Removal of As(V) by Cu(II)-, Ni(II)-, or Co(II)-doped goethite samples

The present study reports removal of As(V) by adsorption onto laboratory-prepared pure and Cu(II)-, Ni(II)-, and Co(II)-doped goethite samples. The X-ray diffraction patterns showed only goethite as the crystalline phase. Doping of ions in the goethite matrix resulted in shift of d-values. Various parameters chosen for adsorption were nature of adsorbent, percentage of doped cations in goethite matrix, contact time, solution pH, and percentage of adsorbate. It was observed that the pH(pzc) of the goethite surface depended on the nature and concentration of metal ions. The surface area as well as the loading capacity increased with the increase of dopant percentage in goethite matrix. A maximum loading capacity of 19.55 mg/g was observed for 2.7% Cu(II)-doped goethite. The adsorption kinetics for Ni(II), Co(II) and for undoped goethite attained a quasi-equilibrium state after 30 min with almost negligible adsorption beyond this time. In case of Cu(II)-doped goethite samples, the quasi-equilibrium state for As(V) adsorption was observed after 60 min. At each studied pH condition, it was observed that the percentage of adsorption of As(V) decreased in the order Cu(II)-doped goethite > or = Ni(II)-doped goethite > Co(II)-doped goethite > pure goethite. The adsorption followed: Langmuir isotherm, indicating monolayer formation.     

Equilibrium sorption of heavy metals and phosphate from single- and binary-sorbate solutions on goethite

The amounts of Cu(II), Zn(II), and phosphate sorbed from single- and binary-sorbate systems on goethite (alpha-FeOOH) were measured. Experiments were carried out as a function of equilibrium pH (2-7), sorbate concentration (0.21-1.57 mM), and temperature (15-35 degrees C). The aqueous phase contained 0.1 M NaNO3 to maintain ionic strength constant. A convenient method was used to obtain sorption isotherms of single Cu(II), Zn(II), and phosphate at a fixed equilibrium pH, which could be well described by the Langmuir equation. Thermodynamic parameters for the sorption of single Cu(II) and phosphate including the free energies, isosteric enthalpies, and entropies were determined. In contrast to the single-sorbate systems, the sorption of metals was inhibited in the binary Cu(II)-Zn(II) system, whereas the sorption of both sorbates was enhanced in the binary Cu(II)-phosphate system under the conditions studied. The validity of the Langmuir competitive model for the prediction of the sorption isotherms in a binary Cu(II)-Zn(II) system was also discussed.     

Copper Adsorption on Chitosan-Derived Schiff Bases

The adsorption of Cu(II) ions onto the chitosan derived Schiff bases obtained from the condensation of chitosan with salicyaldehyde (polymer I), 2,4-dihydroxybenzaldehyde (polymer II) and with 4-(diethylamino) salicyaldehyde (polymer III) in aqueous solutions was investigated. Batch adsorption experiments were carried out as a function of contact time, pH, and polymer mass. The amount of metal-ion uptake of the polymers was determined by using atomic absorption spectrometry (AAS) and the highest Cu(II) ions uptake was achieved at pH 7.0 and by using sodium perchlorate as an ionic strength adjuster for polymers I, II, and III. The isothermal behavior and the kinetics of adsorption of Cu(II) ions on these polymers with respect to the initial mass of the polymer and temperature were also investigated; adsorption isothermal equilibrium data could be clearly explained by the Langmuir equation. The experimental data of the adsorption equilibrium from Cu(II) solution correlates well with the Langmuir isotherm equation.     

Kinetics and equilibrium adsorption of Cu(II), Cd(II), and Ni(II) ions by chitosan functionalized with 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol

Chitosan biopolymer chemically modified with the complexation agent 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol (BPMAMF) was employed to study the kinetics and the equilibrium adsorption of Cu(II), Cd(II), and Ni(II) metal ions as functions of the pH solution. The maximum adsorption of Cu(II) was found at pH 6.0, while the Cd(II) and Ni(II) maximum adsorption occurred in acidic media, at pH 2.0 and 3.0, respectively. The kinetics was evaluated utilizing the pseudo-first-order and pseudo-second-order equation models and the equilibrium data were analyzed by Langmuir and Freundlich isotherms models. The adsorption kinetics follows the mechanism of the pseudo-second-order equation for all studied systems and this mechanism suggests that the adsorption rate of metal ions by CHS-BPMAMF depends on the number of ions on the adsorbent surface, as well as on their number at equilibrium. The best interpretation for the equilibrium data was given by the Langmuir isotherm and the maximum adsorption capacities were 109 mg g-1 for Cu(II), 38.5 mg g-1 for Cd(II), and 9.6 mg g-1 for Ni(II). The obtained results show that chitosan modified with BPMAMF ligand presented higher adsorption capacity for Cu(II) in all studied pH ranges.     

2-line ferrihydrite: synthesis, characterization and its adsorption behaviour for removal of Pb(II), Cd(II), Cu(II) and Zn(II) from aqueous solutions

Nano-structured 2-line ferrihydrite was synthesized by a pH-controlled precipitation technique at 90 °C. Chemical, X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman analyses confirmed the sample to be 2-line ferrihydrite. The nano nature of the prepared sample was studied by transmission electron microscopy (TEM). The surface area obtained by the Brunauer-Emmett-Teller (BET) method was 175.8 m(2) g(-1). The nanopowder so obtained was used to study its behaviour for the removal of Pb(II), Cd(II), Cu(II) and Zn(II) from aqueous solutions. The relative importance of experimental parameters such as solution pH, contact time and concentration of adsorbate on the uptake of various cations was evaluated. By increasing the pH from 2.0 to 5.5, adsorption of the four cations increased. The kinetics parameters were compared by fitting the contact time data to both linear as well as non-linear forms of pseudo-second-order models. Linear forms of both Langmuir and Freundlich models fitted the equilibrium data of all the cations except for Pb(II) which was also fitted to the non-linear forms of both the models as it gave a low R(2) value of 0.85 for the Langmuir model. High Langmuir monolayer capacities of 366, 250, 62.5 and 500 mg g(-1) were obtained for Pb(II), Cd(II), Cu(II) and Zn(II), respectively. Presence of chloride or sulfate had an adverse effect on cation adsorption. The interactive effects on adsorption from solutions containing two, three or four cations were studied. Surprisingly no Cd(II) adsorption was observed in Pb(II)-Cd(II), Pb(II)-Cd(II)-Zn(II) and Pb(II)-Cd(II)-Cu(II)-Zn(II) systems under the studied concentration range. The overall loading capacity of the adsorbent decreased in mixed cation systems. Metal ion loaded adsorbents were characterized by XRD, FTIR and Raman techniques. The high adsorption capability of the 2-lines ferrihydrite makes it a potentially attractive adsorbent for the removal of cations from aqueous solutions.     

Adsorption behavior of copper and cyanide ions at TiO2-solution interface

Adsorption of both copper and cyanide ions in the absence and in the presence of their complexes at TiO2-solution interfaces was investigated. The objective of this study was to demonstrate the possibility of removing heavy metal ions, exemplified by Cu(II), from aqueous solution in the presence of a ligand, e.g., CN-. Several parameters such as pH and Cu(II) and CH- ion concentration that may affect the magnitude of copper and cyanide adsorption were studied. The equilibrium of Cu-CN speciation distribution in solution and stability constant calculations have been investigated to determine the adsorption behavior of Cu(II). Results revealed that free Cu(II) ions (in the absence of CN-) were completely separated at pH8, while the adsorption of free cyanide ions, in the absence of Cu(II), reached a maximum value of 48% at pH 7. For Cu-CN complexes, the presence of CN- in excessive amount with respect to Cu(II) retarded the adsorption of Cu(II). This is attributed to the formation of multivalent anionic cyano-copper complexes such as Cu(CN)2-(3) and Cu(CN)(3-)4.     

The Influence of Temperature on the Adsorption of Cadmium(II) and Cobalt(II) on Goethite

The adsorption of Cd(II) and Co(II) onto goethite was measured at five temperatures between 10 and 70 degrees C. For both cations the amount adsorbed at any given pH increased as the temperature was increased. Cd(II) adsorbed at a slightly lower pH at each temperature than Co(II). Adsorption isotherms at pH 7.00 for Cd(II) could be fitted closely by a simple Langmuir model, but a two-site Langmuir model was needed for Co(II). Potentiometric titrations of goethite suspensions in the presence and absence of added cation could be modeled closely by a constant-capacitance surface complexation model that assumed the adsorption reactions M2+ + SOH ⇋ SOM+ + H+ and M2+ + SOH + H2O ⇋ SOMOH + 2H+, where M represents Cd or Co. This model also fitted the experimental data from the adsorption edge and adsorption isotherm experiments. Thermodynamic parameters estimated from both Langmuir and surface complexation models showed that the adsorption of both metals was endothermic. Values obtained for the adsorption enthalpies from both modeling schemes were similar for both cations. Estimates of the adsorption entropies were model-dependent: Langmuir parameters yielded positive entropies, while some of the surface complexation parameters generated negative adsorption entropies. Copyright 1999 Academic Press.     

Adsorption of Pb(II) and Cu(II) from aqueous solution on magnetic porous ferrospinel MnFe2O4

The adsorption of Pb(II) and Cu(II) from aqueous solution on magnetic porous ferrospinel MnFe(2)O(4) prepared by a sol-gel process was investigated. Single batch experiment was employed to test pH effect, sorption kinetics, and isotherm. The interaction mechanism and the regeneration were also explored. The results showed that Pb(II) and Cu(II) removal was strongly pH-dependent with an optimum pH value of 6.0, and the equilibrium time was 3.0 h. The adsorption process could be described by a pseudo-second-order model, and the initial sorption rates were 526.3 and 2631.5 μmol g(-1)min(-1) for Pb(II) and Cu(II) ions, respectively. The equilibrium data were corresponded well with Langmuir isotherm, and the maximum adsorption capacities were 333.3 and 952.4 μmol g(-1) for Pb(II) and Cu(II) ions, respectively. The adsorbed Pb(II) and Cu(II) ions were in the form of the complex with oxygen in carboxyl and hydroxyl groups binding on the surface of magnetic porous MnFe(2)O(4). The sorbent could be reused for five times with high removal efficiency.     

Copper and arsenate co-sorption at the mineral-water interfaces of goethite and jarosite

The co-sorption reaction products of arsenate (As(V)) and copper (Cu(II)) on goethite (alpha-FeOOH) and natro-jarosite (Na(3)Fe(3)(SO(4))(2)(OH)(6)) were investigated with extended X-ray absorption fine structure (EXAFS) spectroscopy to determine if Cu(II) and As(V) would form precipitates or compete with each other for surface sites. The reaction products were prepared by mixing 250 microM Cu(SO(4)) with 10, 25, or 50 microM Na(2)HAsO(4) at pH 5.65 and allowing the mixture to react in 10 m(2) L(-1) goethite or jarosite suspensions for 12 days. In addition, EXAFS data of Cu(SO(4)) and As(V) sorbed on goethite and jarosite were collected as control species. All reaction conditions were under-saturated with respect to common copper bearing minerals: tenorite (CuO), brochantite (Cu(4)(OH)(6)SO(4)), and hydrated clinoclase (Cu(3)(AsO(4))(2)2H(2)O). The extents of the As(V) and Cu(II) surface adsorption reactions showed a strong competitive effect from Cu(II) on As(V) adsorption for a nominal Cu:As mole-ratio of 25:1. With increasing nominal As(V) concentration, As(V) sorption on goethite and jarosite increased without diminishing the amount of Cu(II) sorption. In the absence of either co-sorbate, As(V) and Cu(II) formed the expected surface adsorption species, i.e., bidentate binuclear and edge-sharing surface complexes, consistent with previously published results. In each other's presence, the local bonding environments of As(V) and Cu(II) showed that the co-sorbates form a precipitate on the goethite and jarosite surface at nominal concentrations of 10:1 and 5:1. At nominal Cu:As mole-ratios of 25:1, Cu(II) did not form significantly different surface complexes on goethite or jarosite from those in the absence of As(V), however, As K-edge EXAFS results distinctly showed Cu(II) atoms in As(V)'s local bonding environment on the goethite surface. The structures of the two precipitates were different and depended on the anion-layer structure and possibly the presence of structural oxyanions in the case of jarosite. On goethite, the copper-arsenate precipitate was similar to hydrated clinoclase, while on jarosite, a euchroite-like precipitate (Cu(2)[AsO(4)](OH)3H(2)O, P 2(1)2(1)2(1)) had formed. Despite under-saturated solution conditions, the formation of these precipitates may have occurred due to a seed-formation effect from densely surface adsorbed Cu(II) and As(V) for which the "new" saturation index was significantly lower than homogeneous values would otherwise suggest. Synergistic reactions between two co-sorbates of fundamentally different surface adsorption behaviour can thus be achieved if the number of available sites for surface adsorption is limited.     

Adsorption of Me-HEDP complexes onto gamma-Al2O3

This work studies the adsorption of Me-1-hydroxiethane-(1,1-diphosphonic acid) (HEDP) complex onto alumina in the pH range from 5.0 to 9.5. The extent of HEDP adsorption is not significatively affected by the presence of Me(II), while, HEDP has an interesting effect on Me(II) adsorption. At high surface covering, Cu(II) adsorption is enhanced at low pH reaching a maximum of 57% at pH nearly 6, however, at pH>6 a decrease about 20% in the amount of Cu(II) adsorbed takes place by the presence of HEDP. The model predicts a ternary surface complex (AlLCu(-)) to justify the increase of Cu(II) adsorbed at lower pH. At the lower pH and at high Zn(II) concentration the presence of equimolar concentration of HEDP also causes a discernible increase in the amount of Zn(II) adsorbed. At pH 5, the percentage of Zn(II) complexed with HEDP increased from negligible to 40% as the HEDP concentration increased. However, in this case the HEDP does not have a suppressor effect on the Zn(II) adsorption at the higher pH. Again, the presence of anionic-type complexation is here postulated to reach a good fit with the experimental results. The effect of HEDP over Zn(II) adsorption becomes less pronounced with the excess of surface sites. Cd(II)-HEDP solution complexes are weaker than those corresponding to Cu(II) and Zn(II), so competitive effects between surface and solution are much less significant in comparison to Cu(II)-HEDP and Zn(II)-HEDP alumina systems. So, the effect of HEDP on the Cd adsorption at low concentration and low pH is more stressed than in the case of Cu(II) and Zn(II). Overall, results indicate that the presence of HEDP in the aquatic systems could have a significant impact on the mobility and distribution of Cu(II), Zn(II) and Cd(II) in the environment.     

Copper (II) adsorption from aqueous solution by herbaceous peat

In this research, the herbaceous peat collected from Gavurgolu peatlands, one of the biggest Turkish peatlands, was utilized as an adsorbent for the removal of copper (II) ions from aqueous solution. Adsorption experiments were conducted under various conditions, i.e., initial concentration, temperature, and pH. While the amount of Cu (II) adsorbed on the peat increased with increasing concentration of Cu (II) ions, it was not markedly affected by temperature and pH. Percentage removal was higher at lower concentration. For example, the maximum percentage removal of Cu (II) ions for initial concentration of 3 x 10(-4) M was 97.04% at 21 degrees C and pH 5.5. The adsorption capacity (Q(0)) of the peat was 4.84 mgg(-1) from Langmuir adsorption isotherm for the concentration range of 3 x 10(-4)-6 x 10(-4) M at 21 degrees C and pH 5.5. The equilibrium time of adsorption of Cu (II) ions was 150 min and independent of concentration and temperature. The amount of Cu (II) adsorbed at equilibrium time did not considerably change with temperature and pH. It was also determined that adsorption isotherm followed both Freundlich and Langmuir. Uptake mechanism of Cu (II) ions by the peat occurs via cation exchange (especially by means of Ca(2+) and Mg(2+)) as well as copper/peat complexation. Adsorption kinetic was consistent with the pseudo-second-order model.     

Modeling the adsorption of Cd(II) onto Muloorina illite and related clay minerals

The adsorption of Cd(II) onto goethite, kaolinite, and illite was measured as a function of pH (adsorption edges) and concentration (adsorption isotherms) at 25 degrees C. As the pH was increased, adsorption onto goethite occurred mainly in the pH range 5.5-8, whereas adsorption onto kaolinite occurred in two stages, separated by a plateau in the pH region 5.5 to 7. Adsorption onto illite increased steadily as the pH was increased, with far less Cd(II) adsorbing onto illite than onto goethite or kaolinite per m(2) of mineral surface area. Potentiometric titrations of suspensions of each mineral, with and without Cd(II) present, were also completed. Results from all three types of experiments were modeled using an extended constant- capacitance surface complexation model. The reactions [Formula: see text] [Formula: see text] and [Formula: see text] best described Cd(II) adsorption onto goethite, while [Formula: see text] and [Formula: see text] best described Cd(II) adsorption onto kaolinite. A combination of the first, second, and fourth of these reactions best fitted the data for Cd(II) adsorption onto illite. In each case the model fitted all experimental data well. The results suggest that adsorption onto the variable charge (SOH) sites on illite more closely resembles adsorption onto goethite than onto kaolinite.     

Effect of Cr(VI) anions on adsorption and desorption behavior of Cu(II) in the colloidal systems of two authentic variable charge soils

Heavy metals in wastes exist as multiple pollutants. The study of the interactions between multiple pollutants and soils should be of significance in practice. In the present study, the effect of chromate on adsorption and desorption behavior of Cu(II) in two variable charge soils was investigated, with the emphasis on the adsorption and desorption equilibria of Cu(II). The results showed that chromate can affect adsorption and desorption of Cu(II) in the colloidal systems of two variable charge soils. The extent of the effect was related to the initial concentrations of chromate and Cu(II), the system pH, and the nature of the soils. The presence of chromate led to an increase in the adsorption of Cu(II). For example, in the presence of 0.5, 0.8, 1.0, and 1.5 mmol L(-1) of chromate, for the rhodic ferralsol the adsorption of Cu(II) increased by 15.3, 18.0, 19.0, and 20.2%, respectively. For the hyperrhodic ferrasol, the corresponding figures were 11.9, 17.0, 20.3, and 26.1%, respectively. The presence of chromate also caused an increase in the desorption of Cu(II). For instance, in the presence of 0.5, 1.0, and 1.5 mmol L(-1) of chromate, the desorption for the rhodic ferralsol increased by 16.9, 27.5, and 34.1%, respectively. For the hyperrhodic ferralsol, the corresponding figures were 18.1, 35.6, and 51.4%, respectively. The increments of the adsorption and desorption increased with the increase in equilibrium concentration of Cu(II) in the solution. For instance, when the equilibrium concentrations were 0.5, 1.0, 1.5, and 2.0 mmol L(-1), the increments for the rhodic ferralsol were 2.5, 3.2, 3.3, and 3.0 mmol kg(-1), respectively. For the hyperrhodic ferralsol, the corresponding figures were 2.9, 3.5, 4.0, and 4.2 mmol kg(-1), respectively. The effect of chromate for the hyperrhodic ferralsol was greater than that for the rhodic ferralsol. This is caused by the difference in the content of iron oxides for the two soils. The increments of the adsorption and the desorption of Cu(II) increased with the rise in pH, reaching a maximum value, and then decreased. It can be assumed that the increment of the adsorption was caused by the change in surface charge of the soils induced by the adsorption of chromate and the cooperative adsorption of chromate adsorbed and Cu(II). The increase of electrostatically adsorbed Cu(II) was responsible for the increase in the desorption of Cu(II).     

The influence of temperature on the adsorption of mellitic acid onto goethite

The adsorption of mellitic acid (benzene-1,2,3,4,5,6-hexacarboxylic acid) onto goethite was investigated at five temperatures between 10 and 70 degrees C. Mellitic acid adsorption increased with increasing temperature below pH 7.5, but at higher pH the effect of increasing temperature was to reduce the amount adsorbed. Potentiometric titrations were conducted and adsorption isotherms were measured over the same temperature range, and the data obtained were used in conjunction with adsorption edge data to develop an Extended Constant Capacitance Surface Complexation Model of mellitic acid adsorption. A single set of reactions was used to model the adsorption for the three different experiment types at the five temperatures studied. The adsorption reactions proposed for mellitate ion (L(6-)) adsorption at the goethite surface (SOH) involved the formation of two outer-sphere complexes: SOH + L(6-) + 3H+ <==> [(SOH2)+ (LH2)(4-)]3-, 2SOH + L(6-) + 2H+ <==> [(SOH2)2(2+) (L)(6-)]4-. This mechanism is consistent with recent ATR-FTIR spectroscopic measurements of the mellitate-goethite system. Thermodynamic parameters calculated from the temperature dependence of the equilibrium constants for these reactions indicate that the adsorption of mellitic acid onto goethite is accompanied by a large entropy increase.     

气体临界温度以上吸附平衡的预测研究

Experimental adsorption isotherms of CH4 and N2 higher than critical temperatures on K02 activated carbon were measured with the volumetric method The pressure and temperature ranges were 0～12 MPa and 273～333 K respectively. A model, which took into account the adsorbate properties above critical temperatures and the adsorbent surface heterogeneity by pore size distribution, was proposed in this paper to predict the equilibrium data only using one adsorption isotherm. The gamma distribution was adopted to express the pore size distribution of the activated carbon, and the adsorption potential was calculated bythe 10-4-3 equation for slit shape micro pores. The relationships between the adsorbate density, the saturated adsorption amount and the equilibrium temperature have been discussed in detail. Through this method, the experimental adsorption data of CH4 and N2 were compared with the prediction equilibria. The study illustrates that the predicting method could present the adsorption equilibria accurately in the whole research range. And the mean relative deviations of the prediction of CH4 and N2 are only about 1.9% and 2.9%. This proves that the analyses of the adsorbate properties are reasonable. Inaddition, the model was applied to calculating the equilibrium data of various supercritical adsorption systems published in literatures. Despite different adsorbents and equilibriaconditions, the investigation results demonstrate that the suggested model performs well in predicting the gases adsorption equilibrium data with all mean relatived eviations less than 6.8%. Therefore, the model could be utilized to calculate the gases adsorption equilibrium data above critical temperatures in a wide range.     

Adsorption of metal ions onto Moroccan stevensite: kinetic and isotherm studies

The aim of this paper is to study the adsorption of the heavy metals (Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II)) from aqueous solutions by a natural Moroccan stevensite called locally rhassoul. We carried out, first, a mineralogical and physicochemical characterization of stevensite. The surface area is 134 m2/g and the cation exchange capacity (CEC) is 76.5 meq/100 g. The chemical formula of stevensite is Si3.78Al0.22Mg2.92Fe0.09Na0.08K0.08O10(OH)2.4H2O. Adsorption tests of Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II) in batch reactors were carried out at ambient temperature and at constant pH. Two simplified models including pseudo-first-order and pseudo-second- order were used to test the adsorption kinetics. The equilibrium time and adsorption rate of adsorption were determined. The increasing order of the adsorption rates follows the sequence Mn(II) > Pb(II) > Zn(II) > Cu(II) > Cd(II). The Dubinin-Radushkevich (D-R), Langmuir, and Redlich-Peterson (R-P) models were adopted to describe the adsorption isotherms. The maximal adsorption capacities at pH 4.0 determined from the D-R and Langmuir models vary in the following order: Cu(II) > Mn(II) > Cd(II) > Zn(II) > Pb(II). The equilibrium data fitted well with the three-parameter Redlich-Peterson model. The values of mean energy of adsorption show mainly an ion-exchange mechanism. Also, the influence of solution pH on the adsorption onto stevensite was studied in the pH range 1.5-7.0.     

Adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II), and As(V) on bacterially produced metal sulfides

The adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II) and As(V) onto bacterially produced metal sulfide (BPMS) material was investigated using a batch equilibrium method. It was found that the sulfide material had adsorptive properties comparable with those of other adsorbents with respect to the specific uptake of a range of metals and, the levels to which dissolved metal concentrations in solution can be reduced. The percentage of adsorption increased with increasing pH and adsorbent dose, but decreased with increasing initial dissolved metal concentration. The pH of the solution was the most important parameter controlling adsorption of Cd(II), Cu(II), Fe(II), Ni(II), Pb(II), Zn(II), and As(V) by BPMS. The adsorption data were successfully modeled using the Langmuir adsorption isotherm. Desorption experiments showed that the reversibility of adsorption was low, suggesting high-affinity adsorption governed by chemisorption. The mechanism of adsorption for the divalent metals was thought to be the formation of strong, inner-sphere complexes involving surface hydroxyl groups. However, the mechanism for the adsorption of As(V) by BPMS appears to be distinct from that of surface hydroxyl exchange. These results have important implications to the management of metal sulfide sludge produced by bacterial sulfate reduction.     

Sequential separation of Cu(II)/Ni(II)/Fe(II) from strong-acidic pickling wastewater with a two-stage process based on a bi-pyridine chelating resin

A self-synthesized bi-pyridine chelating resin (PAPY) could separate Cu(II)/Ni(II)/Fe(II) sequentially from strong-acidic pickling wastewater by a two-stage pH-adjusted process, in which Cu(II), Ni(II), and Fe(II) were successively preferred by PAPY. In the first stage (pH 1.0), the separation factor of Cu(II) over Ni(II) reached 61.43 in Cu(II)-Ni(II)-Fe(II) systems. In the second stage (pH 2.0), the separation factor of Ni(II) over Fe(II) reached 92.82 in Ni(II)-Fe(II) systems. Emphasis was placed on the selective separation of Cu(II) and Ni(II) in the first-stage. The adsorption amounts of Cu(II) onto PAPY were 1.2 mmol/g in the first stage, while those of Ni(II) and Fe(II) were lower than 0.3 mmol/g. Cu(II) adsorption was hardly affected by Ni(II) with the presence of dense Fe(II), but Cu(II) inhibited Ni(II) adsorption strongly. Part of preloaded Ni(II) could be replaced by Cu(II) based on the replacement effect. Compared with the absence of Fe(II), dense Fe(II) could obviously enhance the separation of Cu(II)-Ni(II). More than 95.0% of Cu(II) could be removed in the former 240 BV (BV for bed volume of the adsorbent) in the fixed-bed adsorption column process with the flow rate of 2.5 BV/h. As proved by X-ray photoelectron spectrometry (XPS) and density functional theory (DFT) analyses, Cu(II) exerted a much stronger deprotonation and chelation ability toward PAPY than Ni(II) and Fe(II). Thus, the work shows a great potential in the separation and purification of heavy metal resources from strong-acidic pickling wastewaters.     

Competitive adsorption behavior of heavy metals on kaolinite

Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 microM in the single-element system and 33.3 microM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu相似文献   

Adsorption of tetracycline onto goethite in the presence of metal cations and humic substances

Adsorption of tetracycline, one of the most widely used antibiotics, onto goethite was studied as a function of pH, metal cations, and humic acid (HA) over a pH range 3-10. Five background electrolyte cations (Li(+), Na(+), K(+), Ca(2+), and Mg(2+)) with a concentration of 0.01 M showed little effect on the tetracycline adsorption at the studied pH range. While the divalent heavy metal cation, Cu(2+), could significantly enhance the adsorption and higher concentration of Cu(2+), stronger adsorption was found. The results indicated that different adsorption mechanisms might be involved for the two types of cations. Background electrolyte cations hardly interfere with the interaction between tetracycline and goethite surfaces because they only form weak outer-sphere surface complexes. On the contrary, Cu(2+) could enhance the adsorption via acting as a bridge ion to form goethite-Cu(2+)-tetracycline surface complex because Cu(2+) could form strong and specific inner-sphere surface complexes. HA showed different effect on the tetracycline sorption under different pH condition. The presence of HA increased tetracycline sorption dramatically under acidic condition. Results indicated that heavy metal cations and soil organic matters have great effects on the tetracycline mobility in the soil environment and eventually affect its exposure concentration and toxicity to organisms.