A survey of multi-component sorption models for the competitive removal of heavy metal ions using bush mango and flamboyant biomasses

A Review on Advances in the Use of Raw and Modified Agricultural Lignocellulosic Residues in Mono- and Multicomponent Continuous Adsorption of Inorganic Pollutants for Upscaling Technologies

Using raw and modified lignocellulosic residues as bioadsorbents in continuous adsorption is challenging but it marks significant progress in water treatment and the transition to a bio-based circular economy. This study reviews the application of bioadsorbents in fixed-bed columns for treating water contaminated with inorganic species, offering guidance for future research. It evaluates chemical modifications to enhance adsorptive properties, explores adsorption mechanisms, and analyzes bioadsorbent performance under competitive adsorption conditions. Analysis of adsorption data included evaluation of adsorption capacity in mono- and multicomponent solutions, regeneration, reuse, bed efficiency, and disposal of spent bioadsorbents. This enabled assessing their scalability to sufficiently high levels of maturity for commercialization. In multicomponent solutions, selectivity was influenced by the characteristics of the bioadsorbents and by competitive adsorption among inorganic species. This affected adsorption performance, increasing the complexity of breakthrough curve modeling and controlling the biomaterial selectivity. Models for mono- and multicomponent systems are presented, including mass transfer equations and alternatives including "bell-type" equations for overshooting phenomena and innovative approaches using artificial neural networks and machine learning. The criteria discussed will assist in improving studies conducted from cradle (synthesis of new biomaterials) to grave (end use or disposal), contributing to accurate decision making for transferring the developed technology to an industrial scale and evaluating the technical and economic feasibility of bioadsorbents.

Prewetting Electron Beam Irradiated and Native Sheep Wool Can Affect Their Sorptivity

In this work, the effect of prewetting native and electron beam-modified wool on the resulting sorption of Cu(II) from wool solutions was studied. The following conditions and combinations were applied: 6 mM and 50 mM solutions, prewetting time 0-24 h, contact time 1-24 h. The sorption results showed that wetting the wool before sorption from the low concentrated solution can fundamentally improve the efficiency of the separation process. The opposite result was achieved when applying a more concentrated solution; that is, prewetting slightly reduced the sorptivity. The reasons for such results are discussed. The application of these findings can be used to optimize the separation process in technological practice, however, will require solute specification.

Single and Binary Removals of Pb(II) and Cd(II) with Chemically Modified Opuntia ficus indica Cladodes

In this study, cladodes of Opuntia ficus indica (OFIC), chemically modified with NaOH (OFICM), have been prepared, characterized, and tested as an effective biomass to remove Pb(II) and/or Cd(II) from aqueous media. At an optimum pH of 4.5, the adsorption capacity, qe, of treated OFICM was almost four times higher than that of untreated OFIC. The maximum adsorption capacities (qmax) in the single removal of Pb(II) and Cd(II) were 116.8 and 64.7 mg g-1, respectively. These values were 12.1% and 70.6% higher than those for the corresponding qmax in binary removal, which indicates the strong inhibitive effect of Pb(II) on the co-cation Cd(II) in a binary system. Structural and morphological characterization have been carried out by FTIR, SEM/EDX, and point of zero charge (pHPZC) measurements. The SEM/EDX results confirmed that the metals are adsorbed on the surface. The presence of C-O, C=O, and COO- functional groups were identified by FTIR on both OFIC and OFICM surfaces. On the other hand, we found that the adsorption processes followed the pseudo-second-order kinetics for both single and binary systems, with a fast biosorption rate of Pb(II) and Cd(II). The equilibrium data (adsorption isotherms) were better described by Langmuir and modified-Langmuir models for single and binary systems, respectively. A good regeneration of OFICM was obtained with an eluent of 0.1 M HNO3. Therefore, OFICM can be efficiently reused to remove Pb or Cd, up to three times.

Competitive Cation Adsorption on Electron-Irradiated Sheep Wool Changes the Fitting of Adsorption Isotherms for Single-Component Solutions

This work analyses 10 adsorption isotherm models applied to adsorption of Cr(III) and Cu(II) from binary solutions on electron-irradiated sheep wool (0-24-100) kGy. The results are compared with fitting the same adsorbates from corresponding single solutions. The competing cation significantly changes the fitting of the selected isotherms to the extent that even simultaneous fitting of the same cation in the single and binary solution is rare. In the case of Cr(III), 4 favourable matches were found out of 30 compared cases, while in the case of Cu(II), only 2 conformities were found. Having the Cr(III) coordination number exclusively of 6, but Cu(II) up to 4, 5, 6, the last coordinates more easily with the ligands provided by keratin, resulting in preferential chemisorption. If there is still a lack of cysteic acid in the wool to interact with Cr(III) also, this is adsorbed on the wool physically, too. The amount of cysteic acid increasing in the wool with the absorbed dose of energy improves the chemisorption of Cr(III), as well. It can be summarized that during competitive adsorption, Cu(II) binds by chemisorption and Cr(III) by both physisorption and chemisorption, depending on the dose of energy absorbed by the wool.

Competitive Adsorption of Cr(III) and Cu(II) on Electron Beam-Irradiated Sheep Wool from Binary Solutions Can be Controlled by the Absorbed Dose

Sheep wool irradiated by an electron beam was tested for adsorption of Cr(III) and Cu(II) from binary solutions within the same concentration of each cation from 15 to 35 mmol·dm^-3. The wool sorptivity examination was aimed at searching the effect of the dose absorbed by wool on simultaneous sorption of these cations due to surface and bulk changes. The partners affected each other under these conditions. In the whole concentration range, the sorptivity of nonirradiated wool (0 kGy) for Cu(II) fluctuated within the range of 14.5-20.7 mg·g^-1, while sorptivity for Cr(III) ranged from 14.8 to 7.5 mg·g^-1. However, sorptivity for Cu(II) was always superior to Cr(III). At a 24 kGy dose, the wool sorptivity for both cations decreased approximately by half and tended to converge, whereby at 20 mmol·dm^-3, a slight predominance for Cr(III) was already observed. However, the sorptivity of 100 kGy dosed wool acquired a clear predominance for Cr(III) over Cu(II) in the entire concentration range, showing some leveling around 14.5 mg·g^-1. Sorptivity for Cu(II) was suppressed and increased nonlinearly with concentrations from 1.7 to 10.2 mg·g^-1. It was concluded that optimally dosed wool could provide a special adsorbent suitable to control preferential sorption of some cations from binary solutions.

A feasible biochar derived from biogas residue and its application in the efficient adsorption of tetracycline from an aqueous solution

The recovery of carbon materials from biogas residue (BR) could efficiently promote the efficient utilization of waste and the preparation of novel materials. In this study, a green and feasible reagent of citric acid was introduced and applied in the modification of biogas residue biochar (BRC). The modified biogas residue biochar (CABRC) showed a superior adsorption ability due to its higher specific surface area (approximately 6 times that of the BRC). Additionally, the adsorption capacities of CABRC and BRC for TC were 58.25 mg/g and 20.77 mg/g, respectively, while the TC adsorption performance of CABRC was 2.8 times that of BRC. The adsorption of TC by both BRC and CABRC was primarily controlled by physical adsorption and chemical adsorption (including pore filling, hydrogen bonding, π-π DEA interaction, and electrostatic interaction). Therefore, CABRC should be considered an environmentally friendly material due to its higher adsorption performance, which could expand its application in wastewater treatment.

Full factorial design and dynamic modelling of silent and ultrasound-assisted lead and cadmium removal by porous biosorbent

Present work aimed to analyse single and competitive lead and cadmium batch adsorption, using experimental studies and mathematical modelling. The experiments were conducted in silent and ultrasound-assisted systems, in aqueous environment, using grinded hazelnut shells as porous biosorbent. The influence of process factors (pH, adsorbent concentration, adsorbent particle size, and initial species concentration in liquid phase) on species removal efficiency was evaluated when process equilibrium was attained. The statistical study, following a 2⁴ factorial experimental design, allowed the development of a model to predict variables influence. Based on the obtained results a deeper analysis of the separation efficiency, depending on process factors, was conducted. The dynamic study was performed based on experimentally obtained removal rates, modelled considering species diffusion, with reversible kinetics of sorption inside solid particles. Hence, the dynamics of removal efficiency was determined for several representative experiments. The equilibrium isotherms data, best fitted by an appropriate Langmuir model, were used in the dynamic model to reduce the number of model parameters which normally require experimental identification.

A Review of the Modeling of Adsorption of Organic and Inorganic Pollutants from Water Using Artificial Neural Networks

The application of artificial neural networks on adsorption modeling has significantly increased during the last decades. These artificial intelligence models have been utilized to correlate and predict kinetics, isotherms, and breakthrough curves of a wide spectrum of adsorbents and adsorbates in the context of water purification. Artificial neural networks allow to overcome some drawbacks of traditional adsorption models especially in terms of providing better predictions at different operating conditions. However, these surrogate models have been applied mainly in adsorption systems with only one pollutant thus indicating the importance of extending their application for the prediction and simulation of adsorption systems with several adsorbates (i.e., multicomponent adsorption). This review analyzes and describes the data modeling of adsorption of organic and inorganic pollutants from water with artificial neural networks. The main developments and contributions on this topic have been discussed considering the results of a detailed search and interpretation of more than 250 papers published on Web of Science ® database. Therefore, a general overview of the training methods, input and output data, and numerical performance of artificial neural networks and related models utilized for adsorption data simulation is provided in this document. Some remarks for the reliable application and implementation of artificial neural networks on the adsorption modeling are also discussed. Overall, the studies on adsorption modeling with artificial neural networks have focused mainly on the analysis of batch processes (87%) in comparison to dynamic systems (13%) like packed bed columns. Multicomponent adsorption has not been extensively analyzed with artificial neural network models where this literature review indicated that 87% of references published on this topic covered adsorption systems with only one adsorbate. Results reported in several studies indicated that this artificial intelligence tool has a significant potential to develop reliable models for multicomponent adsorption systems where antagonistic, synergistic, and noninteraction adsorption behaviors can occur simultaneously. The development of reliable artificial neural networks for the modeling of multicomponent adsorption in batch and dynamic systems is fundamental to improve the process engineering in water treatment and purification.

Adsorption capacity of composite bio-modified geopolymer for multi-component heavy metal system: optimisation, equilibrium and kinetics study

Industrialisation and urbanisation contribute greatly to the deposition of toxic waste and metalloids to the environment. Therefore, the use of efficient and eco-friendly materials such as geopolymers and biopolymers is essential for the adsorption of the toxic metals. The implementation of these low-cost sorbents has fascinated a great deal of interest owing to effectiveness, ease of operation, less environmental impact, etc. In this study, biocomposites were synthesised from bio-treatment of geopolymer (kaolin and palm oil fuel ash) using an anionic biopolymer. The biocomposites were utilised as biosorbent for removal of Cu, Fe and Zn in a multi-component system, with the process parameters optimised. FTIR and SEM/EDX outcomes clearly denoted the microporous framework of geopolymer structures and the presence of bio-molecules from the biopolymer. XRD and XRF techniques on the precursors described suitability for geopolymerisation due to the rich aluminate-silicate content. Based on response surface methodology, the adsorption capacities for Cu, Fe and Zn are 35.01 mg/g, 45.175 mg/g and 44.630 mg/g at optimal conditions of pH (7.5), time (40.5 min), metal ion concentration (80 mg/l), biosorbent dosage (0.2 g) and biopolymer concentration (0.75 g in 50 ml). The multi-component system was apt with the modified competitive Langmuir isotherm which described the homogeneity of the prominent sites of the biocomposites. Based on the adsorption kinetics, Cu was only dominated by the pseudo-first-order reaction (PFOR) while Fe and Zn were influenced by both PFOR and intra-particle diffusion processes. The result obtained from the synthesised biocomposites recommends application to actual wastewater systems.

Competitive and non-competitive zinc, copper and lead biosorption from aqueous solutions onto flax fibers

Competitive and non-competitive batch experiments were conducted on flax fibers to study Zn²⁺, Cu²⁺, and Pb²⁺ ions biosorption performance. Biosorption efficiency was dependent on contact time, pH, and biosorbent concentration. The results under competitive conditions were different from those obtained in non-competitive form. A high affinity of lead, with a selectivity sequence in general of Pb > Cu > Zn was observed. The biosorption data fitted very well the Langmuir model for lead in both types of solutions and for zinc and copper in the monometal form. The fit with the Freundlich model was not as successful, except for copper in the ternary system. Regarding zinc under competitive conditions, the sorption process was quite difficult and thus the equilibrium data could not fit well the adsorption models. The maximum adsorption capacities (mmol.kg^-1) were respectively 112, 122 and 71, for Pb, Cu and Zn in the single metal ion solution and 82, 57 and 8 only in the ternary, showing thus a high competition between metal ions when added simultaneously. Overall, lead could still be efficiently removed in spite of the presence of other ions while zinc would be overcome in the presence of lead and copper.

Guidelines for the use and interpretation of adsorption isotherm models: A review

Adsorption process is considered as one of the most used separation and purification processes, in which adsorption occurs by the formation of the physical or chemical bonds between a porous solid medium and a mixture of liquid or gas multi-component fluid. By taking into consideration the equilibrium data and the adsorption properties of both the adsorbent and the adsorbate, adsorption isotherm models can describe the interaction mechanisms between the adsorbent and the adsorbate at constant temperature. Therefore, understanding modelling of the equilibrium data is a very essential way of predicting the adsorption mechanisms of various adsorption systems. Furthermore, adsorption isotherms in batch experiments can be used for the determination of the solid-water distribution coefficient (K_id). This review paper discusses the guidelines of using mono/multi-parametric isotherm models with different applications. The aim of this paper is to establish criteria for choosing the optimum isotherm model through a critical review of different adsorption models and the use of various mathematically error functions such as linear regression analysis, nonlinear regression analysis, and error functions for adsorption data optimization. In this paper, 15 mono-parametric adsorption isotherm models having one, two, three, four and five parameters were investigated. In addition, 10 multi-parameter isotherm models were reviewed as well as addressing their applications.

Insights into the isotherm and kinetic models for the coadsorption of pharmaceuticals in the absence and presence of metal ions: A review

Pharmaceuticals are a wide class of emerging pollutants due to their continuous and the increasing consumption of users. These pollutants are usually found in the real environment as mixtures alone or with metal ions. Thus, the migration risk increases, which complicates the removal of pharmaceuticals because of the combined and synergistic effects. The focus of treatment of pharmaceutical mixtures and their coexistence with metals is of considerable importance. For this purpose, adsorption has been efficiently applied to several studies for the treatment of such complex systems. In this article, the coadsorption behavior of pharmaceuticals in the absence and existence of metals on several adsorbents has been reviewed. The adsorption isotherms and kinetics of these two systems have been analyzed using different models and discussed. Important challenges and promising routes are suggested for the future development of the coadsorption of the studied systems. This article provides an overview on the most utilized and effective adsorbents, widely studied adsorbates, best applied isotherm and kinetic models, and competitive effect in coadsorption of pharmaceuticals, both with and without metals.

Why Natural or Electron Irradiated Sheep Wool Show Anomalous Sorption of Higher Concentrations of Copper(II)

Sorption of higher concentrations of Cu(II) solution onto natural sheep wool or wool irradiated by an electron beam was studied. Sorption isotherms were of unexpected character, showing extremes. The samples with lower absorbed doses adsorbed less than non-irradiated wool, while higher doses led to increased sorption varying with both concentration and dose. FTIR spectra taken from the fibre surface and bulk were different. It was concluded that there was formation of Cu(II)-complexes of carboxylic and cysteic acids with ligands coming from various keratin macromolecules. Clusters of chains crosslinked through the ligands on the surface limit diffusion of Cu(II) into the bulk of fibre, thus decreasing the sorption. After exhausting the available ligands on the surface the remaining Cu(II) cations diffuse into the keratin bulk. Here, depending on accessibility of suitable ligands, Cu(II) creates simple or complex salts giving rise to the sorption extremes. Suggestion of a mechanism for this phenomenon is presented.

Single and binary sorption of Cr(III) and Ni(II) onto modified pine bark

This study aims to investigate the single and binary biosorption of Cr(III) and Ni(II) by pine bark chemically treated with NaOH solution (MPB). The studies involved the effect of initial pH in the equilibrium, as well as kinetic uptake using synthetic solutions. Equilibrium tests were also conducted with an industrial effluent. The kinetic model of pseudo-second order described well the data of single and binary systems. The equilibrium data were better described by the Langmuir model for both metals. The maximum adsorption capacity (q_max) to single system was 31.4 and 23.7 mg/g for Cr(III) and Ni(II), respectively. To analyse the competitive sorption between chromium and nickel ions, the modified Langmuir and Freundlich models were tested for two different concentration (mEq/L) ratios Cr(III)/Ni(II) of 1:1 and 2:1. The modified Langmuir model is also the best to fit the experimental data for both syntetic and industrial effluents. In the synthetic effluent, the q_max value for Cr(III) in MPB was about 25 mg/g, while q_max for Ni(II) decreased from 12.4 to 5.5 mg/g. The results showed that Ni(II) did not significantly interfere in Cr(III) adsorption capacity, whereas Cr(III) decreased the uptake of Ni(II). The industrial effluent contains several species, and thus, the sorption capacities for Cr(III) and Ni(II) were significantly affected.