Single- and multi-component adsorption of cadmium and zinc using activated carbon derived from bagasse--an agricultural waste

Wood ash application for crop production, amelioration of soil acidity and contaminated environments

Agriculture is vital to human life and economic development even though it may have a detrimental influence on soil quality. Agricultural activities can deteriorate the soil quality, endangers the ecosystem health and functioning, food safety, and human health. To resolve the problem of soil degradation, alternative soil conditioners such as wood ash are being explored for their potential to improve soil-plant systems. This study provides an overview of the production, properties, and effects of wood ash on soil properties, crop productivity, and environmental remediation. A comprehensive search of relevant databases was conducted in order to locate and assess original research publications on the use of wood ash in agricultural and environmental management. According to the findings, wood ash, a byproduct of burning wood, may improve the structure, water-holding capacity, nutrient availability, and buffering capacity of soil as well as other physico-chemical, and biological attributes of soil. Wood ash has also been shown to increase agricultural crop yields and help with the remediation of polluted regions. Wood ash treatment, however, has been linked to several adverse effects, such as increased trace element concentrations and altered microbial activity. The examination found that wood ash could be a promising material to be used as soil conditioner and an alternative supply of nutrients for agricultural soils, while, wood ash contributes to soil improvement and environmental remediation, highlighting its potential as a sustainable solution for addressing soil degradation and promoting environmental sustainability in agricultural systems.

Impacts of controlled microwave field irradiation on o-cresol and p-cresol adsorption capability of activated carbon

To access the feasibility of microwave in promoting adsorbability of carbonaceous adsorbents, microwave irradiation on activated carbon (AC) was conducted at powers of 400-800 W and duration of 10 min. Accordingly, the temperature rising of AC under microwave field were studied. Moreover, the alterations in physicochemical properties of AC and impacts on cresol isomer adsorption were investigated. Results indicated that the heating curve of AC displays the initial fast temperature rising stage and the final slow stage. Additionally, the bulk temperature at irradiation terminal increases with microwave power. The temperature rising further increases the pores with a diameter range of 1.00-6.00 nm of AC; it also increases the oxygenic functional groups of AC after irradiation at 400 W and 800 W, but decreases that of AC after irradiation at 640 W. The saturation adsorption capacity of o-cresol and p-cresol on the irradiated AC rises with elevated temperature. Additionally, the cresol isomer adsorption kinetics on the irradiated AC follows the Elovich model. The above-mentioned equilibrium and kinetics suggest that the cresol isomer adsorption on the irradiated AC is dominant by chemisorption. Finally, the optimum irradiation power for o-cresol and p-cresol adsorption is 800 W and 400 W, respectively, thereby fabricating AC with developed pores and abundant oxygenic functional groups. Accordingly, the saturation adsorption capacity of o-cresol and p-cresol reaches up to 111.11 mg·g-1 and 95.97 mg·g-1, respectively. Overall, microwave irradiation is a viable option to promote cresol isomer adsorption on AC.

The application of machine learning methods for prediction of heavy metal by activated carbons, biochars, and carbon nanotubes

Carbonaceous materials are commonly used as adsorbents for heavy metals. The determination of the adsorption capacity needs time and energy, and the key factors affecting the adsorption capacity have not been determined. Therefore, a new and efficient method is needed to predict the adsorption capacity and explore the decisive factors in the adsorption process. In this study, three tree-based machine learning models (i.e., random forest, gradient boosting decision tree, and extreme gradient boosting) were developed to predict the adsorption capacity of eight heavy metals (i.e., As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) on activated carbons, biochars, and carbon nanotubes using 3674 data points extracted from 151 journal articles. After a comprehensive comparison, the gradient boosting decision tree had the best performance for a combined model based on all data (R2 = 0.9707, RMSE = 0.1420). Moreover, independent models were developed for three datasets classified by the adsorbent and eight datasets classified by the heavy metals. In addition, a graphical user interface was built to predict the adsorption capacity of heavy metals. This study provides a novel strategy and convenient tool for the removal of heavy metals and can help to improve the removal efficiency of heavy metals to build a healthier world.

Pseudo-Second-Order Kinetic Equation for Describing the Effect of Sorbent and Sorbate Concentrations

The sorbent concentration (Cs) effect and sorbate initial concentration (C0) effect are common phenomena observed in the study of adsorption kinetics at solid-liquid interfaces. That is, adsorption rate constants simulated with classical kinetic equations, such as the pseudo-second-order (PSO) model, for a given system vary with Cs and C0. The classical kinetic equations cannot predict or describe the "Cs-effect" and "C0-effect" (called "C-effects" here). In the current work, the dynamic partition coefficient of sorbate between solid and liquid phases (Kt) was used to describe the adsorption kinetic processes. Based on the surface component activity (SCA) model, which assumes the activity coefficients of the surface components (fs) are not equal to unity but rather a function of Cs and the adsorption capacity (or C0) and referring to the classical PSO model, a new kinetic equation was established, called the "SCA-PSO kinetic model", and its two parameters, the intrinsic equilibrium partition coefficient (Ke0) and the intrinsic rate constant (k20), are independent of Cs and C0. In addition, the new model relates Kt and the rate constant (k2) to Cs and C0 via fs, and can thus describe the C-effects. The fs can be estimated from the change of equilibrium partition coefficient (Ke) with Cs and C0. The new model predicts that with the increase of Cs and C0, Ke decreases while k2 increases. Its rationality was confirmed by the literature-reported adsorption kinetic data of heavy metals on inorganic and biomass sorbents with the C-effects.

Insights into adsorption behavior and mechanism of Cu(II) onto biodegradable and conventional microplastics: Effect of aging process and environmental factors

The widespread promotion attempt of biodegradable plastics is considered as an effective solution to address conventional plastic pollution. However, the interaction of microplastics (MPs) easily broken down from biodegradable plastics with the coexisting pollutants in aquatic environments has gained less attention. Herein, we investigated the effects of the aging process and environmental factors on copper (Cu(II)) adsorption behavior by biodegradable polylactic acid and conventional polystyrene MPs. Results demonstrated that the aging process significantly altered physicochemical properties of both types of MPs, and PLA showed less resistance to aging. The aged polylactic acid MPs (aged-PLA) exhibited the far highest Cu(II) maximum adsorption capacity (7.13 mg/g) mainly due to its abundant oxygen-containing functional groups (OCFGs), followed by pristine polylactic acid (PLA, 6.08 mg/g), aged polystyrene (aged-PS, 0.489 mg/g) and pristine polystyrene (PS, 0.365 mg/g). The adsorption kinetics of Cu(II) on PLA MPs were controlled by film and intraparticle diffusion, while film diffusion governed the Cu(II) adsorption onto PS MPs. In addition to roles of rougher surface structure, greater surface area and pore filling, the complexation of OCFGs and electrostatic interaction were critical to the adsorption mechanism of aged-PLA and aged-PS, and cation-π interaction was associated with adsorption of aged-PS. Moreover, the adsorption capacity of Cu(II) on aged MPs gradually grew with the increasing pH from 4 to 7. Besides, humic acid significantly promoted the adsorption of Cu(II) at a low concentration (0-20 mg/L) due to the formation of binary mixtures of MPs-HA but inhibited the adsorption at a high concentration (50 mg/L) because of its competitive effect, suggesting the dual roles of humic acid in the adsorption process. Overall, our findings provide a better understanding of the adsorption behavior of metals on biodegradable MPs and emphasize their non-negligible risk as carriers of contaminant.

Highly selective and sensitive recognition of multi-ions in aqueous solution based on polymer-grafted nanoparticle as visual colorimetric sensor

A novel, selective and sensitive colorimetric sensor for naked-eye detection and adsorption of multi-ions in aqueous solution was synthesized using hybridization of organic-inorganic phase. The polymer-grafted nanoparticles (PGNPs) was synthesized via atom transfer radical polymerization (ATRP) of monomers on modified TiO2 NPs and applied under optimized conditions for naked-eye detection: sensor mass: 15 mg; response time: 30 s with limits of detection (LODs) as small as 10, 1, 0.5, and 1 ppb Hg (II), Cd (II), Cu (II), and UO2 (II) at pH = 8, 9, 6, and 7, respectively. The efficient selectivity of the naked eye sensor to multi-ions in the presence of various ions was affirmed wherein the color of the chemosensor in the presence of Hg (II), Cd (II), Cu (II), and UO2 (II) shifted from gray to violet, orange, green and yellow, respectively. The salient advantages of this method comprise expeditious, selectable, high reproducibility, with reasonable adsorption capacity (133 mg g-1) and inexpensive nature for rapid detection of heavy metal ions contamination in aqueous solution in an inexpensive manner. The adsorption mechanism was studied via adsorption kinetics and adsorption isotherm models and the accuracy of the chemosensor has been confirmed and supported by XRD, FT-IR, TGA, 1H-NMR, SEM, TEM, EDX mapping, DLS, BET, and EDS analysis.

Adsorption behavior of trace elements of 90Sr on MnO2-ZrO2 loaded with polyacrylonitrile polymer from aqueous solutions

A MnO2-ZrO2-polyacrylonitrile (MnO2-ZrO2-PAN) composite ion exchanger was produced and its properties were examined by Fourier-transformed infrared spectroscopy, scanning electron microscopy, The BET (Brunauer, Emmett and Teller) surface area, X-Ray diffraction analysis and thermogravimetric analysis. The adsorption of Strontium (Sr) from solutions by MnO2-ZrO2-PAN composite was studied thru batch experiments. The distribution Coefficient of Sr (II) on the composite sorbent was investigated against pH, interaction time, and primary concentration ion. To study the kinetics of adsorption, Pseudo-first-order and Pseudo second-order adsorption kinetics were studied and the results revealed that adsorption kinetics better fit to the pseudo-second-order model. Three iso-temperature models, Langmuir, Freundlich, and Temkin were applied to fit the experimental results. Among those models, Langmuir revealed the most suitable one with minimum deviation. The created composite exhibited strong compatibility to the elimination of Y (III), Ni (II), Pb (II), and Co (II) from radioactive waste streams. On the other, it is evident from the data that the quantifiable extraction of Sr (II) ions from Zr (IV), Mo (VI), and La (III) is feasible. MnO2-ZrO2 Loaded with (PAN) Polymer was figured out to have high ion exchange capacity and thermal stability and selectivity for strontium.

Environmental Potential of Carbonized MOF-5/PANI Composites for Pesticide, Dye, and Metal Cations-Can They Actually Retain Them All?

The environmental application of the carbonized composites of the Zn-containing metal-organic framework MOF-5 and polyaniline (PANI) in its emeraldine salt and base forms (C-(MOF-5/PANI)) was investigated for the first time. Textural properties and particle size distributions revealed that composites are dominantly mesoporous and nanoscale in nature, while Raman spectroscopy revealed the ZnO phase beneath the carbon matrix. Adsorption of pesticide, dye, and metal cation on C-(MOF-5/PANI) composites in aqueous solutions was evaluated and compared with the behavior of the precursor components, carbonized MOF-5 (cMOF), and carbonized PANIs. A lower MOF-5 content in the precursor, a higher specific surface area, and the pore volume of the composites led to improved adsorption performance for acetamiprid (124 mg/g) and Methylene Blue (135 mg/g). The presence of O/N functional groups in composites is essential for the adsorption of nitrogen-rich pollutants through hydrogen bonding with an estimated monolayer capacity twice as high as that of cMOF. The proton exchange accompanying Cd2+ retention was associated with the Zn/Cd ion exchange, and the highest capacity (9.8 mg/g) was observed for the composite synthesized from the precursor with a high MOF-5 content. The multifunctionality of composites was evidenced in mixtures of pollutants where noticeably better performance for Cd2+ removal was found for the composite compared to cMOF. Competitive binding between three pollutants favored the adsorption of pesticide and dye, thereby hindering to some extent the ion exchange necessary for the removal of metal cations. The results emphasize the importance of the PANI form and MOF-5/PANI weight ratio in precursors for the development of surface, porosity, and active sites in C-(MOF-5/PANI) composites, thus guiding their environmental efficiency. The study also demonstrated that C-(MOF-5/PANI) composites retained studied pollutants much better than carbonized precursor PANIs and showed comparable or better adsorption ability than cMOF.

Biogenic adsorbents for removal of drugs and dyes: A comprehensive review on properties, modification and applications

This comprehensive review explores the potential and versatility of biogenic materials as sustainable and environmentally benign alternatives to conventional adsorbents for the removal of drugs and dyes. Biogenic adsorbents derived from plants, animals, microorganisms, algae and biopolymers have bioactive compounds that interact with functional groups of pollutants, resulting in their binding with the sorbent. These materials can be modified mechanically, thermally and chemically to enhance their adsorption properties. Biogenic hybrid composites, which integrate the characteristics of more than one material, have also been fabricated. Additionally, microorganisms and algae are analyzed for their ability to uptake pollutants. Various influential factors that contribute to the adsorption process are also discussed. The challenge, limitations and future prospects for research are reviewed and bridging gap between large scale application and laboratory scale. This comprehensive review, involves a combination of various biogenic adsorbents, going beyond the existing literature where typically only specific adsorbents are reported. The review also covers the isotherms, kinetics, and desorption studies of biogenic adsorbents, providing an improved framework for their effective use in removing pharmaceuticals and dyes from wastewater.

Correlation of endocrine disrupting chemicals with essential elements in biological samples of children (1-5 years) with different infectious diseases and impact on sustainable outdoor activities

Endocrine disrupting chemicals (EDCs) have been extensively explored due to their harmful effects on individual health and the environment by interfering with hormone activity and disrupting the endocrine system. However, their relationship with essential trace elements remains uncertain. This research aimed to investigate the possible correlation between essential trace elements and toxic metals, including cadmium (Cd), and lead (Pb) in children aged 1-5 years with various infectious diseases, including gastrointestinal disorders, typhoid fever, and pneumonia. The study was conducted on biological testing and specimen (scalp hair and whole blood) of diseased and non-diseased children of the same residential area and referent/control age-matched children from developed cities consuming domestically treated water. The media of biological samples were oxidized by an acid mixture before being analyzed by atomic absorption spectrophotometry. The accuracy and validity of the methodology were verified through accredited reference material from scalp hair and whole blood sample. The study results revealed that diseased children had lower mean values of essential trace elements (iron, copper, and zinc) in both scalp hair and blood, except for copper, which was found to be higher in blood samples of diseased children. This implies that the deficiency of essential residue and trace elements in children from rural areas who consume groundwater is linked to various infectious diseases. The study highlights the need for more human biomonitoring of EDCs to better comprehend their non-classical toxic properties and their concealed costs on human health. The findings suggest that exposure to EDCs could be associated with unfavorable health outcomes and emphasizes the need for future regulatory policies to minimize exposure and safeguard the health of current and forthcoming generations of children. Furthermore, the study highlights the implication of essential trace elements in maintaining good health and their potential correlation with toxic metals in the environment.

Sustainable Low-Cost Phosphorus Recovery Using Nanostructured Materials with Reusability Potential

A new low-cost material with a polymeric base formed from sodium silicate was developed. The material presents a nanostructured, highly rich iron surface with a large phosphorus retention capacity and potential reuse as a crop fertilizer. In the present study, we demonstrate that iron is the element that acts as an adsorbent for phosphate, while the polymeric base functions exclusively as a support for iron. The iron is uniformly adsorbed on the surface of the material, forming nanostructures, which ensure that iron works similarly to nanoparticles in solution but avoid other problems, such as particle agglomeration or the difficulty of separating them after the removal process. Materials were characterised by SEM, EDS, N₂ sorption, and image processing, and the effect of pH, ionic strength, and temperature was studied. Sorption kinetics were analysed using Boyd's diffusion model, and adsorption equilibria were studied using several adsorption models. A maximum iron adsorption on the polymeric base of 23.9 ± 0.3 mg Fe∙g^-1 was found, while maximum phosphorus adsorption was 366 ± 21 mg P∙g^-1 Fe. Thus, phosphorus is recovered from the aqueous medium with an inexpensive material that has the potential to be used directly as a fertilizer.

A sustainable biosorption technique for treatment of industrial wastewater using snail shell dust (Bellamya bengalensis)

Water, an essential commodity available to mankind, is constantly under pollution threat. Industries are one of the major causative factors for its poor quality and therefore all organisms depending upon it, directly or indirectly are affected by various life-threatening problems. Thus, the treatment of discharge waste into the freshwater ecosystem is the dire need of the hour. The objective of the study is valorization of discarded snail shells for treatment of industrial wastewater. In the present study, industrial wastewater was treated using snail shell dust obtained from Bellamya bengalensis to assess change in water quality parameters. Various physico-chemical parameters like pH, total dissolved solids, electric conductivity, dissolved oxygen, biological oxygen demand, chemical oxygen demand, calcium, magnesium, total hardness, chlorides, bicarbonates, orthophosphates, sulfates, nitrates, and ammonia-N were assessed after its treatment with snail shell dust. Based on the present observation, it was concluded that all studied parameters except dissolved oxygen showed a remarkable decline in concentration after treatment with snail shell dust at the rate of 15 g per liter at the end of 4 days. Moreover, increased dissolved oxygen concentration also endorsed an enhancement in water quality. Statistical analysis through Pearson correlation and indices, viz., WQI (Water quality index) as well as Nemerow's Pollution index when applied to the present data, also supported an improvement in the water quality. The findings thus endorsed the utilization of snail shell dust as an eco-friendly technique and can be substituted as a sustainable method for the treatment of industrial wastewater.

Microplastics existence affected heavy metal affinity to ferrihydrite as a representative sediment mineral

The coexistence of minerals, heavy metals and microplastics in sediment has been widely reported, while the interactions between minerals and heavy metals may be affected by the presence of microplastics. Therefore, to elucidate the effect of microplastics on the interactions between heavy metals and sediment minerals, this study conducted a series of experiments using polystyrene (PS) microplastics, Pb/Cr/Cd and ferrihydrite (Fh). The presence of PS microplastics with ferrihydrite (Fh-MPs200, mass ratio of ferrihydrite to PS of 200:1) improved the adsorption capacity of ferrihydrite, especially with an increase of 36 % for Pb. Morphological characterization demonstrated that the nano-ferrihydrite particles were dispersed on the surface of the PS microplastics, increasing the available reaction sites of the ferrihydrite particles. Furthermore, the results of zeta potential and pH effect showed that the reduction in electrostatic repulsion after adding PS was another critical reason for the increase in Pb adsorption by Fh-MP200. As a result, the presence of PS microplastics enhanced the complexation of Pb ions and the hydroxyl groups on the ferrihydrite surface. This study demonstrated that the presence of microplastics in the sedimentary environment can alter the dispersion and surface properties of minerals, thereby affecting the accumulation and transportation of heavy metals at the water-sediment interface.

Adsorption and immobilization of phosphorus from eutrophic seawater and sediment using attapulgite - Behavior and mechanism

The adsorption behavior of phosphorus on raw sediment (RS), attapulgite (AT), purified attapulgite (PAT) and AT/PAT-amended sediments conforms to the Langmuir, pseudo first-order kinetics and liquid film diffusion model. The adsorption process is spontaneous and monolayer adsorption, and the adsorption rate is mainly controlled by liquid film diffusion. The addition of attapulgite improved the adsorption capacity of phosphorus in the sediments of mariculture ponds. The results of long-term sediment core incubation showed that the average reduction rates of total phosphorus (TP) and soluble reactive phosphorus (SRP) in overlying water and SRP in pore water by adding 20% purified attapulgite (S/PAT20) were 62.11%, 70.83% and 56.32% respectively, and the phosphorus flux in sediments decreased by 53.81%. The addition of attapulgite reduces the risk of phosphorus release in sediments, and changes sediments from "source" to "pool". The specific surface area and pore volume of PAT increased to 203.254 cm²/g and 0.395 cm³/g respectively, but the phosphorus adsorption capacity was only increased by 2 times compared with AT (1431.3-2671.8 mg P/kg), indicating that the changes of mineral structure and chemical composition jointly determine the phosphorus adsorption effect. Adsorption mechanisms include physical adsorption, surface chemical precipitation, ligand effects, electrostatic attraction and ion exchange. Therefore, seeking modification methods with low energy consumption, low production cost, no damage to rod crystal, expansion of pore volume, increase of hydroxyl and other functional groups, and great retention of effective components are issues that need to be considered to improve the phosphorus adsorption capacity of attapulgite.

Adsorption of Arsenic, Lead, Cadmium, and Chromium Ions from Aqueous Solution Using a Protonated Chabazite: Preparation, Characterization, and Removal Mechanism

The adsorption of As(V), Pb(II), Cd(II), and Cr(III) ions from aqueous solutions on natural and modified chabazite was studied. The functionalization of chabazite was performed via a protonation and calcination with the aim of generating Lewis acid sites to improve its anion exchange properties. The surface and physicochemical properties of both adsorbents were studied and compared. The adsorption isotherms of tested heavy metal ions were quantified and modeled to identify the best isotherm equation. Steric parameters for the adsorption of these ions were also calculated with a monolayer statistical physics model. Natural chabazite showed the maximum adsorption capacity for Pb(II), while the modified zeolite improved its As(V) properties in 79%. These results showed that the modified zeolite was able to remove both cations and anions from aqueous solution. The application of this functionalized chabazite can be extended for the removal of other anionic pollutants from water, thus opening the possibility of preparing new adsorbents with tailored properties for water treatment.

Comparing the influence of humic/fulvic acid and tannic acid on Cr(VI) adsorption onto polystyrene microplastics: Evidence for the formation of Cr(OH)3 colloids

Microplastics (MPs) can act as vectors for various contaminants in the aquatic environment. Although some research has investigated the adsorption characteristics and influencing factors of metals/organic molecules on MPs, the effects of dissolved organic matter (DOM) (which are ubiquitous active species in ecosystems) on metal oxyanions such as Cr(VI) capture by MPs are largely unknown. This study explored the adsorption behaviors and mechanisms of Cr(VI) oxyanions onto polystyrene (PS) MPs using batch adsorption experiments and multiple spectroscopic methods. The effects of representative DOM components (i.e., humic acid (HA), fulvic acid (FA) and tannic acid (TA)) on Cr(VI) capture by PS were particularly studied. Results revealed a significantly enhanced adsorption of Cr(VI) on PS in the presence of TA. The Cr(VI) adsorption capacity was increased from 2876 μg g^-1 to 4259 μg g^-1 and 5135 μg g^-1 when the TA concentrations raised from 0 to 10 and 20 mg L^-1, respectively. Combined microscopic and spectroscopic investigations revealed that Cr(VI) was reduced to Cr(III) by TA and formed stable Cr(OH)₃ colloids on PS surfaces. Contrarily, HA and FA inhibited Cr(VI) adsorption onto PS, especially at pH > 2.0 and higher DOM concentrations, due to site competition and electrostatic repulsion. Increase in pH was found to reduce zeta potentials of MPs, resulting in inhibited Cr(VI) adsorption. The adsorbed Cr(VI) declined with increasing ionic strength, implying that outer-sphere surface complexation affected the adsorption process in the presence of DOM. These new findings improved our fundamental understanding of the fate of Cr(VI) and MPs in DOM-rich environmental matrices.

Influence of Doping-Ion-Type on the Characteristics of Al2O3-Based Nanocomposites and Their Capabilities of Removing Indigo Carmine from Water

Globally, the continuous contamination of natural water resources is a severe issue, and looking for a solution for such a massive problem should be the researcher’s concern. Herein, Al2O3, Al2O3-CuO, Al2O3-NiO, and Al2O3-CoO were prepared via a simple and fast route, utilizing glucose as a capping material. All synthesis conditions were uniform to make the fabricated nanomaterials’ characteristics exclusively influenced by only the ion type. The SEM analysis showed that the particles of the synthesized Al2O3, Al2O3-CuO, Al2O3-NiO, and Al2O3-CoO were all less than 25 nm. The Al2O3-NiO showed the smallest particle size (11 to 14 nm) and the best BET surface area of 125.6 m2 g−1. All sorbents were tested for removing organic pollutants, as exemplified by indigo carmine (IGC) dye. The Al2O3-NiO possessed the highest adsorption capacity among the other sorbents for which it had been selected for further investigations. The IGC sorption reached equilibrium within 2.0 h, and the kinetic study revealed that the IGC removal by Al2O3-NiO nanocomposite fitted the FOM and the LFM. The sorbent showed an experimental adsorption capacity (qt) of 456.3 mg g−1 from a 200 mg L−1 IGC solution and followed the Langmuir model. The thermodynamic findings indicated an endothermic, spontaneous, and physisorption nature. The seawater and groundwater samples contaminated with 5.0 mg L−1 IGC concentrations were fully remediated using the Al2O3-NiO nanocomposite. The reuse study showed 93.3% average efficiency during four successive cycles. Consequently, prepared Al2O3-NiO nanocomposite is recommended for the treatment of contaminated water.

Aloe Vera Functionalized Magnetic Nanoparticles Entrapped Ca Alginate Beads as Novel Adsorbents for Cu(II) Removal from Aqueous Solutions

CABs (Ca alginate beads), AVCABs (Aloe vera Ca alginate beads), and AVMNCABs (Aloe-vera functionalized magnetic nanoparticles entrapped Ca alginate beads) were developed as adsorbents for the removal of Cu(II) from aqueous solutions. The materials were characterized using Fourier-transform infrared (FTIR) spectroscopy, high-resolution scanning electron microscopic (HR-SEM) analysis, X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, and a vibrating-sample magnetometer (VSM). The effect of several parameters, such as pH, time, temperature, adsorbent dose, etc., were investigated. The adsorption isotherm of Cu(II) was adjusted best to the Langmuir model. The maximum adsorption capacities were 111.11 mg/g, 41.66 mg/g, and 15.38 mg/g for AVMNCABs, AVCABs, and CABs, respectively. The study of the adsorption kinetics for Cu(II) ions on beads followed a pseudo-second-order kinetic model, with a very good correlation in all cases. The adsorption studies used a spectrophotometric method, dealing with the reaction of Cu(II) with KSCN and variamine blue.

A comprehensive analysis of evolution and underlying connections of water research themes in the 21st century

This work aimed to reflect the advancements in water-related science, technology, and policy and shed light on future research opportunities related to water through a systematic overview of Water Research articles published in the first 21.5 years of the 21st century. Specific bibliometric analyses were performed to i) reveal the temporal and spatial trends of water-related research themes and ii) identify the underlying connections between research topics. The results showed that while top topics including wastewater (treatment), drinking water, adsorption, model, biofilm, and bioremediation remained constantly researched, there were clear shifts in topics over the years, leading to the identification of trending-up and emerging research topics. Compared to the first decade of the 21st century, the second decade not only experienced significant uptrends of disinfection by-products, anaerobic digestion, membrane bioreactor, advanced oxidation processes, and pharmaceuticals but also witnessed the emerging popularity of PFAS, anammox, micropollutants, emerging contaminants, desalination, waste activated sludge, microbial community, forward osmosis, antibiotic resistance genes, resource recovery, and transformation products. On top of the temporal evolution, distinct spatial evolution existed in water-related research topics. Microplastics and Covid-19 causing global concerns were hot topics detected, while metagenomics and machine learning were two technical approaches emerging in recent years. These consistently popular, trending-up and emerging research topics would most likely attract continuous/increasing research input and therefore constitute a major part of the prospective water-related research publications.

A Review of the Dynamic Mathematical Modeling of Heavy Metal Removal with the Biosorption Process

Biosorption has great potential in removing toxic effluents from wastewater, especially heavy metal ions such as cobalt, lead, copper, mercury, cadmium, nickel and other ions. Mathematically modeling of biosorption process is essential for the economical and robust design of equipment employing the bioadsorption process. However, biosorption is a complex physicochemical process involving various transport and equilibrium processes, such as absorption, adsorption, ion exchange and surface and interfacial phenomena. The biosorption process becomes even more complex in cases of multicomponent systems and needs an extensive parametric analysis to develop a mathematical model in order to quantify metal ion recovery and the performance of the process. The biosorption process involves various process parameters, such as concentration, contact time, pH, charge, porosity, pore size, available sites, velocity and coefficients, related to activity, diffusion and dispersion. In this review paper, we describe the fundamental physical and chemical processes involved in the biosorption of heavy metals on various types of commonly employed biosorbents. The most common steady state and dynamic mathematical models to describe biosorption in batch and fixed-bed columns are summarized. Mathematical modeling of dynamic process models results in highly coupled partial differential equations. Approximate methods to study the sensitivity analysis of important parameters are suggested.

Removal of inorganic toxic contaminants from wastewater using sustainable biomass: A review

Lignocellulosic biomass is most abundant, ecofriendly and sustainable material on this green planet which has received great attention due to exhaustion of petroleum reserves and various environmental complications. Due to its abundance and sustainability, it has been opted in number of advanced applications i.e. synthesis of green chemicals, biofuels, paper, packaging, biocomposite and for discharge of toxic contaminants from wastewaters. Utilization of sustainable biomass for removal of toxic pollutants from wastewater is robust technique due to its low-cost and easy availability. In this review, we have summarized removal of inorganic pollutants by sustainable lignocellulosic biomass in their natural as well as in chemically functionalized form. Various techniques for modification of sustainable biomass have been discussed and it was found that modified biomass showed better biosorption ability as compared to natural biomass. We conclude that modified biomass biosorbents are useful for removal of toxic inorganic pollutants to deficient levels. Several modification strategies can improve the qualities of biosorbent, however grafting is the most successful among them, as demonstrated in this work. The numerous grafting methods using a free radical grafting process are also summarized in this review article. This review also gathers studies comparing sorption capabilities with and without modification using modified and unmodified biosorbents. Chemically modified cellulosic biomass is favoured over untreated biomass because it has a higher adsorption efficiency, which is favoured by a large number of reactive binding sites, improved ion-exchange characteristics, and more functional groups available after modification.

Effects of Biochar Production Methods and Biomass Types on Lead Removal from Aqueous Solution

Biochar has proven its potential in removing heavy metal ions from water. The objective of this study was to evaluate locally obtained biomass feedstocks for biochar production and their efficiency as a sorbent for aqueous lead (Pb2+) removal. The biomass feedstocks consisted of avocado seed, avocado peel, grapefruit peel, and brown seaweed, which represent agricultural and marine biomasses. The biochar materials were produced in two different methods: (1) a laboratory tube furnace at 300 °C and (2) a Do-It-Yourself (DIY) biochar maker, “BioCharlie Log”. The biochars were characterized for selected physicochemical properties, and batch adsorption tests with 10 mg Pb2+ L−1 were conducted. All biochars exhibited >90% Pb2+ removal with the avocado seed and grapefruit peel biochars being the most effective (99%) from the tube-furnace-produced biochars. BioCharlie-produced-biochars showed similar Pb2+ removal (90–97%) with brown seaweed and avocado seed biochars being the most effective (97%). Land-based biochars showed a higher carbon content (>53%) than the brown seaweed biochar (28%), which showed the highest ash content (68%). Our results suggested that oxygen-containing surface functional groups in land-based biochar and mineral (ash) fraction in marine-based biochar play a key role in Pb2+ removal.

Activated Carbon as Superadsorbent and Sustainable Material for Diverse Applications

Activated carbon is a carbonaceous material with highly porous structure. Different functionalities can be introduced to its surface by various physical and chemical treatments. Various precursors can be used for the synthesis of activated carbon such as fossil fuels, agricultural wastes, and lignocellulosic wastes, etc. Number of papers have been reported in literature devoted to the synthesis, characterization, and various applications of activated carbon. Herein, in this review, special attention has been paid to the basic properties of activated carbon and its surface chemistry originated due to physical and chemical treatment. In addition, a general introduction to adsorption process, various adsorption isotherms, and adsorption kinetics is also included. A brief description of mechanism of adsorption onto activated carbon is also presented. At last, most probable applications of activated carbon such as adsorption of pollutants (e.g., dyes, heavy metal ions, pesticides, pharmaceutical waste products, and volatile organic organic), as catalyst support, anduse in food and pharmaceutical industries is also presented.

Fabrication of environmentally-friendly composited sponges for efficient removal of fluoroquinolones antibiotics from water

In this study, two environmentally-friendly macroscopically formal (PVF) composited sponges (PL and PLS) functionalized with lignin and lignosulfonate, respectively, were fabricated by a one-step mechanical foaming method. PLS, obtained with the fed mass ratio of 0.3:1 lignosulfonate to PVF in the preparation process, possessed a large specific surface area of approximately 22.396 m²/g, a three-dimensional skeleton structure with a skeletal density of 3.236 g/cm³, and 0.338 mmol/g of acidic oxygen-containing groups. Thus, it showed a high adsorption capacity of 0.16-0.24 mmol/g in removing seven antibiotics, of the popular fluoroquinolones (FQs) family from water. The contributions of hydrogen bonding, electrostatic attraction (EA) and π-π electron donor-acceptor interaction to the adsorption of FQs onto the PL and PLS sponges were analyzed systematically by investigating the pH dependence of the adsorption capacity, and the changes in adsorption of two sub structural analogs of FQs as molecular probes, and by performing theoretical calculations. The EA between the acidic oxygen-containing groups on the sponges and the amino groups of FQs played a dominant role in adsorption in near neutral conditions, leading to a superior adsorption performance for PLS. Overall, the composited sponges have the advantages of simple production, environmental-friendliness, convenient recycle, and low cost, which renders them potentially viable in treating real wastewater containing FQs.

Comparative Study on the Efficiency of Mercury Removal From Wastewater Using Bacterial Cellulose Membranes and Their Oxidized Analogue

A comparative study was conducted on the efficiency of mercury removal using bacterial nanocellulose (BNC) membranes obtained from the fermentation of the microorganism Komagataeibacter medellinensis, in contrast with its oxidized analog obtained by modifying the bacterial nanocellulose membranes via oxidation with 2,2,6,6-Tetramethylpiperidine-1-oxyl. Both types of membranes (modified and unmodified) were characterized to identify variations in the Physico-chemical parameters after modification. FTIR spectra confirmed the chemical modification of cellulose in all reaction conditions by the presence of a new characteristic band at ∼1730 cm⁻¹, corresponding to the new carboxylic groups produced by the oxidative process, and the decline of the band at ∼1,650 cm⁻¹, corresponding to the hydroxyl groups of the C6 carbon. While the XRD profiles indicated that the percentage of BNC crystallinity decreased and the SEM images showed that the nanoribbon network was interrupted as the amount of oxidizing agent increased. The kinetics of mercury removal from both types of membrane was evaluated by calculating the concentration of mercury at different times and establishing a mathematical model to describe the kinetics of this process. The modified membranes improved significantly the adsorption process of the metal ion and it was found that the modification that results in the greatest adsorption efficiency was BNC-m 7.5 with a value of 92.97%. The results obtained suggest that the modification of the bacterial nanocellulose membranes by oxidation transcendentally improves the mercury removal capacity, outlining the modified membranes as an excellent material for mercury removal in wastewater.

Layer-by-Layer Assembly of Polyelectrolytes on Urchin-like MnO2 for Extraction of Zn2+, Cu2+ and Pb2+ from Alkaline Solutions

Three-dimensional (3D) urchin-like MnO2@poly (sodium 4-styrene sulfonate) (PSS)/poly (diallyl dimethylammonium chloride) (PDDA)/PSS particles were prepared via the layer-by-layer (LBL) assembly of polyelectrolytes for the extraction of Zn2+ from alkaline media. The adsorption performance of Zn2+ on MnO2, MnO2@PSS/PDDA/PSS, and MnO2@(PSS/PDDA)3/PSS was investigated in batch experiments. The adsorption of Zn2+ on MnO2@PSS/PDDA/PSS has been studied under various conditions, such as initial Zn2+ concentration, adsorbent dosage, the solution’s pH, and reaction time. The Zn2+ adsorption process is well represented by the pseudo-second-order kinetic model, and the equilibrium data fit the Freundlich isotherm well. MnO2@PSS/PDDA/PSS also showed high efficiency for Pb2+ and Cu2+ removal from slightly alkaline water. Thus, our research provides a deep insight into the preparation of 3D manganese oxides with polyelectrolyte films for the extraction of heavy metal ions, such as Pb2+, Cu2+, and Zn2+, from slightly alkaline wastewater.

Single-Step Hydrothermal Synthesis of Biochar from H3PO4-Activated Lettuce Waste for Efficient Adsorption of Cd(II) in Aqueous Solution

Developing an ideal and cheap adsorbent for adsorbing heavy metals from aqueous solution has been urgently need. In this study, a novel, effective and low-cost method was developed to prepare the biochar from lettuce waste with H3PO4 as an acidic activation agent at a low-temperature (circa 200 °C) hydrothermal carbonization process. A batch adsorption experiment demonstrated that the biochar reaches the adsorption equilibrium within 30 min, and the optimal adsorption capacity of Cd(II) is 195.8 mg∙g-1 at solution pH 6.0, which is significantly improved from circa 20.5 mg∙g-1 of the original biochar without activator. The fitting results of the prepared biochar adsorption data conform to the pseudo-second-order kinetic model (PSO) and the Sips isotherm model, and the Cd(II) adsorption is a spontaneous and exothermic process. The hypothetical adsorption mechanism is mainly composed of ion exchange, electrostatic attraction, and surface complexation. This work offers a novel and low-temperature strategy to produce cheap and promising carbon-based adsorbents from organic vegetation wastes for removing heavy metals in aquatic environment efficiently.

Arsenic contamination, impact and mitigation strategies in rice agro-environment: An inclusive insight

Arsenic (As) contamination and its adverse consequences on rice agroecosystem are well known. Rice has the credit to feed more than 50% of the world population but concurrently, rice accumulates a substantial amount of As, thereby compromising food security. The gravity of the situation lays in the fact that the population in theAs uncontaminated areas may be accidentally exposed to toxic levels of As from rice consumption. In this review, we are trying to summarize the documents on the impact of As contamination and phytotoxicity in past two decades. The unique feature of this attempt is wide spectrum coverages of topics, and that makes it truly an interdisciplinary review. Aprat from the behaviour of As in rice field soil, we have documented the cellular and molecular response of rice plant upon exposure to As. The potential of various mitigation strategies with particular emphasis on using biochar, seed priming technology, irrigation management, transgenic variety development and other agronomic methods have been critically explored. The review attempts to give a comprehensive and multidiciplinary insight into the behaviour of As in Paddy -Water - Soil - Plate prospective from molecular to post-harvest phase. From the comprehensive literature review, we may conclude that considerable emphasis on rice grain, nutritional and anti-nutritional components, and grain quality traits under arsenic stress condition is yet to be given. Besides these, some emerging mitigation options like seed priming technology, adoption of nanotechnological strategies, applications of biochar should be fortified in large scale without interfering with the proper use of biodiversity.

Lignocellulose-Based Superabsorbent Polymer Gel Crosslinked with Magnesium Aluminum Silicate for Highly Removal of Zn (II) from Aqueous Solution

Lignocellulose (LCE) was ultrasonically treated and intercalated into magnesium aluminum silicate (MOT) clay to prepare a nano-lignocellulose magnesium aluminum silicate polymer gel (nano-LCE-MOT) for the removal of Zn (II) from aqueous solution. The product was characterised using nitrogen adsorption/desorption isotherm measurements, Fourier-transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The conditions for the adsorption of Zn (II) on nano-LCE-MOT were screened, and adsorption kinetics and isotherm model analysis were carried out to explore the adsorption mechanism and achieve the optimal adsorption of Zn (II). Optimal adsorption was achieved at an initial Zn (II) concentration of 800 mg/L at 60 °C in 160 min at a pH of 4.52. The adsorption kinetics were explored using a pseudo-second-order model, with the isotherm adsorption equilibrium found to conform to the Langmuir model. The maximum adsorption capacity of the nano-LCE-MOT polymer gel toward Zn (II) is 513.48 mg/g. The materials with adsorbed Zn (II) were desorbed using different media, with HCl found to be the most ideal medium to desorb Zn (II). The optimal desorption of Zn (II) was achieved in 0.08 mol/L HCl solution at 65 °C in 60 min. Under these conditions, Zn (II) was almost completely desorbed from the adsorbents, with the adsorption effect after cycling being slightly different from that of the initial adsorption.

Biologically produced sulfur as a novel adsorbent to remove Cd2+ from aqueous solutions

Biological desulfurization processes of landfill gas yield an enormous amount of biologically produced S (BPS) as a byproduct. Capability of BPS to remove Cd²⁺ from aqueous solutions was tested and its removal efficiency was compared to that of granular activated carbon (GAC). Kinetics of Cd²⁺ removal by BPS was a two-stage process with an initial rapid adsorption showing 45% of initial Cd²⁺ was removed within 5 min, followed by a slower adsorption. Cadmium adsorption onto the BPS fitted the Langmuir isotherm model and maximum adsorption capacity of the BPS (63.3 mg g^-1) was 1.8 times higher than that of GAC (36.1 mg g^-1). Thermodynamic parameters showed that Cd²⁺ adsorption by BPS was favorable and endothermic. Data from XPS proved the main adsorption mechanism to be complexation of Cd²⁺ with sulfides in the BPS. Results demonstrated that BPS can be recycled as a novel adsorbent for Cd²⁺ removal from wastewater.

Novel adsorbent based on carbon-modified zirconia/spinel ferrite nanostructures: Evaluation for the removal of cobalt and europium radionuclides from aqueous solutions

Herein, a novel adsorbent based on carbon-modified zirconia/spinel ferrite (C@ ZrO₂/Mn_0.5Mg_0.25Zn_0.25Fe₂O₄) nanostructures were chemically prepared to remove ⁶⁰Co and ^152+154Eu radionuclides from liquid media using batch experiments. The XRD pattern confirms the successful preparation of the C@ZrO₂/MnMgZnFe₂O₄ composite. Also, SEM and TEM images confirmed that the composite owns a heterogeneous morphology in the nanoscale range. The optical band gap value of Mn_0.5Mg_0.25Zn_0.25Fe₂O₄, ZrO₂, and the composite samples was 1.45, 2.38, and 1.54 eV, respectively. Many parameters have been studied as the effect of time, solution pH, and initial ion concentration. The kinetics models for the removal process of ^152+154Eu and ⁶⁰Co radionuclides were studied. The second-order kinetic equation could describe the sorption kinetics for both radionuclides. The Langmuir monolayer capacity for ⁶⁰Co was 82.51 mg/g and for ^152+154Eu was 136.98 mg/g. The thermodynamic parameters such as free energy ΔG^o, the enthalpy ΔH^o, and the entropy ΔS^o were calculated. The results indicated that the sorption process has endothermic nature for both two radionuclides onto C@ZrO₂/MnMgZnFe₂O₄ composite.

Enhancement of Cd(II) adsorption by rice straw biochar through oxidant and acid modifications

To develop high-efficient biochar adsorbents, the effects and mechanisms of oxidant modification and acid modification on Cd(II) adsorption by rice straw biochar were investigated. Three rice straws from Langxi in Anhui Province, Yingtan in Jiangxi Province, and Lianyungang in Jiangsu Province were collected to prepare biochars by anaerobic pyrolysis in a muffle furnace. Rice straw biochars were modified by 15% H₂O₂ and 1:1 HNO₃/H₂SO₄ mixed acid, respectively, to obtain modified biochars. The untreated rice straw biochar and HCl-treated rice straw biochar with carbonate removed were used as controls. The functional groups on the surfaces of the biochars were qualitatively and quantitatively determined by Fourier transform infrared spectra and Boehm titration, respectively. The adsorption and desorption of Cd(II) onto and from the biochars and modified biochars were measured under various pH conditions. The results showed that oxidant modification with 15% H₂O₂ and acid modification with 1:1 HNO₃/H₂SO₄ significantly increased the number of carboxyl functional groups on the surfaces of the biochars, and acid modification was more effective than oxidant modification in amplifying carboxyl functional groups on the surfaces of the biochars. The increase of surface functional groups effectively enhanced the specific adsorption of Cd(II) on the modified biochars. Therefore, both oxidant modification and acid modification enhanced the adsorption of Cd(II) on the biochars through increasing functional groups on the surfaces of the biochars.

Detoxification of toxic cations Pb(II) and Cd(II) from liquid phase by employing Pennisetum glaucum biowaste: a kinetic investigation

Biosorption potential of Pennisetum glaucum has elaborated by investigating its kinetic behavior in nonlinear fashion. RMSE values supported the pseudo second order (PSO) and elovich model, but correlation coefficient (R²) values supported the PSO only. Study of intra-particle diffusion model (IPDM) and Boyd plots revealed the multi-linear diffusion pattern of the studied metal ions toward biosorbent. Initially, IPDM was found to be the rate-determining step, however boundary layer diffusion was found to be the slowest step later on. There was no correlation between calculated and experimental values of intercept, calculated by applying mass transfer model. Conclusive findings of Boyd plot supported the governing of biosorption process by film diffusion.Novelty StatementIn this work, biosorption potential of Pennisetum glaucum has been investigating in terms of kinetic studies in nonlinear fashion.Biosorbent is obtained from indigenous sources and its processing is easy, which in turns leads to its cost-effectiveness for better removal of toxic materials from waste water streams.All related theoretical investigations were summarized for showing biosorption efficiency of this novel material.

Exploring Factors Influencing Farmers' Continuance Intention to Crop Residue Retention: Evidence from Rural China

Over the past decade, crop residue burning after harvest is prevalent in developing countries. Promoting crop residue retention to replace residue burning is effective in improving air quality and contributing to the mitigation of global climate change. This study examines farmers’ continuance intention of crop residue retention, using the expectation confirmation model (ECM) and survey data from 542 rice farmers in Hubei Province, P.R. The results show that farmers’ perceived usefulness, confirmation, perceived ease of use, and satisfaction significantly have direct or indirect positive impacts on their continuance intention on adopting crop residue retention. In particular, perceived ease of use contributes the most. Perceived usefulness and perceived ease of use act as intermediaries in the relationship between confirmation and farmers’ continuance intention to residue retention. This study provides a valuable governance reference and scientific basis for the government to adjust and improve existing policies, including how to stimulate farmers to continue to adopt agricultural waste treatment technologies such as residue retention.

Functionalization and Evaluation of Inorganic Adsorbents for the Removal of Cadmium in Wastewater

This study presents the feasibility of using various functionalized substrates, Fe₃O₄ nanoparticles (NPs) and Al₂O₃ spheres, for the removal of Cd from aqueous solution. To improve the materials’ affinity to Cd, we explored four different surface modifications, namely (3-Aminopropyl) triethoxysilane (APTES), L-Cysteine (Cys) and 3-(triethoxysilyl) propylsuccinic anhydride (CAS). Particles were characterized by FTIR, FIB-SEM and DLS and studied for their ability to remove metal ions. Modified NPs with APTES proved to be effective for Cd removal with efficiencies of up to 94%, and retention ratios up to 0.49 mg of Cd per g of NPs. Batch adsorption experiments investigated the influence of pH, contact time, and adsorbent dose on Cd adsorption. Additionally, the recyclability of the adsorbent and its potential phytotoxicity and animal toxicity effects were explored. The Langmuir, Freundlich, pseudo-first-order and pseudo-second-order models were applied to describe the behavior of the Cd adsorption processes. The adsorption and desorption results showed that Fe₃O₄ NPs modified with APTES are promising low-cost platforms with low phytotoxicity for highly efficient heavy metal removal in wastewater.

Cucumber peel bead biosorbent for multi-ion decontamination of drinking water collected from a mine region in New Zealand

Cucumber peel as a bead was examined for its ability to remove heavy metals from drinking water. Deionised laboratory water was spiked with seven toxic ions namely, arsenic, cadmium, chromium, copper, mercury, lead and nickel at 0.1 mg L^-1 and kinetic studies were performed over 72 h. Kinetic data were modelled using film diffusion, pore diffusion, Weber-Morris, pseudo-first-order, pseudo-second-order and Elovich equation. The bead surface was imaged before and after biosorption using scanning electron microscopy coupled with energy dispersive spectroscopy (EDS). Results indicated that different ions contained in a multi-ion solution were biosorbed by different mechanisms and at different rates. Equilibrium biosorption for Cd, Hg and Ni was ∼91, 90 and 67%, respectively, at 24 h. These ions diffused through the pores of the bead, as they were not identified by EDS, and their biosorption increased with an increase in temperature. The least biosorbed ions were As and Cr with ∼21 and 17% equilibrium biosorption, respectively. The removal of only Cu, Hg, Pb and Ni was pH-dependent. Cucumber peel beads removed all spiked ions from real drinking water collected near the Macraes gold mine in New Zealand, but the biosorption percentage was lower for Cd, Cu, Pb and Ni compared to spiked deionised laboratory water. The results of this study suggest that cucumber peel when immobilised on a sodium alginate bead can be used as a potential biosorbent for the removal of multiple toxic ions from drinking water and their use warrants further examination in contaminated drinking water.

Application of diatomite for sorption of Pb, Cu, Cd and Zn from aqueous solutions: kinetic, thermodynamic studies and application of response surface methodology (RSM)

Contamination of water and soil with toxic metals is a serious environmental issue. To study the Pb, Cu, Cd, and Zn sorption behavior by diatomite, batch experiments were carried out with increasing levels of initial concentration (0-200 mg/L) under different contact times (0-360 min) and temperatures (283, 293, 303, and 313 K). The effects of concentration (0-200 mg/L), pH (3-6), and ionic strength (0.01-0.06 mol/L) on the sorption were modeled using response surface methodology (RSM). Results showed that adsorption data were well-fitted by the Langmuir equation. The sorption of metals intensified by increasing initial concentration and pH but ionic strength had inverse effect. High value for R² (0.99) and adjusted R² (0.99) showed that the removal of ions can be described by response surface method. One-way ANOVA showed (p-value < 0.0001) that quadratic model is the best model for determining the interaction of variables. The values of the sorption energy parameter from Dubinin-Radushkevich model (E < 8 kJ K^-1  mol^-1 ) and negative values of ∆G showed that the sorption of the metals was physical and spontaneous. The positive values of enthalpy (ΔH) indicated that the sorption reaction of metals was endothermic at 283-313 K. PRACTITIONER POINTS: Applications of diatomite increased the sorption of Pb, Cd, Zn, and Cu from aqueous solutions. Diatomite, as low-cost adsorbent, had significant potential to sorption of ions. The sorption of heavy metals by adsorbent intensified by increasing initial concentration and pH but ionic strength had inverse effect. High value for R² (0.99) and adj-R² (0.99) showed that removal of metals can be described by response surface method (RSM) and the initial concentration of metal was the most significant factor.