Mercury and cadmium are priority hazardous substances. Some titanosilicates have been tested for the removal of Cd²⁺ and Hg²⁺ from single solutions by ion exchange. In this work, the competition between both contaminants for the exchanger binding sites of titanosilicate Engelhard titanosilicate material number 4 (ETS-4) was studied by performing batch experiments with aqueous solutions containing the two counter ions. The results evidenced the large capacity of ETS-4 and shown that the cadmium(II) diffusivity through the sorbent is higher than that of mercury(II). Furthermore, the ETS-4 exhibited higher kinetic and equilibrium selectivities for Cd²⁺, which attained values in the ranges 8.9–12.5 and 7.9–12.8, respectively. With respect to modelling, the pseudo-second-order equation described successfully the competitive removal of Cd²⁺ and Hg²⁺.

The performance of the Purolite A847 weak basic anion exchanger in the simultaneous removal of the azo dye Lanasyn Navy M-DNL (LNCr) and the phthalocyanine dye Acid Blue 249 (CuPc) from acidic aqueous solutions was studied under dynamic conditions. The comparison of FTIR spectra of unloaded and dye-loaded anion exchangers made it possible to consider suitable sorption mechanisms. The results of dynamic experiments revealed that anion exchanger had a greater dynamic sorption capacity with a longer breakthrough time and a shorter length of mass transfer zone when both dyes LNCr and CuPc were removed from the one-component solution as compared to those of their mixture. Models of Wolborska and Juang were found to be suitable to predict the character of breakthrough curves and to determine the characteristic parameters of the Purolite A847 column useful for process design: the mass transfer coefficient β (1/min) and time at the break point τ (minutes). The result would be useful in the design of wastewater treatment plants for removal of azo and phthalocyanine dyes from aqueous solutions and water recycling.

The accumulation of Ag by the marine herbivorous gastropod, Littorina littorea, has been studied in a series of exposures in which the metal was added in aqueous form and as nanoparticles, both in the presence and absence of contaminated algal food (Ulva lactuca). Significant accumulation occurred in the gill, kidney, stomach and visceral mass when the snail was exposed to aqueous Ag in the absence of food. Despite the consumption of U. lactuca that had been previously contaminated by Ag, no accumulation was observed from the dietary route. When added as nanoparticles, accumulation of Ag was only measured in the head and gill and only in the absence of contaminated food. These observations suggest that Ag is most bioavailable to L. littorina when in true solution and that Ag measured in external tissues of the snail following exposure to nanoparticles arises from some physical association that does not result in significant transfer of the metal to internal organs.

Natural palygorskite was used as an adsorbent for the removal of copper, cobalt and nickel from an aqueous solution. All assays were performed under controlled conditions to establish the adsorption capacity of the solid. Initially, the clay was characterized by chemical analysis, XRD, infrared spectroscopy and thermogravimetry. Adsorption experiments for the ions in aqueous solution were carried out by a batch method through which the reaction time, initial concentration of cations, temperature and pH of the aqueous solution were systematically varied. First-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data. The results show that the processes were fitted well by the pseudo-second-order model. Moreover, the equilibrium solid–cation systems followed the Langmuir isotherm model. The results indicate that raw palygorskite could be employed as a low-cost material for the removal of heavy metals from aqueous solution.

In this study, residues of passion fruit skin were examined as biosorbent materials, evaluating their capacity to adsorb lead(II) ions in in natura skin (SK-N) and two modified skins, with NaOH (SK-S) and with NaOH and citric acid (SK-SCA). The biomass characterization was done through Fourier transform infrared spectroscopy which confirmed the chemical modification by a peak at 1,730 cm⁻¹. Also, scanning electron microscopy analyses were done, where the increase of residue roughness was observed after the modification. And finally, the values of point of zero charge were determined and were lower than 5.5 for all residues. In the experiments of adsorption in function of pH, it was verified that after pH 4, the adsorbed amount was practically constant. Regarding the necessary time to reach equilibrium, the value that was found was approximately 170 min, and kinetics followed the behavior described by the pseudo-second-order equation. The maximum adsorption capacity was 204 mg g⁻¹ for the SK-SCA biomass. The residues followed Langmuir adsorption model. Through thermodynamic parameters, it was verified that adsorption occurs spontaneously due to the negative values of Gibbs' energy. Moreover, desorption studies showed that adsorbed ions may be recovered in two cycles. Thus, due to the high adsorption capacity of lead ions, passion fruit skin can be utilized in filters to retain this metal in the future.

The present study consisted of an in vitro experiment based on columns to restore a soil affected by the tsunami of 27 February 2010 that struck the Coliumo District, Bio-Bio region, Chile. The agricultural productivity of many coastal lands was severely affected, rendering them unfit for crop production. Composite soil samples were taken at 0 to 20 cm soil depth in Coliumo, Bio-Bio region. The initial physical and chemical analysis showed textural changes, low pH, high levels of electrical conductivity (EC), sodium (Na⁺), and sulfate (SO₄²⁻), whereas bioassay tests showed severe toxicity for lettuce (Lactuca sativa L.) seeds. Germination index (GI), length of hypocotyl (LH), and length of radicle (LR) were used as indicators in the bioassay tests. Two different treatments were used: T1 = soil amended with 7.7 t ha⁻¹ of limestone (CaCO₃) and T2 = soil amended with 7.7 t ha⁻¹ of gypsum (CaSO₄). A control treatment (T0) with unamended soil was included. Each treatment received a total of 1,100 mm of clean water (4 water loads, 275 mm each), which was equivalent to the mean annual precipitation of the area studied. The T2 treatment produced a significant decrease in the concentration of Na⁺ (8.27 to 0.16 meq L⁻¹), decreased EC (1.58 to 0.03 dS m⁻¹), and increased pH from 4.83 to 6.27 in the soil under study. Leaching of Na⁺ and SO₄²⁻ with successive water loads was effective in the soil. The bioindicators as GI, LH and LR revealed that T2 was more effective than T1 and control in removing Na and SO₄ analytes from the soil matrix. The CaSO₄ amendment showed good potential for seed development, but further research on plant growth to maturity is required to determine yield parameters in the affected area.

Tobacco (Nicotiana tabacum L.) stem ash (TSA) was evaluated as an adsorbent for removal of methylene blue (MB) from aqueous solution by batch adsorption method. MB adsorption increased with increase in contact time, initial solution pH, and adsorbent dose. Contact time for adsorption equilibrium was 180 min. The MB adsorption per unit mass of adsorbent (in milligram per gram) increased with the increasing initial dye concentration. Adsorption of MB onto TSA followed the pseudo-second-order kinetic model with a rate constant (k ₂) of 0.017 g mg⁻¹ min⁻¹. The mechanism of adsorption was described with intra-particle diffusion model. It was found that the intra-particle diffusion was not a sole rate-controlling step. Equilibrium adsorption was investigated by the Freundlich, Langmuir, Temkin, and Jovanoic isotherms. On the basis of coefficient of determination, the order of isotherm fit was Langmuir (R ² = 0.974) > Freundlich (R ² = 0.957) = Temkin (R ² = 0.957) > Jovanoic (R ² = 0.764) isotherm. The maximum monolayer adsorption capacity of TSA was 35.7 mg g⁻¹. The dimensionless separation factor (R L) was low (0.137), indicating favorable adsorption of MB onto TSA. The results clearly demonstrate the potential of TSA as a low-cost and an easily available adsorbent for sequestering MB from wastewater.

The removal of lead (II) and iron (III) from aqueous solutions using empty fruit bunch (EFB), oil palm leaves (OPL), oil palm frond (OPF), and oil palm bark (OPB) as biosorbents was investigated. The biosorbents were characterized through scanning electron microscopy, Brunauer–Emmett–Teller analysis, and Fourier transform infrared spectroscopy. Variables such as pH (2–12), biosorbent particle size (200–1,400 μm), adsorbent dosage (0.25–1.75 g/l), and agitation time (5–80 min) were investigated. The suitable pH range, particle size, adsorbent dosage, and agitation time for the removal of both metals were 5 to 6, 200 μm, 1 g/l, and 40 min, respectively. Under optimum conditions, OPB showed the highest adsorption efficiency of 80 % and 78 % for lead and iron, respectively. The adsorption equilibrium data were fitted to three adsorption isotherm models. The Langmuir isotherm showed the best result for both metals. The kinetics of the biosorption process was analyzed using pseudo-first-order and pseudo-second-order models. The latter showed a better fit for both metals. OPB biomass introduced the lowest chemical oxygen demand into the treated solution, with an average amount of 32.9 mg/l.

We study the adsorption and desorption of chromium on two soils (a forest soil and a vineyard soil), both individually or after being combined with ground mussel shell, and on various materials (mussel shell, pyritic material from a dump site, and slate processing fines). The adsorption capacity depends mainly on the initial Cr concentration, on the pH, and on the abundance of noncrystalline Fe. The highest adsorption percentage (94 %) corresponds to the pyritic material, which also shows very low desorption rates (1.4 %), has the lowest pH, and has the highest concentration of noncrystalline Fe. The adsorption isotherms in most cases fit the Freundlich and Lineal models, rather than the Langmuir model, with no easily predictable maximum for chromium adsorption.

Constructed wetlands have been successfully used throughout the world for wastewater treatment. Nowadays, one of the most discussed questions is their long-term performance. The present study summarizes the performance of a constructed wetland designed to treat the municipal wastewater from a rural community in northwestern Spain during a period of 12 years. The monitoring of water quality for organic matter, suspended solids, nutrients, and indicator bacteria revealed that, in general, the effluent concentrations were significantly lower than influent concentrations. Moreover, differences among years were not statistically significant. Metals and metalloids were also monitored in wastewater, sediment, and vegetation. Results showed that these pollutants have mainly accumulated in the sediments, whereas only a minor fraction has been removed by plant uptake. © 2013 Springer Science+Business Media Dordrecht.