Presence Of Other Ions Research Articles

Hydrothermal development of magnetic-hydrochar nanocomposite from pineapple leaves and its performance as an adsorbent for the uptake of Mn2+ and reuse of the metal loaded adsorbent in latent fingerprint

Manganeseis one of the heavy metals that isa major environmental concern when present in large amount. Manganese is discardedinto water systems by numerous industries, includingmining, batteries and electroplating etc. Pineapple leaves were applied as a biomass source to produce a magnetic hydrothermal treated hydochar nanocomposite; Fe3O4-HC. The BET surface area of Fe2O3-HC nanocomposite was 21.27 m2/g. Batch adsorption experiments revealed that the uptake of Mn2+ fit well in the pseudo second kinetics model, while the adsorption isotherm best fit the Freundlich model, with a maximum adsorption capacity of 2.99 mg/g at 25 °C and a pH of 5. The obtained thermodynamic parameters demonstrated that Mn2+ ion adsorption using the Fe2O3-HC nanocomposite was endothermic and nonspontaneous. Additionally, Fe2O3-HC nanocomposite demonstrated to be highly selective towards Mn2+ ions in the presence of other ions. The removal percentage of Mn2+ from a real water sample spiked with 50 mg/L Mn2+ was reported to be 53.2%. The spent adsorbent was then used to detect latent fingerprints, which revealed that Mn2+-Fe2O3-HC nanocomposite generated better and clear latent fingerprints than Fe2O3-HC nanocomposite.

SORPTION AND X-RAY FLUORESCENCE DETERMINATION OF MICRO QUANTITIES OF SOME TOXIC METALS IN NATURAL OBJECTS AFTER THEIR PRECONCENTRATION ON MODIFIED SILICA GEL

A method for X-ray fluorescence determination of trace amounts of Pb(II), Cd(II) and Hg(II) ions (up to 250 μg/ml) directly in the sorbent phase after their extraction from solutions in a dynamic sorption mode has been developed. Merck silica gel (particle d 0.1-0.2 mm, specific surface 428.61 m2/g), chemically modified with 4-(2-pyridylazo)-resorcinol functional groups in one step, was used as a sorbent. An energy dispersive X-ray fluorescence analyzer with a semiconductor detector "ElvaX" ("Elvatex", Kyiv) was used in the study.
 It was found that the combined analysis of micro quantities of Pb, Cd and Hg by sorption-x-ray fluorescence method after their preconcentration on silica gel with chemically fixed surfactant requires the use of calibration curves for each metal, taking into account the presence of other ions in solutions.
 The developed by us method of sorption-x-ray fluorescence determination of micro quantities of Pb(II), Cd(II) and Hg(II) after their extraction and preconcentration on silica gel with chemically fixed 4-(2-pyridylazo)-resorcinol can be effectively used for the analysis of natural and man-made objects of complex chemical composition.

Surfactant assisted APTES functionalization of graphene oxide intercalated layered double hydroxide (LDH) for uranium adsorption from alkaline leach liquor

The efficacy of uranium adsorption by modified layered double hydroxide (LDH) has been studied in detail in this work. The effects of initial uranium (U) concentration, solution pH, adsorbent dose, temperature and the presence of other ions were investigated. The removal efficiency varied from 98% to 92% for the initial U concentration 54–216 mg/L. However, the removal efficiency was decreased to 84% when the feed concentration was increased to 432 mg/L. The removal of uranium increased with the solution pH and beyond 8.5 it was invariant indicating the adsorbent is highly suitable for treatment of alkaline leach liquor. The adsorption capacity decreased with temperature and the Langmuir capacity of the adsorbent were found to be 948, 1,026, and 1162 mg/g at 323, 313, and 303 K, at pH 8.5. Evaluation of isotherm in alkaline pH is rare in the literature and the adsorption capacity of U of the LDH based adsorbents are reported in the range of 180 to 1143 mg/g with a pH variation of 3–7 at 298 K. Second order rate equation described the adsorption kinetics adequately. It was shown that switching of pH to 11.5 resulted remarkable desorption of U. Thus, the developed adsorbent has tremendous potential to separate U from alkaline leach liquor. Much research is required to immobilize the nano-sized adsorbents in a suitable media for preparation of the commercial scale filters.

Removal of toxic arsenic(iii) from an old endemic black-foot disease groundwater by oxidative electrosorption

Environmental context Naturally occurring arsenic was the likely cause of endemic black foot disease in groundwaters in Taiwan, and levels still exceed Taiwan EPA water quality standards. A method for the clean-up of these groundwaters that is both feasible and environmentally friendly is urgently needed. Oxidation of As(III) as H3AsO3 to the less toxic As(V)− and removal of As in groundwater was performed quantitatively by electrosorption using materials derived from agricultural wastes; this shows that this method has the potential to be a novel, green remediation method. Rationale Naturally occurring arsenic in the groundwater caused black-foot disease (BFD) in the 1950s on the southwest seashore of Taiwan. Recently, we found that the concentration of arsenic in groundwater taken from currently sealed wells in areas previously affected by BFD remained higher than the Taiwan (EPA) water quality standard. Although clean tap water is available in that area, removal of arsenic from the groundwater is of great importance to expand possible utilisation. Methodology Removal of arsenic from two old endemic BFD groundwaters with activated carbon (AC) electrodes recycled from agricultural wastes by electrosorption using capacitive deionisation (CDI) processes was studied. A better understanding of arsenic electrochemistry involved in electrosorption was investigated by in situ X-ray absorption near-edge structure spectroscopy. Results Arsenic removal efficiencies (61–93%) remained high across concentrations (5 and 196 mg/L). A high oxidation rate constant (0.93 h−1) for As(III)0 to As(V)− was found, allowing the electrosorption of As(V)− onto the meso- and micro-pores of the AC CDI electrodes with rate constants of 0.021 and 0.0013 h−1, respectively. Removal of arsenic from contaminated groundwater for drinking water was achieved with six CDI reactors in series. Moreover, in the presence of other ions (such as Na+, Mg2+ and Ca2+), 60–73% of As(III)0 and As(V)− ions were removed from the groundwaters by electrosorption. Discussion We have developed an engineering-feasible method for converting As(III)0 to less toxic As(V)−, enabling its removal by electrosorption, which demonstrates the feasibility for green remediation of BFD waters as well as other arsenic-contaminated groundwaters.

Direct magnetic sorbent sampling flame atomic absorption spectrometry (DMSS-FAAS) for highly sensitive determination of trace metals

A procedure of direct magnetic sorbent sampling in flame atomic absorption spectrometry (DMSS-FAAS) was developed in this work. Metal-loaded magnetic sorbents were directly inserted in the flame of the FAAS for direct metal desorption/atomization. Magnetic graphene oxide aerogel (M-GOA) particles were synthesized, characterized, and used as a proof-of-concept in the magnetic dispersive solid phase extraction of Pb2+ ions from water samples. M-GOA was selected because is a light and porous sorbent, with high adsorption capacity, that is quickly burned by the flame. Magnetic particles were directly inserted in the flame by using a metallic magnetic probe, thereby avoiding the need for a chemical elution step. As all the extracted Pb2+ ions arrive to the flame without passing through the nebulization system, a drastic increase in the analytical signal was achieved. The improvement in the sensitivity of the proposed method (DMSS-FAAS) for Pb2+ determination was at least 40 times higher than the conventional procedure in which the Pb2+ is extracted, eluted, and analyzed by conventional flame atomic absorption spectrometry (FAAS) via the nebulization system. The analytical curve was linear from 5.0 to 180.0 μg L−1 and the limit of detection was found to be 1.30 μg L−1. Background measurements were insignificant, and the atomic absorption peaks were narrow and reproducible. Precision assessed as a percentage of the relative standard deviation %RSD was found to be 17.4, 7.1, and 7.8% for 10, 70, and 180 μg L−1 levels, respectively. The method showed satisfactory results even in the presence of other ions (Al3+, Cr3+, Co2+, Cu2+, Fe3+, Mn2+, Ba2+, Mg2+, and Li+). The performance of the new system was also evaluated for Cd2+ ions, as well as by using other magnetic particles available in our lab: magnetic carbon nanotubes (M-CNTs), magnetic restricted access carbon nanotubes (M-RACNT), magnetic poly (methacrylic acid-co-ethylene glycol dimethacrylate) (M-PMA), magnetic nanoparticles coated with orange powder peel (M-OPP), and magnetic nanoparticles covered with SiO2 (M − SiO2). Analytical signals increased for both analytes in all sorbents (increases of about 4–37 times), attesting the high potential and applicability of the proposed method. Simplicity, high analytical frequency, high detectability and reproducibility, low cost, and possibility of being totally mechanized are the most relevant advantages.

Mercury (II) removal from aqueous solutions by iron nanoparticles synthesized from extract of Eucalyptus grandis

Artisanal mining is the main source of mercury emissions in South America, which generates a serious environmental impact due to this toxic metal, recent research is directed to minimize the impact, therefore this study focuses on the green synthesis of nanoparticles for the absorption of mercury in water. For the synthesis of iron nanoparticles, an extract of Eucalyptus grandis was used with iron chloride salts using water as solvent. The synthesized nanoparticles showed a specific surface area of 131.90 m2/g, determined by Brunauer-Emmett-Teller isotherm (BET). Nanoparticles were characterized by Fourier transformed infrared spectroscopy (FTIR) and transmission electron microscopy (MET). The behavior of nanoparticles synthesized during Hg (II) retention was evaluated measuring pH, temperature, nanoparticle dosing, presence of other ions and comparing with other adsorbents. All analyses measured by atomic absorption spectroscopy by the cold vapor technique (CVAAS), presenting a retention percentage for Hg (II) between 75.05 and 79.59% with pH between 4 and 7. The adsorption isothermal was adjusted to the Freundlich model and the percentage of retention of Hg by the synthesized nanoparticle was 79.26%. This work shows a method for obtaining an environmentally friendly mercury adsorbent from iron and E. grandis with a mercury retention capacity comparable to commercial adsorbents.

An efficiency strategy for cobalt recovery from simulated wastewater by biphasic system with polyethylene glycol and ammonium sulfate

Today, biphasic aqueous systems have received more attention than conventional separation methods due to their advantages, such as biocompatibility, low cost, and easy operation. The extraction of cobalt ions from the aqueous phase with the absence and the presence of other ions was investigated using polyethylene glycol, and ammonium sulfate salt without using an extractant. The efficiency was evaluated using operating parameters such as aqueous pH, salt and polymer concentrations, phase volume ratio, and initial metal concentration. The higher temperature, and the lower aqueous pH showed a maximum transfer rate for cobalt ions into the PEG1000 phase. Extraction efficiency under optimal conditions equal to 50% (w/w) polyethylene glycol 1000, 4 M ammonium sulfate, aqueous pH = 2, and 15 min extraction time was over 98%. Results from infrared spectroscopy, and thermo-gravimetric analysis illustrated the presence of the PEG-cobalt ion complex. The observation demonstrated that the biphasic system is the proper technology for wastewater purification.

Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite.

The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, and the presence of other ions in the system such as nitrate (NO3-), sulfate (SO42-), and arsenate (AsO43-). Although the mechanism of Fh transformation and oxyanion complexation have been separately studied, the effect of surface complex type and strength on the rate and pathway remains only partly understood. We have developed a kinetic model that describes the effects of surface complex type and strength on Fh transformation to goethite (Gt) and hematite (Hm). Two sets of oxyanion-adsorbed Fh samples were prepared, nonbuffered and buffered, aged at 70 ± 1.5 °C, and then characterized using synchrotron X-ray scattering methods and wet chemical analysis. Kinetic modeling showed a significant decrease in the rate of Fh transformation for oxyanion surface complexes dominated by strong inner-sphere (SO42- and AsO43-) versus weak outer-sphere (NO3-) bonding and the control. The results also showed that the Fh transformation pathway is influenced by the type of surface complex such that with increasing strength of bonding, a smaller fraction of Gt forms compared with Hm. These findings are important for understanding and predicting the role of Fh in controlling the transport and fate of metal and metalloid oxyanions in natural and applied systems.

Adsorption of Heavy Metals Ions from Mining Metallurgical Tailings Leachate Using a Shell-Based Adsorbent: Characterization, Kinetics and Isotherm Studies.

This study defines the optimal parameters that allow the use of waste mollusk shells (WS) to remove heavy metals from three mining and metallurgical leachates. First, the influence of parameters such as pH, contact time, initial metal concentration, adsorbent dose and the presence of co-ions in Cu2+, Cd2+, Zn2+ and Ni2+ adsorption was investigated in synthetic solutions. Metal uptake was found to be dependent on the initial pH of the solution, the removal rate increasing with the increase in pH, showing the highest affinity at pH 5–6. The removal efficiency at lower concentrations was greater than at higher values. The competitive adsorption results on bimetallic solutions showed that the adsorption capacity of the sorbent was restricted by the presence of other ions and suppressed the uptake of heavy metals compared to the single adsorption. Cu2+ was the metal that most inhibited the removal of Cd2+, Zn2+ and Ni2+. The Langmuir isotherm provided the best fit to the experimental data for Cu2+, Cd2+ and Zn2+ and the Freundlich isotherm, for Ni2+. The data showed that the maximum adsorption capacity amax for Zn2+, Cd2+ and Cu2+, was 526.32 mg g−1, 555.56 mg g−1 and 769.23 mg g−1, respectively. Sorption kinetics data best fit the pseudo-second-order kinetic model. The results obtained in the tests with three mining and metallurgical leachates showed that WS were effective in simultaneously removing several heavy metals ions such as Cu, Ni, Zn, Cd, Ni, As and Se.

Probing the supramolecular assembly in solid, solution and gel phase in uriede based thiazole derivatives and its potential application as iodide ion sensor

A simple series of thiazole-urea-aliphatic chain-based compounds (1–7) were designed and synthesized using the principle of Crystal Engineering. The aliphatic alkyl chain of compounds was varied to obtain the delicate hydrophobic-hydrophilic balance between solute–solvent molecules required to attain the supramolecular gelation. Interestingly, all the compounds turned out to be excellent gelators for polar solvents including water mixtures with alcohols and acetonitrile. To get an insight into the packing of molecules in solid-state, solution, and gel phases various physicochemical techniques were employed such as SANS, SEM, PXRD, DFT calculation, etc. UV–Vis spectrometric measurements of compound 1 in the solution phase were carried out to establish the anion sensing capability. Very high sensitivity and selectivity of iodide ion in presence of other ions and degelation of acetonitrile gel of compound 1 in presence of iodide salts, make these compounds a unique class of LMOGs.

Ultra‐Rapid Removal of Pb(II) Ions by a Nano‐MoS2 Decorated Graphene Aided by the Unique Combination of Affinity and Electrochemistry (Adv. Sustainable Syst. 7/2022)

Water Purification The image representing article 2200039 by K. Y. Sandhya and co-workers is a symbolic depiction of a partially reduced graphene oxide-molybdenum disulfide nanocomposite (prGO-MoS2) for the ultra-rapid and selective removal of Pb(II) ions from contaminated water within ≤3 minutes in the presence of other ions, due to the selective interaction and the electrochemistry between the Pb(II) and S2− and oxygen moieties of prGO-MoS2.

Activity and Stability of Pd Bimetallic Catalysts for Catalytic Nitrate Reduction

In this work, we study the effect of modifying the metal loading (0.5–1.5 wt.% Pd and 0.1–1 wt.% Sn or In), the impregnation order of noble or promoter metal (Pd–Sn or Sn–Pd), and the type of promoter metal (Sn or In) during the preparation process for a Pd bimetallic catalyst, supported on γ-alumina, used in the catalytic reduction of nitrate. The deposition of the noble metal over the promoter metal, especially with Pd:Sn ratios (wt.) of 1:10 and 1:2, favored the hydrogen spillover rate and increased the H concentration on the catalyst surface, enhancing NH4+ production. On the other hand, Pd–In catalysts showed higher activity than the Sn catalysts, as well as higher NH4+ selectivity. The stability of the Pd–Sn/Al2O3 (1.5–1 wt.%) catalyst was evaluated in long-term experiments for the treatment of synthetic water (100 mg L−1 NO3−) and three different commercial drinking waters. This Pd–Sn/Al2O3 catalyst achieved a stable nitrate conversion for a duration of 50 h in the synthetic water treatment. However, the catalyst showed a significant activity loss in the presence of other ions (different to NO3−) in the reaction medium, increasing slightly the selectivity to NH4+.

Effect of Sulfate Ions on Galvanized Post-Tensioned Steel Corrosion in Alkaline Solutions and the Interaction with Other Ions.

Zinc protection of galvanized steel is initially dissolved in alkaline solutions. However, a passive layer is formed over time which protects the steel from corrosion. The behavior of galvanized steel exposed to strong alkaline solutions (pH values of 12.7) with a fixed concentration of sulfate ions of 0.04 M is studied here. Electrochemical measurement techniques such as corrosion potential, linear polarization resistance and electrochemical impedance spectroscopy are used. Synergistic effects of sulfate ions are also studied together with other anions such as chloride Cl− or bicarbonate ion HCO3− and with other cations such as calcium Ca2+, ammonium NH4+ and magnesium Mg2+. The presence of sulfate ions can also depassivate the steel, leading to a corrosion current density of 0.3 µA/cm2 at the end of the test. The presence of other ions in the solution increases this effect. The increase in corrosion current density caused by cations and anions corresponds to the following orders (greater to lesser influence): NH4+ > Ca2+ > Mg2+ and HCO3− > Cl− > SO42−.

A fluorescence probe of sulfur quantum dots for sensitive detection of copper ions in Paris polyphylla var. yunnanensis

The excessive residue of copper ion (Cu2+) has an important impact on the quality of traditional Chinese medicine (TCM). In this work, a sulfur quantum dots (SQDs) fluorescent probe was developed for rapid and sensitive detection of Cu2+ in Paris polyphylla. Smith var. yunnanensis (Franch.) Hand. -Mazz. (P. polyphylla var. yunnanensis). SQDs were synthesized by the “assemble-fission” method. The synthesized SQDs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), and their fluorescence properties were studied. The prepared SQDs have advantages of ultra-small size, good optical properties and excellent stability. The addition of Cu2+ could effectively quench the fluorescence of SQDs due to the inner filter effect (IFE) between Cu2+ and SQDs. The detection linear range of this method was 20–200 μM. The limit of detection (LOD) was 6.78 μM. It has high selectivity in the simultaneous presence of other ions, and the possible fluorescence quenching mechanism was discussed in detail. Finally, the prepared SQDs were applied to the detection of actual samples of P. polyphylla var. yunnanensis with satisfactory results, which confirmed the great potential of SQDs in the actual measurement of Cu2+ in TCM.

A ratiometric fluorescent sensor based azo compound of 4-(4-Dimethylamino-phenylazo)-N-pyridin-2-ylmethyl-benzamide for rapid and selective detection of Fe3+ ion

A novel colorimetric and ratiometric ligand based on azo dye 4-(4-Dimethylamino-phenylazo)-N-pyridine-2-ylmethyl-benzamide (L) was synthesized in high yield and was carefully investigated. The sensing activity of the ligand toward different cation ions was studied. The ligand demonstrated a highly selective colorimetric sensing toward Fe3+ in acetonitrile aqueous solution with a detection limit of 1.8 × 10-8 M. The developed ligand showed a visual color change from yellow to red with naked-eye, a very effective way to identify Fe3+ instead of spectroscopic instrumentation. In contrast, no color change was observed in the presence of other ions. In addition, the ratio of metal-ligand interaction, determined by Job’s plot method, was 1:1. Furthermore, cation binding character was determined using visual inspection, UV–vis, fluorescence, and 1H NMR analyses. In addition, interactions between the receptor and Fe3+ ion were investigated by spectroscopy and DFT computational studies. The theoretical study showed that oxygen and nitrogen atoms of L are coordinated as a bi-dentate ligand in the L-Fe3+ by making sevenmember rings.

Effect of ion interactions on the Raman spectrum of NO3−: Toward monitoring of low-activity nuclear waste at Hanford

Raman spectroscopy is a valuable in-situ technique for many applications. The concentrations of species in complex ionic mixtures of nuclear waste can be estimated using Raman measurements. However, it has been experimentally observed that ion interactions can cause a modification of Raman peak intensities and positions. The present work explores the nonlinear behavior associated with the nitrate anion, NO3−, which is present in abundance in low activity nuclear waste. We examine changes in the main Raman peak of the nitrate anion in the presence of other ions. A wide range of concentrations are covered, including those expected during direct-feed low-activity waste (DFLAW) processing at the Hanford site in the State of Washington. The experiments showed that the ions interact and associate to form ion pairs, which results in a blue shift (i.e., a shift towards higher wavenumbers) in the main Raman peak of nitrate. The results indicate that cation concentration is a better predictor of the peak shift, compared to ionic strength, both for binary and multicomponent mixtures. These findings have direct implications on the development of spectra-to-composition models for the DFLAW system, since they show deviations from the linearity assumptions used in common chemometric models.

Sequestration of heavy metal ions from multi-metal simulated wastewater systems using processed agricultural biomass

Industrial effluents generally contain several metals, so during adsorptive treatment, they may influence the removal of each other. It is essential to explore the effect of co-cations on metal removal in multi-metal solutions. The present study examined the possibility of processed rice husk and saw dust to remove Cr6+, Ni2+, Cu2+, Cd2+ and Zn2+, from the single, binary and multi-component aqueous solutions. A substantial lesser removal of metal ions was observed in the presence of co-ions. This study revealed antagonistic effect on the removal of a particular metal ion, from the industrial effluent, even at optimum process parameters if other metal ions are present in the effluent. Although, a higher concentration of one metal ion than others in effluents increased its removal due to a greater number of ions as compared to other for the biosorption, yet presence of other ions influences the uptake of individual ions. In case of industrial effluents, maximum adsorption was obtained at pH 2.0 for Cr6+, 5.0 for Ni2+ and Cd2+ and 6.0 for Zn2+ and Cu2+. The study confirms the beneficial use of the studied biosorbents in water remediation.

“Turn-on” fluorescence probe for Al (III) and Hg (II) ions in aqueous medium: Synthesis, characterization, cytotoxicity, visual results in solution and cancer cells

In this study, An efficient OFF–ON fluorescent compound integrated with nitrobenzofurazan and phenolphthalein (NBFP) has been prepared for the detection of metals ions. NBFP was characterized with 1H NMR, 13C NMR, COSY-NMR, FTIR, and Mass spectrometry. The fluorescent response towards metal ions displayed that NBFP is selective for Hg (II) and Al (III), with a detection limit of 14.7 µM and 16.3 µM for Hg(II) and Al(III), respectively. Job’s plot for NBFP + Hg (II) complex, and NBFP + Al (III) complex confirmed the 1:2 ligand–metal stoichiometry. Binding constant (Ksv) from Stern-Volmer equation was found to be 1.60 × 102 M−1 for NBFP + Hg (II) complex and 9.25 × 102 M−1 for NBFP + Al (III) complex respectively, indicating a strong interaction between ligand and selective metal ions in the presence of other ions. The quantum yield of NBFP was found to be ΦL = 0.028, exhibiting a weak and wide emission band. Cytotoxicity of NBFP has been evaluated before application in living cell fluorescent imaging for the detection of metal ions. The result showed that NBFP exhibits good biocompatibility in living cells and displayed a good response for the detection of Al (III) and Hg (II) ions in living cells using the confocal microscope.

Removal of Erythrosine B using Prosopisspicigera L. wood carbon-iron oxide composite

The present study investigates the removal of Erythrosine B (EB), a neurotoxin and carcinogenic dye from aqueous system using Prosopisspicigera L. wood (PsLw) carbon-iron oxide composite. The adsorbent is well characterized by Fourier Transform Infra Red spectroscopy (FTIR), Scanning Electron Microscope (SEM) for surface morphology, Brunauer-Emmett-Teller nitrogen adsorption method (BET)/methylene blue method for surface area determination and potentiometric methods for surface charge (pHzpc) determination. The removal capacity of the adsorbent has been evaluated by batch method under varying pH, contact time, adsorbate initial concentrations, and in the presence of other ions. The Langmuir maximum adsorption capacity is found to be 487.8 mg/g at pH = 2.0 for an initial concentration of 250 mg/L. The adsorption follows pseudo second order kinetics and fits to Langmuir isotherm. The adsorption is thermodynamically spontaneous and exothermic in nature. Pore diffusion and mass transfer studies are performed. Column mode analysis is applied in the process for industrial applications.

Schwertmannite: A review of its occurrence, formation, structure, stability and interactions with oxyanions

In this article, we provide a critical review on the occurrence, formation, structure and stability of schwertmannite – an enigmatic Fe(III) oxyhydroxy-sulfate mineral that is of widespread interest in the soil science, environmental geochemistry , hydrometallurgy and wastewater fields. We also review interactions between schwertmannite and selected, environmentally relevant oxyanions (arsenate, phosphate, antimonate, selenate , chromate , and molybdate). Schwertmannite is one of the most common minerals to form via direct precipitation of iron in acid sulfate waters at pH 2 – 4. As such, it has been found to occur in systems that are affected by acid mine drainage , acid sulfate soils , natural acid rock drainage, and hydrometallurgical settings involving oxidation of iron-sulfide minerals. Despite its official recognition as a new mineral almost 30 years ago, schwertmannite’s poor crystallinity , fine particle size, variable composition and metastability have constrained our ability to conclusively resolve its crystal structure, possibly polyphasic nature, and solubility/stability. Nevertheless, since the early 1990’s, there has been a steadily-growing body of literature showing that, in acid-sulfate systems, schwertmannite strongly impacts iron and sulfur cycling, acidity dynamics, and electron flow. In addition, interactions with schwertmannite also strongly influence the mobility and fate of co-associated oxyanionic species. In parallel, many oxyanions have themselves been found to also exert a powerful control on schwertmannite’s geochemical behavior and mineralogical stability. Schwertmannite-oxyanion interactions occur via adsorption to the schwertmannite surface, anionic exchange with sulfate in the schwertmannite tunnel structure, and co-precipitation by substitution for either structural sulfate or Fe(III) during schwertmannite formation. This array of distinct sorption mechanisms results in oxyanions being able to both stabilize and conversely destabilize schwertmannite. This distinction appears to reflect an interplay of kinetic and thermodynamic constraints, which depend heavily on the specific oxyanion, its concentration (i.e. level of loading on/in schwertmannite), and other background geochemical conditions (e.g. pH and presence of other ions). Resolving these complex interactions and their importance in controlling schwertmannite occurrence and stability represents a challenge for future research.