Adsorption characteristics of some Cu(II) complexes on aluminosilicates

The adsorption of Cu(II) by aluminosilicates with varying Si/Al ratios was investigated. The presence of complex-forming organic ligands [nitrilotriacetate (NTA) and glycine (Gly)] alters metal electrovalency and, in so doing, modifies Cu(II) adsorption characteristics which can influence its fate, biological activity and transport in aquatic systems. Electrostatic attraction by a positively-charged aluminosilicate surface is an important mechanism whereby anion CuNTA⁻ complexes were adsorbed. Two distinct mechanisms are involved in the adsorption of cationic complexes: (1) an exchange reaction at permanent structural sites and (2) interfacial accumulation in response to the pH-dependent surface charge. The contribution of each mechanism to the total amount of CuGly⁺ adsorbed is related to the Si/A1 ratio. At the critical Si/A1 ratio (Si/A1_iso), the aluminosilicates have zero net pH-dependent surface charge. In the absence of specific adsorption, aluminosilicates for which Si/A1 ≥ Si/A1_iso can only function as cation exchangers. For Si/A1 < Si/A1_iso simultaneous adsorption of anions and cations is possible.     

Recovery of chromium(VI) from wastewaters with iron(III) hydroxide—I: Adsorption mechanism of chromium(VI) on iron(III) hydroxide

Chromium(VI) [Cr(VI)] is adsorbed as HCrO⁻₄ on iron(III) hydroxide at pH below 8.5. The Cr(VI) adsorption is suppressed by the presence of other anions such as SO²⁻₄ and SCN⁻, and enhanced by the presence of metal ions such as Cd(II) and Pb(II). The suppression is due to the competitive adsorption of other anions, depending upon the stability of their iron complexes. The enhancement is probably due to the increase in adsorption sites as a result of coprecipitation of metal ion with iron(III) hydroxide.     

Hybrid adsorbents based on hydrated oxides of Zr(IV), Ti(IV), Sn(IV), and Fe(III) for arsenic removal

Synthesized are hybrid organoinoragnic adsorbents based on organic resins Dowex SBR-P, Dowex Marathon II and hydrated oxides Zn(IV), Ti(IV), Sn(IV) and Fe(III). Specific conductivity was measured of the specified resins and hybrid organoinorganic adsorbents in the initial form and after absorption of ions As(V) from 10^–2 M aqueous solution of NaH₂AsO₄. Introduction of hydrated tin oxide increases ionic conductivity of organic resin Dowex SBR-P by 2.5 times. During the conversion to the arsenate form the conductivity of hybrid adsorbents changes insufficiently at the adsorption from the solution with pH 7 and increased by 2–10 times at adsorption from the solution with pH 2.     

Adsorption mechanism of selenate and selenite on the binary oxide systems

Removal of selenium oxyanions by the binary oxide systems, Al- or Fe-oxides mixed with X-ray noncrystalline SiO₂, was previously not well understood. This study evaluates the adsorption capacity and kinetics of selenium oxyanions by different metal hydroxides onto SiO₂, and uses X-ray absorption spectroscopy (XAS) to assess the interaction between selenium oxyanions and the sorbents at pH 5.0. The binary oxide systems of Al(III)- or Fe(III)-oxides mixed with SiO₂ were prepared, and were characterized for their surface area, point of zero charge (PZC), pH envelopes, X-ray diffraction analysis (XRD), and then macro-scale adsorption isotherm and kinetics of selenite and selenate, micro-scale adsorption XAS. The adsorption capacity of selenite and selenate on Al(III)/SiO₂ is greater than on Fe(III)/SiO₂. Adsorption isothermal and kinetic data of selenium can be well fitted to the Langmuir isotherm and pseudo-second-order kinetic models. Based on simple geometrical constraints, selenite on both the binary oxide systems forms bidentate inner-sphere surface complexes, and selenate on Fe(III)/SiO₂ forms stronger complexes than on Al(III)/SiO₂.     

Adsorption from Brazilian soils of Cu(II) and Cd(II) using cattle manure vermicompost

The potential of cattle manure vermicompost and Brazilian soils (whole soils and soils incubated with vermicompost) was assessed for adsorption of heavy metals such as Cu(II) and Cd(II) from aqueous solutions. Experimental data have been fitted to Langmuir and Freundlich isotherms to obtain the characteristic parameters of each model, with R ² values from 0.89 to 0.99. Based on the maximum adsorption capacity obtained from the Langmuir isotherm the affinity of the studied metals for the vermicompost and soils have been established as Cu(II) > Cd(II). The values of the separation factor, R _L, which has been used to predict affinity between adsorbate and adsorbent were between zero and 1, indicating that sorption was very favourable for Cu(II) and Cd(II) in synthetic solution. Addition of vermicompost to soils resulted in higher distribution coefficient, K _d, as compared with whole soils. The thermodynamic parameter, the Gibbs energy changes, was calculated for each system and the negative values obtained confirm that the adsorption processes are spontaneous. The ΔG° values for the substrates were between ?2.630±1.41 kJ mol^?1 and ?13.700±1.250 kJ mol^?1. Adsorption tests from multimetal systems confirm the affinity order obtained in the individual metal tests. The adsorption capacity for Cu(II) measured in individual tests is not reduced by the presence of Cd(II). There is also desorption of Cu(II) and Cd(II) previously bound to vermicompost, whole soils and soils incubated with vermicompost by DTPA. The experiment indicates the importance of cattle manure vermicompost and oxisol amended with vermicompost in relation to Cu(II) and Cd(II) adsorption from aqueous solution.     

Adsorption of Cu(II) from industrial liquid waste on Na-bentonite and Al-PILC following a full factorial design

The paper reports a study of the performance of Maghnia bentonite in a purified and modified state for the removal of Cu(II) from industrial liquid waste in the region of Oran (North West Algeria). Bentonite was firstly treated to produce a Na-bentonite, then modified with an aluminum solution containing molar ratio OH/Al of 1.8 and finally calcined at 450 °C. The polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ formed in solution was adsorbed by surface complexation on the bentonite, which is known to have a high capacity to fix metal cations. The prepared materials were characterized by DRX, BET and EDX. In order to find the optimum conditions, a full factorial design of 2⁴ allowed us to determine the main effects and interactions of the factors studied: pH, mass of materials, contact time and temperature. The results obtained show that the best rate of adsorption of copper requires a pH = 10, a mass = 0.8 g, a stirring time = 80 min, and a temperature = 25 °C. The adsorption capacity of treated bentonite increased considerably from 4.147 mg/g for Na-bentonite to 7.173 mg/g for pillared aluminum bentonite. This shows the strong adsorption of copper compared with Na-bentonite, caused by its high surface area.     

Laboratory study on the adsorption of Mn²⁺ on suspended and deposited amorphous Al(OH)₃ in drinking water distribution systems

Manganese (II) is commonly present in drinking water. This paper mainly focuses on the adsorption of manganese on suspended and deposited amorphous Al(OH)₃ solids. The effects of water flow rate and water quality parameters, including solution pH and the concentrations of Mn²⁺, humic acid, and co-existing cations on adsorption were investigated. It was found that chemical adsorption mainly took place in drinking water with pHs above 7.5; suspended Al(OH)₃ showed strong adsorption capacity for Mn²⁺. When the total Mn²⁺ input was 3 mg/L, 1.0 g solid could accumulate approximately 24.0 mg of Mn²⁺ at 15 °C. In drinking water with pHs below 7.5, because of H⁺ inhibition, active reaction sites on amorphous Al(OH)₃ surface were much less. The adsorption of Mn²⁺ on Al(OH)₃ changed gradually from chemical coordination to physical adsorption. In drinking water with high concentrations of Ca²⁺, Mg²⁺, Fe³⁺, and HA, the removal of Mn²⁺ was enhanced due to the effects of co-precipitation and adsorption. In solution with 1.0 mg/L HA, the residual concentration of Mn²⁺ was below 0.005 mg/L, much lower than the limit value required by the Chinese Standard for Drinking Water Quality. Unlike suspended Al(OH)₃, deposited Al(OH)₃ had a much lower adsorption capacity of 0.85 mg/g, and the variation in flow rate and major water quality parameters had little effect on it. Improved managements of water age, pipe flushing and mechanical cleaning were suggested to control residual Mn²⁺.     

Layered double hydroxide of cobalt-zinc-aluminium intercalated with carbonate ion: preparation and Pb(II) ion removal capacity

Ternary layered double hydroxide (Co–Zn–Al LDH) intercalated with carbonate was synthesised via a simple co-precipitation method at pH ≥10. It was characterised using the Fourier transform infrared (FTIR) spectrometer, X-ray diffractometer (XRD), surface area and porosity analyser, Thermo-gravimetric/differential thermal analysis (TGA–DTA), and Scanning Electron Microscope (SEM). The Pb(II) adsorption properties, mechanism, and possible reuse of the LDH were also investigated by the batch technique. The characterisation results showed the presence of hydroxyl group as well as the intercalated carbonate anions within the well-defined LDH crystal structure. The TGA-DTA results confirmed the presence of these anionic groups which were liberated from the structure at ≈200 and 300°C, respectively. The LDH-specific surface area, pore diameter and width are 54.0 m²/g, 41.3 and 25.1 nm, respectively. Adsorption results showed that Pb(II) equilibrium could be achieved in 120 min, and adsorption increased with concentration and temperature. A Pb(II) adsorption capacity of 130.34 mg/g was reached for this LDH, and the adsorption process was spontaneous, endothermic and mainly electrostatic with most of the adsorption occurring within the pores. Desorption test suggested that approximately 90% of the adsorbed Pb(II) could be desorbed; hence, the Co–Zn–Al–CO₃ LDH may be reused.     

Oxidative removal of aqueous steroid estrogens by manganese oxides

This study investigated the oxidative removal of steroid estrogens from water by synthetic manganese oxide (MnO₂) and the factors influencing the reactions. Using 1 × 10⁻⁵ M MnO₂ at pH 4, estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2), all at 4 × 10⁻⁶ M, were rapidly removed within 220 min, indicating the effectiveness of MnO₂ as an oxidizing agent towards estrogens. E2 removal increased with decreasing pH over the tested range of 4-8, due most likely to increased oxidizing power of MnO₂ and a cleaner reactive surface in acidic solutions. Coexisting metal ions of 0.01 M (Cu(II), Zn(II), Fe(III) and Mn(II)) and Mn(II) released from MnO₂ reduction competed with E2 for reactive sites leading to reduced E2 removal. Observed differential suppression on E2 removal may be related to different speciations of metals, as suggested by the MINTEQ calculations, and hence their different adsorptivities on MnO₂. By suppressing the metal effect, humic acid substantially enhanced E2 removal. This was attributed to complexation of humic acid with metal ions. With 0.01 M ZnCl₂ in solutions containing 1 mg l⁻¹ humic acid, the binding of humic acid for Zn(II) was determined at 251 mmol g⁻¹. An in vitro assay using human breast carcinoma MCF-7 cells indicated a near elimination of estrogenic activities without secondary risk of estrogen solutions treated with MnO₂. Synthetic MnO₂ is therefore a promising chemical agent under optimized conditions for estrogen removal from water. Metal chelators recalcitrant to MnO₂ oxidation may be properly used to further enhance the MnO₂ performance.     

Rose biomass as a potential biosorbent to remove chromium,mercury and zinc from contaminated waters

Rose flowers are used for the extraction of essential oil or rose water. The vast majority of the leftover biomass is generally wasted. The aim of the present study was to analyse the rose flower biomass as a potential biosorbent for metals chromium(III), mercury(II) and zinc(II), to remove them from industrial effluents. A number of variables were analysed, including untreated, acid-treated and base-treated biomass, biomass dosage, metal ion concentration, contact time, and pH. Increase in biomass dosage and metal ion concentration increased biosorption. The pH proved to be a very important factor and all the metals showed high adsorption at slightly acidic to moderately basic pH 6–10. They showed very low uptake at low pH. Contact time had little effect on the adsorption capacity of zinc, but was very crucial in the case of mercury. Base treatment favoured adsorption of mercury and zinc. The adsorption of Cr³⁺, Hg²⁺ and Zn²⁺ on rose biomass can be explained by Langmuir and Freundlich isotherms equally well, and the adsorption process followed pseudo second order kinetics. The study suggests that the rose flower biomass can be used in the removal of these metals from contaminated waters employing optimum conditions indicated by the present work.     

Speciation (including adsorbed species) of copper, lead, nickel and zinc in the Meuse River: Observed results compared to values calculated with a chemical equilibrium computer program

The adsorption of trace metals on sediments of the Meuse River was interpreted in terms of competition between metals and protons for surface sites. Surface constants (^*β₁^surf) were determined for Cu, Zn and Cd (10^−1.8, 10^−3.6 and 10^−3.7). The constants for Pb, Ni, Ca and Mg (10^−1.7, 10^−3.8, 10^−6.5 and 10^−5.2) were estimated using a correlation between hydrolysis and surface constants. A chemical equilibrium computer program in which surface sites (for adsorption reactions) are treated as conventional ligands was used to calculate the speciation of Cu, Pb, Ni and Zn in the Meuse River. Calculated values of the adsorbed/dissolved distribution agreed well with observed values, after some realistic data manipulation. This work indicates that dissolved trace metal concentrations in the Meuse River are controlled by adsorption and not by precipitation mechanisms. The relationship between organic matter and suspended matter greatly influences the adsorption of metals like Cu and Pb.     

The removal of chromium(VI) from dilute aqueous solution by activated carbon

The removal of chromium(VI) by activated carbon, filtrasorb 400, is brought by two major interfacial reactions: adsorption and reduction. Chemical factors such as pH and total Cr(VI) that affect the magnitude of Cr(VI) adsorption were investigated. The adsorption of Cr(VI) exhibits a peak value at pH 5–6. The particle size of carbon and the presence of cyanide species do not change the magnitude of chromium removal. The reduced Cr(VI), e.g. Cr(III) is less adsorbable than Cr(VI).The free energy of specific chemical interaction, ΔG^chem was computed by the Gouy-Chapman-Stern-Grahame model. The average values of ΔG^chem are −5.57 RT and −5.81RT, respectively, for Cr(VI) and CN. These values are significant enough to influence the overall magnitude of Cr(VI) and CN adsorption. Results also indicate that HCrO⁻₄ and Cr₂O²⁻₇ are the major Cr(VI) species involved in surface association.     

Anodic stripping voltammetric study of the lability of Cd, Pb, Cu ions sorbed on humic acid particles

The sorption of Cd, Pb and Cu by humic acid particles has been studied at μg l⁻¹ levels using A.S.V. on a Hg film electrode as the measuring technique. The variables examined included amount of solid present (0.01–0.2% w/v), initial metal ion concn (10–100 μg l⁻¹), systems pH (5.3, 6.35, 8.15) and base electrolyte composition. The calculated capacity for specific adsorption of the metal ions was a few mmol M²⁺ kg⁻¹, or less. The apparent lability of part of the sorbed material was examined by analysing the base solution before and after filtering, and by adding Chelex 100 particles to the suspension. Some sorbed Cd²⁺ was A.S.V. labile, another fraction transferred to the resin. The effect of solution reactions on uptake was studied by making the 1 M CH₃COONa base solution 0.2 M in a range of Na⁺ salts (8 different anions), or in carboxylic acid content (5 acids) or in compounds having S-type bonding groups. Formation of complex ions in solution altered the extent of metal ion uptake, and in the case of Cu A.S.V. peak size, shape and position were varied. It is suggested that natural waters containing suspended matter should be analysed by A.S.V. “as received”, as well as after filtration since response differences provide guidance in respect to the lability of sorbed ions.     

Factor interactions and aquatic toxicity testing

Hypothesizing that experimental variables constituting an exposure situation act independently when in combination, we have reviewed two published data sets dealing with effects of metal mixtures on aquatic animals in order to assess the potential practical significance of factor interactions and their implication to the design of aquatic toxicity tests. Both data sets were re-analyzed using each of the following predictive models: (1) simple-additive, y = a_x + b_y, where y is an estimated response, a_x is the observed response to a concentration of toxicant x when y = 0, and b_y is the observed response to a level of toxicant y when x = 0; (2) linear-additive, y = a + b₁x₁ + b₂x₂, in which y is a predicted value, a and b are pooled estimates involving all treatments in the exposure assay; (3) quadratic response, y = a + b₁x₁ + b₂x₂ + b₁₂x₁x₂ + b₁₁x₁² + b₂₂x₂², which provides for estimates of interactions and non-linear effects. The relative effectiveness of each model in predicting joint effects of independent test variables was evaluated in terms of calculated mean-square error and goodness-of-fit (R²) values, as well as by how well predicted treatment effects compared with responses observed by original investigators.Our analyses show that in one case all three models provided similar estimates that closely approximated observed responses, despite the presence of a statistically significant two-factor metal interaction. In comparison, in the second instance, the quadratic response model was the most effective predictor and was appreciably better than the linear-additive model in terms of the calculated parameters. The simple-additive model on the other hand, tended to over-estimate treatment effects, by as much as 80% in some instances, and was least effective of the three models examined. Our re-analyses show that the working hypothesis is rejected, i.e. an assumption of factor independence is not to be accepted a priori.A sequential testing protocol is presented which would permit an evaluation of the existence of factor interactions.     

Removal of arsenite and arsenate ions from aqueous solution by basic yttrium carbonate

A new method has been developed to remove arsenite and arsenate ions from aquatic systems by using basic yttrium carbonate (BYC). Various parameters such as pH, anion concentration and reaction time were studied to establish optimum conditions. The removal by adsorption of arsenite and arsenate ions was found to be > 99% depending on initial concentration in the pH range of 9.8–10.5 and 7.5–9.0, respectively. The arsenate was also removed by precipitation at pH lower than 6.5 due to dissolution of BYC. The kinetic study shows that the adsorption follows the first order reaction. The adsorption isotherms of these anions were also studied at different temperatures. The equilibrium data fit well in the Langmuir model of adsorption. The Langmuir constants were calculated at different temperatures and the adsorption capacity for both anions increases with temperature. Anions such as Cl⁻, Br⁻, I⁻, NO⁻₃ and SO²⁻₄ have no interference in the removal process. The mechanism of the removal by adsorption was interpreted in terms of the surface charge and ligand orientation of BYC. The method was applied on synthetic wastewaters. Arsenite was oxidized to arsenate by 3% hydrogen peroxide. The yttrium was regenerated as basic yttrium carbonate.     

Nitrite reduction with hydrous ferric oxide and Fe(II): Stoichiometry, rate, and mechanism

Fe(II)/Fe(III) oxide is an important redox couple in environmental systems. Recent studies have revealed unique characteristics of Fe(II)/Fe(III) oxide and reactions with oxidizing or reducing agents. Nitrite was used as an oxidizing agent in this study in order to probe details of these reactions and hydrous ferric oxide (HFO) was used as the Fe(III) oxide phase. Abiotic nitrite reduction is a significant global producer of nitric oxide (a catalyst for production of tropospheric ozone) and nitrous oxide (a greenhouse gas and contributor to stratospheric ozone depletion). All experiments were conducted at pH 6.8 using a strictly anoxic environment with mass-balance measurements for Fe(II). Oxidation of Fe(II) was negligible in the absence of HFO. The reaction was fast in the presence of HFO and was described by d[Fe(II)]/dt = −k_overall [Fe(II)_diss] [Fe(II)_solid-bound] [NO₂⁻] (k_overall = 2.59 × 10⁻⁷ μM⁻² min⁻¹) for Fe(II)/Fe(III) molar ratios less than 0.30. The reaction was inhibited for higher Fe(II)/HFO ratios. The concentration of solid-bound Fe(II) was constant after an initial equilibration period and the reaction stopped when dissolved Fe(II) was depleted even though substantial solid-bound Fe(II) and nitrite remained. The results regarding rate-dependence and conservation of solid-bound Fe(II) and inhibition of reaction at high Fe(II)/Fe(III) ratios were similar to our earlier results for the Fe(II)/HFO/O₂ system [Park, B., Dempsey, B.A., 2005. Heterogeneous oxidation of Fe(II) on ferric oxide at neutral pH and a low partial pressure of O₂. Environmental Science and Technology 39(17), 6494-6500.].     

Measuring the saturation limit of low-volatility organic compounds in soils: implications for estimates of dermal absorption

Estimating dermal absorption from contaminated soils typically requires extrapolations from measurements obtained on soils artificially contaminated at much larger concentrations. Such extrapolations should be constrained by the fact that maximum absorption will occur for the largest possible concentration of chemical on the soil without neat chemical being present; i.e., at the soil saturation limit (S_soil). Saturation limits of two low-volatility model compounds (4-cyanophenol and methyl paraben) were determined on the 38-63 μm sieve fraction of four soils with different fractions of organic carbon (f_oc = 0.015-0.45) and specific surface areas (σ_soil = 4-34 m² g^− 1) using two methods: equilibrium uptake into silicone rubber membranes and differential scanning calorimetry. Except for Pahokee peat, which had the largest f_oc, a model assuming contributions from both surface adsorption and organic carbon absorption provided excellent predictions of S_soil. In all soils, the surface saturation concentration of both chemicals was estimated at 2.2 mg m^− 2. The saturation concentration of 4-cyanophenol in the soil organic carbon was 1.7-fold higher than methyl paraben, which is consistent with the estimated solubility limits of these two chemicals in octanol.     

Experiments utilizing FeO4 for purifying water

The reduction of the metal ion content of river and well water by chemical treatment with Na₂FeO₄ has been studied.Pb(II), Cu(II), Zn(II) Fe(III), Hg(II), Cd(II) and Cr(III) are reduced to low levels by the addition of Na₂FeO₄ and its subsequent decomposition to a Fe(OH)₃ gel. The odors (presumably due to sulfur compounds) are completely removed, the bacterial action greatly reduced and the sedimentation rate significantly increased by this reagent.     

Experiments utilizing FeO42− for purifying water

The reduction of the metal ion content of river and well water by chemical treatment with Na₂FeO₄ has been studied.Pb(II), Cu(II), Zn(II) Fe(III), Hg(II), Cd(II) and Cr(III) are reduced to low levels by the addition of Na₂FeO₄ and its subsequent decomposition to a Fe(OH)₃ gel. The odors (presumably due to sulfur compounds) are completely removed, the bacterial action greatly reduced and the sedimentation rate significantly increased by this reagent.     

Mineral‐induced degradation of halogentated organic pollutants from aquatic systems

Several laboratory tests were conducted to examine Fe(II) as an enhancing agent in the dehalogenation of CHC1₃ in batch mode. The CHC1₃ degradation was found to be negligible when only Fe(II) is present as a reductant in the (aqueous) reaction system. However, in the presence of Fe(II) coated goethite, the rate of CHC1₃ degradation was enhanced to some extent. This observation can be explained by considering a surface mediated electron transfer step in the overall process. Substantial increase of the degradation rate was observed when the goethite particles first coated with fulvic acid were employed in the adsorption of Fe(II) for the degradation of CHC1₃.