Preparation of a novel two-dimensional carbon material and enhancing Cu(II) ions removal by phytic acid

A novel two-dimensional carbon material using phytic acid-functionalized graphene oxide was successfully synthesized by a simple hydrothermal method. Properties of the material were characterized by SEM, FT-IR, FITR-Rama and BET. Some factors like contact time, pH, and temperature were studied to investigate the adsorption characteristics on Cu(II) ions of the material. Experiment results showed that the material can reach equilibrium adsorption in 20 min and get maximum adsorption capacity (316.586 mg g) under the condition of pH 4.0, 304 K. The adsorption of Cu(II) ions was an exothermic and spontaneous process, and could be better simulated by the pseudo-second-order kinetics and Freundlich isotherm model.     

Simulation of biofilter used for removal of air contaminants (ethanol)

Mathematic modeling and simulation of a biofilter system was developed for biofilters filled by three different packing materials such as granular activated carbon (GAC), compost mixed with diatomaceous earth (DE), and compost, respectively, and the effects of biofilter length, packing material, biological activity and the operation time of system on the removal of ethanol (influent contaminant) were studied. The mathematical model for analysis of mass transport phenomena in the biofilter was solved using a two-step, explicit finite difference approximation technique and computer simulation was carried out. The obtained results show that at the early stage of biofiltration the dominant mechanism is adsorption and after saturation of packing by contaminant, biological processes became the dominant mechanism. GAC packed biofilter needs more time to reach to steady state in comparison to the two other packing. GAC is the best adsorbent for contaminant removal; however, compost provides a better environment for microbial growth and activity. The proposed procedure is applicable to analyze the behavior of a biofiltration system used in removal of volatile organic compounds.     

The automated photometric determination of vanadium in geological samples with 4-(2-pyridylazo) resorcinol

Vanadium is determined in geological samples utilising the red complex formed between V⁵⁺ and 4-(2-pyridylazo) resorcinol. The determination is performed with the Technicon Auto Analyzer. The method has been applied to the determination of the element in standard rock and mineral samples after fusion with sodium carbonate and magnesium oxide. Using this sensitive method, it is possible to determine as little as 1 p.p.m. vanadium in a 200-mg sample of silicate rock or mineral.     

Enhancement of gaseous mercury (Hg0) adsorption for the modified activated carbons by surface acid oxygen function groups

This article discussed the benzoic acid activated carbons which have changed the types and content of acid oxygen-function groups on the surface of activated carbons and their effect on the adsorption for Hg~0 in simulated flue gas at 140 ℃. These surface acid oxygen function groups were identified by Boehm titration, Fourier transformation infrared spectrum, temperature programmed desorption and X-ray photoelectron spectroscopy. It indicates that the carboxyl, lactone and phenolic were formed when the benzoic acid is loaded on the surface of activated carbons. Among the surface acid oxygen function groups, the carboxyl groups enhance the adsorption capacities of Hg~0 for activated carbons to a greater extent.     

Synthesis of poly(amidoamine)-graft-poly(methyl acrylate) magnetic nanocomposite for removal of lead contaminant from aqueous media

Poly(amidoamine)-graft-poly(methyl acrylate) magnetic nanocomposite was synthesized via radical polymerization of methyl acrylate onto modified magnetic nanoparticles followed by the functionalization of the methyl ester groups with poly(amidoamine) dendrimer. The resulting poly(amidoamine)-graft-poly(methyl acrylate) magnetic nanocomposite was then characterized by infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, scanning electron microscope and X-ray diffraction analysis. Its application as an adsorbent for the removal of Pb(II) ions was studied. The removal capability of the adsorbent was investigated in different pH values, contact time (kinetics) and initial concentration of lead. Moreover, adsorption isotherms were investigated to describe the mechanistic feature of this nanocomposite for adsorption. Accordingly, its high adsorption capacity (310 mg/g) and efficient adsorption toward lead ions in aqueous solution were shown. To further study of the chemistry behind the adsorption process, a comprehensive density functional theory-based study was performed, and a relatively strong interaction between metal ions and adsorbent was observed based on the calculated adsorption free energies.     

Characterization and evaluation of a tropical peat for the removal of Cr(VI) from solution

Tropical peat soils present higher ash content than those generated at temperate climate areas. Therefore, this study evaluated the characteristics of a Brazilian organic soil (OS), commercialized as peat, as well as its capacity in removing Cr(VI) from contaminated waters. The OS is composed of 35.5 wt% of organic matter and 56 wt% of inorganic fraction (ash), which is formed by minerals and phytoliths rich in silica (29.2 wt%) and alumina (23.6 wt%). The Cr(VI) removal tests were carried out in batch and column systems using OS and solutions of Cr(VI) prepared with distilled water and groundwater. Batch tests revealed that the organic substances in the OS caused the reduction of Cr(VI) to Cr(III), with an efficiency depending on solution pH. At pH 5.0 the Cr(VI) removal was 0.45 mg g^?1 in 24 h; whereas at pH 2.0, this removal increased to 1.10 mg g^?1. Since this redox reaction is very slow, the removal of Cr(VI) at pH 5.0 increased to around 2 mg g^?1 after 5 days. The removal of Cr(VI) was more effective in the column tests than in the batch test due to the greater solid/solution ratio, and their half-lives were 4.4 and 26.2 h, respectively. Chemical analysis indicated that Cr(VI) was reduced by the humic substances of OS, followed by the precipitation and/or adsorption of Cr(III) into the organic and inorganic components, as anatase. The presence of Cr(III) increased the stability of anatase structure, avoiding its transformation into rutile, even after being heated at 800 °C/2 h.     

Adsorption of copper (II) on mesoporous silica: the effect of nano-scale confinement

Nano-scale spatial confinement can alter chemistry at mineral–water interfaces. These nano-scale confinement effects can lead to anomalous fate and transport behavior of aqueous metal species. When a fluid resides in a nanoporous environments (pore size under 100 nm), the observed density, surface tension, and dielectric constant diverge from those measured in the bulk. To evaluate the impact of nano-scale confinement on the adsorption of copper (Cu²⁺), we performed batch adsorption studies using mesoporous silica. Mesoporous silica with the narrow distribution of pore diameters (SBA-15; 8, 6, and 4 nm pore diameters) was chosen since the silanol functional groups are typical to surface environments. Batch adsorption isotherms were fit with adsorption models (Langmuir, Freundlich, and Dubinin–Radushkevich) and adsorption kinetic data were fit to a pseudo-first-order reaction model. We found that with decreasing pore size, the maximum surface area-normalized uptake of Cu²⁺ increased. The pseudo-first-order kinetic model demonstrates that the adsorption is faster as the pore size decreases from 8 to 4 nm. We attribute these effects to the deviations in fundamental water properties as pore diameter decreases. In particular, these effects are most notable in SBA-15 with a 4-nm pore where the changes in water properties may be responsible for the enhanced Cu mobility, and therefore, faster Cu adsorption kinetics.     

Applications on agricultural and forest waste adsorbents for the removal of lead (II) from contaminated waters

At present, there is growing interest in using low cost, commercially available materials for the adsorption of heavy metals. The major advantages of adsorption technologies are its effectiveness in reducing the concentration of heavy metal ions to very low levels and the use of inexpensive adsorbent materials. In this review, agricultural and forest waste adsorbents were used to remove Pb²⁺ ions in wastewater treatment, and their technical feasibilities were reviewed in studies mainly from 2000 to 2010. They all were compared with each other by metal binding capacities, metal removal performances, sorbent dose, optimum pH, temperature, initial concentration and contact time. Although commercial activated carbon is widely used in wastewater treatment applications, it has high costs. The use of agricultural by-products as adsorbent material to purify heavy metal contaminated water has become increasingly popular through the past decade because they are less expensive, biodegradable, abundant and efficient. Instead of activated carbon, this study was focused on the inexpensive materials such as agricultural and forest waste. It was shown that these alternative adsorbents had sufficient binding capacity to remove Pb²⁺ ions from wastewater.     

Preparation and solubility of northupite from brine and its adsorption properties for Cu(II) and Cd(II) in seawater

The mineral northupite Na₃Mg(CO₃)₂Cl was synthesized from a solar Adriatic seawater brine pond to which Na₂CO₃ was added at 373°K. The precipitated northupite had a surface area (P) of 6.0 ± 0.4 m²g⁻¹, and the thermodynamic solubility product was estimated to be log K Na₃Mg(CO₃)₂Cl = −4.8 ± 0.3 at 25°C. This value was used to calculate the interfacial energy (σ = 50 erg cm⁻²) for the homogeneous nucleation of northupite. The solubility constant determined in this study has been used to examine the saturation state of Mahega Lake and Lake Katwe (Uganda). The waters from Lake Katwe were found to be supersaturated with respect to northupite.The adsorption of Cu and Cd onto northupite particles was studied in seawater. Both metals are strongly adsorbed. Adsorption constants and the specific area of northupite occupied by Cd and Cu using Langmuir adsorption isotherms and equilibrium constants for surface complex formation have been determined.     

A geochemical model for removal of iron(II)(aq) from mine water discharges

A steady state geochemical model has been developed to assist in understanding surface-catalysed oxidation of aqueous Fe(II) by O₂(aq), which occurs rapidly at circumneutral pH. The model has been applied to assess the possible abiotic removal of Fe(II)(aq) from alkaline ferruginous mine water discharges using engineered reactors with high specific-surface area filter media. The model includes solution and surface speciation equilibrium, oxidation kinetics of dissolved and adsorbed Fe(II) species and mass transfer of O₂(g). Limited field data for such treatment of a mine water discharge were available for model development and assessment of possible parameter values. Model results indicate that an adsorption capacity between 10⁻⁶ and 10⁻⁵ mol l⁻¹ is sufficient for complete removal, by oxidation, of the Fe(II)(aq) load at the discharge. This capacity corresponds approximately to that afforded by surface precipitation of Fe(III) oxide onto plastic trickling filter media typically used for biological treatment of wastewater. Extrapolated literature values for microbial oxidation of Fe(II)(aq) by neutrophilic microbial populations to the simulated reactor conditions suggested that the microbially-mediated rate may be several orders-of-magnitude slower than the surface-catalysed oxidation. Application of the model across a range of mine water discharge qualities shows that high Fe(II)(aq) loadings can be removed if the discharge is sufficiently alkaline. Additional reactor simulations indicate that reactor efficiency decreases dramatically with pH in the near acid region, coinciding with the adsorption edge for Fe²⁺ on Fe oxyhydroxide. Alkaline discharges thus buffer pH within the range where Fe(II)(aq) adsorbs onto the accreting Fe hydroxide mineral surface, and undergoes rapid catalytic oxidation. The results suggest that the proposed treatment technology may be appropriate for highly ferruginous alkaline discharges, typically associated with abandoned deep coal mines.     

Preparation of magnetic microgels for catalytic reduction of 4-nitrophenol and removal of methylene blue from aqueous medium

This work describes the synthesis of poly(acrylic acid) microgels and fabrication of magnetic cobalt nanoparticles in the prepared microgels. Cobalt nanoparticles were fabricated by loading the cobalt (II) ions in microgels from aqueous solution and their subsequent reduction with sodium borohydride (NaBH₄). Bare and composite microgels were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The catalytic properties of the prepared microgel composites were investigated by using them as catalyst for the reduction of 4-nitrophenol and methylene blue. The effect of temperature and catalyst dose on the rate of reduction of these toxic pollutants was investigated. The reusability of prepared catalysts was also studied for the five consecutive cycles, and an increase in catalytic activity was observed after every cycle. The prepared bare and magnetic microgels were found as very effective adsorbent for the removal of methylene blue from aqueous medium. Very rapid adsorption rate was found for the removal of methylene as its 100 mg was adsorbed on per gram of dried hydrogels in about 25 min. The effects of different parameters like amount of adsorbate and concentration of adsorbent on the adsorption process were studied. Langmuir, Freundlich and Temkin adsorption isotherms were applied, and it was found that adsorption of MB follows Freundlich model better than others. Furthermore, pseudo-first-order and pseudo-second-order kinetic models were also applied and adsorption of MB was found to abide by pseudo-second-order kinetics.     

Oxidative removal of Mn(II) from solution catalysed by the γ-FeOOH (lepidocrocite) surface

A laboratory study was undertaken to ascertain the role of surface catalysis in Mn(II) oxidative removal. γ-FeOOH, a ferric oxyhydroxide formed by O₂ oxidation of ferrous iron in solution, was studied in the following ways: surface charge characteristics by acid base titration, adsorption of Mn(II) and surface oxidation of Mn(II). A rate law was formulated to account for the effects of pH and the amount of surface on the surface oxidation rate of Mn(II). The presence of milli-molar levels of γ-FeOOH was shown to reduce significantly the half-life of Mn(II) in 0.7 M NaCl from hundreds of hours to hours. The numerical values of the surface rate constants for the γ-FeOOH and that reported for colloidal MnO₂ are comparable in order of magnitude.     

Towards a consistent geochemical model for prediction of uranium(VI) removal from groundwater by ferrihydrite

Uranium(VI), which is often elevated in granitoidic groundwaters, is known to adsorb strongly to Fe (hydr)oxides under certain conditions. This process can be used in water treatment to remove U(VI). To develop a consistent geochemical model for U(VI) adsorption to ferrihydrite, batch experiments were performed and previous data sets reviewed to optimize a set of surface complexation constants using the 3-plane CD-MUSIC model. To consider the effect of dissolved organic matter (DOM) on U(VI) speciation, new parameters for the Stockholm Humic Model (SHM) were optimized using previously published data. The model, which was constrained from available X-ray absorption fine structure (EXAFS) spectroscopy evidence, fitted the data well when the surface sites were divided into low- and high-affinity binding sites. Application of the model concept to other published data sets revealed differences in the reactivity of different ferrihydrites towards U(VI). Use of the optimized SHM parameters for U(VI)-DOM complexation showed that this process is important for U(VI) speciation at low pH. However in neutral to alkaline waters with substantial carbonate present, Ca–U–CO₃ complexes predominate. The calibrated geochemical model was used to simulate U(VI) adsorption to ferrihydrite for a hypothetical groundwater in the presence of several competitive ions. The results showed that U(VI) adsorption was strong between pH 5 and 8. Also near the calcite saturation limit, where U(VI) adsorption was weakest according to the model, the adsorption percentage was predicted to be >80%. Hence U(VI) adsorption to ferrihydrite-containing sorbents may be used as a method to bring down U(VI) concentrations to acceptable levels in groundwater.     

Acid-treated zeolite (clinoptilolite) and its potential to zinc removal from water sample

Zinc compounds are important group of pollutants which enter water flows from industrial factories sewage. In this research, use of both natural zeolite (clinoptilolite) and its sulfuric acid-modified form as a cheap adsorbent for removing zinc from its solutions has been investigated. The effect of acid concentration, contact duration, pH of solution, initial concentration of zinc, amount of adsorbent and its size was investigated. On average, the maximum adsorption amount is calculated to be 91.1 % with contact duration of 300 min. By increasing contact duration, more adsorption is achieved. Results show that if the more zeolite is used, the more adsorption is achieved. According to results, Langmuir and Freundlich isotherm models were investigated and the adsorption of zinc by modified zeolite was described by both models very well.     

Evaluation of natural quartz and zeolitic tuffs for As(V) removal from aqueous solutions: a mechanistic approach

Naturally occurring pyroclastic materials, quartz-rich tuffs (Qz) and stellerite tuffs, were evaluated for their capacities to remove As(V) from aqueous solutions. The mechanism of As(V) uptake was evaluated using sequential extraction of As(V)-loaded adsorbent which entailed that the plausible removal mechanism is sorption to short-range ordered hydrous oxides of iron and aluminum. In addition, buffering effects of adsorbents could form favorable charges upon them through hydrolysis of amphoteric oxides, enhancing the performance of sorption. The influence of anions co-existing with As(V) in water such as carbonate, bicarbonate, nitrate, chloride, phosphate, and sulfate was studied in a batch sorption process. The impact of most anions on As(V) removal was found to be negligible except phosphate. The sorption behavior well fitted to Langmuir and Freundlich models. Estimated maximum sorption capacities of 0.42 and 0.23 mg/L were observed using quartz-rich tuffs and stellerite tuffs, respectively. As(V) concentration of 0.8 mg/L was easily decreased to below the drinking water standard of 0.01 mg/L using Qz adsorbent, whereas 0.1 mg/L As(V) decreased to below this limit upon the use of stellerite tuffs under similar conditions. The buffering capacity of quartz-rich tuffs and stellerite tuffs induced a pH increase to 5.76 and 5.40, respectively, from initial pH of 3.50, which will incur an important asset in real applications.     

Advantage of almond green hull over its resultant ash for chromium(VI) removal from aqueous solutions

The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.     

The selective removal of Co(II) from Ni(II) by coprecipitation with manganese in ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with manganese in ammoniacal solutions has been studied. It was found that cobalt and nickel were precipitated with the aid of manganese at pH 9.3–10.2. However, the rate of precipitation of manganese was about five times that of cobalt. The recovery of these divalent ions by precipitation increased as the pH of the solution increased, while the selectivity of cobalt against nickel decreased with the increase of pH. The partial pressure of oxygen had also an important role in the precipitation of manganese and cobalt but little effect on the up-take of nickel. As the oxygen pressure increased, manganese and cobalt oxidized at a fast rate and the rate of coprecipitation of cobalt with manganese increased. Typically, more than 90% of cobalt was recovered readily by coprecipitation with manganese, while very little nickel was removed from the solution.