Sorption of divalent metal ions on CrPO4

The divalent metal ion sorption (Cu(2+), Cd(2+), Ni(2+), and Pb(2+)) on chromium phosphate (CrPO(4)) was studied as a function of pH, temperature, and concentration of metal ions. The sorption of metal ions is observed to increase with the increase in pH, temperature, and concentration of metal ions in solution. The mechanism of sorption is found to be the exchange of the hydrolyzed metal cations with the protons from solid at high temperature. The sorption at low temperature is found to be accompanied by the precipitation of the corresponding metal phosphates such as Pb(3)(PO(4))(2).     

The sorption of divalent metal ions on AlPO4

The sorption of Cu(2+), Pb(2+), Ni(2+), and Cd(2+) ions on the aluminum(III) phosphate was observed to increase with increases in the concentration, temperature, and pH of the system. The apparent dissociation (pK(a)), binding (pK(b)) and exchange (pK(ex)) constants of aluminum(III) phosphate were evaluated and found to be dependent upon the temperature and nature of the metal cations. The values of the dissociation constants (pK(a)) followed the order Pb(2+)相似文献   

pH effect on phosphate sorption by crystalline MnO(2)

The phosphate anions sorption on manganese dioxide was studied as a function of pH in the range 3-9 and at 293 K. The sorption was observed to increase with the increase in concentration of phosphate and decrease with the increase in pH. No effect of the phosphate adsorption upon the PZC of the solid suggested that the only outer sphere complexes were formed on the surface of the solid. The potentiometric titrations studies of the solid were also performed in the presence of different phosphate concentrations (0.53, 1.053, and 2.11 mmol L(-1)). The calculated pKa values showed that the solid protonation played a dominant role in the uptake of phosphate anions by the solid.     

A comparative study on textural characterization: cation-exchange and sorption properties of crystalline alpha-zirconium(IV), tin(IV), and titanium(IV) phosphates

Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous.     

腐殖酸对La~(3+),Nd~(3+)等重金属离子混合体系吸附的研究

对含有La~(3+),Nd~(3+)的重金属混合体系进行吸附选择性试验,筛选出腐殖酸浓度为1.2 g·L~(-1)时吸附La~(3+),Nd~(3+)的最佳条件(pH=5.4,温度313 K,振荡时间8 h,重金属离子初始浓度0.15 mmol·L~(-1)),得出此条件下吸附优先顺序为:La~(3+)>Pb~(2+)>Cu~(2+)>Nd~(3+)>Cd~(2+)>Zn~(2+)>Co~(2+)>Cr~(3+);HA的吸附总量在室温下拟合二级动力学方程的效果最好;Langmuir方程则能更好地描述HA对重金属离子的等温吸附过程,并且随着温度的升高,HA的最大吸附量逐渐增加;HA对La~(3+),Nd~(3+)等重金属离子的吸附优先顺序受到pH值、温度、振荡时间、重金属离子初始浓度和本身性质的综合影响,且重金属的地球化学性质是主导因素.     

Efficiency of Cd(II) removal from aqueous media using chemically modified polystyrene foam

The removal of Cd(II) using polystyrene foam chemically modified with 2,2′-bipyridine has been investigated. The modified polystyrene foam has been characterized by FT-IR spectroscopy, thermogravimetry, elemental analysis and scanning electron microscopy. The solid was employed as a Cd(II) adsorption from aqueous solutions at room temperature. The effects of several variables (pH, shaking speed, agitation time, metal concentration and presence of other ions in the medium) have been studied using batch technique. Flame atomic absorption spectrometry was used to determine the Cd(II) ion concentration in the filtrate after the adsorption process. Maximum sorption 90% was achieved at pH 7 after 30 min of shaking time. Sorbed metal ions have been desorbed with 5 ml of 2 M HNO₃ with the detection limit of 16.7 ng ml⁻¹. The Langmuir, Freundlich and D–R isotherm equation were used to describe partitioning behavior of the system at room temperature. Kinetic and thermodynamic behavior of modified polystyrene foam for Cd(II) ion removal was also studied. Br⁻, PO₄³⁻, Pb²⁺, Ni²⁺ and Cr(VI) suppress the sorption to some extent. The possible sorption mechanism of Cd(II) ions onto modified sorbent is also discussed. Method was utilized to remove Cd(II) ions from aqueous media.     

Adsorption of some bivalent heavy metal ions from aqueous solutions by manganese nodule leached residues

The leached residue, generated after selective extraction of Cu, Ni, and Co in sulfur dioxide-ammonia leaching of manganese nodules, was characterized and batch isothermal adsorption experiments were conducted at ambient temperature to evaluate the effectiveness of the water-washed leached residue for removal of different bivalent metal ions from aqueous synthetic solutions. The effects of pH, initial metal ion concentrations, amount of adsorbent, interfering ions, and heat treatment were also investigated. The uptake of metal ions increased with increasing pH. Under identical conditions the adsorption capacity increased in the order Cd(2+)相似文献   

Sorption of Th(IV) ions onto TiO2: Effects of contact time, ionic strength, thorium concentration and phosphate

Summary The sorption of Th(IV) onto TiO₂ was studied by the batch technique as a function of pH and ionic strength at moderate concentration (10^-4-10^-5 mol/l) and in the presence and absence of phosphate. It was found that the sorption rate of Th(IV) was relatively slow, the sorption percent was abruptly increased from pH 2 to 4, and the sorption was decreased with increasing ionic strength as a whole. In the concentration range of Th(IV) from trace concentration to 1.4 ^. 10^-4 mol/l and in the absence of phosphate, the sorption isotherms were roughly fitted the Freundlich equation at different ionic strengths and approximately constant pH. These sorption characteristics of Th(IV) onto TiO₂ were compared with those of uranyl on the same sorbent. In addition, the positive effect of phosphate on the sorption of Th(IV) onto TiO₂ was demonstrated obviously and can be attributed to strong surface binding of phosphate, and the subsequent formation of ternary surface complexes of Th(IV). The difference between the sorption characteristics of Th(IV) ions and uranyl ions onto TiO₂ is discussed.     

Metal-ion-coordinating properties of the dinucleotide 2'-deoxyguanylyl(5'-->3')-2'-deoxy-5'-guanylate (d(pGpG)3-): isomeric equilibria including macrochelated complexes relevant for nucleic acids

The interaction between divalent metal ions and nucleic acids is well known, yet knowledge about the strength of binding of labile metal ions at the various sites is very scarce. We have therefore studied the stabilities of complexes formed between the nucleic acid model d(pGpG) and the essential metal ions Mg2+ and Zn2+ as well as with the generally toxic ions Cd2+ and Pb2+ by potentiometric pH titrations; all four ions are of relevance in ribozyme chemistry. A comparison of the present results with earlier data obtained for M(pUpU)- complexes allows the conclusion that phosphate-bound Mg2+ and Cd2+ form macrochelates by interaction with N7, whereas the also phosphate-coordinated Pb2+ forms a 10-membered chelate with the neighboring phosphate diester bridge. Zn2+ forms both types of chelates with formation degrees of about 91% and 2.4% for Zn[d(pGpG)]cl/N7 and Zn[d(pGpG)]-cl/PO, respectively; the open form with Zn2+ bound only to the terminal phosphate group, Zn[d(pGpG)]-op, amounts to about 6.8 %. The various intramolecular equilibria have also been quantified for the other metal ions. Zn2+, Cu2+, and Cd2+ also form macrochelates in the monoprotonated M[H;d(pGpG)] species (the proton being at the terminal phosphate group), that is, the metal ion at N7 interacts to some extent with the P(O)2(OH)- group. Thus, this study demonstrates that the coordinating properties of the various metal ions toward a pGpG unit in a nucleic acid differ: Mg2+, Zn2+, and Cd2+ have a significant tendency to bridge the distance between N7 and the phosphate group of a (d)GMP unit, although to various extents, whereas Pb2+ (and possibly Ca2+) prefer a pure phosphate coordination.     

Cation exchange and sorption properties of crystalline alpha-titanium(IV) phosphate

The ion-exchange and sorption properties of alpha-titanium bis(monohydrogen orthophosphate) monohydrate of composition Ti(HPO(4))(2).H(2)O was studied in aqueous electrolyte solutions of KCl over the temperature range of 300-320 K, varying the pH and metal ion concentration in the solution. The data were explained on the basis of the law of chemical equilibrium and the metal ion sorption data were fitted to Langmuir parameters. Further, the extent of sorption was found to increase with increasing temperature and metal ion concentration in the selectivity order Fe(3+)>Cu(2+)>Co(2+)>Mn(2+)>Cr(3+)>Ni(2+). The values of Langmuir constants were used to calculate the various thermodynamic parameters, such as DeltaG(0), DeltaH(0), and DeltaS(0), during the sorption process.     

Sorption of thallium(III) ions from aqueous solutions using titanium dioxide nanoparticles

Titanium dioxide nanoparticles (NPs) were employed for the sorption of Tl(III) ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, Tl(III) concentration, temperature, and amount of sorbent. The sorption was found to be fast and to reach equilibrium within 2 min, to be less efficient at low pH values, and to increase with pH and temperature. The sorption fits the Langmuir equation and follows a pseudo second order model. The mean energy of the sorption is approximately 15 kJ mol^?1 as calculated from the Dubinin–Radushkevich isotherm. The thermodynamic parameters for the sorption were also determined, and the ΔH ⁰ and ΔG ⁰ values indicate endothermic behavior.     

Characterisation of human foetal liver Zn-metallothioneins using differential pulse polarography

A study on electrochemical characterisation of three isoforms of human foetal liver Zn-metallothioneins, labelled MT-0, MT-1 and MT-2, has been performed by using differential pulse polarography (DPP). Two different peaks, attributed to two different Zn complexes with metallothioneins, have been detected. The electrochemical behaviour is similar for the three studied isoforms. Studies on the addition of Cd(2+) and Zn(2+) as well as studies as a function of pH have been carried out. The association and dissociation equilibria of metal ions with MTs are reversible in the studied pH range. The behaviour of Zn complexes in human foetal liver Zn-metallothioneins is comparable to the Cd complexes obtained using other mammalian Cd, Zn-metallothioneins, particularly as a function of pH.     

Influence of Mg2+ and Cd2+ on the interaction between sparfloxacin and calf thymus DNA

Mg(2+) and Cd(2+) have different binding capacity to sparfloxacin, and have different combination modes with calf thymus DNA. Selecting these two different metal ions, the influence of them on the binding constants between SPFX and calf thymus DNA, as well as the related mechanism have been studied by using absorption and fluorescence spectroscopy. The result shows that Cd(2+) has weak binding capacity to SPFX in the SPFX-Cd(2+) binary system, but can decrease the binding between SPFX and DNA obviously in SPFX-DNA-Cd(2+) ternary system. Mg(2+) has strong binding capacity to SPFX. It can increase the binding between SPFX and DNA at concentrations <0.01 mM, and decrease the binding between them at concentrations >0.01 mM. Referring to the different modes of Mg(2+) and Cd(2+) binding to DNA, the mechanism of the influence of metal ions on the binding between SPFX and DNA has been proposed. SPFX can directly bind to DNA by chelating DNA base sites. If a metal ion at certain concentration mainly binds to DNA bases, it can decrease the binding constants between SPFX and DNA through competing with SPFX. While if a metal ion at certain concentration mainly binds to phosphate groups of DNA, it can increase the binding constants by building a bridge between SPFX and DNA. The influence direction of metal ions on the binding between quinolone and DNA relays on their binding ratio of affinity for bases to phosphate groups on DNA. Our result supports Palumbo's conclusion that the binding between SPFX and the phosphate groups is the precondition for the combination between SPFX and DNA, which is stabilized through stacking interactions between the condensed rings of SPFX and DNA bases.     

Ion exchange of some transition metal cations on hydrated titanium dioxide in aqueous ammonia solutions

The adsorption of transition metal cations on hydrated titanium dioxide in complexing ammonia and amine solutions has been studied as a function of ammonia (amine) concentration. The relationships between the distribution coefficients and ammonia concentration as well as the effects of various amines on sorption of transition metals indicate that a coordinate bond is formed between the metal ions and the hydroxy groups of the sorbent. The distribution coefficients of silver(I) and cobalt(III), which form strong ammonia complexes in aqueous solutions, decrease with increasing concentration of ammonia already at concentrations exceeding 10^–3. mol·dm^–3. Cations of zinc, manganese and mercury which form much weakerammonia complexes do not exhibit any effect of ammonia concentration in the whole range investigated. In the case of sorption of macroamounts of ammonia or amine complexes of silver, the molecular sieve effect plays an important role. The differences in the affinity of hydrated titanium dioxide for ammonia solvates of various transition metal ions can serve as a tool for effective separation of these ions in ammonia solutions.     

The Effect of pH and Temperature on the Sorption of Zinc(II), Cadmium(II), and Aluminum(III) onto New Metal-Ligand Complexes of Sporopollenin

Sorption of metal ions from aqueous solution onto metal-ligand complexes of sporopollenin derivatives has been measured as a function of pH at several temperatures between 20 and 50°C. Novel metal-ligand exchange resins possessing oxime and carboxylic acid sidearm functionality were prepared through the reaction of diaminosporopollenin with dichloro-antiglyoxime and bromoacetic acid. The pH dependencies and sorption isotherms of various metal ions such as Zn(II), Cd(II), and Al(III) on the resin were investigated from aqueous solution. The sorption behavior of these metal-ligand complexes of sporopollenin derivatives and the possibilities of selectively removing and recovering heavy metals are explained on the basis of their chemical nature and complex properties and the results are interpreted in terms of the variations of pH.     

Cation Exchange and Sorption Properties of TIN(IV) Phosphate

The ion exchange and sorption properties of crystalline Tin bis(monohydrogen orthophosphate) monohydrate of composition Sn(HPO(4))(2).H(2)O were studied in an aqueous solution of KCl over the temperature range 300-320 K, varying the pH and metal ion concentration in the solution. The data were explained on the basis of the law of chemical equilibrium. The metal ion sorption data were fitted to the Langmuir adsorption equation to evaluate the Langmuir parameters. The extent of adsorption was found to increase with an increase in temperature and metal ion concentration in the selectivity order Cu(2+)>Co(2+)>Ni(2+). The Langmuir parameters were used to calculate the thermodynamic functions like standard entropy, enthalpy, and free energy changes during the process of sorption. Copyright 2000 Academic Press.     

Influence of Cd2+, Hg2+ and Pb2+ on (+)-catechin binding to bovine serum albumin studied by fluorescence spectroscopic methods

The effect of heavy metal ions, Cd(2+), Hg(2+) and Pb(2+) on (+)-catechin binding to bovine serum albumin (BSA) has been investigated by spectroscopic methods. The results indicated that the presence of heavy metal ions significantly affected the binding modes and binding affinities of (+)-catechin to BSA, and the effects depend on the types of heavy metal ion. One binding mode was found for (+)-catechin with and without Cd(2+), while two binding modes - a weaker one at low concentration and a stronger one at high concentration were found for (+)-catechin in the presence of Hg(2+) and Pb(2+). The presence of Cd(2+) decreased the binding affinities of (+)-catechin for BSA by 20.5%. The presence of Hg(2+) and Pb(2+) decreased the binding affinity of (+)-catechin for BSA by 8.9% and 26.7% in lower concentration, respectively, and increased the binding affinity of (+)-catechin for BSA by 5.2% and 9.2% in higher concentration, respectively. The changed binding affinity and binding distance of (+)-catechin for BSA in the presence of Cd(2+), Hg(2+) and Pb(2+) were mainly because of the conformational change of BSA induced by heavy metal ions. However, the quenching mechanism for (+)-catechin to BSA was based on static quenching combined with non-radiative energy transfer irrespective of the absence or presence of heavy metal ions.     

Stabilities and isomeric equilibria in aqueous solution of monomeric metal ion complexes of adenosine 5'-diphosphate (ADP3-) in comparison with those of adenosine 5'-monophosphate (AMP2-)

Under experimental conditions in which the self-association of the adenine phosphates (AP), that is, of adenosine 5'-monophosphate (AMP(2-)) and adenosine 5'-diphosphate (ADP(3-)), is negligible, potentiometric pH titrations were carried out to determine the stabilities of the M(H;AP) and M(AP) complexes where M(2+)=Mg(2+), Ca(2+), Sr(2+), Ba(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), or Cd(2+) (25 degrees C; I=0.1 M, NaNO(3)). It is concluded that in the M(H;AMP)(+) species M(2+) is bound at the adenine moiety and in the M(H;ADP) complexes at the diphosphate unit; however, the proton resides in both types of monoprotonated complexes at the phosphate residue. The stabilities of nearly all the M(AMP) and M(ADP)(-) complexes are significantly larger than what is expected for a sole coordination of M(2+) to the phosphate residue. This increased complex stability is attributed, in agreement with previous (1)H NMR shift studies and further information existing in the literature, to the formation of macrochelates of the phosphate-coordinated metal ions with N7 of the adenine residues. On the basis of recent measurements with simple phosphate monoesters and phosphonate ligands (R-MP(2-)) as well as with diphosphate monoesters (R-DP(3-)), where R is a noncoordinating and noninhibiting residue, the increased stabilities of the M(AMP) and M(ADP)(-) complexes due to the M(2+)-N7 interaction could be evaluated and the extent of macrochelate formation calculated. The results show that the formation degrees of the macrochelates for the complexes of the alkaline earth ions are small (about 15 % at the most), whereas for the 3d metal ions as well as for Zn(2+) and Cd(2+) the formation degrees vary between about 15 % (Mn(2+)) and 75 % (Ni(2+)) with values of about 40 and 50 % for Zn(2+) and Cu(2+), respectively. It is interesting to note, taking earlier results for M(ATP)(2-) complexes also into account (ATP(4-)=adenosine 5'-triphosphate), that for a given metal ion in nearly all instances the formation degrees of the macrochelates are within the error limits the same for M(AMP), M(ADP)(-) and M(ATP)(2-) complexes; except for Co(2+) and Ni(2+) it holds M(AMP) > M(ADP)(-) approximately M(ATP)(2-). This result is astonishing if one considers that the absolute stability constants of these complexes, which are determined largely by the affinity of the phosphate residues, can differ by more than two orders of magnitude. The impact and conclusions of these observations for biological systems are shortly lined out.     

Effect of environmental conditions on 109Cd(II) sorption to MnO2

The sorption of Cd(II) from aqueous solution on MnO₂ was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on MnO₂ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin–Radushkevich models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (ΔG ⁰, ΔS ⁰, ΔH ⁰) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on MnO₂ was an spontaneous and endothermic process.     

Influence of Solvent Acidity on Equilibrium Sorption of Zn(II) and Cd(II) by Cellulose-based Polymers

The influence of the solvent acidity on the sorption capacity of cellulose ethers and esters for Zn(II) and Cd(II) ions was studied. The suggested scheme of pH dependence of the sorption equilibrium of Zn(II) and Cd(II) ions in anaqueous electrolyte solution-polymer heterogeneous system, takes into account the speciation of metal ions in the aqueous phase (cationic aqua complexes).