Development and characterization of yttrium-ferric binary composite for treatment of highly concentrated arsenate wastewater

Enhancing fluoride removal from wastewater using Al/Y amended sludge biochar

This study explored the potential of utilizing aluminum and yttrium amended (Al/Y amended) sewage sludge biochar (Al/Y-CSBC) for efficient fluoride removal from wastewater. The adsorption kinetics of fluoride on bimetallic modified Al/Y-CSBC followed the pseudo-second-order model, while the adsorption isotherm conformed to the Freundlich equation. Remarkably, the material exhibited excellent fluoride removal performance over a wide pH range, achieving a maximum adsorption capacity of 62.44 mg·g-1. Moreover, Al/Y-CSBC demonstrated exceptional reusability, maintaining 95% removal efficiency even after six regeneration cycles. The fluoride adsorption mechanism involved ion exchange, surface complexation, and electrostatic adsorption interactions. The activation and modification processes significantly increased the specific surface area of Al/Y-CSBC, leading to a high isoelectric point (pHpzc = 9.14). The incorporation of aluminum and yttrium metals exhibited a novel approach, enhancing the adsorption capacity for fluoride ions due to their strong affinity. Furthermore, the dispersing effect of biochar played a crucial role in improving defluoridation efficiency by enhancing accessibility to active sites. These findings substantiate the significant potential of Al/Y-CSBC for enhanced fluoride removal from wastewater.

Facile Synthesis of Ce-MOF for the Removal of Phosphate, Fluoride, and Arsenic

Ce-MOF was synthesized by a solvothermal synthesis method and was used to simultaneously remove phosphate, fluoride and arsenic (V) from water by adsorption. Ce-MOF was characterized by a nitrogen adsorption-desorption isotherm, scanning electron microscopy, and infrared spectroscopy. The effects of initial concentration, adsorption time, adsorption temperature, pH value and adsorbent on the adsorption properties were investigated. A Langmuir isotherm model was used to fit the adsorption data, and the adsorption capacity of phosphate, fluoride, and arsenic (V) was calculated to be 41.2 mg·g-1, 101.8 mg·g-1 and 33.3 mg·g-1, respectively. Compared with the existing commercially available CeO2 and other MOFs, Ce-MOF has a much higher adsorption capacity. Furthermore, after two reuses, the performance of the adsorbent was almost unchanged, indicating it is a stable adsorbent and has good application potential in the field of wastewater treatment.

Recovery of rare earth elements from mine wastewater using biosynthesized reduced graphene oxide

Recycling rare earth elements (REEs) from sources of secondary waste such as REEs mine wastewater has emerged as a sustainable approach with both waste reuse and wastewater processing. In this study, green reduced graphene oxide (G-rGO) was prepared utilizing green tea extract with the advantages of being environmentally friendly, sustainable, and low cost. To understand how G-rGO functions, it was compared to commercial reduced graphene oxide (rGO), and the efficiencies in adsorbing Y(III) were 91.6% and 11.9%, respectively. This indicated there is a synergistic adsorption between the capping layer of G-rGO and rGO alone. G-rGO and rGO were characterized before and after exposure to Y(III). This comparison indicated that Y(III) was adsorbed on the surface of G-rGO through complexation and electrostatic interaction. The adsorption kinetics best fit the pseudo-second-order model and the Langmuir model isotherm model, with adsorption capacities of 24.54 mg g^-1. A probable adsorption mechanism of Y(III) by G-rGO was proposed, involving electronic complexation, electrostatic adsorption and ion exchange. Furthermore, the adsorption efficiencies of G-rGO for Y(III), Ce(III) and Zn(II) in mine wastewater were 22.1%, 89.1% and 14.6%, respectively. These results demonstrate that G-rGO has great potential in the recovery of REEs from mine wastewater.

Understanding the adsorption of iron oxide nanomaterials in magnetite and bimetallic form for the removal of arsenic from water

Arsenic decontamination is a major worldwide concern as prolonged exposure to arsenic (>10 µg L-1) through drinking water causes serious health hazards in human beings. The selection of significant, cost-effective, and affordable processes for arsenic removal is the need of the hour. For the last decades, iron-oxide nanomaterials (either in the magnetite or bimetallic form) based adsorptive process gained attention owing to their high arsenic removal efficiency and high regenerative capacity as well as low yield of harmful by-products. In the current state-of-the-art, a comprehensive literature review was conducted focused on the applicability of iron-based nanomaterials for arsenic removal by considering three main factors: (a) compilation of arsenic removal efficiency, (b) identifying factors that are majorly affecting the process of arsenic adsorption and needs further investigation, and (c) regeneration capacity of adsorbents without affecting the removal process. The results revealed that magnetite and bimetallic nanomaterials are more effective for removing Arsenic (III) and Arsenic (V). Further, magnetite-based nanomaterials could be used up to five to six reuse cycles, whereas this value varied from three to six reuse cycles for bimetallic ones. However, most of the literature was based on laboratory findings using decided protocols and sophisticated instruments. It cannot be replicated under natural aquatic settings in the occurrence of organic contents, fluctuating pH and temperature, and interfering compounds. The primary rationale behind this study is to provide a comparative picture of arsenic removal through different iron-oxide nanomaterials (last twelve yearsof published literature) and insights into future research directions.

Adsorptive behavior of thallium using Fe3O4-kaolin composite synthesized by a room temperature ferrite process

Thallium (Tl) contaminants pose serious threats to the ecological environment and human health due to its acute/chronic poisoning on the health of most organisms even at low concentrations. To find a rapid and efficient technology in removing Tl from waters thus becomes a crucial issue. A magnetic Fe₃O₄-kaolin composite (denoted by FKC) with high specific surface area (133.7 m²/g) was successfully synthesized via a simple and low-cost technique for Tl(I) removing from various water media. The HRTEM images confirmed the existence of lattice fingers Fe₃O₄ and displayed that a large number of Fe₃O₄ nanoparticles dispersed on the surface of kaolin sheets. Compared with kaolin or Fe₃O₄ alone, FKC enhanced obviously the adsorption rate and capacity of Tl(I) over a wide pH range (4.5-9.0). The maximum adsorption capacity of FKC for Tl(I) was 19,347 mg/kg (calculated by Langmuir model), which was almost one hundred times and two times higher than those of kaolin and Fe₃O₄, respectively. Importantly, FKC was observed to have a great potential in removing Tl(I) from surface water, groundwater, and tap water in more alkaline conditions. By applying the external magnetic field, FKC could be recovered efficiently (99%) and rapidly (20 s). Moreover, Tl L₃-edge XANES spectra revealed that Tl(I) was adsorbed on the FKC and would not be converted to more toxic Tl(III). The cations (CaCl₂, NaCl, and KCl) and the ionic strength with concentrations of 0.001-1.0 mol/L showed a great influence on the adsorption of Tl(I) by FKC, implying that this adsorption was dominated by outer-sphere surface complexation at investigated pH values. The information provided is essential for designing a rapid and effective scavenger for removing Tl in various natural waters.

Multifunctional hybrid membranes for photocatalytic and adsorptive removal of water contaminants of emerging concern

This work focuses on the combination of multifunctional photocatalytic and adsorbent materials in a unique polymeric membrane. For this purpose, Au/TiO₂ and Y₂(CO₃)₃ nanoparticles were immobilised onto a poly (vinylidene fluoride-hexafluoropropylene), (PVDF-HFP) membrane, and the physical-chemical characterisation of these materials was performed, as well as pollutant removal efficiency. An efficient TiO₂ functionalisation with gold nanoparticles was achieved, endowing these particles with the capability to absorb visible radiation absorption. A favourable porous structure was obtained for the membranes, with an average pore size of 4 μm, and the nanoparticles immobilisation did not alter the chemical properties of the polymeric membrane. The produced hybrid materials, including both the Au/TiO₂ and Y₂(CO₃)₃ nanoparticles, presented an efficiency of 57% in the degradation of norfloxacin (5 mg/L) under ultraviolet radiation for 120 min, 80% under visible radiation for 300 min, and 58% in arsenic adsorption for 240 min. These membranes represent a new multifunctional platform for removing several pollutants, which may allow their incorporation in more efficient and less energy-consuming water treatment processes favouring its application, even in low energy resources countries.

One-step removal of high-concentration arsenic from wastewater to form Johnbaumite using arsenic-bearing gypsum

High-level arsenic-containing wastewater (HAW) causes serious environmental pollution. Chemical precipitation is the most widely used technology for treating HAW. However, chemical precipitation generates huge amounts of hazardous solid wastes, which leads to secondary pollution. In this work, an efficient method, producing no secondary pollution was developed for one-step complete removal of As(V) from HAW using a hazardous solid waste namely arsenic-bearing gypsum (ABG). After the treatment, ABG was transformed into highly stable and environment-friendly mineral Johnbaumite. Meanwhile, the arsenic concentration in the wastewater decreased from 10,000 mg L^-1 to 0.22 mg L^-1 under optimized hydrothermal conditions (ABG dosage of 50 g L^-1, solution pH of 13.5, temperature of 150 °C for 12 h). The mechanism mainly included the following processes: (i) The phase transformation of ABG resulted in the release of calcium and hydrogen arsenate ions in ABG, (ii) Hydrogen arsenate ions transformed into arsenate ions in alkaline environment, and (iii) Under alkaline conditions, calcium ions combined with arsenate ions to form Johnbaumite, whereas the hydrothermal conditions accelerated the crystal growth of Johnbaumite. This study provides a new idea for the synchronous treatment of toxic heavy metal-containing wastewaters and hazardous solid wastes.

Establishing the state-of-the-art on the adsorption of coexisting pnictogens in water: A literature review

The occurrence of pnictogens, namely phosphorus, arsenic, and antimony, can be observed in soils, sediments and mining areas, and their coexistence requires a multifaceted approach to the design of adsorption systems to maximize their simultaneous removal efficiency. Therefore, this work aims to provide an extensive literature review of P, As, and Sb adsorption in multicomponent systems and the statistical treatment of the quantitative results. Binary As-P systems have been the most studied in the literature. The oxidation state did not significantly affect the P influence in As adsorbed amount (p = 0.955), but this influence was correlated with the As:P ratio (p < 0.05). A few works have explored As-Sb and Sb-P systems, demonstrating that effective treatments for As do not always reveal a good removal efficiency of the other pnictogens. The Sb adsorbed amount was significantly less affected in the trivalent than in the pentavalent state in both As-Sb and Sb-P systems (p < 0.05). Most of the interactions were competitive, with a few studies reporting synergistic effects for Sb due to the presence of the other elements. Many topics have been identified as lacking in-depth research: ternary As-Sb-P systems, the effect of concentration ratios, pH, and redox conditions (namely those that lead to trivalent species' prevalence), the surface interactions with materials other than iron oxides, and the influence of other aqueous components. This review provides a first step in gathering the relevant literature and approaching the study of adsorption treatment methodology as a complex subject involving many factors.

Smectite-supported chain of iron nanoparticle beads for efficient clean-up of arsenate contaminated water

Prolonged exposure to inorganic arsenic (As) via drinking water is a major concern as it poses significant human health risks. Removal of As is crucial but requires effective and environment-friendly clean-up technology to avoid any additional risk to the environment. In this study, we developed Australian smectite (smec)-supported nano zero-valent iron (nZVI) composite for arsenate i.e., As(V) sorption. We used a range of tools, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and energy dispersion X-ray (EDS) spectroscopy to characterise the material. SEM and TEM images and elemental mapping of the composite reflect that the smectite layer was surrounded by a chain of iron nanobeads evenly distributed on clay particles, which is quite exceptional among currently available nZVIs. The maximum As(V) sorption capacity of this composite was 23.12 mg/g in the ambient conditions. Using X-ray photoelectron spectroscopy we unveiled chemical states of As and Fe before and after the sorption process. Additionally, the release of iron nanoparticles from the composite at various pHs (3-10) were found negligible, which demonstrates the effectiveness of smec-nZVI to remove As(V) from contaminated water without posing any secondary pollutant.

Efficient degradation of roxarsone and simultaneous in-situ adsorption of secondary inorganic arsenic by a combination of Co3O4-Y2O3 and peroxymonosulfate

Roxarsone (ROX), as one of aromatic organoarsenic compounds (AOCs), is extensively used in livestock industry, which tends to transform into high-toxic inorganic arsenic in environments. Herein, a bifunctional Co₃O₄-Y₂O₃, possessing extremely excellent catalytic and adsorption performance due to the synergy of Co₃O₄ and Y₂O₃, was designed and employed to activate peroxymonosulfate (PMS) for the elimination of ROX and the simultaneous in-situ adsorption of secondary inorganic arsenic, in which Co₃O₄ acted as the primary catalyst, and Y₂O₃ served as the main adsorbent. 50 μM (3.75 mg-As/L) of ROX was almost completely degraded, coupled with the conversion of As(III) to As(V) in the system of Co₃O₄-Y₂O₃ (0.2 g/L) and PMS (0.5 mM) within 15 min at initial pH 7. Meanwhile, > 99.3% of the secondary As(V) would be removed within 120 min. The reactive oxygen species (ROS) were identified to be ^•OH, SO₄^•-, and ¹O₂, which were responsible for the ROX degradation and the formation of As(V). Simultaneously, the produced As(V) were effectively adsorbed via the ligand/anion exchange with surface -OH and CO₃^2- anions of Co₃O₄-Y₂O₃. The possible degradation pathways of ROX were further proposed on the basis of the intermediates identification. Our findings may provide an insight into the degradation of AOCs and the simultaneous removal of secondary inorganic arsenic via the PMS activation with Co₃O₄-Y₂O₃.

Cu(II)-Fe(III) oxide doped anion exchangers - Multifunctional composites for arsenite removal from water via As(III) adsorption and oxidation

The aim of the present study was to investigate As(III) oxidation and adsorption on the surface of hybrid anion exchangers containing Cu(II)-Fe(III) binary oxide deposited in their porous structure with the same Cu:Fe ratio of 1:2 but with different amounts and distribution of inorganic deposit within polymeric beads. The equilibrium studies confirmed high adsorption capacity of the best hybrid polymer: 94.4 mg As/g. Moreover, the adsorption was effective over a wide pH range, selective in the presence of interfering ions, and the material was effectively regenerated. The performance of the hybrid polymer was also confirmed in the column process which enabled both As(III) and As(V) concentrations to be lowered from 500 μg/L to below 10.0 μg/L in a solution with a composition similar to natural groundwater. The breakthrough point of the bed was reached after the solution amounting to 1833 bed volumes passed through the column. Desorbed As speciation, FTIR and XPS studies showed that As(III) was mainly adsorbed on the surface of Cu-Fe oxides followed by its oxidation to As(V). In the oxidation reaction metal oxides acted as catalysts and adsorbents, while the oxidant was probably oxygen dissolved in solution.

An innovative lanthanum carbonate grafted microfibrous composite for phosphate adsorption in wastewater

Excessive presence of phosphorus in waters can cause eutrophication, a global unsolved environmental problem that has caused harmful effects to our eco-system and the source of our drinking water. In the study presented in this paper, a novel lanthanum carbonate grafted microfibrous composite (LC-MC) adsorbent was synthesized aiming at removing large amount of phosphate in wastewater efficiently. An optimized LC-MC was firstly prepared. The most suitable pH for the phosphate uptake was pH 7 to 9. The adsorption showed similar behavior in a wide range of ionic strength. The presence of co-existing anions was proved to have a less significant effect on the removal. The adsorption isotherm data were better fitted by the Freundlich isotherm than the Langmuir isotherm. The equilibrium was reached at about 300 min of contact time. 80 % of original adsorption capacity can be achieved even after 5 cycles of adsorption- desorption operations, indicating great regenerative performance of the adsorbent. The adsorption mechanism study showed that the ligand exchange played a key role during the phosphate adsorption.

Study on adsorption properties and mechanism of thallium onto titanium‑iron magnetic adsorbent

Thallium (Tl) contamination caused by the industrial wastewater leakage has become a serious environmental problem due to thallium's high toxicity. In this study, a novel titanium‑iron magnetic nano-sized adsorbent was synthesized and applied for the effective removal of thallium(I). The physicochemical properties of the adsorbent were investigated by a series of techniques such as scanning electron microscope (SEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). About 83% of equilibrium adsorption capacity could be accomplished within the initial 30 min. The adsorption of Tl(I) was found to be highly dependent on solution pH. The maximum adsorption capacity of Tl(I) was 111.3 mg/g at pH 7.0. The presence of such co-existing cations as Na⁺, Mg²⁺, Ca²⁺ and Cu²⁺ could have a certain influence on the uptake of Tl(I). The adsorption mechanism was proposed as a surface complexation process of Tl(I) ions by binding to deprotonated sites of hydroxyl groups on the adsorbent surface. The prepared magnetic adsorbent would be suitable for effectively treating thallium-containing water due to its promising adsorption ability towards Tl(I) and ease in operation.

Simultaneous arsenic and fluoride removal using {201}TiO2-ZrO2: Fabrication, characterization, and mechanism

The coexistence of arsenic (As) and fluoride (F) in drinking water is an urgent environmental issue that causes increasing public concerns. The need for effective simultaneous removal of As and F has motived great research efforts. Herein, a novel {201}TiO₂-ZrO₂ composite was synthesized and its application mechanism was explored. Batch adsorption experiments show that the As(III), As(V), and F adsorption followed the pseudo-second-order kinetics with the Langmuir adsorption capacity at 58.5, 21.6, and 13.1 mg/g, respectively. EXAFS and in situ ATR-FTIR results suggested that TiO₂ surface sites were occupied by As(III) and As(V) in bidentate binuclear structures, and ZrO₂ sites preferentially adsorbed As(III) and F in monodentate mononuclear configurations. This molecular structure obtained in the mono-adsorption system was integrated with the charge distribution multisite surface complexation model to accurately predict the As and F co-existing adsorption behaviors. The results in competitive adsorption, regeneration, and application evidenced that the {201}TiO₂-ZrO₂ composite is a promising adsorbent for simultaneous As and F removal.