Electrokinetic properties of unexpanded and expanded perlite samples in suspensions of various electrolytes and surfactants were studied as a function of ionic strength, pH and, type and concentration of electrolyte and surfactant. Electrokinetic properties of a series of unexpanded and expanded perlite samples have been investigated using the microelectrophoresis technique. From the experimental results, it was found that (i) zeta potential increased with increasing ionic strength for both perlite samples, (ii) zeta potential values of unexpanded and expanded perlite suspensions in CaCl2 solutions in the studied pH range were higher than that in NaCl solutions and, perlite samples had no isoelectrical point, (iii) Ca2+ ions were potential determining ions for both perlite samples and adsorbed specifically in Stern layer, (iv) Na, Cl−, SO42− and PO43− ions compressed the double layer as indifferent electrolytes, (v) the sign of the surface charge of both perlite samples increased with increasing N-cetyl-N,N,N-trimethylammoniumbromide (CTAB) and N-cetylpyridiniumchloride (CPC) concentration, and (vi) when zeta potential values of N-cetyl-N,N,N-trimethylammoniumbromide (CTAB) and N-cetylpyridiniumchloride (CPC) were positive in all studied pH range, those of other surfactants sodiumdodecylsulfate (SDS) and benzyltriethylammonium chloride (BTEAC) were negative.

The dissolution rates of ulexite in oxalic acid solutions were investigated statistically and graphically using homogeneous and heterogeneous reaction models at different stirring speeds, particle sizes, acid concentrations, and calcination and solution temperatures. It was found that the dissolution rate increased with increasing acid concentration and temperature and decreasing particle size, but was not affected by the stirring speed. The sample preheated at 140 degreesC had the highest dissolution rate. The activation energy for the process, E-d, was calculated to be 7.20 kcal mol(-1), which implies that the reaction rate was controlled by product-layer diffusion. The dissolution process correlated reasonably well with the product-layer-diffusion-controlled model.

Perlite samples activated by H2SO4 solutions were utilized as adsorbents for the removal of Cu(II) ions from solutions at different pHs, ionic strengths, and temperatures. It has been found that the amount of Cu(II) adsorbed increased with increased pH, whereas it decreased as the ionic strength, temperature, and acid activation increased. Adsorption isotherms correlated reasonably well with the Langmuir adsorption isotherm and Langmuir parameters of adsorption isotherm (Qm and K) were found with the aid of the linearized Langmuir isotherm. The entalphy change for Cu2+ adsorption has been estimated as −5.14±1 and 4.38±1 kJ/mol for unexpanded and expanded perlite samples, respectively. Proton stoichiometry (x) was calculated from Kurbatov plot using the amount of Cu(II) adsorbed at different pH. The dimensionless separation factor (R) has shown that perlite can be used for removal of Cu(II) ion from aqueous solutions, but unexpanded perlite is more effective.

The surface charge behaviour of unexpanded and expanded perlite samples in KNO3and NaCl solutions were investigated as a function of pH and ionic strength. The solutions of KNO3and NaCl ranging from 10−3to 1.0Mwere used. The potentiometric titration method was used to determine the surface charge of perlite samples. It was confirmed that the perlite samples had no the point of zero charge and was negatively charged in the pH range of 3–10. The double extrapolation method was used for determining the intrinsic equilibrium constants for simple ionization and complex ionization reactions. The values obtained arepKinta2

The present work describes a selective and rapid method for the determination of molybdenum with Alizarin Red S (ARS) in the presence of a water soluble polymer, poly(sulfonylpiperidinylmethylene hydroxide) (PSPMH). The ARS modified by PSPMH reacts with molybdenum(VI) in the solutions of pH 3.4–4.0 to produce a red complex. The composition of the complex is 1:4:1 mol ratio of Mo(VI): ARS:PSPMH. The complex obeys Beer's law from 0.05 to 5.50 μg ml−1 with an optimum range. The molar absorptivity is 2.1×104 l mol−1 cm−1 at 500 nm. The interference effects of the foreign cations have been examined and it has been determined that only Cu(II), Al(III) and Fe(III) have to be masked by EDTA and tungsten can be tolerated till 4-fold of molybdenum in case of masking by citrate. The method has been applied to the determination of geological samples without solvent extraction or separation steps.

The removal of copper ions from aqueous solutions by kaolinite was investigated by using a batch-type method. Effects of factors such as pH, ionic strength, temperature, acid-activation and calcination on copper adsorption were investigated. The uptake of copper was determined from changes in concentration as measured by atomic absorption spectrometry. The extent of copper adsorption increased with increasing pH and temperature and with decreasing ionic strength, acid-activation and calcination temperature. The Langmuir and Freundlich adsorption models were used to determine the isotherm parameters associated with the adsorption process. The results provide support for the adsorption of copper ions onto kaolinite. Thermodynamic parameters indicated the endothermic nature of copper adsorption on kaolinite. The experimental results were applied a batch design. As a result, the kaolinite may be used for removal of copper ions from aqueous solutions. (c) 2007 Elsevier B.V. All rights reserved.

Peroxidase (EC 1.11.1.7; donor: hydrogen-peroxide oxidoreductase) catalyses the oxidation of various electron donor substrates (e.g. phenols, aromatic amines). In this study, the peroxidase was extracted from Thymbra spicata L. var. spicata and, then partially purified with (NH4)(2)SO4 precipitation and dialysis. The substrate specificity of peroxidase was investigated using 2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS), o-dianisidine, o-phenylenediamine, catechol and guaiacol as substrates. Furthermore, the effects of buffer concentration, pH, temperature and thermal inactivation on enzyme activity were also studied. The results obtained have shown that (i) the best substrate is o-dianisidine, followed by ABTS, catechol, guaiacol and o-phenylenediamine, respectively; (ii) the best buffer concentration is 40 mM for o-dianisidine and catechol, 10 mM for ABTS and guaiacol, and 100 mM for o-phenylenediamine; (iii) optimum pH is 2.5 for ABTS and o-phenylenediamine, 6.0 for o-dianisidine, and 7.0 for catechol and guaiacol; (iv) optimum temperature is 20 degrees C for catechol, 40 degrees C for ABTS, guaiacol and o-dianisidine, and 50 degrees C for o-phenylenediamine; and (v) the enzyme activity in the thermal inactivation experiments was enhanced with increase in temperature with o-dianisidine as a substrate while its activity decreased with o-phenylenediamine.

Co(II), Ni(II) and Cu(II) nitrate complexes with btmpp, namely ([Co(btmpp)(H(2)O)(2)(NO(3))]NO(3) (1), [Ni(btmpp)(H(2)O)(NO(3))]NO(3) (2) and [Cu(btmpp)(MeOH)(NO(3))]NO(3) (3), where btmpp = 2,6-bis(3,4,5-trimethyl-N-pyrazolyl)pyridine), have been synthesized and characterized by physicochemical and spectroscopic methods. The crystal structure of complex 1 has been determined by single crystal diffraction at 100K. In all the complexes, btmpp is coordinated in a tridentate mode through its nitrogen atoms. One of the nitrates in complex 1 is terminally bonded to the metal center through the oxygen atom, whereas the other one is out of the coordination sphere. The Co(II) atom in complex 1 is hexa-coordinated with a CoN(3)O(3) distorted octahedral environment. Decomposition of three complexes was analyzed thermogravimetrically. All three complexes decompose similar to explosive material.

Total phosphorus in five soils with different compositions which were obtained from different places were extracted by using Na-2CO-3 fusion, HClO-4 digestion, HClO-4 + HNO-3 digestion, HF + HClO-4 digestion or NaOBr oxidation methods. In order to test the suitability of the HF + HClO-4 digestion the results obtained by this method were compared with the others above, especially the Na-2CO-3 fusion which is accepted as a standard method. The phosphorus amount found with the HF + HClO-4 digestion method were almost the same as the phosphorus amount by the Na-2CO-3 fusion method, while the superiority in extracting phosphorus when compared to other methods were obvious. The methods used in the study were evaluated according to the recovery of total phosphorus, ease of application and rapidity with which they were performed. Orthophosphate in the soil extracts was determined by the molybdenum blue colour method. The relationships between methods are examined statistically.

Surface modification of clay minerals has become increasingly important for improving the practical applications of clays such as fillers and adsorbents. An investigation was carried out on the surface modification of sepiolite with aminopropylsilyl groups in 3-aminopropyltriethoxysilane (3-APT). The zeta potential of the modified sepiolite suspensions was measured as a function of initial electrolyte concentration and equilibrium pH using a Zeta Meter 3.0 for modified sepiolite. The utility of the 3-APT-modified sepiolite was investigated as an adsorbent for removal of various heavy metal ions such as Fe, Mn, Co, Zn, Cu, Cd and Ni from aqueous solutions. The effects of various factors on the adsorption, such as pH, ionic strength and temperature of the solution were studied. The results showed that the amount adsorbed increases with solution pH in the pH range of 1.5 and 7.0; indicated that the modified sepiolite adsorbed Fe and Mn ions more than other metal ions such as Co, Zn, Cu, Cd and Ni. It was found that the temperature had an important effect on metal ion adsorption by the modified sepiolite. The adsorption isotherm has been determined and data have been analyzed according to the Langmuir and Freundlich models. (C) 2007 Elsevier B.V. All rights reserved.