Studies on manganese nodule leached residues 2. Adsorption of aqueous phosphate on manganese nodule leached residues

Adsorption of phosphate onto manganese nodule leached residues was investigated as a possible alternative to conventional methods of phosphate removal from industrial effluents. Adsorption behaviors were studied as a function of time, temperature, pH, and concentration level of adsorbate and adsorbent in acetic acid-sodium acetate buffer medium. The adsorption of phosphate follows the Langmuir adsorption isotherms. The magnitude of adsorption of phosphate in manganese nodule leached residues was compared with that in naturally occurring Mn nodule. Manganese nodule leached residues show better affinity toward phosphate adsorption.     

Heavy metal (Cd2+, Ni2+, Pb2+ and Ni2+) adsorption in aqueous solutions by oxidized starches

Superabsorbent materials based on natural products have been synthesized by free radical oxidation of corn starch using a redox system consisting of potassium permanganate and sodium bisulfite. The resulting oxidized starches were characterized by analyzing the variation of carbonyl and carboxyl contents. The swelling ability of these samples has been determined by gravimetric method in water and in saline solutions. The effect of oxidant concentration and bleaching procedure on the water absorption capacity has been studied. The ability to remove heavy metals in water solution has been tested against Cd²⁺, Ni²⁺, Pb²⁺ and Zn²⁺ ions, showing higher percentage of remotion for the unbleached oxidized starches, in particular against nickel ions. Copyright © 2014 John Wiley & Sons, Ltd.     

Studies on manganese nodule leached residue 4. Physicochemical characterization and catalytic activity of acetic acid treated manganese nodule leached residue

The catalytic activity of water-washed manganese nodule leached residue (WMNLR) samples improved by treating with acetic acid. The effects of acetic acid treatment on the physicochemical properties and catalytic activity of manganese nodule leached residue have been studied. The surface area, surface oxygen, surface hydroxyl groups, surface acidity, electron donating properties, etc., increase gradually with acid treatment up to 0.5 M and thereafter show a decreasing trend. The rate constant of H2O2 decomposition, catalytic activity of CO oxidation, and esterification of acetic acid also show a similar trend to that of surface properties.     

Synthesis and characterization of nano-composite ion-exchanger; its adsorption behavior

A novel organic-inorganic nanocomposite cation-exchanger has been synthesized via sol-gel method. It was characterized on the basis of FTIR, XRD, SEM, TEM, AFM and Raman studies. The structural studies reveal semi-crystalline nature of the material with the particle size ranging from 1-5 nm. Physiochemical properties such as ion-exchange capacity, chemical and thermal stability of composite material have also been determined. Bifunctional behavior of the material has been indicated by its pH titrations curves. The nanocomposite material exhibits improved thermal stability, higher ion-exchange capacity and better selectivity for toxic heavy metals. The ion-exchange material shows an ion-exchange capacity of 1.8 meq g(-1) for Na(+) ions. Sorption behavior of metal ions on the material was studied in different solvents. The cation exchanger was found to be selective for Pb(II), Hg(II) and Zr(IV) ions. The limit of detection (LOD) and the limit of quantification (LOQ) for Pb(II) ion was found to be 0.85 and 2.85 μg L(-1). Analytically important separations of heavy metal ions in synthetic mixtures as well as industrial effluents and natural water were achieved with the exchanger. The practical utility of polyanilineZr(IV)sulphosalicylate cation exchanger has been established for the analysis and recovery of heavy metal ions in environmental samples.     

Preparation, characterization, and Zn(2+) adsorption behavior of chemically modified MCM-41 with 5-mercapto-1-methyltetrazole

A mesoporous silica (MCM-41) has been chemically modified with 5-mercapto-1-methyltetrazole using the homogeneous route. This synthetic route involved the reaction of 5-mercapto-1-methyltetrazole with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material (MTTZ-MCM-41) has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry, and elemental analysis. The solid was employed as a Zn(II) adsorbent from aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration, addition of ethanol, presence of other metals in the medium) has been studied using batch and column techniques. Flame atomic absorption spectrometry was used to determine the Zn(II) concentration in the filtrate or in the eluted solution after the adsorption process. Results obtained indicate that under the optimum conditions (pH 8 and 2 h stirring time), the maximum adsorption value for Zn(II) was 1.59+/-0.01 mmol/g, whereas the adsorption capacity of the unmodified mesoporous silica was about 0.010+/-0.001 mmol/g. On the other hand, the Zn(II) adsorption on the MTTZ-MCM-41 was independent of the presence of ethanol and other metals (Cu(II), Mn(II), Ca(II), and Mg(II)) in the medium. Finally, experiments carried out in order to study the regeneration capacity of the MTTZ-MCM-41 revealed that the adsorption capacity of this material was maintained after 3 cycles of the adsorption/desorption process.     

Mixed complexes of Ni(2+) or Zn(2+) and citric acid with 2,2'-bipyridyl in aqueous solution

The stability constants of ternary Ni(2+) or Zn(2+) complexes with 2,2'-bipyridyl and citric acid have been determined by means of pH-titrations at 25.0 +/- 0.2 degrees and an ionic strength of 0.1M (KNO(3)). The stability constants of ternary complexes have been compared with those of similar ternary species.     

Physicochemical characterization and adsorption behavior of calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution

A Zn/Al hydrotalcite-like compound (HTlc) was prepared by co-precipitation (at constant pH) method and was characterized by XRD, TG/DTA, FTIR, and BET surface area. The ability of Zn/Al oxide to remove F- from aqueous solution was investigated. All the adsorption experiments were carried out as a function of time, pH, concentration of adsorbate, adsorbent dose, temperature etc. It was found that the maximum adsorption takes place within 4 h at pH 6.0. The percentage of adsorption increases with increase in the adsorbent dose, but decreases with increase in the adsorbate concentration. From the temperature variation it was found that the percentage of adsorption decreases with increase in temperature, which shows that the adsorption process is exothermic in nature. The adsorption data fitted well into the linearly transformed Langmuir equation. Sulfate and phosphate were found to have profound effects on fluoride removal. Thermodynamic parameters such as DeltaG0, DeltaH0, and DeltaS0 were calculated. The negative value of DeltaH0 indicates that the adsorption process is exothermic. The apparent equilibrium constants (Ka) are also calculated and found to decrease with increase in temperature. With 0.01 M NaOH the adsorbed F- could be completely desorbed from Zn/Al oxide in 6 h.     

O-羧甲基壳聚糖纳米微粒制备及对Ni~(2+)吸附研究

将壳聚糖与氯乙酸反应,通过控制反应条件制备了取代度为0.71的O-羧甲基壳聚糖,将改性后的O-羧甲基壳聚糖与多聚磷酸钠反应,制备了粒径分布在370-710nm的O-羧甲基壳聚糖纳米微粒,透射电镜观察表明该微粒呈球状,平均粒径为450nm.在此基础上研究了O-羧甲基壳聚糖纳米微粒对工业电镀镍废水Ni~(2+)吸附性能,考察了溶液pH、Ni~(2+)起始浓度、平衡吸附时间、粒径等因素的影响,结果表明:O-羧甲基壳聚糖微粒最佳吸附条件是Ni~(2+)溶液pH为8.0、Ni~(2+)溶液起始浓度为33.28mg/ml、平衡吸附时间为0.5h、粒径较小的O-羧甲基壳聚糖纳米微粒对Ni~(2+)的吸附量要大于粒径较大的吸附量.     

胺固化环氧酚醛树脂对Hg~(2+)的吸附性能

螯合树脂能与金属离子形成稳定的配合物,在无机、冶金、分析药物、催化、海洋化学、放射化学、环境保护各领域都有非常重要的应用[1-3]。我们曾以酚醛树脂为大分子骨架与多胺反应制备了一系列螯合树脂并对其结构及对多种金属离子的吸附性能进行了探讨[4,5]。本文则以线型环氧酚醛树脂为大分子骨架、多乙烯多胺为固化剂,制备了五种不同氮含量的氨基环氧酚醛螯合树脂,并考察其对金属离子Ｈｇ2+的吸附性能。1　实验部分1.1　仪器与试剂ＮｉｃｏｌｅｔＭＡＧＮＡ ＩＲ550(ＳｅｒｉｅｓＩＩ)红外分光光度计,ＳＨＡ-Ｃ水浴恒温振荡器,ＰＥ2000…     

Metal-metal bonding in mixed valence Ni2(5+) complexes and spectroscopic evidence for a Ni2(6+) species

Dinickel(II) complexes of the ligands N,N'-di-p-anisylformamidinate (DAniF) and N,N',N'-triphenylguanidinate (TPG) have been synthesized and crystallographically characterized, along with their one-electron-oxidized analogues. In both systems, the Ni-Ni distances become shorter by approximately 0.1 A upon oxidation, in accord with the proposal that the resulting Ni2(5+) complexes are appropriately described as having one electron removed from a metal-based sigma orbital and an overall Ni-Ni bond order of 1/2. Although conventional DFT calculations on the model compounds Ni2(HNCHNH)4 and [Ni2(HNCHNH)4]+ appear to predict that the lowest energy state of the latter species would have one unpaired electron in an essentially ligand-based orbital. A single-point calculation of Ni2(DAniF)4 employing the geometry of its crystal structure with the full ligand included reveals a reversal of the previously predicted order of the HOMO and HOMO-1, and suggests that the unpaired electron in [Ni2(DAniF)4]+ is in a metal-based orbital of sigma symmetry. This is verified by the axial EPR spectrum of the compound in solution. The compound Ni2(DAniF)4 shows an unexpectedly rich cyclic voltammogram with four stepwise reversible oxidation waves. Coulometric experiments show that the doubly oxidized species has a significant lifetime at -25 degrees C, and by spectroelectrochemistry, its UV-vis spectrum was recorded. We propose that this species contains a Ni2(6+) core with a single Ni-Ni sigma bond.     

The effect of triethylenetetraamine (Trien) on the ion flotation of Cu(2+) and Ni(2+)

Ion flotation is a separation process involving the adsorption of a surfactant and counterions at an air/aqueous solution interface. It shows promise for removing toxic heavy metal ions from dilute aqueous solutions. Here we report the effect of a neutral chelating ligand, triethylenetetraamine (Trien), on the ion flotation of cations with dodecylsulfate, DS(-), introduced as sodium dodecylsulfate, SDS. Ion flotation in the aqueous SD-Cu(II)-Ca(II)-Trien system gave strongly preferential removal of Cu(II) over Ca(II), which is a reversal of the order of selectivity seen in the SDS-Cu(II)-Ca(II) system containing no Trien. The removal rates of Cu(2+) and Ni(2+) with DS(-) were much faster in the presence of Trien than for simple aquo ions, and the final metal concentration was significantly lower. Surface tension measurements showed that Trien enhanced the surface activity and adsorption density for SDS-Cu(II) and SDS-Ni(II) solutions. The overall change in the Gibbs free energy for adsorption resulting from complexation was -3.60 kJ/mol for Cu(II) and -3.50 kJ/mol for Ni(II). This included the effects of hydrophobic interactions between the metal-Trien complexes at the air/solution interface, along with changes in the amount of dehydration associated with cosorption of the metal-Trien complex with DS(-) at the air/solution interface.     

Study of the selection mechanism of heavy metal (Pb2+, Cu2+, Ni2+, and Cd2+) adsorption on clinoptilolite

The study was carried out on the sorption of heavy metals (Ni2+, Cu2+, Pb2+, and Cd2+) under static conditions from single- and multicomponent aqueous solutions by raw and pretreated clinoptilolite. The sorption has an ion-exchange nature and consists of three stages, i.e., the adsorption on the surface of microcrystals, the inversion stage, and the moderate adsorption in the interior of the microcrystal. The finer clinoptilolite fractions sorb higher amounts of the metals due to relative enriching by the zeolite proper and higher cleavage. The slight difference between adsorption capacity of the clinoptilolite toward lead, copper, and cadmium from single- and multicomponent solutions may testify to individual sorption centers of the zeolite for each metal. The decrease of nickel adsorption from multicomponent solutions is probably caused by the propinquity of its sorption forms to the other metals and by competition. The maximum sorption capacity toward Cd2+ is determined as 4.22 mg/g at an initial concentration of 80 mg/L and toward Pb2+, Cu2+, and Ni2+ as 27.7, 25.76, and 13.03 mg/g at 800 mg/L. The sorption results fit well to the Langmuir and the Freundlich models. The second one is better for adsorption modeling at high metal concentrations.     

1H and (113)Cd NMR Investigations of Cd(2+) and Zn(2+) Binding Sites on Serum Albumin: Competition with Ca(2+), Ni(2+), Cu(2+), and Zn(2+)

1H and (113)Cd NMR studies are used to investigate the Cd(2+) binding sites on serum albumin (67 kDa) in competition with other metal ions. A wide range of mammalian serum albumins possess two similar strong Cd(2+) binding sites (site A 113-124 ppm; site B 24-28 ppm). The two strong sites are shown not to involve the free thiol at Cys34. Ca(2+) influences the binding of Cd(2+) to isolated human albumin, and similar effects due to endogenous Ca(2+) are observed for intact human blood serum. (1)H NMR studies show that the same two His residues of human serum albumin are perturbed by Zn(2+) and Cd(2+) binding alike. Zn(2+) displaces Cd(2+) from site A which leads to Cd(2+) occupation of a third site (C, 45 ppm). The N-terminus of HSA is not the locus of the two strong Cd(2+) binding sites, in contrast to Cu(2+) and Ni(2+). After saturation of the N-terminal binding site, Cu(2+) or Ni(2+) also displaces Cd(2+) from site A to site C. The effect of pH on Cd(2+) binding is described. A common Cd(2+)/Zn(2+) binding site (site A) involving interdomain His residues is discussed.     

Studies of polyfunctional O-ligands: Formation and stability of Mg(2+) and Ca(2+) complexes of 1,2,4,5-benzenetetracarboxylic acid in aqueous solution at 25 degrees

The stabilities of the Ca(2+) and Mg(2+) complexes with 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) were studied potentiometrically, at 25 degrees . The species ML, MHL, MH(2)L, and M(2)L [L = pyromellitate(4-); M = Ca(2+), Mg(2+)] were found to be present in solution (for Mg(2+) the species MH(3)L was also found). The dependence of the formation constants on ionic strength, and the stability trends of the Ca(2+) and Mg(2+) complexes with carboxylate ligands, are discussed.     

DH-2树脂对镝的吸附及机理

研究了镝离子在HD-2树脂上的吸附行为。在HAc-NaAc体系pH=6.20时吸附最佳,测得静态饱和吸附容量为356mg/g(树脂),用0.1~2.0 mol/L HC l可定量洗脱,表观速率常数k198=1.16×105s-1,表观活化能Ea=16.1kJ/mol。等温吸附服从Freun ilich经验式,吸附热力学参数△H=16.5kJ/mol,△S=58.2 J/(mol.K),△G298=-0.859kJ/mol。用化学和红外光谱等方法讨论了吸附机理。     

Kinetics and adsorption behavior of carboxymethyl starch on alpha-alumina in aqueous medium

The adsorption of carboxymethyl starch (CMS) at the alpha-alumina/aqueous solution interface has been investigated through adsorption studies, electrokinetics mobility measurements, and FTIR spectroscopy. Zeta potential measurements show that the addition of CMS results in a more dramatic increase in the absolute zeta potential in the alkaline region, as well as a shift of the isoelectric point to lower values, indicating the adsorption of CMS from the aqueous solution onto the alumina surface. The positive hydrophilic surface sites of alumina are responsible for the adsorption of CMS molecules. The adsorption of CMS is possible after charge reversal by the addition of excess CMS. Nearly 30 min of contact time are found to be sufficient for the adsorption of CMS to reach equilibrium. CMS adsorption follows a Langmuir isotherm with adsorption capacities of 91.74 mg CMS per gram of alpha-alumina. For the adsorption of CMS, pseudo-second-order chemical reaction kinetics provides the best correlation with the experimental data. FTIR analysis indicated that CMS forms outer complexes with alumina surfaces depending on the shifting of the asymmetric and symmetric bands.     

Synthesis,characterization and H<Subscript>2</Subscript> adsorption performances of polymeric Co(II) and Ni(II) complexes of pyrazine-2,3-dicarboxylic acid and 1-vinylimidazole

We studied the synthesis and characterization of polymeric coordination complexes of Co(II) and Ni(II) ions with pyrazine-2,3-dicarboxylic acid and 1-vinylimidazole. The e lemental analysis, infrared spectroscopy, powder X-ray diffraction, magnetic susceptibility, thermal analysis and X-ray single crystal techniques were used in the characterization. The X-ray single crystal analysis suggests that the pyrazine-2,3-dicarboxylato ligand acts as a bridging ligand through the oxygen atoms of the carboxylate groups and the nitrogen atoms on the pyrazine ring. The 1-vinylimidazole ligand behaves as a monodentate ligand via the ring nitrogen atom. Further, the H₂ adsorption studies were carried out at 75 K for various increasing pressures and the highest H₂ adsorption performances for Co(II) and Ni(II) complexes were estimated as 2.66 and 2.99 wt% at 87 bar. The theoretical calculations using the crystal data were also performed to determine the voids in the structure of Co(II) complex.     

Studies on the behaviour of beta-ethylthioethylenethioglycollate in aqueous Ni(II) and Cu(II) solutions

The stability constants of the 1:1 and 1:2 complexes of nickel and copper(II) with beta-ethylthioethylenethioglycollic acid have been determined at 25 degrees at ionic strength 1.0 (NaClO(4)). The values for the nickel complexes are K(1) = 1.11 +/- 0.06 x 10(2) (spectrophotometrically) or 1.25 +/- 0.11 x 10(2) (potentiometrically) and K(2) = 3.04 +/- 0.24 x 10(2) (potentiometrically). The corresponding values for the copper complexes are K(1) = 1.27 +/- 0.02 x 10(3) or 1.28 +/- 0.03 x 10(3) and K(2) = 7.29 +/- 0.30 x 10(2).     

Molecular beam induced changes in adsorption behavior of NO on NiO(111)/Ni(111)

We have examined the adsorption behavior at approximately 110 K of NO on NiO(111) overlayers prepared on a Ni(111) substrate. High-resolution electron-energy-loss spectroscopy shows fundamental changes in the vibrational spectrum for the beam dosed surface in comparison with the background dosed surface. Three vibrational peaks are observed after beam dosing, two of which are not observed after conventional background dosing. The peaks can be assigned to NO stretches for a previously observed NO state, a new NO bonding geometry, and a new NO2 surface species, previously unobserved under NO dosing. The difference is accounted for by increased NO uptake due both to kinetically activated adsorption and to increased exposure.