tests showed that Brochothrix thermosphacta and Vibrio alginolyticus have the potential to remove aluminium from wastewater. Brochothrix thermosphacta removed up to 49.60%, while Vibrio alginolyticus was capable of removing up to 59.72% of 100 mg/L aluminium in acidic conditions. The removal of aluminium by V. alginolyticus was well fitted with pseudo-first-order kinetics (k 1 = 0.01796/min), while B. thermosphacta showed pseudo-second-order kinetics (k 2 = 0.125612 mg substrate/g adsorbent. hr) in the process of aluminium removal. V. alginolyticus had a higher rate constant under acidic conditions, while B. thermosphacta had a higher rate constant under neutral pH conditions. Graphical abstract Image 1 Highlights • Biosorption of aluminium by isolated indigenous bacteria was assessed. • Kinetics of aluminium removal by indigenous bacteria were calculated. • Brochothrix thermosphacta and Vibrio alginolyticus have potential in aluminium removal. [ABSTRACT FROM AUTHOR]

This review is based on the adsorption characteristics of sorghum (Sorghum bicolor) for removal of heavy metals from aqueous media. Different parameters like pH, temperature of the medium, sorghum concentration, sorghum particle size, contact time, stirring speed and heavy metal concentration control the adsorption efficiency of sorghum biomass for heavy metal ions. Sorghum biomass showed maximum efficiency for removal of heavy metal ions in the pH range of 5 to 6. It is an agricultural waste and is regarded as the cheapest biosorbent, having high adsorption capacity for heavy metals as compared to other reported adsorbents, for the treatment of heavy metal polluted wastewater. Adsorption of heavy metal ions onto sorghum biomass follows pseudo second order kinetics. Best fitted adsorption isotherm models for removal of heavy metal ions on sorghum biomass are Langmuir and Freundlich adsorption isotherm models. Thermodynamic aspects of heavy metal ions adsorption onto sorghum biomass have also been elaborated in this review article. How adsorption efficiency of sorghum biomass can be improved by different physical and chemical treatments in future has also been elaborated. This review article will be highly useful for researchers working in the field of water treatment via biosorption processing. The quantitative demonstrated efficiency of sorghum biomass for various heavy metal ions has also been highlighted in different sections of this review article. [ABSTRACT FROM AUTHOR]

Zero valent iron nanoparticles (nZVI) were synthesized using anaerobic granular sludge under anaerobic conditions. UV–vis spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy and SEM-EDX were used for characterization of Bio-nZVI. The nZVI loaded anaerobic granular sludge (Bio-nZVI) was subsequently evaluated for removing methyl orange from aqueous solutions. Central composite design with three level factors has been employed for the determination of efficient process parameters such as methyl orange initial concentration (10–50 mg/L), weight of anaerobic granules (10–30 mg dry weight) and interaction time (90–240 min) for methyl orange removal from aqueous solution. Under the optimized conditions (weight of Bio-nZVI: 30 mg; interaction time: 240 min and initial methyl orange concentration: 10 mg/L), the removal percentage and removal capacity was found to be 99% and 168 mg/g respectively. The reduction of methyl orange by Bio-nZVI followed pseudo-second order kinetics. The granules were characterized for possible changes in the morphology and surface chemistry after methyl orange removal. The process applicability was further evaluated for removing methyl orange from ground water and lake water samples spiked with known concentrations of methyl orange. [ABSTRACT FROM AUTHOR]

Conventional technologies for the removal of dyes from the waste water are proving expensive due to non-regenerable materials used and their high costs. The use of dried biomass from Haloxylon recurvum plant stems (HRS) was studied for the removal of methylene blue, a textile dye, from its aqueous solution. FTIR studies revealed a variety of functional groups on the plant surface including carboxyl and amino groups. The pH at the point of zero charge (pHpzc) was found to be 6.3. The dye uptake by the plant increased with increasing pH, time of contact and dye concentration. Lagergren Pseudo first order and the Ho’s pseudo second order models were used to study the kinetics. The Langmuir and Freundlich equilibrium models were studied and the qmax was 22.93 mg/g. The changes in the values of free energy (ΔGo) and enthalpy (ΔHo) indicated the spontaneous, feasible and exothermic nature of the sorption process. H. recurvum plant is locally available in large quantities, so the powdered stems can act as a cost-effective and ecofriendly biosorbent for the removal of the dye from its aqueous solutions.

A green and novel approach was demonstrated for successful remediation of arsenic from contaminated water by citric acid (CA) cross-linked water hyacinth root powder (RP). Different analytical techniques were used to investigate the binding and structural properties of prepared materials. Titanium dioxide played a significant role in the cross-linking process. Incorporation of CA into RP enhanced its integrity, and thus removal efficiency remained unaffected after several cyclic runs. Also the turbidity which formed due to treatment with uncross-linked RP was reduced to below the permissible limit. Effect of the amount of CA, material dose, treatment time, initial ion concentration, and pH were investigated. Use of 10% ( w/w) CA was found to be sufficient to bring down the turbidity of the treated water below 2.5 nephelometric turbidity unit (NTU) without hampering the removal capacity/rate. A material dose of 5 g/L removed successfully total inorganic arsenic concentration to below 10 μg/L. The sorption process could be reasonably explained by Langmuir isotherm, and the maximum adsorption capacity was found to be 28 μg of arsenic/g. The material was found to be more efficient at acidic pH (pH = 6.72). The sorption process was governed by a pseudo-second-order kinetic model. [ABSTRACT FROM AUTHOR]

The ability of tetrakis-thiomethyl-C-4-methoxyphenylcalix[4]resorcinarene for trapping Pb(II) and Cd(II) from aqueous solution at different pH, contact times, and initial metal concentration was investigated. Concentration of metal ions before and after interaction was analyzed by Atomic Absorption Spectrophotometer (AAS). The result indicated that tetrakis-thiomethyl-C-4-methoxyphenylcalix[4]resorcinarene is a good host for metal ions, where Cd(II) sorption capacity was higher than that of Pb(II). Effect of pH on batch experiments for the mentioned ions indicated that the optimum pH for metal binding were 5 for both of lead(II) and cadmium(II). In order to investigate the mechanism of adsorption, the 1st-order, pseudo 1st-order, and pseudo 2nd-order kinetic models were used. The adsorption model of metal ions on the resorcinarene followed pseudo second order of Ho & McKay expression. The equilibrium adsorption isotherm has been analyzed by Langmuir and Freundlich equations. Langmuir model had the higher correlation coefficient than that of Freundlich model.

[Display omitted] • A review of the use of MILs MOFs for the adsorption of bisphenols (BPA, BPF, BPAF, and BPS) was conducted. • The review examined the adsorption capacity of various MILs MOFs (MIL-100, MIL-101, MIL-53, and MIL-88) for bisphenols removal. • The review analyzed adsorption equilibrium, kinetic, and thermodynamic studies of bisphenols adsorption using MILs MOFs. • The review evaluated the regeneration/reusability and feasibility of MIL MOFs for bisphenols adsorption studies. Achieving the Sustainable Development Goals (SDGs) 2023 required prioritizing the reduction of water pollution, including bisphenols pollution, in order to protect the environment and human health. Metal − organic frameworks (MOFs), specifically MILs (MIL = Material Institute of Lavoisier), acquired recognition as promising materials for bisphenols adsorption because of their adaptability and unique properties. This review summarized the recent updates of knowledge on MILs, including an overview of bisphenols in wastewater environments and MILs MOFs, synthesis techniques, mechanisms, equilibrium, kinetic modelling and thermodynamic studies, the effect of pH and ionic strength, regeneration/reusability studies, the feasibility of MILs MOFs as well as challenges and prospects for bisphenols adsorption. However, further research was needed to understand the mechanisms and relationships underlying MILs and enable their practical, commercial − scale use in bisphenols remediation. This review highlighted the growing importance of MILs MOFs in environmental applications and the necessity in green technologies for substantial remediation. [ABSTRACT FROM AUTHOR]

Biosorption is a cheaper and more eco-friendly process for the removal of dyes from the aqueous media than filtration, chemical oxidation/reduction, electrochemical action, color irradiation, membrane technology, ozonation, etc. In this study, we have evaluated the efficiency of the fibers of Luffa cylindrica sponge for removing Alizarin Yellow-R dye from water. The fibers were chemically treated with NaOH for enhancing their sorption capacity. The sorption experiments were conducted batch wise and the following optimized conditions were recorded: 6.0 ppm initial concentration of the dye, 0.125 g biosorbent dosage, 100 minutes contact time, pH 3.0, 25 rpm speed and 20°C temperature. The equilibrium study was also conducted by fitting the sorption data to Langmuir and Freundlich isotherms. The maximum biosorption capacity of alkali treated Luffa cylindrica fibers was 3.59 mg/g, which was thrice to that with the non-treated one's (1.07 mg/g). The kinetic studies manifested that the pseudo second order rate of reaction was applicable in the biosorption process. The FT-IR study of the biosorbent confirmed the presence of functional groups such as hydroxyl, carboxylic, etc. At low pH these functional groups became protonated and, through hydrogen bonding, more dye molecules were attached to the biosorbent surface. The SEM represented an etched and porous structure after alkali treatment with large surface area. Thus the following study revealed that the alkali treated fibers of Luffa cylindrica sponge can be used efficiently for removing Alizarin Yellow-R dye from the waste water. [ABSTRACT FROM AUTHOR]

Phaseolus vulgaris husk as a novel, very common milling agro waste, showed good performance for mutagenic Cr(VI) removal from chromium enriched aqueous solution. The study involves batch experiments to investigate the effects of influencing parameters, such as pH, temperature, contact time, initial Cr(VI) concentration, and adsorbent dose, on the adsorption process. Results showed a maximum of 99.88% removal of Cr(VI) at pH 1.16, temperature 20 °C and adsorbent dose of 6 g L. The adsorption equilibrium data followed the Freundlich model, suggesting a heterogeneous nature of the adsorbent surface and the correlation coefficient for pseudo-second-order kinetic model was found to be very high, showing its applicability during the adsorption process. The maximum Cr(VI) uptake capacity was 3.4317mg g. Thermodynamic parameters like standard free energy change (−7.175 kJ mol), enthalpy change (−8.29 kJ mol) and entropy change (0.005 kJ mol K) revealed the spontaneous and exothermic nature of adsorption of Cr(VI) onto P. vulgaris husk. Desorption with 1mol L NaOH followed by 1mol L HCl was effective (92.76%) and, hence, it exhibited the possibility of recycling of used husk. [ABSTRACT FROM AUTHOR]

Photocatalytic degradation and removal by adsorption of the Reactive Red 2 (RR2) dye in the presence of different pristine and functionalized one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) carbon structures were investigated and compared, considering also the loading of catalyst/adsorbent. Previous to photocatalytic and adsorption evaluation, all carbon materials were characterized to verify functionalization, structural changes, and surface properties useful in the removal of this pollutant in water. Materials were analyzed by Raman and infrared spectroscopies, transmission electron microscopy, and besides, the pH of the point of zero charge (pHpzc) was determined by potentiometric titrations, and band gap by ultraviolet-visible spectroscopy through Tauc plot. Removal of RR2 increases with the load of carbon materials. One-dimensional materials showed better performance in the decolorization of RR2 dye, removing the whole color of the solution. RR2 removal values obtained by the photocatalytic and adsorption processes are very similar. Thus, the adsorption process predominates over the photocatalytic activity, only the samples of graphene and graphene oxide present slight photocatalytic activity. The adsorption process was strongly influenced by the carbon material dimension. However, other factors like surface oxygenated groups, surface area, and the shape of the carbon structures, as well as the structure and nature of the dye also play an important role in this process. Experimental adsorption data of all carbon materials were best fitted to pseudo second-order kinetic model, and, it is concluded that physisorption with strong interaction is the process by which carbon materials adsorb to the dye. Thus, the mechanism of RR2 adsorption on carbon materials is by the aromatic rings of the RR2 and π delocalized electrons on carbon materials. [ABSTRACT FROM AUTHOR]

Abstract: Ngella sativa seeds, an agriculture material was used for the adsorption of Zn (II) ions from aqueous solutions. The Ngella sativa seeds were extracted with diethyl ether and dried in oven at 105 °C, burned at 500 °C for one hour. The adsorption capacity of the adsorbent was studied using batch adsorption technique at different conditions such as initial pH of adsorbate, contact time between adsorbent and adsorbate and initial concentration of adsorbate. Two kinetic models were applied include first-order and pseudo second-order. It was found that, the present work is follows the pseudo second- order. High adsorption capacity was observed at initial pH of 4. The adsorption capacity was reached equilibrium after 90 minute and at adsorbate initial concentration of 764 mg/l. The Freundlich adsorption model fits well when compared to the Langmuir model. The maximum adsorption capacity of this novel adsorbent was found to be 93 mg/g at temperature 30 °C. Two kinetic models such as first-order and pseudo second-order were tested, in order to study the mechanism of the adsorption. [Copyright &y& Elsevier]

The present work describes dynamic uptake of the antibiotic drug ciprofloxacin hydrochloride (CH), by using a cost-effective agricultural by-product - sawdust (SD). The sawdust was characterised by FTIR and SEM analysis. The sorbent particles were highly porous with average pore diameter of nearly 10 μm. The optimum pH and solid/liquid ratio for sorp?tion of CH were found to be 5.8 and 2.0, respectively. The dynamic drug uptake data was applied to various kinetic models and their order of fitness was found to be pseudo second order > Elovich equation > power function model, as indicated by their regression values. The experimental equilibrium uptake values (qe) were in close agreement with those evalu?ated from the pseudo second order equation for initial sorbate concentrations of 10 and 20 mg·l-1-1 at 33°C. The drug uptake mechanism was found to be attractive non-electrostatic interactions, involving H-bonding interactions between H atoms and other electronegative species such as F, O and N of the drug molecule. The mechanism is discussed on the basis of pHpzc of sawdust and zwitterionic nature of drug CH. Mass transfer analysis was carried out using the drug uptake data obtained with sorbate concentrations of 10 and 20 mg·l-1-1. The used sorbent could be regenerated using 1.0 mol·l-1-1 HCl solution with a regeneration efficiency of nearly 85%. [ABSTRACT FROM AUTHOR]

90Sr having moderate half life (t1/2 = 30 yr) is of major concern for radioactive waste management. Metal antimonate compounds have been employed for the removal of 90Sr from low level liquid waste stream (LLW). Antimonate compounds of tin, manganese, and zirconium were synthesized and their composite materials were prepared by coating with polymethyl metha acrylate beads (PMMA). The composite materials were evaluated for the removal of radiostrontium. The Kd value of about 1800-2000 was observed for all the three metal antimonate composite materials. Effect of pH, salt concentration, temperature, and strontium ion concentration on Kd value was studied. The sorption behavior was examined with various sorption isotherms like Langmuir, Freundlich, and Dubinin-Radushkevich. The thermodynamic parameters for the three composite materials were evaluated. The sorption was observed to be spontaneous and endothermic in nature. From the practical utilization point of view, the rate of uptake of radiostrontium by the composite material was investigated. Weber Morris diffusion model of the uptake studies suggested an intraparticle diffusion mechanism. The kinetics was found to follow pseudo first order pattern with intraparticle diffusion. However, intraparticle diffusion is not the rate controlling step. [ABSTRACT FROM AUTHOR]

Adsorption behaviour of cadmium from its aqueous solution by growing and non-growing cells of a mutant strain of Bacillus cereus M116 has been studied to explore the possibility of the biomass to address environmental pollution due to this toxic metal. The results establish that about 75% and 88% of the cadmium can be removed by growing and non-growing cells of the selected strain respectively from its aqueous solution at pH 6.8 ± 0.2, temperature 30 ± 1°C and 120 rpm shaking speed. For growing cells, inoculum size 2% and medium volume 50 mL is found to be optimum. The adsorption rate of cadmium on the biomass is very fast initially and attains equilibrium within 60 min following pseudo second-order rate model (R2 = 0.99). The equilibrium adsorption isotherm can be best described by Langmuir - Freundlich dual model (R2 = 0.99) indicating that both physisorption and chemisorption take place simultaneously. Cadmium can be desorbed from the loaded biomass using mineral acids (0.1 M). [ABSTRACT FROM AUTHOR]

The article discusses adsorption of cadmium onto the agricultural rice-processing byproduct rice husk ash. Sensitivity analyses are conducted to assess influences of various parameters including pH, contact time, and adsorbent concentration. A second-order model was found to best describe reaction kinetics. Several kinetic parameters were calculated including an effective diffusion coefficient, the thermodynamic equilibrium constant, and Gibbs free energy. Adsorption was found to be spontaneous and chemical in nature.

Abstract: The basic oxygen furnace waste generated in steel plant has been used as a low cost adsorbent for the removal of Pb(II) from aqueous solution. The effect of pH, adsorbent dosage, initial metal ion concentration, contact time and temperature on adsorption process was studied in batch experiments. Results of the equilibrium experiments showed that the solution pH was the key factor affecting the adsorption characteristics. Optimum pH for the adsorption was found to be 5 with corresponding adsorbent dosage level of 5g/L. The equilibrium was achieved within 1h of contact time. Kinetics data were best described by pseudo second order model. The effective particle diffusion coefficient of Pb(II) is the order of 10−10 m2/s. The maximum uptake was 92.5mg/g. The adsorption data can be well fitted by Freundlich isotherm. The result of the equilibrium studies showed that the solution pH was the key factor affecting the adsorption. External mass transfer analysis was also carried out for the adsorption process. The thermodynamic studies indicated that the adsorption is spontaneous and endothermic. The sorption energy (10.1745kJ/mol) calculated from Dubinin–Radushkevich isotherm indicated that the adsorption process is chemical in nature. Desorption studies were carried out using dilute mineral acids to elucidate the mechanism of adsorption. Application studies were carried out considering the economic viewpoint of wastewater treatment plant operations. [Copyright &y& Elsevier]

Zinc ions are present in different types of industrial effluents, being responsible for environmental pollution. Biosorption is a process in which solids of natural origin are employed for binding heavy metals. It is a promising alternative method to treat heavy metal wastes mainly because of high metal binding capacity. The effect of some important parameters on sorption capacity of cyanobacterial biosorbent for zinc uptake was studied. The optimum conditions pH, time, initial ion concentration, adsorbent dose; were found to be 8,90 mins, 100 ppm and 1gm/100mL respectively. Immobilization of biomass was done in calcium alginate and agar matrices for reuse of biosorbent. Freundlich and Langmuir isotherms were applied to equilibrium data ofzincions biosorption and Freundlich isotherm was found to fit the data. The maximum adsorption capacity was 71.42 mg/g for A. variabilis. The value of value of Kf and n were ranged from 0.4458 to 2.797 and 0.7726 to 2.797 for the cyanobacterial biosorbents. 0.1 M EDTA was used as an eluant and the biosorbent was reused up to five biosorption desorption cycles and percentage desorption of zinc ions was 93 to 84 from first to fifth cycle for the cyanobacterial biosorbents. Fourier transform infra-red analysis of algae with and without biosorption revealed the presence of carboxyl, hydroxyl, amino, amide and imine groups, which were responsible for biosorption of Zn+2 ions. The rate law for a pseudo-second- order model fits the experimental data with a very high correlation coefficient and it was greater than 0.9771. [ABSTRACT FROM AUTHOR]

Activated carbon prepared from sulphuric acid treated Flame tree pods' has been used for the removal of Hg(II) from aqueous solution. Batch mode experiments were conducted to assess the potential for the removal of Hg(II) from water using the above carbon. Adsorption experiments showed that the adsorption process follows the pseudo second order kinetic model and the equilibrium data were fitted well with both Freundlich and Redlich-Peterson isotherm model. About 92% of mercury (II) adsorbed was recovered from the spent carbon using distilled water (pH: 1) and 3% KI solution. [ABSTRACT FROM AUTHOR]

Abstract: Clarified sludge is a major waste generating during steel making process. In India and in most industrial countries, the use of clarified sludge as a road ballast and land filter has had a very long history. In present study, clarified sludge has been characterized and used for the removal of Cd(II) from aqueous solutions. The effect of pH, adsorbent dosage, adsorbate concentration, contact time and temperature on adsorption process was studied in batch experiments. Kinetics data were best described by pseudo-second order model. The effective diffusion co-efficient of Cd(II) is of the order of 10−11 m2/s. The maximum uptake was 36.23 mg/g. The adsorption data can be well described by Langmuir isotherm. The result of the equilibrium studies showed that the solution pH was the governing factor affecting the adsorption. Mass transfer analysis was also carried out for the adsorption process. The thermodynamic studies indicated that the adsorption was spontaneous and exothermic in nature. The sorption energy calculated from Dubinin–Radushkevich isotherm indicated that the adsorption process is chemical in nature. Desorption as well as the application studies were carried out considering the economic viewpoint of wastewater treatment plant operations. [Copyright &y& Elsevier]

An investigation has been undertaken to determine the removal of heavy metals (Cd2+, Cu2+, Ni2+ and Zn2+) of high environmental priority due to their toxicity from dilute aqueous solutions by biosorption using inexpensive biomaterials like activated sludge. Activated sludge is used widely in water treatment plants and is easily available. Each experiment was performed over a period of time to determine the biosorption of heavy metals from the aqueous phase to the solid phase. The maximum sorption uptake of the studied metal ions by activated sludge showed the following order: Cd2+ > Cu2+ > Ni2+ > Zn2+. The pseudo first- and second-order kinetic models were used to describe the kinetic data. The experimental data fit with the second-order kinetic model very well. The type of mechanism involved is analyzed in terms of the intraparticle diffusion model. Other models are also reviewed. Quantification of metal-biomass interactions, nature of adsorption, kinetics, ion-exchange as well as models used to characterize activated sludge biosorption are reviewed. All solutions are analyzed using inductively coupled plasma (ICP). [ABSTRACT FROM AUTHOR]

Submerged aquatic plants can be used for the removal of heavy metals. In this paper, the adsorption properties of Myriophyllum spicatum (Eurasian watermilfoil) for lead, zinc, and copper were investigated and the results were compared with other aquatic submerged plants. Data obtained from the initial batch adsorption studies have indicated that M. spicatum is capable of removing lead, zinc, and copper from solution. Metal biosorption was fast and equilibrium was attained within 20 min. Data obtained from further batch studies fitted the Langmuir model. The maximum adsorption capacities (qmax) were 10.37 mg/g for Cu(II), 15.59 mg/g for Zn(II) and 46.49 mg/g for Pb(II). The kinetics of adsorption of zinc, lead and copper were also analysed and rate constants were derived for each metal. It was found that the overall adsorption process was best described by the pseudo second order kinetics. The results showed that this submerged aquatic plant M. spicatum can be successfully used for heavy metal removal. [Copyright &y& Elsevier]

Removal of dyestuffs by adsorption on to live activated sludge was investigated. Two dyes, one acid dye (Acid Yellow 17) and one basic dye (Maxilon Red BL-N), were tested. Initial adsorption studies showed that binding of Acid Yellow 17 onto activated sludge was not promising while Maxilon Red BL-N was adsorbed well by activated sludge and the dye-sludge system conformed to the Langmuir Model. Kinetic studies were also performed for Maxilon Red and live activated sludge system. According to the results obtained, the initial part of the adsorption followed a first-order process, controlled by film diffusion. Intraparticle diffusion also played a significant role. The kinetics of sorption have been analyzed by three kinetic models, the first order Lagergren model, a pseudo second order model and the second order model. Rate constants for each of the models were derived and correlation coefficients were calculated. The overall process was best described by the pseudo second order model rather than first order model or the second order model. [Copyright &y& Elsevier]

• APTMS used as cross linkage agent in the preparation of MZ-A/RGO nanocomposite. • MZ-A/RGO shows high removal performance for MB and Pb+2 using adsorption technique. • The kinetic data of adsorption follow a pseudo-second order kinetic model. • The experimental data of equilibrium follow Langmuir isotherm model. In this work, 3-aminopropyl- trimethoxysilane (APTMS) used as a mesopore generating and cross linkage agent in the preparation of modified mesoporous zeolite-A /reduced graphene oxide nanocomposite (MZ-A/RGO) using hydrothermal method for the high-performance dual removal of methylene blue (MB) and lead ions (Pb2+), which are toxic pollutants of wastewater. Different characterization techniques were used to characterize the MZ-A/RGO. Parameters that included the contact time, initial adsorbate concentrations, pH, sorbent dosages, temperature and ionic strength were varied to investigate the removal efficiency of MB and Pb2+ ions by MZ-A/RGO. The reusability of MZ-A/RGO sorbent was studied for removal of MB and Pb2+ ions in five cycles adsorption/desorption process. The sorption kinetics data were fitted using pseudo-first-order, pseudo-second-order and Elovich kinetic models. In addition, four different adsorption isotherm models – the Freundlich, Langmuir, Temkin and Dubinin–Radushkevich (D-R) – were applied to study the adsorption mechanism. The results indicate that the maximum removal efficiency was achieved during the first 20 min for both MB and Pb2+ ions and equal to 98.5% for MB and 93.9% for Pb2+ ions, respectively. The adsorption process followed pseudo-second-order kinetics. Furthermore, the Langmuir model provided the best fit of the MB and Pb2+ ions adsorption isotherms, with correlation coefficients equal to 0.996 and 0.995, respectively. The reusability experiment exhibits good adsorption result, that indicate the economic and efficient adsorbent in wastewater treatment. In addition, the results indicate that the dual removal efficiency of MZ-A/RGO for MB and Pb2+ ions from wastewater. [ABSTRACT FROM AUTHOR]

Adsorption rate is a critical parameter in the design of effective biosorbent treatment systems for heavy metals removal. Though numerous studies have identified the physico-chemical properties of biosorbents that exert influence on the adsorption rate, such influence has not been mathematically defined, limiting the effective design of adsorption systems. This study quantifies the influence of biosorbent physico-chemical properties including, specific surface area, surface functional groups, pore size, pore volume and zeta potential on the adsorption rate in relation to three divalent metal cations. Mathematical equations were developed to predict the influence of physico-chemical properties on pseudo second order kinetic constant and thereby predict the adsorption rate. Tea factory waste and coconut shell biochar were mixed in different weight percentages to vary the physico-chemical properties under consideration. Four different initial metal ion concentrations were used. Relationship between pseudo second order kinetic constant at each concentration with physico-chemical properties was quantified using regression analysis. The experimental analysis revealed that among the physico-chemical properties, acidic surface functional groups had the most profound influence on sorption mechanisms. Reliability and accuracy of the predictive models were significantly improved when separate models were developed for two ranges of initial metal ion concentrations. The outcomes of this study will contribute to the effective design and optimization of biosorbent mixtures with the capacity to remove Pb2+, Cu2+ and Cd2+ in wastewater. • Increase in acidic surface functional groups can increase reaction rates. • Models improved when developed for two ranges of initial metal ion concentrations. • High specific surface area with micropores structures reduce adsorption rate. • Single mixture of biosorbents can be designed using proposed equations. [ABSTRACT FROM AUTHOR]

This study investigated the use of copper smelter slag for the removal of phosphorus from secondary wastewater effluent through batch tests. The media was physically and chemically characterized and showed presence of Fe 2 O 3 (45.22%), SiO 2 (14.98%), Al 2 O 3 (3.21%), CaO (1.99%), SO 3 (1.77%) and MgO (1.33%). Scanning electron microscopy monographs revealed smooth and flat surface and no heterogeneity on the surface of the slag with visible micro pores before the experiment and less visible after the experiment. The point of zero charge of the media was 5.0. Equilibrium was reached after 4 h at 29.5 ± 0.71% phosphorus removal efficiency and media dosage of 0.4/100 mL. The kinetic data was best described by Pseudo second order equation. More than one mechanisms were involved in the adsorption of phosphorus onto copper smelter slag as suggested by multi-linearity of intra particle diffusion model. Ninety seven percent (97.5 ± 0.0%) removal efficiency was achieved at an equilibrium dosage of 160 gL -1 . The equilibrium isotherm was described better by Langmuir equation with observed maximum adsorption capacity of 0.16 mg P g -1 media and the experimental maximum adsorption capacity was 0.26 mg P g -1 media. Regeneration studies showed low performance with maximum efficiency of 11.7% revealed during the first regeneration trial therefore low practical benefits. Copper smelter slag is a poor adsorbent for phosphorus and further studies on the media should be conducted., (© 2020 The Authors.)

Conventional technologies for the removal of dyes from the waste water are proving expensive due to non-regenerable materials used and their high costs. The use of dried biomass from Haloxylon recurvum plant stems (HRS) was studied for the removal of methylene blue, a textile dye, from its aqueous solution. FTIR studies revealed a variety of functional groups on the plant surface including carboxyl and amino groups. The pH at the point of zero charge (pH pzc ) was found to be 6.3. The dye uptake by the plant increased with increasing pH, time of contact and dye concentration. Lagergren Pseudo first order and the Ho’s pseudo second order models were used to study the kinetics. The Langmuir and Freundlich equilibrium models were studied and the q max was 22.93 mg/g. The changes in the values of free energy (Δ G o ) and enthalpy (Δ H o ) indicated the spontaneous, feasible and exothermic nature of the sorption process. H. recurvum plant is locally available in large quantities, so the powdered stems can act as a cost-effective and ecofriendly biosorbent for the removal of the dye from its aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract: The present communication reports a short history on the pseudo second order kinetic models previously reported for sorption systems. This present paper presents the information citing the original presentation of pseudo second order kinetic expression. [Copyright &y& Elsevier]

Laboratory and field investigations were performed in this study to evaluate the efficacy of a fine-grained clayey soil as a low-cost primary liner material for attenuating chrome-laden leachate from a chrome sludge disposal site of a tannery plant. On-site soil and water samples exhibited the existence of in excess of the permissible limit as prescribed for discharging inland surface water. Batch adsorption kinetic results showed that removal in equilibration increases with elevation of temperature. The soil mass in use exhibited reasonable capability of adsorbing , and the kinetic results demonstrated that the pseudo second-order kinetic model fitted reasonably well. The triaxial test results revealed a maximum permissible overburden pressure of from deposited waste if the clayey soil is to be used as a liner material. The use of a compacted clay soil with a thickness of 600 mm is recommended for effective containment of leachate transmission with regard to a leachable hexavalent chromium with an initial concentration of . [ABSTRACT FROM AUTHOR]