Adsorption of heavy metal cations by Na-clinoptilolite: equilibrium and selectivity studies

An overview of in situ remediation for groundwater co-contaminated with heavy metals and petroleum hydrocarbons

Groundwater is an important component of water resources. Mixed pollutants comprising heavy metals (HMs) and petroleum hydrocarbons (PHs) from industrial activities can contaminate groundwater through such processes as rainfall infiltration, runoff and discharge, which pose direct threats to human health through the food chain or drinking water. In situ remediation of contaminated groundwater is an important way to improve the quality of a water environment, develop water resources and ensure the safety of drinking water. Bioremediation and permeable reactive barriers (PRBs) were discussed in this paper as they were effective and affordable for in situ remediation of complex contaminated groundwater. In addition, media types, technology combinations and factors for the PRBs were highlighted. Finally, insights and outlooks were presented for in situ remediation technologies for complex groundwater contaminated with HMs and PHs. The selection of an in situ remediation technology should be site specific. The remediation of complex contaminated groundwater can be approached from various perspectives, including the development of economical materials, the production of slow-release and encapsulated materials, and a combination of multiple technologies. This review is expected to provide technical guidance and assistance for in situ remediation of complex contaminated groundwater.

Neodymium sorption on the Na-form of Transcarpathian clinoptilolite

The sorption properties of Na-modified Ukrainian Transcarpathian clinoptilolite towards neodymium aqueous solutions under dynamic conditions have been investigated. The sorption capacity of the Na-from of Transcarpathian clinoptilolite towards Nd(III) significantly depends on the concentration of neodymium salt, the pH of the solution, and the heat treatment temperature of the sorbent. Nd(III) is most efficiently sorbed from slightly alkaline solutions (pH 8.5), mainly by adsorption of neutral hydrolyzed forms of Nd(OH)3 on the surface of Na-clinoptilolite samples preheated at 75 °C. During the passage of an Nd(III) solution with a concentration of 1 μg mL-1 through the sorbent at a rate of 3 mL min-1 under optimal conditions, the sorption capacity of Na-clinoptilolite is 7.2 mg g-1, which is in 4 and 2.3 times higher than that of natural and acid-modified forms of this zeolite. It is shown that under the experimental conditions with an increase in the flow rate, the thickness of the stationary surface layer decreases, which leads to a decrease in the sorption capacity of Na-clinoptilolite. The best Nd(III) desorbents are solutions of mineral acids and acidified solutions of alkali metal salts (except NaCl), which provide 93-98 % extraction of lanthanide from the zeolite matrix. The method for neodymium trace amounts preconcentration from aqueous solutions in a solid-phase extraction mode with a further determination of this rare earth element by a spectrophotometric method was developed. The detection limit of this method is 0.75 ng mL-1 and the linearity was evaluated in the range of 2.5-500 ng mL-1.

Novel glass-based membranes for Cu adsorption: From alkali activation to sintering

A porous membrane was developed through alkali activation of pharmaceutical boro-alumino-silicate glass powders suspended in diluted NaOH and KOH aqueous solutions (2.5 M). A consolidated porous structure was obtained by the binding of unreacted particles mediated by a surface gel, developed upon drying of the suspensions and their curing at 40 °C for 14 days. The binding phase was sufficiently stable to resist immersion in boiling water and in acidic solutions. Copper adsorption tests were carried out under acidic pH, immersing the membranes in a Cu(NO₃)₂ solution for different periods of time. To determine the effect of surface washing on capture of copper ions, adsorption experiments with washed and unwashed membranes were also carried out, at varying pH. It was determined that the adsorption kinetics follow the pseudo-second-order kinetic model. The main adsorption mechanism observed is the electrostatic interaction between the negative surface charge of the washed membrane and the Cu²⁺ ions present in solution. An adsorption higher than 60% was observed at pH = 5, while at pH = 2 the efficiency decreased due to the presence of H₃O⁺ ions. To ensure immobilization of copper, the membranes were densified by viscous flow sintering at a moderate temperature (700 °C). Leaching tests on membranes demonstrated the efficiency of the process in terms of copper ions immobilization.

Adsorption of heavy metals on natural zeolites: A review

Water pollution has jeopardized human health, and a safe supply of drinking water has been recognized as a worldwide issue. The increase in the accumulation of heavy metals in water from different sources has led to the search for efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites are promising materials for removing heavy metals from different sources contaminating the water. It is important to know the structure, chemistry, and performance of the removal of heavy metals from water, of the natural zeolites to design water treatment processes. This review focuses on critical analyses of the application of distinct natural zeolites for the adsorption of heavy metals from water, specifically, arsenic (As(III), As(V)), cadmium (Cd(II)), chromium (Cr(III), Cr(VI)), lead (Pb(II)), mercury(Hg(II)) and nickel (Ni(II)). The reported results of heavy-metal removal by natural zeolites are summarized, and the chemical modification of natural zeolites by acid/base/salt reagent, surfactants, and metallic reagents has been analyzed, compared, and described. Furthermore, the adsorption/desorption capacity, systems, operating parameters, isotherms, and kinetics for natural zeolites were described and compared. According to the analysis, clinoptilolite is the most applied natural zeolite to remove heavy metals. It is effective in removing As, Cd, Cr, Pb, Hg, and Ni. Additionally, an interesting fact is a variation between the natural zeolites from different geological origins regarding the sorption properties and capacities for heavy metals suggesting that natural zeolites from different regions of the world are unique.

Heavy metal pollution in the aquatic environment: efficient and low-cost removal approaches to eliminate their toxicity: a review

Heavy metal contamination of water sources has emerged as a major global environmental concern, threatening both aquatic ecosystems and human health. Heavy metal pollution in the aquatic environment is on the rise due to industrialization, climate change, and urbanization. Sources of pollution include mining waste, landfill leachates, municipal and industrial wastewater, urban runoff, and natural phenomena such as volcanic eruptions, weathering, and rock abrasion. Heavy metal ions are toxic, potentially carcinogenic, and can bioaccumulate in biological systems. Heavy metals can cause harm to various organs, including the neurological system, liver, lungs, kidneys, stomach, skin, and reproductive systems, even at low exposure levels. Efforts to find efficient methods to remove heavy metals from wastewater have increased in recent years. Although some approaches can effectively remove heavy metal contaminants, their high preparation and usage costs may limit their practical applications. Many review articles have been published on the toxicity and treatment methods for removing heavy metals from wastewater. This review focuses on the main sources of heavy metal pollution, their biological and chemical transformation, toxicological impacts on the environment, and harmful effects on the ecosystem. It also examines recent advances in cost-effective and efficient techniques for removing heavy metals from wastewater, such as physicochemical adsorption using biochar and natural zeolite ion exchangers, as well as decomposition of heavy metal complexes through advanced oxidation processes (AOPs). Finally, the advantages, practical applications, and future potential of these techniques are discussed, along with any challenges and limitations that must be considered.

Synthesis of Metakaolin Based Alkali Activated Materials as an Adsorbent at Different Na2SiO3/NaOH Ratios and Exposing Temperatures for Cu2+ Removal

Water contamination is a major issue due to industrial releases of hazardous heavy metals. Copper ions are among the most dangerous heavy metals owing to their carcinogenicity and harmful effects on the environment and human health. Adsorption of copper ions using alkali activated materials synthesized through the polycondensation reaction of an alkali source and aluminosilicates is the most promising technique, and has a high adsorption capability owing to a large surface area and pore volume. This research focuses on the effect of the alkaline activator ratio, which is a sodium silicate to sodium hydroxide ratio. Various exposing temperatures on metakaolin based alkali activated materials on a surface structure with excellent functional properties can be used as adsorbent materials for the removal of copper ions. A variety of mix designs were created with varying sodium silicate to sodium hydroxide ratios, with a fixed sodium hydroxide molarity, metakaolin to alkali activator ratio, hydrogen peroxide, and surfactant content of 10 M, 0.8, 1.00 wt%, and 3.0 wt%, respectively. Most wastewater adsorbents need high sintering temperatures, requiring an energy-intensive and time-consuming manufacturing process. In this way, metakaolin-based alkali activated materials are adsorbent and may be produced easily by solidifying the sample at 60 °C without using much energy. The specific surface area, water absorption, microstructure, phase analysis, functional group analysis, and adsorption capability of copper ions by metakaolin based alkali activated materials as adsorbents were evaluated. The water absorption test on the samples revealed that the sodium silicate to sodium hydroxide 0.5 ratio had the highest water absorption percentage of 36.24%, superior pore size distribution, and homogeneous porosity at 60 °C, with a surface area of 24.6076 m²/g and the highest copper ion uptake of 63.726 mg/g with 95.59% copper ion removal efficiency at adsorption condition of pH = 5, a dosage of 0.15 g, 100 mg/L of the initial copper solution, the temperature of 25 °C, and contact time of 60 min. It is concluded that self-supported metakaolin based alkali activated material adsorbents synthesized at low temperatures effectively remove copper ions in aqueous solutions, making them an excellent alternative for wastewater treatment applications.

A Novel Adsorbent of Attapulgite & Carbon Composites Derived from Spent Bleaching Earth for Synergistic Removal of Copper and Tetracycline in Water

Simultaneously eliminating tetracycline (TC) and copper (Cu-II) from wastewater was investigated by applying a novel adsorbent fabricated by transforming spent bleaching earth (SBE) into attapulgite & carbon composites (A&Cs). Pyrolysis temperature for A&Cs preparation exhibited a positive effect on Cu(II) adsorption, while the AC500 possessed the greatest performance for TC remediation. Interestingly, a synergistic effect instead of competitive adsorption occurred between Cu(II) and TC under the combined binary system, as both TC and Cu(II) adsorption amount on A&C500 increased more than that in the single system, which could be mainly attributed to the bridge actions between the TC and Cu(II). In addition, hydrogen bonding, ᴨ-ᴨ EDA interaction, pore-filling and complexation exerted significant roles in the adsorption process of TC and Cu(II). In general, this study offered a new perspective on the regeneration of livestock and poultry industry wastewater polluted with antibiotics and heavy metals.

Surveying the elimination of hazardous heavy metal from the multi-component systems using various sorbents: a review

In this review, several adsorbents were studied for the elimination of heavy metal ions from multi-component wastewaters. These utilized sorbents are mineral materials, microbes, waste materials, and polymers. It was attempted to probe the structure and chemistry characteristics such as surface morphology, main functional groups, participated elements, surface area, and the adsorbent charges by SEM, FTIR, EDX, and BET tests. The uptake efficiency for metal ions, reusability studies, isotherm models, and kinetic relations for recognizing the adsorbent potentials. Besides, the influential factors such as acidity, initial concentration, time, and heat degree were investigated for selecting the optimum operating conditions in each of the adsorbents. According to the results, polymers especially chitosan, have displayed a higher adsorption capacity relative to the other common adsorbents owing to the excellent surface area and more functional groups such as amine, hydroxyl, and carboxyl species. The high surface area generates the possible active sites for trapping the particles, and the more effective functional groups can complex more metal ions from the polluted water. Also, it was observed that the uptake capacity of each metal ion in the multi-component solutions was different because the ionic radii of each metal ion were different, which influence the competition of metal ions for filling the active sites. Finally, the reusability of the polymers was suitable, because they can use several cycles which proves the economic aspect of the polymers as the adsorbent.

A State-of-the-Art Review on Innovative Geopolymer Composites Designed for Water and Wastewater Treatment

There is nothing more fundamental than clean potable water for living beings next to air. On the other hand, wastewater management is cropping up as a challenging task day-by-day due to lots of new additions of novel pollutants as well as the development of infrastructures and regulations that could not maintain its pace with the burgeoning escalation of populace and urbanizations. Therefore, momentous approaches must be sought-after to reclaim fresh water from wastewaters in order to address this great societal challenge. One of the routes is to clean wastewater through treatment processes using diverse adsorbents. However, most of them are unsustainable and quite costly e.g. activated carbon adsorbents, etc. Quite recently, innovative, sustainable, durable, affordable, user and eco-benevolent Geopolymer composites have been brought into play to serve the purpose as a pretty novel subject matter since they can be manufactured by a simple process of Geopolymerization at low temperature, lower energy with mitigated carbon footprints and marvellously, exhibit outstanding properties of physical and chemical stability, ion-exchange, dielectric characteristics, etc., with a porous structure and of course lucrative too because of the incorporation of wastes with them, which is in harmony with the goal to transit from linear to circular economy, i.e., "one's waste is the treasure for another". For these reasons, nowadays, this ground-breaking inorganic class of amorphous alumina-silicate materials are drawing the attention of the world researchers for designing them as adsorbents for water and wastewater treatment where the chemical nature and structure of the materials have a great impact on their adsorption competence. The aim of the current most recent state-of-the-art and scientometric review is to comprehend and assess thoroughly the advancements in geo-synthesis, properties and applications of geopolymer composites designed for the elimination of hazardous contaminants viz., heavy metal ions, dyes, etc. The adsorption mechanisms and effects of various environmental conditions on adsorption efficiency are also taken into account for review of the importance of Geopolymers as most recent adsorbents to get rid of the death-defying and toxic pollutants from wastewater with a view to obtaining reclaimed potable and sparkling water for reuse offering to trim down the massive crisis of scarcity of water promoting sustainable water and wastewater treatment for greener environments. The appraisal is made on the performance estimation of Geopolymers for water and wastewater treatment along with the three-dimensional printed components are characterized for mechanical, physical and chemical attributes, permeability and Ammonium (NH4+) ion removal competence of Geopolymer composites as alternative adsorbents for sequestration of an assortment of contaminants during wastewater treatment.

Adsorption and Release Characteristics of Purified and Non-Purified Clinoptilolite Tuffs towards Health-Relevant Heavy Metals

The occurrence of health-relevant contaminants in water has become a severe global problem. For treating heavy-metal-polluted water, the use of zeolite materials has been extended over the last decades, due to their excellent features of high ion exchange capacity and absorbency. The aim of this study was to assess the effect of heavy metal uptake of one purified (PCT) and two non-purified clinoptilolite tuffs (NPCT1 and NPCT2) in aqueous solutions on monovalent ions Ni+, Cd+, Cs+, Ba+, Tl+, and Pb+. Experiments were furthermore carried out in artificial gastric and intestinal fluids to mimic human digestion and compare removal efficiencies of the adsorbent materials as well as release characteristics in synthetic gastric (SGF) and intestinal fluids (SIF). Batch experiments show low sorption capacities for Ni+ and Cd+ for all studied materials; highest affinities were found for Ba+ (99–100%), Pb+ (98–100%), Cs+ (97–98%), and Tl+ (96%), depending on the experimental setup for the PCT. For the adsorption experiments with SGF, highest adsorption was observed for the PCT for Pb+, with an uptake of 99% of the lead content. During artificial digestion, it was proven that the PCT did not release Ba+ cations into solution, whereas 13,574 ng·g−1 and 4839 ng·g−1 of Ba+ were measured in the solutions with NPCT1 and NPCT2, respectively. It was demonstrated that the purified clinoptilolite tuff is most effective in remediating heavy-metal-polluted water, particularly during artificial digestion (99% of Pb+, 95% of Tl+, 93% of Ba+). In addition, it was shown that the released amount of bound heavy metal ions (e.g., barium) from the non-purified clinoptilolite tuffs into the intestinal fluids was significantly higher compared to the purified product.

Lead (Pb) sorption to hydrophobic and hydrophilic zeolites in the presence and absence of MTBE

The co-contamination of the environment by metals and organic pollutants is a significant concern, and one such example is lead (Pb) and methyl tert-butyl ether (MTBE) due to their historic use as fuel additives. Clinoptilolite is an abundant and efficient zeolite for metal removal, but the potential interference of co-existing organic pollutants on metal removal, such as MTBE, have rarely been discussed. In this study, a combination of batch sorption tests and synchrotron-based X-ray absorption spectroscopic analyses were employed to investigate Pb sorption mechanism(s) onto clinoptilolite in the presence and absence of MTBE. A comparison was made to synthetic ZSM-5 zeolite to gain insights into differences in Pb binding mechanisms between hydrophilic (clinoptilolite) and hydrophobic (ZSM-5) zeolites. Site occupancy and surface precipitation contributed equally to Pb removal by clinoptilolite, while surface precipitation was the main Pb removal mechanism for ZSM-5 followed by site occupancy. Despite the negligible effect of 100 mg/L MTBE on observed Pb removal from solution by both zeolites, a surface-embedded Pb removal mechanism, through the Mg site on clinoptilolite surface, arises when MTBE is present. This study provides an understanding of atomic-level Pb uptake mechanisms on zeolites, with and without co-contaminating MTBE, which aids in their application in water treatment at co-contaminated sites.

Carbon sphere-zinc sulphate nanohybrids for smart delivery of zinc in rice (Oryza sativa L)

The laboratory research was attempted to find nano zinc fertilizer utilizing the carbon sphere as a substrate. Typically the encapsulation techniques are followed in the drug delivery system, the limited work was done in nano-based zinc micronutrient for slow release of nutrients to crop. The use efficiency of zinc micronutrients in the soil is only less than 6 percentage. In universal, the deficiency of zinc micronutrients causes malnutrition problems in human beings, especially in children. After considering this problem we planned to prepare zinc nano fertilizer by using the carbon sphere for need-based slow release and increase the use efficiency of zinc micronutrient in soil. In this study we synthesis the carbon sphere nanoparticle after the formation of carbon sphere the zinc sulphate was loaded and characterized by utilizing Scanning Electron Microscopy, Surface Area and Porosity, X-ray diffraction analysis, Fourier Transform Infrared Spectroscopy, Transmission Electron Microscopy. The research result shows that the nano carbon sphere was excellently loaded with zinc sulphate to the tune of 8 percentage and it was confirmed by Energy dispersive X-beam spectroscopy. The zinc loaded carbon sphere release nutrient for a prolonged period of up to 600 h in the case of conventional zinc sulphate zinc release halted after 216 h in percolation reactor studies. The zinc nano fertilizer is recommended in agriculture to increase zinc use efficiency, crop yield without any environmental risk.

Clinoptilolite mediated activation of peroxymonosulfate through spherical dispersion and oriented array of NiFe2O4: Upgrading synergy and performance

Inspired by the features of both transition metal oxide and natural clinoptilolite (flaky structure with suitable pore diameter and open skeleton structure), we adopted a robust strategy by immobilization of nickel ferrite nanoparticles (NiFe₂O₄) on the clinoptilolite surface via typical citric acid combustion method. The hybrid catalyst exhibited enhanced peroxymonosulfate (PMS) activation efficiency and bisphenol A (BPA) degradation performance. Calculated by effective equivalent of NiFe₂O₄, it is found that the reaction rate constant (k) of NiFe₂O₄/clinoptilolite/PMS system (0.1859 min^-1) was 11.9 times higher than that of bare NiFe₂O₄/PMS system (0.0156 min^-1), which demonstrated that catalyst would be conjugated to PMS or contaminant efficiently and renders the rapid degradation and mineralization in the presence of clinoptilolite. After comprehensive characterization analysis and DFT simulations, natural mineral carrier effect (i.e. decreased crystalline size, increased oxygen vacancy content, etc.), abundant surface-bonded and structural hydroxyl groups as well as effective bonding with iron or nickel ions charged for the potential activation mechanism of PMS by NiFe₂O₄/clinoptilolite composite. And it is indicated that not only ^•OH and SO₄^•-, but also ¹O₂ was involved into series reactions. Overall, this study put forward a green and promising technology for high-toxic wastewater treatment.

Kinetic Studies of Cs+ and Sr2+ Ion Exchange Using Clinoptilolite in Static Columns and an Agitated Tubular Reactor (ATR)

Natural clinoptilolite was studied to assess its performance in removing caesium and strontium ions, using both static columns and an agitated tube reactor (ATR) for process intensification. Kinetic breakthrough curves were fitted using the Thomas and Modified Dose Response (MDR) models. In the static columns, the clinoptilolite adsorption capacity (qe) for 200 ppm ion concentrations was found to be ~171 and 16 mg/g for caesium and strontium, respectively, highlighting the poor material ability to exchange strontium. Reducing the concentration of strontium to 100 ppm, however, led to a higher strontium qe of ~48 mg/g (close to the maximum adsorption capacity). Conversely, halving the column residence time to 15 min decreased the qe for 100 ppm strontium solutions to 13–14 mg/g. All the kinetic breakthrough data correlated well with the maximum adsorption capacities found in previous batch studies, where, in particular, the influence of concentration on the slow uptake kinetics of strontium was evidenced. For the ATR studies, two column lengths were investigated (of 25 and 34 cm) with the clinoptilolite embedded directly into the agitator bar. The 34 cm-length system significantly outperformed the static vertical columns, where the adsorption capacity and breakthrough time were enhanced by ~30%, which was assumed to be due to the heightened kinetics from shear mixing. Critically, the increase in performance was achieved with a relative process flow rate over twice that of the static columns.

Effects of different filtration techniques on quality and toxicology of post treatment effluent from an anaerobic reactor

The early stages of the fish life cycle correspond to the phase that is most susceptible to deleterious effects caused by exposure to pollution. The aim of this study was to evaluate the quality of the anaerobic reactor effluent after three filtration-based treatments, namely, Double-Filtration in gravel and sand (DF), Triple-Filtration in gravel, sand and Activated Charcoal (TF-AC) and Triple-Filtration in gravel, sand and clinoptilolite (TF-C). The toxic effects on the population dynamics of larvae and embryos of catfish (Rhamdia quelen) to the final effluent were evaluated using an individual-based model (IBM). The results indicate that the three post-treatments produced effluents with significant improvement of the physicochemical parameters evaluated in relation to the anaerobic reactor effluent. In addition, all post-treatments improved the removal of metal ions. Experimental data showed high mortality rates for Rhamdia quelen embryos and larvae for most treatments, except for the effluent treated by TF-C. The results demonstrated that the concentration of ammoniacal nitrogen in relation to AR treatments (69.0); DF (44.0); TF-AC (46.6) and TF-C (0.33) in mg/L can be a limiting factor for the development of embryos and larvae during the ecotoxicity tests.

Silica Aerogels/Xerogels Modified with Nitrogen-Containing Groups for Heavy Metal Adsorption

Heavy metals are common inorganic pollutants found in the environment that have to be removed from wastewaters and drinking waters. In this work, silica-derived aerogels and xerogels were modified via a co-precursor method to obtain functional adsorbents for metal cations. A total of six formulations based upon four different functional precursors were prepared. The materials′ structural characterization revealed a decreased porosity and surface area on modified samples, more prominent in xerogel counterparts. Preliminary tests were conducted, and the prepared samples were also compared to activated carbon. Three samples were selected for in-depth studies. Isotherm studies revealed that the pre-selected samples remove well copper, lead, cadmium and nickel, and with similar types of interactions, following a Langmuir trend. The adsorption kinetics starts very fast and either equilibrium is reached quickly or slowly, in a two-stage process attributed to the existence of different types of active sites. Based on the previous tests, the best sample, prepared by mixing different functional co-precursors, was selected and its behavior was studied under different temperatures. For this material, the adsorption performance at 20 °C is dependent on the cation, ranging from 56 mg·g⁻¹ for copper to 172 mg·g⁻¹ for lead.

A Comparative Study on Cu2+, Zn2+, Ni2+, Fe3+, and Cr3+ Metal Ions Removal from Industrial Wastewaters by Chitosan-Based Composite Cryogels

Materials coming from renewable resources have drawn recently an increased attention in various applications as an eco-friendly alternative in the synthesis of novel functional materials. Polysaccharides, with their prominent representative - chitosan (CS), are well-known for their sorption properties, being able to remove metal ions from dilute solutions either by electrostatic interactions or chelation. In this context, we proposed here a comparative study on Cu2+, Zn2+, Ni2+, Fe3+, and Cr3+ metal ions removal from industrial wastewaters by CS-based composite cryogels using batch technique. The composite cryogels consisting of CS embedding a natural zeolite, namely clinoptilolite, were synthesized by cryogelation, and their sorption performance were compared to those of CS cryogels and of acid-activated zeolite. A deeper analysis of thermodynamics and kinetics sorption data was performed to get insights into the sorption mechanism of all metal ions onto sorbents. Based on the optimized sorption conditions, the removal of the above-mentioned ions from aqueous solutions by the composite sorbent using dynamic technique was also evaluated.

Ironmaking and Steelmaking Slags as Sustainable Adsorbents for Industrial Effluents and Wastewater Treatment: A Critical Review of Properties, Performance, Challenges and Opportunities

This paper critically discusses the structure, properties and applications of ironmaking and steelmaking slags and their silicate-based variants as low-cost adsorbents for removing cations and anions from industrial effluents and wastewater. Undoubtedly, the performance of slag-based adsorbents depends on their physical, chemical and phase chemical properties. The presence of crystalline phases, for example, has a significant effect on the adsorption capacity. However, despite their low cost and ubiquity, their chemical and geometric heterogeneity significantly affects the performance and applications of slag-based adsorbents. These challenges notwithstanding, the efficacy of slag-based adsorbents can be significantly enhanced through purposeful activation to increase the specific surface area and density of adsorption sites on the surfaces of adsorbent particles. The synthesis of functionalised adsorbents such as geopolymers, zeolites and layered double hydroxides from silicate and aluminosilicate precursors can also significantly increase the performance of slag-based adsorbents. In addition, the ability to stabilise the dissolved and/or entrained toxic metal species in stable phases in slags, either through controlled post-process fluxing or crystallisation, can significantly enhance the environmental performance of slag-based adsorbents. Most critical in the design of future slag-based adsorbents is the integration of the engineered properties of molten and solidified slags to the recovery and stabilisation of dissolved and/or entrained metals.

Heavy metal leachability in soil amended with zeolite- or biochar-modified contaminated sediment

In this work, reuse probability of heavy metal-contaminated sediment for land application was discussed using a 100-day column leaching assessment under the situation of simulated acid rain. For comparison, NaCl-modified zeolite and biochar were firstly studied for their adsorption capacity for Cu, Cd, and Pb in aqueous solution, and then their stabilizing effects on the three metals in sediment-soil mixture. Characteristic results indicated that NaCl-modified zeolite had properties more conducive to metal adsorption than biochar, including higher BET surface area and more negative surface charges. Adsorption capacities of NaCl-modified zeolite fitted by Langmuir isotherm model were 24.83, 35.57, and 133.16 mg g^-1 for Cu, Cd, and Pb, respectively. Leaching results demonstrated that metal concentrations in the leachates of soil receiving zeolite- or biochar-modified sediment reduced significantly after 100 days compared with that of soil receiving bare sediment. Moreover, the NaCl-modified zeolite presented a better performance in stabilizing the three metals than biochar from the BCR sequential extraction result. Therefore, stabilization of the dredged contaminated sediment by modified zeolite ensures an environmentally friendly reuse of the sediment on land and makes the sediment treatment operation-able and cost-effective.

Adsorption and desorption of potentially toxic metals on modified biosorbents through new green grafting process

Six lignocellulosic waste-derived biosorbents [cantaloupe peel (CAN), pine cone (PC), litchi fruit peel (LP), annona squamosal (AS), bamboo shoot (BS), and sugarcane bagasse (SB)] were selected as low-cost and renewable materials to prepare chemically modified biosorbent. The modified biosorbent was prepared through a newer carboxyl groups-grafting process onto the biosorbent's surface using acrylic acid. The results showed that the cation exchange capacity (CEC) of biosorbents increased by approximately 66.3-104% after modified. The modified biosorbent exhibited significantly higher adsorption capacity of Pb²⁺, Cu²⁺, and Cd²⁺ ions than the pristine biosorbent. The maximum Langmuir adsorption capacity (Q^o_max) of both pristine and modified biosorbents toward three metal ions (Pb²⁺, Cu²⁺, and Cd²⁺) followed the decreasing order: CAN > PC > LP > AS > BS > SB. The preference ranking of three metal ions on the pristine and modified biosorbents (mmol/kg) was generally in the order: Pb²⁺ > Cu²⁺ > Cd²⁺. Among these biosorbents, cantaloupe peel exhibited an excellent adsorption affinity to metal cations compared to the five others. The Q^o_max values of modified and pristine cantaloupe peels were ordered as follows: 143.2 and 81.1 mg/g for Pb²⁺ adsorption, > 45.4 and 30.4 mg/g for Cd²⁺ adsorption, > 33.1 and 23.5 mg/g for Cu²⁺ adsorption. After five adsorption-desorption cycles, the removal efficiency of Pb²⁺ by modified CAN was maintained at around 70%. The ion exchange played a determining role in adsorption mechanism. It can be concluded that modified cantaloupe peel can serve as a newer and promising biosorbent with a high adsorption capacity to various potentially toxic metals.

Competitive removal of heavy metal ions from squid oil under isothermal condition by CR11 chelate ion exchanger

Heavy metal ions (HMIs) are serious threats to the environment. Sub-critical water treatment was used to mimic contamination of squid oil in aqueous, metal-soap and oil phases. Isothermal adsorption of HMIs (Cu²⁺, Pb²⁺, Cd²⁺ and Zn²⁺) was studied from aqueous phase to oil phase (493, 523, 548, and 573K) for solutions with different initial concentration of HMIs was studied. Decomposition of glycerides into fatty acids was favored at high subcritical temperatures, with metal-soap phase showing the highest chelation ability toward Cu²⁺ (96%, isotherm 573K). The removal-ability of HMIs from contaminated oil was performed by CR11 chelate ion exchanger, showing facilitated removal from metal-soap and oil phases at low temperatures compared to general-purpose PEI-chitosan bead and PEI-chitosan fiber sorbents. The chelation behavior of Pb²⁺ and Cd²⁺ was the same in the OIL, with maximum values of 5.7×10^-3 (mol/l) and 5.0×10^-3 (mol/l) at 573K, respectively. By contrast, concentration of Zn²⁺ ion showed a slight increase with increasing temperature due to electrostatic forces between Zn²⁺ and active sites of glycerides in oil phase. For oil solution, the selectivity of adsorption for CR11, especially for Zn²⁺, was at least five-fold larger compared to PEI-chitosan bead and PEI-chitosan fiber adsorbents.

Assessment of TiO2 photoactivity on the lead removal: kinetic and mechanistic processing

Removal of lead ions from aqueous solutions, in the presence and in absence of commercial TiO₂, under UV-light was studied. The influence of catalyst mass, concentration of Pb(II) ions and of citric acid in the starting solution as well as the impact of illumination conditions on the removal rate were also investigated. The results were fitted on the pseudo-first order, pseudo-second order and Elovich kinetic models, Weber-Morris intraparticle and liquid film diffusion models, in order to establish the photoreduction mechanism. The Pb removal rate increased in time by a combined linear-exponential mechanism. The catalyst had a positive influence on the removal rate at the start of the photoreduction. At a low concentration of Pb(II) ions (20 mg/L), the amount of photoreduced Pb(II) ions was proportional to the concentration of the citric acid solution, but at high concentrations (240 mg/L), the correlation was inversely proportional. The rate limiting steps in the removal of lead were both the photoreduction on the TiO₂ surface and the diffusion through the film surrounding the catalyst particle. The lead removal was significantly influenced by the mobility and by the concentration of the species in solution.

A comprehensive study on photocatalytic activity of supported Ni/Pb sulfide and oxide systems onto natural zeolite nanoparticles

The Ni(II)-Pb(II) exchanged clinoptilolite nanoparticles (NCP) were transformed to corresponding oxides and sulfides via calcination and sulfiding processes, respectively. The obtained catalysts were characterized by XRD, FT-IR, TEM and DRS and used in photodegradation of p-nitrophenol (4-NP) aqueous solution under Hg-lamp irradiation. Results showed considerable increase in activity of the coupled semiconductors with respect to monocomponent one. In NiO-PbO-NCP system, conduction band (CB) of NiO is enough negative for easily migration of photogenerated electrons to CB-PbO level, while such phenomena take place from more negative CB-PbS level to CB-NiS level in NiS-PbS-NCP. These phenomena significantly prevented from electron-hole recombination which increased photocatalytic activity of the coupled semiconductors. Best photodegradation activities obtained by NiO1.3%-PbO14.7%-NCP and NiS2.1%-PbS10.0%-NCP, confirming semiconductors' mass-ratio dependence of the photocatalytic process. The supported coupled semiconductors showed blue shifts in band gap energies with respect to the bulk semiconductors which confirm formation of semiconductors nanoparticles inside the zeolite framework. The highest degradation percentage of 4-NP was obtained at: 0.5gL(-1) photocatalysts, 15mgL(-1) 4-NP at pH 7.5.

Superparamagnetic nanomaterial Fe3O4-TiO2 for the removal of As(V) and As(III) from aqueous solutions

A magnetically separable nanomaterial Fe3O4-TiO2 was synthesized and characterized which was subsequently used for the removal of arsenic (V) from aqueous solutions. The surface morphology, magnetic properties, crystalline structure, thermal stability and Brunauer-Emmet-Teller surface area of the synthesized Fe3O4-TiO2 nanoparticles (NPs) are characterized by scanning electron microscope and high-resolution transmission electron microscope, vibrating sample magnetometry, X-ray diffractometer, thermogravimetric analysis and multi point function surface area analyzer. The saturation magnetization of Fe3O4-TiO2 NPs was determined to be 50.97 emu/g, which makes them superparamagnetic. The surface area of Fe3O4-TiO2 NPs was as much as 94.9 m(2)/g. The main factors affecting adsorption efficiency, such as solution pH, reaction time, initial As(V) concentration and adsorbent concentration are investigated. When the adsorption isotherms were analyzed by the Langmuir, Freundlich and Dubinin-Radushkevich models, equilibrium data were found to be well represented by Freundlich isotherm, and adsorption on Fe3O4-TiO2 NPs fitted well with pseudo-second-order kinetic model. The maximum adsorption capacity of As(V) on Fe3O4-TiO2 NPs, calculated by the Freundlich model was determined at 11.434 µg/g. 1.0 g/L of Fe3O4-TiO2 NPs was efficient for complete removal of 100 µg/L As(V) in 1 h. Fe3O4-TiO2 NPs was also effective for 93% removal of 100 µg/L As(III). Matrix effect was determined using As(V)-contaminated well water. Successfull results were obtained for purification of real well water containing 137.12 µg/L As(V). Results show that Fe3O4-TiO2 NPs are promising adsorbents with an advantage of magnetic separation.

Removal of heavy metal ions from aqueous solution by zeolite synthesized from fly ash

Zeolite was synthesized from coal fly ash by a fusion method and was used for the removal of heavy metal ions (Pb(2+), Cd(2+), Cu(2+), Ni(2+), and Mn(2+)) in aqueous solutions. Batch method was employed to study the influential parameters such as adsorbent dosage, pH, and coexisting cations. Adsorption isotherms and kinetics studies were carried out in single-heavy and multiheavy metal systems, respectively. The Langmuir isotherm model fitted to the equilibrium data better than the Freundlich model did, and the kinetics of the adsorption were well described by the pseudo-second-order model, except for Cd(2+) and Ni(2+) ions which were fitted for the pseudo-first-order model in the multiheavy metal system. The maximum adsorption capacity and the distribution coefficients exhibited the same sequence for Pb(2+) > Cu(2+) > Cd(2+) > Ni(2+) > Mn(2+) in both single- and multiheavy metal systems. In the end, the adsorption capacity of zeolite was tested using industrial wastewaters and the results demonstrated that zeolite could be used as an alternative adsorbent for the removal of heavy metal ions from industrial wastewater.

A green technology for the synthesis of cellulose succinate for efficient adsorption of Cd(ii) and Pb(ii) ions

Cellulose succinate, directly prepared by a simple and green mechanical activation-assisted solid-phase synthesis method in a stirring ball mill, was used as environmental-friendly adsorbent for efficient adsorption of heavy metals.

Preparation of geopolymer-based inorganic membrane for removing Ni(2+) from wastewater

A type of novel free-sintering and self-supporting inorganic membrane for wastewater treatment was fabricated in this study. This inorganic membrane was synthesised using metakaolin and sodium silicate solutions moulded according to a designed molar ratio (SiO2/Al2O3=2.96, Na2O/Al2O3=0.8 and H2O/Na2O=19) which formed a homogenous structure and had a relative concentration pore size distribution, via scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analyses. In this work, the Ni(2+) removal effect of geopolymer inorganic membrane was studied under different pH value, initial concentration of Ni(2+) solutions and initial operation temperature. Results showed that geopolymer inorganic membrane efficiently removes Ni(2+) from wastewater because of the combined actions of the adsorption and rejection of this membrane on Ni(2+) during membrane separation. Therefore, geopolymer inorganic membrane may have positive potential applications in removing Ni(2+) or other heavy metal ions from aqueous industrial wastewater.

Porous geopolymeric spheres for removal of Cu(II) from aqueous solution: synthesis and evaluation

Porous geopolymeric spheres were synthetized by a suspension and solidification method, which were used as adsorbents for the removal of Cu(II) from aqueous solution. The influences of pH, geopolymeric spheres dosage, contact time, and initial Cu(II) concentration on adsorption capacity were investigated in detail. The adsorption kinetics and adsorption isotherms were fitted well by a pseudo-second-order model and a Langmuir isotherm model, respectively. The maximum adsorption capacity of Cu(II) by the spheres calculated from Langmuir isotherm model was 52.63 mg/g. The porous geopolymeric spheres showed higher adsorption capacity than the commercial spherical 4A molecular sieve and some other reported spherical materials. The continuous removal of Cu(II) from an effluent was also conducted in column mode. The results confirmed that porous geopolymeric spheres could be used for the cleanup of heavy metal ions from wastewater in a continuous column process.