Inorganic Adsorbents Research Articles

PS-C09-13: NEW COMPREHENSIVE THERAPEUTIC STRATEGY FOR HYPERTENSION AND UREMIA USING INORGANIC SUBSTANCES WITH SPECIAL ADSORPTION PROPERTIES

Background: In order to remove uremic toxins accumulated in patients with chronic kidney disease (CKD), removal of uremic toxin-causing substances from the intestinal tract by administration of spherical adsorbed charcoal and removal of uremic toxins from the blood by hemodialysis are being performed. However, existing treatment methods are still inadequate for the removal of protein-bound uremic toxins (PBUT) and other medium- to large-sized uremic toxins, which leads to a decreased quality of life and worse prognosis in CKD patients. In order to solve this remaining problem, we are currently investigating the use of inorganic materials for the treatment of uremia. Methods: To evaluate the adsorption performance of our inorganic material, we compared the adsorption performance of various uremic substances in solution, healthy subjects’ plasma, and hemodialysis patients’ plasma, using Kremezin® as a control. Results: Kremezin® was able to adsorb small molecular weight substances in each solution and plasma, while medium to large molecules were poorly adsorbed. On the other hand, the inorganic material we are developing has high adsorption performance not only for small molecules but also for medium to large molecules including inflammatory cytokines and PBUT, and selectively adsorbs cations such as sodium, potassium, and inorganic phosphorus. Conclusion: Inorganic substances with special adsorption performance adsorbed not only uremic substances but also cations, whose accumulation is a problem in CKD patients. Therefore, the inorganic adsorbent may contribute not only to the treatment of uremia but also to the comprehensive treatment of hypertension, hyperkalemia, and CKD-MBD, which are common complications in CKD patients.

Research progress of CO2 separation technology by solvent absorption

The combustion of fossil fuels emits a large amount of CO2, which causes the greenhouse effect and leads to global warming and poses a serious threat to life on earth. CO2 capture technology can effectively reduce the concentration of CO2 in the atmosphere, alleviate the greenhouse effect, and improve the environment. CO2 capture technologies include absorption, membrane separation and adsorption separation, among which chemical absorption and separation have the advantages of high efficiency, low cost and easy availability of materials. In this paper, the advantages and disadvantages of three main chemical absorption and separation methods (inorganic reagents, organic amines and ionic liquids) adsorb CO2 are summarized. Among inorganic adsorbents, NH3·H2O can achieve rapid and efficient absorption of CO2, and it is relatively stable and not easy to degrade. Common types of organic amine adsorbents are monoethanolamine, methanolamine, and sterically hindered amine. However, it is difficult for a single organic amine adsorbent to meet the requirements of high absorption rate, high absorption capacity and low reaction heat at the same time. Therefore, mixing organic amine absorbents with different characteristics can improve their performance in absorbing CO2. Ionic liquids have the advantages of good thermal stability, very low saturation vapor pressure, and designable structure, and are a new type of CO2 adsorbent, but ionic liquids have high viscosity themselves. Combining ionic liquids with organic or inorganic porous materials to form loaded ionic liquid materials, which can be used as CO2 adsorbent not only to improve the separation effect, but also to avoid the problem of high viscosity caused by direct absorption of ionic liquids, thus improving CO2 adsorption efficiency.

One Step Sol-Gel Synthesis and Morphostructural Characterization of Sodium Titanate Particles

Titanate-based materials are attractive inorganic adsorbents for wastewater treatment but also could be used as high performances ceramics. In this study, platelets and wires like morphologies of sodium titanate were successfully synthesized via an unconventional sol-gel method, starting with titanium tetrachloride, TiCl4 and sodium hydroxide, NaOH precursors, and coupled with hydrothermal maturation at 160°C for 24h. Afterwards, through an alkaline hydrothermal maturation, this intermediate phase gradually converted into a sodium titanate with a preserved morphology. The powder thus obtained, was compositionally characterized using X-Ray Diffraction (XRD) and Electron Dispersive Spectroscopy (EDS), structural properties were highlighted by imaging through Scanning Electron Microscopy (SEM) and Thermogravimetric measurements were carried out to determine the transformations that occur between 25-1000 °C. It is shown that a mix of two titanate phase Na2TinO2n+1 with n = 3 and 6 was obtained, having wires and platelet like morphology and micron sizes particles, with a crystallite size of 22 nm grown on Miller indices plane (200). This work was designed to improve the production yield by using an unconventional titanate synthesis method and precursors.

Application of Activated Carbon Nanosilica Composite for Heavy Metal and Organic Matter Removals

Contamination of water sources is a prevalent issue in some parts of the world. The threat of heavy metal ions and organic materials entering sources of drinking water has grown with mankind’s expanding industrialization. Heavy metal ions, such as nickel, are typically byproducts of metal finishing, and mining. When these ions are introduced into a water source, they can cause health issues in affected populations. These can range from developmental challenges in young or unborn children, to the development of certain types of cancers. Similarly, organic materials like methylene blue are byproducts of pharmaceutical and dye producing industries. Once these organic materials have entered the water in sufficient concentrations, consumption can lead to respiratory sickness and cancer. In addition, methylene blue are harmful to both marine and plant life as they can disrupt photosynthesis, stunt plant growth, and inhibit basic functions. With the contamination of water sources becoming more prevalent, new solutions are required to solve this problem. Activated carbon and zeolite are two cheap materials that have shown promise in use as contaminant removers. The price and commercial availability of these compounds could assist in promoting their accessibility in economically disadvantaged areas. Solid phase extractor is the most economical and effective method. Therefore, nanomaterials as adsorbents have been used in environmental remediation and in improving many other areas related to energy, catalysis, biomaterials and sensing applications [1-27].The aim of this study is to synthesize and investigate the effectiveness of inorganic adsorbent such as zeolite and organic based adsorbent such as activated carbon and its composite between zeolite and activation carbon. These different adsorbents have been used for removal of organic pollutants and heavy metal contaminants. The absorption efficiency of these materials were monitored by UV-Vis Spectrophotometer. For example, zeolite, activated carbon and the composite adsorbed 54%, 37% and 48% of nickel from water, respectively.

Rapid and highly selective capture of U(VI) from water by copper phosphate

The removal of highly hazardous U(VI)-containing contaminants of concern has been a major issue for effluent discharge and ecological protection because current some inorganic adsorbents lack ion selectivity and are economically viable. Inspired by these limitations, here we reported a simple and controlled technique for the synthesis of copper phosphate (CP) that combines chemical oxidation with in-situ precipitation, able to selectively capture uranium (VI) ions. The resulting CP has been analyzed using powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy. Adsorption experiments with U(VI) show that CP quickly adsorbs U(VI) from acidic water within 1 min, with a high removal efficiency of up to 97.8%. A maximum adsorption capacity of 1000 mgU g−1 adsorbent can be achieved at pH 3.0. Importantly, the selective adsorption experiments for a total of 11 metal ions show that the U(VI) capture is very effective, with an adsorption capacity of 1.64 mmol g−1 for U(VI) and a total adsorption capacity of 4.89 mmol g−1 for Ln-An metal ions. Finally, XRD and XPS results reveal that the underlying mechanism for U(VI) capture is driven through the dissolution-precipitation and surface complexation. Overall, this work proposes a new metal ion trapping agent that may find potential applications in the fields of water purification and environmental remediation.

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Unraveling the Origin of Enhanced Activity of the Nb2O5/H2O2 System in the Elimination of Ciprofloxacin: Insights into the Role of Reactive Oxygen Species in Interface Processes.

The overlooked role of reactive oxygen species (ROS), formed and stabilized on the surface of Nb2O5 after H2O2 treatment, was investigated in the adsorption and degradation of ciprofloxacin (CIP), a model antibiotic. The contribution of ROS to the elimination of CIP was assessed by using different niobia-based materials in which ROS were formed in situ or ex situ. The formation of ROS was confirmed by electron paramagnetic resonance (EPR) and Raman spectroscopy. The modification of the niobia surface charge by ROS was monitored with zeta potential measurements. The kinetics of CIP removal was followed by UV–vis spectroscopy, while identification of CIP degradation products and evaluation of their cytotoxicity were obtained with liquid chromatography–mass spectrometry (LC-MS) and microbiological studies, respectively. Superoxo and peroxo species were found to significantly improve the efficiency of CIP adsorption on Nb2O5 by modifying its surface charge. At the same time, it was found that improved removal of CIP in the dark and in the presence of H2O2 was mainly determined by the adsorption process. The enhanced adsorption was confirmed by infrared spectroscopy (IR), total organic carbon measurements (TOC), and elemental analysis. Efficient chemical degradation of adsorbed CIP was observed upon exposure of the Nb2O5/H2O2 system to UV light. Therefore, niobia is a promising inorganic adsorbent that exhibits enhanced sorption capacity toward CIP in the presence of H2O2 under dark conditions and can be easily regenerated in an environmentally benign way by irradiation with UV light.

Versatile inorganic adsorbent for efficient and practical removal of hexavalent chromium in water

The development of efficient and practical adsorbent on eliminating hexavalent chromium (Cr(VI)) is a valuable and challenging target. In this work, various layered double hydroxide (LDH) and its calcined products (layered double oxide, LDO) were used as the adsorbent to optimize the efficiency and performance on removing Cr(VI) (from Cr2O72−) in water. NiAl-LDH, CoAl-LDH, NiFe-LDH and CaFe-LDH, as well as their calcined materials were prepared and characterized by various techniques. The magnetic-composite adsorbent was carried out by mechanical grinding NiAl-LDO and CaFe-LDH with the benefit of easy solid-liquid separation. The as-prepared adsorbents exhibited the differences in the structural phase, surface characteristic, and magnetic and optical properties. The saturation magnetization and magnetic interaction of NiAl-LDO to the external magnet were generated (5.4 emu/g) by mixing with CaFe-LDH (22.8 emu/g). The maximum adsorption capacity was decreased in the order of NiAl-LDO > CoAl-LDO > CaFe-LDH@NiAl-LDO > NiAl-LDH > CaFe-LDH > NiFe-LDO > calcined CaFe-LDH > NiFe-LDH > CoAl-LDO. This work revealed an alternative inorganic adsorbent with efficient and/or practical functionalities for cleaning the wastewater contaminated with Cr(VI) in anionic species.

Selective removal of Sr2+ by cation exchange using silica-based titanate adsorbents

Titanate is regarded as a highly selective inorganic adsorbent for removing 90Sr. A sol-gel method was developed to prepare the K2Ti6O13/SiO2 adsorbent using optimized annealing temperatures. A well-crystallized structure of the K2Ti6O13/SiO2 phase has been identified after the annealing temperature from 500 to 600 ​°C. The crystallized structure shows uniform ion sites for Sr2+ replacement, and the K2Ti6O13/SiO2 adsorbent shows high adsorbability and selectivity for metal ions at neutral pH in radioactive wastewater with the following selectivity orders: Sr2+ ​> ​Ca2+ ​> ​Mg2+ ​> ​Na+. The breakthrough curve of Sr2+ showed that 0.78 ​g of K2Ti6O13/SiO2 was able to decontaminate 152 ​cm3 of blended solution containing 100 ​ppm of Sr2+. In addition, the adsorption mechanism of high selectivity for Sr2+ was also further proposed and proved by Density functional theory (DFT) calculations.

Thermodynamic Study of Phosphate Adsorption and Removal from Water Using Iron Oxyhydroxides

Iron oxyhydroxides (FeOOHs) appear to be the optimal group of materials among inorganic adsorbents for the removal of phosphates from water, providing significant adsorption capacities. This research work presents a thermodynamic study of phosphate adsorption by examining five different FeOOHs sorbent nanomaterials. The otablebtained results indicated that the adsorption process in these cases was spontaneous. When the experiments were performed using distilled water, akageneite (GEH), schwertmannite, and tetravalent manganese feroxyhyte (AquAsZero), displaying ΔH° values of 31.2, 34.7, and 7.3 kJ/mole, respectively, presented an endothermic adsorption process, whereas for goethite (Bayoxide) and lepidocrocite, with ΔH° values of −11.4 and −7.7 kJ/mole, respectively, the adsorption process proved to be exothermic. However, when an artificial (according to NSF) water matrix was used, GEH, schwertmannite, lepidocrocite, and AquAsZero presented ΔH° values of 13.2, 3.3, 7.7, and 3.3 kJ/mole, respectively, indicative of an endothermic process, while only for Bayoxide, with ΔH° of −17 kJ/mole, the adsorption remained exothermic. The adsorption enthalpy values generally decreased with the NSF water matrix, probably due to the competition for the same adsorption sites by other co-existing anions as well to the possible formation of soluble phosphate complexes with calcium; however, an overall positive effect on the uptake of phosphates was observed.

Effect of Mg2+-, Sr2+-, and Fe3+-substitution on 85Sr and 60Co adsorption on amorphous calcium phosphates: Adsorption performance, selectivity, and mechanism

Hydroxyapatite Ca10(OH)2(PO4)6 is a well-known efficient adsorbent of dyes, heavy metal ions, and radionuclides. Its adsorption efficacy strongly depends on crystalline/amorphous structure, defectiveness, texture characteristics, and morphology. Herein, we synthesized Mg2+-, Sr2+-, and Fe3+-substituted (5 mol%) amorphous calcium phosphates as an effective 85Sr and 60Co radionuclides adsorbents. The introduction of Mg2+-, Sr2+-, and Fe3+ ions led to the formation of amorphous calcium phosphates with particles size in the nanoscale range of approximately 10–50 nm. The features of the adsorption behavior of amorphous calcium phosphates were determined depending on the variation of the pH of aqueous, NaCl and CaCl2 solutions. Fe3+-substituted samples demonstrated the superior adsorption efficiency to 85Sr (Kd 7.77 ×103 cm3/g) and 60Co (Kd 6.84 ×104 cm3/g) radionuclides at pH of 10.0 and 4.0, respectively. The adsorption performance of obtained adsorbents slowly decreased at 0.1 M NaCl backgrounds and Kd85Sr and 60Co reached 1.67 × 103 and 2.78 × 104 cm3/g for non-substituted calcium phosphate. The dramatic decrease of calcium phosphates adsorbents efficiency to 85Sr (Kd <150 cm3/g) and 60Co (Kd <1.34 ×103 cm3/g) for 0.05 M CaCl2 model solution was established. The adsorption mechanism of dissolution-precipitation (for 85Sr) and chemisorption (for 60Co) was proposed. Fe3+-substituted calcium phosphate showed the competitive affinity and selectivity to 85Sr and 60Co comparing with described inorganic adsorbents and to be considered as prospective adsorbent for wastewater treatment in nuclear industry.

Advances in Amine-Surface Functionalization of Inorganic Adsorbents for Water Treatment and Antimicrobial Activities: A Review.

In the last decade, adsorption has exhibited promising and effective outcomes as a treatment technique for wastewater contaminated with many types of pollutants such as heavy metals, dyes, pharmaceuticals, and bacteria. To achieve such effectiveness, a number of potential adsorbents have been synthesized and applied for water remediation and antimicrobial activities. Among these inorganic adsorbents (INAD), activated carbon, silica, metal oxide, metal nanoparticles, metal–organic fibers, and graphene oxide have been evaluated. In recent years, significant efforts have been made in the development of highly efficient adsorbent materials for gas and liquid phases. For gas capture and water decontamination, the most popular and known functionalization strategy is the chemical grafting of amine, due to its low cost, ecofriendliness, and effectiveness. In this context, various amines such as 3-aminopropyltriethoxysilane (APTES), diethanolamine (DEA), dendrimer-based polyamidoamine (PAMAM), branched polyethyleneimine (PEI), and others are employed for the surface modification of INADs to constitute a large panel of resource and low-cost materials usable as an alternative to conventional treatments aimed at removing organic and inorganic pollutants and pathogenic bacteria. Amine-grafted INAD has long been considered as a promising approach for the adsorption of both inorganic and organic pollutants. The goal of this review is to provide an overview of surface modifications through amine grafting and their adsorption behavior under diverse conditions. Amine grafting strategies are investigated in terms of the effects of the solvent, temperature, and the concentration precursor. The literature survey presented in this work provides evidence of the significant potential of amine-grafted INAD to remove not only various contaminants separately from polluted water, but also to remove pollutant mixtures and bacteria.

Lithium extraction from geothermal waters; a case study of Ömer-Gecek (Afyonkarahisar) geothermal area

Lithium (Li) is the lightest metal, has unique physicochemical properties and is the main component of lithium-ion batteries. Rechargeable lithium-ion batteries play a very important role in maximizing the performance of electric devices and vehicles. It is predicted that the metal and mineral demand for lithium-ion batteries will increase 56 times by 2050. In order to meet the increasing demand, in addition to known methods, lithium recovery from geothermal waters has become a very popular research subject. There are abundant geothermal water resources in the world, especially in Turkey and in Afyonkarahisar. The aim of this study is to produce an adsorbent for the retention of lithium in geothermal waters and to remove lithium ions from geothermal water with the help of this adsorbent. Geothermal samples for lithium enrichment were obtained from Ömer-Gecek (Afyonkarahisar), where hosts geothermal resources with low-medium enthalpy containing 3.5 mg/L Li. In this context, an inorganic adsorbent was developed by using MnCO3, LiOH and sodium silicate. The characterization and performance parameters of the adsorbent were investigated. As a result of adsorption experiments in fixed bed column, we can perform calculations based on a ton of adsorbent in a column with natural water feed rate of 1.63 t/h. The outcome is 236.7 g of Li, which is equivalent to 2519.6 g of Li2CO3 in 41.6 h. Our findings show that the adsorbent developed in our study can be used to retain Li+ from geothermal waters.

Beneficial roles of Song-Gang stone as a feed additive in aquaculture: a review

Song-Gang® bio-stone (SGS) is a microporous crystalline hydrated aluminosilicate which has found various applications because of their very unique physiochemical characteristics such as ion exchange and absorptive-desorptive properties. Significant progress has been made in recent years on applications of these inorganic adsorbents in different industries including agriculture, aquaculture, water and wastewater treatment. This review article intends to summarize the published reports on the applications of SGS in aquaculture industry. SGS application as a feed additive to enhance fish growth and promote their health and nutritional parameters is the most important discussed areas. According to the technical data that are discussed in this review, SGS should be considered as a material with tremendous potential for application in the aquaculture industry. Considerable amounts of research works are under way to explore other opportunities for application of SGS to benefit aquaculture industry.

Preparation of 134Cs sealed source based on WO3 adsorbent for radiometric calibration purposes

Cesium-134 artylon sealed source based on inorganic adsorbent (as a core) was easily prepared. The sealed source was in the form of a disk constituted of two halves; base and top. Cesium-134 was adsorbed by equilibration of 134CsCl solution with WO3 inorganic adsorbent at pH 4 for 24 h at 25±1°C. Then, the liquid phase was decanted and checked for the remaining activity. Thereafter, the 134Cs-loaded WO3 was dried at 100 °C for 24 h. A definite weight the 134Cs-loaded WO3 adsorbent was placed in the central cavity of the base half-disk. Then the two half-disks were assembled using a commercial epoxy adhesive. The activity values of the sealed source were 7.81×10-2 and 7.70×10-2 Ci, calculated by using the absolute efficiency curve and DETEFF software were found to be closest at a 5 cm source-detector distance; respectively. After radiometric standardization and encapsulation, the sealed source was checked radiometrically before release to the local market for calibration purposes of radiation measurement and identification instruments.

Adsorption Features of Various Inorganic Materials for the Drug Removal from Water and Synthetic Urine Medium: A Multi-Technique Time-Resolved In Situ Investigation.

Pharmaceutical active compounds, including hundreds of different substances, are counted among the emerging contaminants in waterbodies, whose presence raises a growing concern for the ecosystem. Drugs are metabolized and excreted mainly through urine as an unchanged active ingredient or in the form of metabolites. These emerging contaminants are not effectively removed with the technologies currently in use, making them a relevant environmental problem. This study proposes the treatment of urine and water at the source that can allow an easier removal of dissolved drugs and metabolites. The treatment of synthetic urine, with dissolved ibuprofen as a model compound, by adsorption, using various classes of inorganic materials, such as clays, hierarchical zeolites and ordered mesoporous silica (MCM-41), is presented. A multi-technique approach involving X-ray powder diffraction, solid-state NMR, UV-Vis and Raman spectroscopies was employed to investigate the adsorption process in inorganic adsorbents. Moreover, the uptake, the ensuing competition, the efficiency and selectivity as well as the packing of the model compound in ordered mesoporous silica during the incipient wetness impregnation process were all thoroughly monitored by a novel approach, involving combined complementary time-resolved in situ 1H and 13C MAS NMR spectroscopy as well as X-ray powder diffraction.

Simultaneous degumming and deacidification of crude palm oil using mixed matrix PVDF membrane

The research work aimed to investigate the compatibility of polyvinylidene difluoride (PVDF) membrane embedded with various inorganic adsorbents for producing a mixed matrix membrane (MMM) and to examine the capability of mixed matrix PVDF membrane (PVDF-MMM) for simultaneous degumming and deacidification of crude palm oil (CPO). Four different adsorbent were tested which includes calcium silicate (CaS), magnesium silicate (MagS), ZSM-zeolite (ZSM) and activated carbon (AC). The in-house made PVDF-MMM was fabricated according to the dry-jet wet spinning method. The performances of these PVDF-MMMs were assessed with respect to the removals of phosphorus, FFA and colour. Based on finding showed that the combination of 18PVDF embedded with 3 wt% MagS showed the most compatible polymer-inorganic hybrid MMM to perform pre-treatment of CPO. Increasing the MagS concentration from 3 to 8 wt% in the polymer matrix recorded the highest removals of FFA at 16.51 %, phospholipid at 93.31 % and colour at 18.8 %, respectively. Nevertheless, high amount of MagS added to the polymer matrix affected the spinnability and reproducibility performance of MMM. Future work, surface modifications of inorganic adsorbent can be evaluated to facilitate good dispersion of filler in polymer matrix during membrane fabrication to maintain good membrane reproducibility.

High-efficient, broad-spectrum and recyclable mesoporous TiO2 adsorbent for water treatment

Cooperative adsorption and degradation in situ, known as “hook and destroy” strategy, is an appealing idea to scavenge pollutants from water efficiently. However, commercial high-adsorption-capacity adsorbents are usually based on activated carbon, which is easily damaged in the pollutant degradation process, resulting in decreasing of the adsorption performance, while the adsorption capability of most inorganic adsorbents is inadequate for practical applications. To address the issues, we prepared a novel mesoporous titanium dioxide (m-TiO 2 ) by facile one-step hydrolysis method at room temperature. The m-TiO 2 exhibits both high adsorption capacity and short equilibrium time for a wide range of pollutants, such as dyes, pharmaceuticals and pesticides, due to its large surface area and abundant functional groups. The surface charge of the m-TiO 2 adsorbent can be regulated by adjusting the acidity and alkalinity of preparation conditions, hence the m-TiO 2 is capable of adsorbing either positively or negatively charged pollutants. The versatility for adsorption of diverse contaminants was demonstrated in the experiment of purifying lake water with multiple pollutants. More significant, the m-TiO 2 can be regenerated in minutes by in-situ degrading the adsorbed molecules using common oxidants, such as hypochlorite, the active ingredient of disinfectants. The adsorption performance has little deterioration in at least five successive cycles of adsorption and degradation. Considering the excellent adsorption performance, wide applicability and high recyclability, the mesoporous TiO 2 offers a sustainable approach to increasingly complex water environmental problems. ● Cooperative adsorption and degradation of pollutants in situ. ● Simultaneous degradation of adorbates and regeneration of adsorbents. ● Mesoporous structure expediting degradation. ● Large adsorption capacity and short equilibrium time. ● Broad applicability to diverse pollutants.

Iron-doped natural clays: Low-cost inorganic adsorbents for phosphate recovering from simulated urban treated wastewater

Natural inorganic adsorbents are attractive for pollutants removal due to the easy operation, non-toxic characteristics and low cost. In this study, two raw clays (C1 and C2) were doped with iron and evaluated for the recovery of phosphate from simulated urban treated wastewater. The adsorbents' performances were evaluated through batch adsorption assays. Iron was stably retained in doped clays (C1-Fe and C2-Fe) at basal and edge surface at adsorption and desorption stages. Clay adsorbents were effective for adsorption of phosphate at neutral pH 7 and in broad range of phosphate concentrations. The maximum phosphate adsorption capacity values were 21, 38, 21 and 38 for C1, C1-Fe, C2 and C2-Fe, respectively. The equilibrium sorption data of raw and iron-doped clays were well described by the Langmuir isotherm model (R2 > 0.97). Therefore, monolayer phosphate adsorption occurred through hydrogen bonding and complexation between protonated hydroxyl groups and phosphate anions. The raw and iron-doped clay adsorbents reached the equilibrium within 10 min and the equilibrium attainment data were well described by the intraparticular diffusion model (R2 > 0.96). The phosphate monolayer adsorption was followed by diffusion through the internal clay pores. The phosphate adsorption by clays in presence of competing ion was inhibited by the higher ionic charge of sulphate. Besides, the less hydrated chloride and bicarbonate anions promoted the reduction of the sorption capacity of phosphate. Finally, the reusability of iron-doped clays is limited. Therefore, saturated iron-doped clays as single-use adsorbents can be disposed for soil amendment applications.

Iron(III) removal from acidic solutions using mesoporous titania microspheres prepared by vibrational droplet coagulation

The removal of contaminants, such as Fe(III) from acidic leachates, is often needed as its presence as a contaminant hinders the recovery of the desired metals. An inorganic adsorbent of interest for the removal of Fe(III) is titania due to its high specific surface area and good chemical stability. However, besides the material properties, also the macroscopic shape of the adsorbent is important for its implementation. In this study we have shaped monodisperse titania microspheres using vibrating nozzle technology. In a first step, a suspension containing titania nanopowder and sodium alginate is broken up into monodisperse droplets. The droplets are then solidified through ionotropic gelation of the alginate binder molecules with the calcium ions used as solidification species. The thermally treated microspheres had an average diameter 518 µm, a specific surface area 97 mm2 g−1 and an average pore size of 19 nm. These titania microspheres were employed as an adsorbent to remove Fe(III) from acidic solutions (pH 2). A maximum adsorption capacity of 13.2 mg g−1 was found. A high selectivity (kD 449 mL g−1) was observed towards Fe(III) removal in an acidic leachate originating from a spend automotive catalyst. The titania microspheres could be easily separated and regenerated using a 0,1 M EDTA solution which was demonstrated for up to 5 cycles.