Metal Hydrolysis Research Articles

The effect of environment, oxidation and dissolved metal species on the chemistry of coal flotation

The wettability and hence the floatability of coal are influenced markedly by its oxidation as well as the presence of dissolved inorganics in the system. Oxidation results in the formation of oxygenated surface sites that reduce hydrophobicity. Hydrolyzable metal species, whether released from coal itself during processing or added in the process, can drastically affect the flotation process. These phenomena are reviewed and the mechanisms involved are discussed in this paper.

Contribution of membrane surface charge in the interaction of lead and tin derivatives with model lipid membrane

The objective of this study was to determine the interaction of modified bilayer lipid membranes (BLMs) with lead and tin organoderivatives. The relative depolarization, of the lipid membrane, caused by organo metals, was used to estimate their activity. Dodecyltrimethylammonium bromide (TMDA) and sodium dodecylsulfonate (AS-12) were used to modify BLMs. The trialkylderivatives of tin (IV) were found to be the most active towards the lipid membrane, whereas dialkyltin (IV) and trialkyllead (IV) derivatives were less active. Also, a correlation exists between depolarization activity and the lipophilicity of organo metal hydrolysis products. The surface charge of modified membranes had a secondary influence on depolarization efficiency of the tin and lead derivatives.

Sol-Gel as Reaction Matrix for Bacterial Enzymatic Activity

Sol-gel process is a rapid growing field in material chemistry. The sol-gel matrices (SGM) are basically porous wet-gels or xerogels obtained by the hydrolysis and condensation-polymerisation of metal and semimetal alkoxides, mainly SiO2 materials. The current study presents the uses of sol-gel glass matrix (SGM) that allow direct entrapment of biomolecules within and at surface, which can be utilized by microorganisms. This glass type is solid, transparent, porous and can be modulated to form a hydrophobic or hydrophilic surface. In view of all these beneficial characteristics of SGM, preliminary data is presented on biofilm formed on thin films of SGM doped with a fluorochrome (fluorescein diacetate). The esterase/lipase activity of E. coli CN13 and K. oxytoca spp. biofilm grown on top of SGM thin film, doped with fluorescein diacetate, was detected at the level of a single cell by epifluorescence microscopy. In view of these preliminary results, sol-gel glass has a considerable potential as a variable matrix for single bacteria and biofilm investigation.

Ruthenium(III)–aminopolycarboxylato complexes active for the reduction of the N–N bond of hydrazine and phenylhydrazine in aqueous acidic media

Interactions of hydrazines N2H4X+ (X = H or Ph) with tri-, tetra- and penta-chelated ruthenium(III)–aminopolycarboxylic acid complexes giving the respective monomeric hydrazinium (RuIII–N2H4X+) adducts have been investigated by potentiometry, spectrophotometry and voltammetry in aqueous acidic solution at 25 °C. The deprotonation and metal hydrolysis constants of the complexes and their N2H4X+ adducts in 0.1 M Na2SO4 solution were determined. At pH 2.8, the complexes exhibited a quasi-reversible one-electron reduction wave of RuIII → RuII in sampled dc in the potential range between −0.16 and −0.37 V vs. SCE, while their hydrazinium adducts obtained in situ by adding an excess of N2H4X+ showed an additional two-electron reduction wave assigned to RuIII–N2H4X+ → RuI–N2H4X+ in the potential range of −0.02 to −0.35 V vs. SCE. The species RuI–N2H4X+ on successive decomposition and hydrolysis give one mole of each of NH3, NH2X and ruthenium(III) species. Further, the RuIII–N2H4X+ complexes have been used as electro-catalysts for the reduction of N2H4X+ to NH3 and NH2X at a mercury pool cathode in acidic solutions of pH 1.9 and 2.8. The quantity of ammonia produced in all cases is linear with time. The E1/2 of RuIII–N2H4X+ → RuI–N2H4X+ and the turnover number are correlated with the sigma basicity (ΣpKa) of the aminopolycarboxylic acids and the results are discussed in terms of the hydrolytic tendency of the metal, the number of co-ordinating groups and the steric repulsion caused by the increase in size of the aminopolycarboxylic acid.

Surface Complexation Modeling of Copper Sorption by Hydrous Oxides of Iron and Aluminum

Surfacecomplexation models were used to simulate adsorption (ADS) and coprecipitation (CPT) of copper (Cu) by hydrous oxides of iron (HFO) and aluminum (HAO) over a range of pH and surface-loading conditions. The generalized two-layer model was satisfactory for two very different conditions: (1) low sorbate/sorbent ratios where metal–oxide interaction is adequately described as Cu2+ coordination to surface functional groups and (2) under HFO–CPT conditions which result in extremely high adsorption site density (0.425 mol of sites/mol of Fe). As the sorbate/sorbent ratio is progressively increased, the models must account for metal hydrolysis and surface precipitate formation, and Cu interaction with both hydrous oxides could be fitted over a wide range of surface loadings using a comprehensive surface precipitation model. Similar mass law constants for sorption reactions were used for generalized two-layer and surface precipitation modeling, ADS and CPT conditions, and pH-edge and isotherm data. Corroborating sorption and spectroscopic evidence, modeling indicated that Cu precipitated on HAO, unlike HFO, has a markedly lower Ksp than bulk precipitated Cu(OH)2(s). Results also suggest that enhanced Cu removal by CPT was not simply a manifestation of higher surface area.

Trivalent Ion Hydrolysis Reactions: A Linear Free-Energy Relationship Based on Density Functional Electronic Structure Calculations

Metal ion hydrolysis is fundamental in aqueous chemistry because of the influence of coordinating hydroxide ions on reaction rates; examples include enhanced labilization of coordinating water molecules in hydrolyzed complexes and stabilization of oxidized products in electron-transfer reactions involving hydrolyzed reductants. Moreover, the role of metal hydrolysis reactions in defining a baseline for establishing trends in metal-ligand binding has motivated efforts toward comprehensive integration of M{sup z+}{sub x}OH{sub y} stability constants.

Biosorption of Rare Earth Elements

By using X-ray microanalysis, the mechanism of sorption of rare earth elements (REE) and their localization in cells of Candida utilis were found to depend on the metal ion speciation in solution, the permeability of the cytoplasmic membrane (CPM), and elemental composition of cells. Sorption capacity of the yeast cells increased with the increase in the pH of solution, which is connected with the extent of metal hydrolysis. Cells with native permeability of CPM did not sorb either scandium at pH values below 4.5 or lanthanum and samarium at pH values below 5.0. Such cells accumulate rare earth elements on surface structures. Only the cells with impaired CPM could sorb REE from the acid solutions. In this case, REE were accumulated inside the cells due to the interaction with phosphorus-containing compounds; the amount of sorbed REE depended on the content of phosphorus in the yeast cells. The yeast cells were shown to have extremely high affinity to scandium which thus can be selectively sorbed from solutions containing other REE, iron, and aluminum.

Kinetics and equilibrium of the complexation of Al 3+ with poly(maleic, acrylic) acid

Kinetics and equilibrium of the complexation of Al3+ with a polycarboxylic acid (PCA, random copolymer of maleic and acrylic acid with a mean molecular weight of 92 kDa) are investigated by the stopped flow technique and potentiometric titration. The complexation proceeds according to the Eigen–Tamm mechanism, i.e. in first diffusion-controlled step an outer sphere complex is formed. The second rate determining step is the formation of the inner sphere complex, controlled by the exchange rate of hydration water. For this second step the rate constant is k1=3 s-1. It is in the order of magnitude of the water exchange at the Al3+ ion as expected for the Eigen–Tamm mechanism. The activation parameters are also determined. Parallel to this direct reaction path a base catalyzed path is found, typical for complexation reactions of hydrolyzable metal ions.

Effect of hydrolysed metal cations on the liquid–liquid extraction of silica fines with cetyltrimethylammonium chloride

Silica fines of <5 μm were liquid–liquid extracted from aqueous suspension containing cationic surfactant cetyltrimethylammonium chloride (CTAC) to the isooctane–water interface region. The silica depression on addition of hydrolysable metal cations Fe(III), Al(III) and La(III) was investigated to clarify the role of such cations in the hydrophile–lipophile transition of the silica fines together with CTAC. At an addition of only 5 μM CTAC, the silica fines were completely recovered in the dense emulsion phase from metal salt-free suspension in the entire pH range investigated. In contrast, addition of 1-mM total metal cations caused silica depression in a certain pH range, specific for the metal salt used. Speciation distribution diagrams for the respective metal–H 2O systems indicate that decreases in percentage recoveries of the silica in the lower pH range are in line with increases in concentrations of the metal hydroxo complexes. Furthermore, the silica depression disappears when the pH approaches the point-of-zero charge of the hydroxide precipitate. In these pH ranges, the neutral to negative metal precipitates are also extracted into the oil–water interface during the liquid–liquid extraction. It seems that the lipophilic-to-hydrophobic transition, that is, depression by metal-salt addition of silica fines in cationic liquid–liquid extraction is controlled by the presence of metal-hydroxide species and their charges, attributable to the hydroxide coating on the silica surface.

Use of Soil Amendments to Reduce Nitrogen, Phosphorus and Heavy Metal Availability

The primary objectives of this study were to determine (1) the exchange characteristics of various soil amendments using a range of salt solutions, (2) the effect of selected soil amendments on heavy metal (Cu2+, Pb2+, and Zn2+) availability, and (3) the effect of selected soil amendments on NH4 + and P availability. The CEC of zeolite and red mud obtained using solutions of 0.1 M BaCl2 and 0.1 M BaCl2/NH4Cl were significantly lower than values obtained using 1 M KCl and 1 M NH4Cl. The higher CEC obtained with monovalent cations indicated that larger divalent cations could not enter the mineralogical framework of zeolite and red mud, and, consequently, a number of exchange sites were only accessible to the smaller monovalent cations. These findings suggest that 1 M KCl and 1 M NH4NO3 should be used as the extracting solutions to obtain the best estimation of CEC and ECEC of red mud and zeolite. The ability of red mud, zeolite, and calcium phosphate (Ca-P), mixed at rates of 0%, 5%, 10%, and 20% (w/w), to sorb Cu2+, Pb2+, and Zn2+ generally followed the order: red mud>zeolite>>Ca-P, while the affinity sequence for these metals followed the order: Pb2+≥Cu2+>>Zn2+. The higher affinity of the sand/amendment mixtures for Pb2+ and Cu2+ relative to Zn2+ was attributed to metal hydrolysis and subsequent specific adsorption as Pb(OH)+ and Cu(OH)+. Zinc was considered to have been primarily sorbed as the divalent cation species. Rates of 5% (w/w) adequately reduced the availability of heavy metals to concentrations below environmental guidelines based on the Toxicity Characteristic Leaching Procedure. Red mud and zeolite added at a rate of 10% (w/w) to the A and B horizon of a sandy soil significantly increased their ability to remove NH4 + from solution, but had negligible effect on P sorption compared with unamended soils. Increased NH4 + removal was attributed to the associated increase in CEC and the greater selectivity of the exchange sites for this cation relative to resident exchangeable Ca2+ and Na+. The absence of P sorption by these two amendments was attributed to the high pH and predominantly negative surface charge of the red mud and the lack of sorption sites in zeolite. Gypsum, on the other hand, tended to depress NH4 + retention but markedly increased P sorption. The depressive effect on NH4 + was due to increased competition between NH4 + and Ca2 + for a limited number of exchange sites, while formation of calcium phosphates of low solubility was the possible mechanism for increased P sorption.

Investigation on coordination ability of N-chloro-acetylglycine towards Cu(II) in solid and solution state

The solution and solid state behavior of the binary system Cu(II)- N-chloroacetylglycine (Cl-acglyH) and the corresponding ternary systems with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (ophen) were investigated by means of pH-metric and spectrophotometric titrations. The X-ray crystal structure of the complex [Cu(ophen)(Cl-acgly) 2]·2H 2O (Cl-acgly = N-chloroacetylglycine monoanion) is also reported. The crystals of the compound C 20Cl 2CuN 4O 8H 22 are monoclinic, space group P2 1/ c, a = 17.574(3), b = 7.125(2), c = 25.113(6) Å, β = 130.04(2)°, Z = 4, R = 0.077, R w = 0.088. The structure consists of monomeric [Cu(ophen)(Clgly) 2] units and lattice water molecules. The Cu(II) atom is square planar coordinated by two carboxylic oxygens of two amino acid molecules and two nitrogen atoms of the ophen molecule. Two long contacts involve the uncoordinated carboxylic oxygens. Crystal packing is due to ring-stacking interaction involving ophen molecules and to a strong intramolecular hydrogen bond involving the chlorine atom and the amidic nitrogen of one ligand molecule. In solution the species [CuL 2] and [CuALOH] (A = bpy or ophen) prevail in the binary and ternary system, respectively, both arising from carboxylic-oxygen-metal coordination of the amino acid molecule. The coordination of the OH − group in the ternary species prevents metal hydrolysis up to pH 11. The possibility of forming hydrogen bond interactions involving the chlorine atom seems the to be determinant factor in stabilizing the ternary complexes.

Sources of strong primary acidity in the atmosphere

The fly ashes produced by the burning of heavy oil have been identified in this study as carriers of strong primary acidity in the atmosphere in the form of sulphuric acidity and hydrolyzable metal ions. This is an acidity which is strong from the moment of its emission (strong primary acidity, SPA) and different from common sources of weak acidity (SO 2 NO) which give rise to strong acidity only after some time in the atmosphere. The oil ash SPA is transmitted to water on impact resulting in highly acid pH values and high total acidity as well as significant concentrations of heavy metals. Here we present and discuss our results.

Effect of hydrolysed aluminum(III) and chromium(III) cations on the lipophilicity of talc

Abstract Liquid-liquid extraction and electrokinetic studies show that both the talc particles and the isooctane droplets are affected by the presence of hydrolysable metal species of Al(III) and Cr(III). The inherent lipophilicity of talc is unchanged by the hydroxo complexes of these metal species, while positive shifts in zeta potentials of talc and isooctane take place due partly to the strong adsorption of these hydroxo complexes. In the pH range where the hydroxide precipitates, the talc particles are rendered hydrophillic between the precipitation pH and the point-of-zero charge of the metal hydroxide. This hydrophile-lipophile transition of talc in the isooctane-water system relates to heterocoagulation among talc particles, isooctane droplets and hydroxide precipitates.

Testing the Role of Metal Hydrolysis in the Anomalous Electrodeposition of Ni‐Fe Alloys

With the objective of testing several models of the “anomalous codeposition” (ACD) encountered in the electrodeposition of nickel‐iron alloys, the effects of bath pH and complexing agents on the composition of deposits were examined. When the pH of the “base line” bath was increased from 3.0 to 5.0, the Ni/Fe mass ratio of the deposit increased (i.e., the deposition became less anomalous). The presence of tartrate ion in the bath produced a slight decrease in the Ni/Fe of the deposit. This complexing agent complexes ferric ion and thus prevents its precipitation but has little interaction with ferrous ion or nickel ion under the electrodeposition conditions examined. The addition of ethylenediamine to the bath produced a significant increase in the Ni/Fe mass ratio. This complexing agent does not interact significantly with ferric ion or ferrous ion under the test conditions. None of these observations are consistent with the Dahms and Croll model of ACD. The effects of pH and tartaric acid on the deposit composition are consistent with the predictions of the Grande and Talbot model and the Matlosz model. The effect of ethylenediamine is not consistent with the Grande and Talbot model, but may be interpreted within the framework of the Matlosz model and the Hessami and Tobias model.

Amide nitrogen co-ordination of CoIIand NiIIin ternary 2,2′-bipyridine-containing systems. A solution and solid-state study

The ternary systems 2,2′-bipyridine (bipy)–M–amino acid [M = CoII or NiII; amino acid (H2L)=N-p-tolyl-sulfonylglycine (tsgly), -β-alanine (ts-β-ala) or N-benzoylglycine (H2hip)] were investigated in aqueous solution by means of polarography, electronic spectroscopy and potentiometry, in order to identify the type, number and stability of complex species, as a function of pH and bipy : M : amino acid ratio. With tsgly the prevailing species are [MII(bipy)n(HL)]+ and [MII(bipy)nL](n= 1 or 2), with pKNH for the deprotonation of sulfonamide nitrogen 7.8(2) and 7.4(2), for CoII and NiII, respectively and the crystal and molecular structure of [Co(bipy)2(tsglyNO)]·2H2O (NO indicates binding as a N,O-chelating dianion) was determined. The CoII is six-co-ordinated by four nitrogen atoms of the bipy moieties, the deprotonated sulfonamide nitrogen and one carboxylic oxygen of the tsgly dianion. On standing in air, an alkaline solution of bipy–CoII–tsgly turned from orange to wine-red in a few days, indicating the oxidation of CoII to CoIII. With ts-β-ala and H2hip metal hydrolysis prevents the formation of deprotonated complexes.

The influence of hydrolysable metal cations on the electrokinetic behaviour of tin tailings slurry

The profound influence of the hydrolytic behaviour of ions of heavy metals such as Cu, Zn, Pb, Cd, Mn and Ni on the electrophoretic mobility of colloidal clay taken from slurries from ponds from former tin mines was studied. The strong adsorption of soluble hydrolysed species and insoluble metallic hydroxide on the clay surface leads to a reduction in the surface charge of the clay particles and eventually to charge reversal. The results show that the shape of the mobility-pH curves was completely different from those for simple cations. Generally, at concentrations greater than 10 −4 mol dm −3 and pH>6, the metal ions hydrolyse extensively to form positively charged mononuclear and polynuclear species which could become adsorbed and reverse the charge of the clay particles. At higher pH, a second reversal, back to negatively charged surface, occurred owing to the formation of insoluble metal hydroxide. At very low concentration of metal ions, two constant (negative) mobility regions were observed: one under acidic pH and the other under alkaline pH. The hydrolysis was influenced by the presence of particulates in the systems.

NADPH-cytochrome-P450 reductase promotes hydroxyl radical production by the iron complex of ADR-925, the hydrolysis product of ICRF-187 (dexrazoxane).

ICRF-187 (dexrazoxane) is currently in clinical trials as a cardioprotective agent for the prevention of doxorubicin-induced cardiotoxicity. ICRF-187 likely acts through its strongly metal ion-binding rings-opened hydrolysis product ADR-925 by removing iron from its complex with doxorubicin or by chelating free iron. The ability of NADPH-cytochrome-P450 reductase to promote hydroxyl radical formation by iron complexes of ADR-925 and EDTA was compared by EPR spin trapping. The iron-EDTA complex produced hydroxyl radicals at six times the rate that the iron-ADR-925 complex did. The aerobic oxidation of ferrous complexes of ADR-925, its tetraacid analog, EDTA and DTPA was followed spectrophotometrically. The iron(II)-ADR-925 complex was aerobically oxidized 700 times slower than was the EDTA complex. It is concluded that even though ADR-925 does not completely eliminate iron-based hydroxyl radical production, it likely protects by preventing site-specific hydroxyl radical damage by the iron-doxorubicin complex.

The surface chemistry of silicon nitride powder in the presence of dissolved ions

Colloidal processing of silicon nitride (Si3N4) powders depends largely on the control of reactions at the solid-solution interface. The role of dissolved ions in the surface chemistry of Si3N4 powders has been investigated, and the implications of these results for the effects of impurities, contaminants and additives in processing are discussed. The interaction of ions at the solid-solution interface was characterized by particle electrokinetic behaviour determined from electroacoustic measurements in moderately concentrated suspensions. Ions were classified according to chemical similarity and surface specificity. Specific adsorption was inferred from the movement of the isoelectric point relative to the endemic “native” value. Most simple univalent electrolytes behaved indifferently towards the Si3N4 surface, with the exception of fluoride which specifically adsorbed and may have formed a strong complex with surface silicon sites. The alkaline-earth cations exhibited a similar weak specificity. In the presence of hydrolysable transition metal cations, powder surface chemistry was controlled by the adsorption of hydroxy metal complexes and by the solubility of a surface-precipitated metal hydroxide phase. Oxo anions, such as sulphate and carbonate, adsorbed specifically on the Si3N4 surface, but the interactions were weaker than previously observed on metal oxide surfaces.

Alumina surface chemistry at 25, 40, and 60 °C

Potentiometric titrations and metal adsorption measurements on γ-Al 2O 3 at 25, 40, and 60°C indicate that alumina surface chemistry is temperature sensitive. The pH zpc of γ-Al 2O 3 decreases slightly, if at all, from pH 6.45 at 25°C to 6.32 at 60°C. Metal binding constants for Cd ++ and Pb ++, calculated with a constant capacitance model, increase up to 1.5 orders of magnitude between 25°C and 60°C. Enthalpies of unidentate Pb and Cd binding are 21.3 and 81.8 kj/mol, respectively; these are similar in sign and magnitude to the enthalpies of metal hydrolysis. Because temperature favors the latter, surface coordination is favored by increasing temperature (i.e. and increasing depth in the crust).

Intrinsic stoichiometric equilibrium constants for the binding of zinc(II) and copper(II) to the high affinity site of serum albumin.

Intrinsic stoichiometric equilibrium constants were determined for zinc(II) and copper(II) binding to bovine and human serum albumin. Data were obtained from equilibrium dialysis experiments. Metals were presented to apoprotein as metal chelates in order to avoid metal hydrolysis and to minimize nonspecific metal-protein interactions. Scatchard analysis of the binding data indicated that the high affinity class for both zinc and copper was comprised of one site. Results of binding experiments done at several pH values suggested that while both histidyl and carboxyl groups appear to be involved in copper binding, histidyl residues alone were sufficient for zinc binding. These amino acid residues were used in combination to model several binding sites used in the formulation of equilibria expressions from which stoichiometric constants were calculated. The log10K for bovine serum albumin were calculated to be 7.28 for Zn(II) and 11.12 for Cu(II). Those for human serum albumin were determined to be 7.53 and 11.18 for Zn(II) and Cu(II), respectively. These constants were used in equilibria to simulate speciation of metal-albumin and metal-chelator and to illustrate relative binding affinities. This comparison of binding strengths was possible only through the calculation of an intrinsic stoichiometric binding constant.