Formation Of Hydroxo Complexes Research Articles

Thorium Removal, Recovery and Recycling: A Membrane Challenge for Urban Mining.

Although only a slightly radioactive element, thorium is considered extremely toxic because its various species, which reach the environment, can constitute an important problem for the health of the population. The present paper aims to expand the possibilities of using membrane processes in the removal, recovery and recycling of thorium from industrial residues reaching municipal waste-processing platforms. The paper includes a short introduction on the interest shown in this element, a weak radioactive metal, followed by highlighting some common (domestic) uses. In a distinct but concise section, the bio-medical impact of thorium is presented. The classic technologies for obtaining thorium are concentrated in a single schema, and the speciation of thorium is presented with an emphasis on the formation of hydroxo-complexes and complexes with common organic reagents. The determination of thorium is highlighted on the basis of its radioactivity, but especially through methods that call for extraction followed by an established electrochemical, spectral or chromatographic method. Membrane processes are presented based on the electrochemical potential difference, including barro-membrane processes, electrodialysis, liquid membranes and hybrid processes. A separate sub-chapter is devoted to proposals and recommendations for the use of membranes in order to achieve some progress in urban mining for the valorization of thorium.

Water reclamation from anodizing wastewaters by removing reactive silica with adsorption and precipitation methods

Water stress is a current environmental menace mainly driven by over exploitation of aquifers, which is triggering poor water quality with high concentration of minerals in extracted groundwater. Particularly, silica is widespread in natural water supplies due to weathering processes of silicates occurring in contact with water, light, air, and other factors. However, due to groundwater over extraction the concentration of silica has increased during the last years in aquifer reservoirs from Aguascalientes State (México). In this context, it is very important to note that the removal of silica compounds from water is challenging and different methods can be used to avoid embedding problems in different industries. In the present work, the removal of reactive silica from synthetic solutions as well as from real wastewaters from an industrial anodizing process was studied using adsorption and chemical precipitation methods. Twelve commercial materials of different nature were used for adsorption tests, while seven precipitant agents were applied in the precipitation experiments. Adsorption tests were performed in batch systems with constant stirring at 30 °C and at different pH values (7 and 9). Precipitation experiments were carried out in batch systems and the best conditions for silica removal were found using an L9 orthogonal array of the Taguchi method employing molar ratio, pH of wastewater, stirring time and temperature as experimental factors.Adsorption results showed that Ferrolox (Iron (III) hydroxide-base adsorbent) was the most efficient sorbent for reactive silica removal from synthetic solutions and the anodizing wastewater. Also, the reactive silica adsorption was higher at pH 9 as compared to that measured at pH 7 and the adsorbed quantity at pH 9 was 16.22 and 11.25 mg/g for the synthetic solution and anodizing wastewater, respectively. According to molecular simulation, the main interaction between Ferrolox and silica species was related to the formation of hydroxo-complexes and to the interaction of Fe with oxygen of silica species. Additionally, magnesium chloride was the best precipitating reagent for reactive silica achieving up to 87% removal. According to ANOVA analysis of Taguchi method, pH was the most influential factor during the precipitation of reactive silica with a variance value of 81.42, while values lower than 3 were obtained for the rest of parameters. Overall, the present work is reporting for the first time the removal of reactive silica from anodizing wastewaters with promising results that can be implemented at full scale for water reclamation, which may significantly contribute to manage water reservoir in the region sustainably.

Influence of technogenic loading of pyrogenic origin on the geochemical migration of heavy metals

The study of geochemical aspects of the transformation of migration properties of heavy metals under the influence of anthropogenic loading of pyrogenic origin has been given insufficient attention. We studied the concentration of heavy metals in soils by atomic absorption analysis. The results indicate the transformation of their migration properties. The diversity and versatility of behaviour of chemical elements in environmental components after fire was noted. In different ecological conditions, it is possible to observe a wide range of quantitative values of geochemical migration or accumulation of any particular chemical element. The analytical results show that the contents of migrant elements, pH values, areas of disasters which are approximately in the same conditions, but passed by the grass or upper fire differ quite tangibly. Heavy metals that hit the environment can form difficult soluble hydroxides. In addition, in the soil solution, there is a probability of the formation of hydroxocomplexes with different amounts of hydroxide ions by metals. The range of precipitation of hydroxides and the region of predominance of soluble hydroxocomplexes have been studied by constructing concentration-logarithmicdiagrams. On the basis of the calculations it can be argued that the influence of technogenic loading of pyrogenic origin influences the geochemical migration of heavy metals . Compounds Fe3+ at the pH = 4.5-14, Cu2+ at pH = 7-14, Cr2+ at pH = 7-9, Zn2+ at pH= 8-11, Ni2+ at pH = 8-14 have the lowest migration potential. Compounds Pb2+ at pH = 9-12, Fe2+ - pH = 9.5-14 have the lowest migration potential also. In a more acidic environment, soluble substances are formed, but at a pH increase of only 0.5-1, they can decrease their mobility by an order of magnitude which contributes to their concentration in the soils after the fire. In a neutral soil reaction, most of the heavy metals (Al, Cr, Zn, Cu, Fe (II), Ni) are in a slightly soluble form (in the form of hydroxides), with insignificant, migration capacity which leads to the accumulation of these chemical elements in the soil. It is necessary to allocate heavy metals moving in a neutral environment (Fe (II), Cd, Co, Mg, Mn) into a separate group. Any increase in pH values contributes to their fixation. The obtained calculations can be used to predict the geochemical migration of heavy metals in soils which result from anthropogenic disasters of a pyrogenic origin.

Pyrogenic Influence n Geochemistry Migration Ability of Heavy Metal

Purpose. Investigation of dynamics of geochemical migration ability of heavy metals as a result of the effect of man-made loading of pyrogenic origin. Methods. Analytical: atomic absorption analysis, pH-metric; the range of precipitation of hydroxides and the region of predominance of soluble hydroxocomplexes have been studied by constructing concentration-logarithmic diagrams (CRLs). Results. The results indicate the transformation of their migration properties. The diversity and versatility of behavior of chemical elements in environmental components after the fire was noted. In different ecological conditions, it is possible to observe a wide range of quantitative values of geochemical migration or accumulation of any particular chemical element. Analytical results show that the contents of migrant elements, pH values, areas of incidents, which are approximately in the same conditions, but passed by the grass or upper fire differ quite tangibly. Heavy metals that hit the environment can form difficult soluble hydroxides. In addition, in the soil solution, there is a probability of the formation of hydroxocomplexes with different amounts of hydroxide ions by metals. The range of precipitation of hydroxides and the region of predominance of soluble hydroxocomplexes have been studied by constructing concentration-logarithmic diagrams. On the basis of the calculations it can be argued that the influence of the technogenic loading of pyrogenic origin on the geochemical migration of heavy metals takes place. Compounds Fe3+ at the pH = 4.5-14, Cu2+ at pH = 7-14, Cr2+ at pH = 7-9, Zn2+ at pH= 8-11, Ni2+ at pH = 8-14 have the lowest migration potential. Compounds Pb2+ at pH = 9-12, Fe2+ - pH = 9.5-14 have the lowest migration potential also. In a more acidic _____________________________________________________ © Буц Ю. В., Крайнюк О. В., Барбашин В. В., Кобзін В. Г. , 2018 environment, soluble substances are formed, but at a pH increase of only 0,5-1, they can decrease their mobility by an order of magnitude, which contributes to their concentration in the soils after the fire. In a neutral soil reaction, most of the heavy metals (Al, Cr, Zn, Cu, Fe (II), Ni) are in a slightly soluble form (in the form of hydroxides), with their migration capacity insignificant, which leads to the accumulation of these chemical elements in the soil . In a separate group it is necessary to allocate heavy metals moving in a neutral environment (Fe (II), Cd, Co, Mg, Mn). Any increase in pH values contributes to their fixation. Conclusions. The obtained calculations can be used to predict the geochemical migration of heavy metals in soils after the man-made consequences of emergencies of pyrogenic origin.

Thermodynamics of complexation in an aqueous solution of Tb(III) nitrate at 298 K

The pH of the formation of hydroxo complexes and hydrates in an aqueous solution of terbium Tb(III) is determined using combined means of potentiometric and conductometric titration. The stability constants of the hydroxo complexes, the products of hydroxide solubility, and the Gibbs energy of terbium hydroxo complex formation are calculated.

Thermodynamics of the dissolution of amorphous and polymorphic TiO2 modifications in acid and alkaline media

The effect the pH of an aqueous medium has on the molar solubility of polymorphic TiO2 modifications at 25°C is calculated and experimentally tested thermodynamically with allowance for the formation of hydroxo complexes. It is found that molecular–ionic solubility depends substantially on TiO2 structure and dispersity, increasing by three orders of magnitude upon moving from a stable crystalline to an amorphous modification.

Palladium and silver extraction with thiacalix[4]arenes and their acyclic analogs from carbonate and ammonia-carbonate solutions

A quantitative comparison of palladium and silver extraction with p-tert-butylthiacalix[4]arene (TCA) from nitric acid, carbonate, ammonia-carbonate, and ammonia solutions was carried out. It was shown that TCA under optimal conditions can be used for concurrent extraction of palladium and silver from carbonate systems of CARBEX process, selective recovery of palladium from nitric acid solutions, and selective silver extraction from ammonia-carbonate solutions. Metal distribution ratios and effective extraction constants decrease when the complex-forming ability of aqueous phase rises (Na2CO3 > NH4HCO3). The ammonia complexation of Ag+ is determining factor for silver, solution pH plays a certain role for palladium due to formation of hydroxo complexes.

Experimental and quantum-chemical studies of anabasine complexes with copper(II) and zinc(II) ions

Anabasine copper(II) and zinc(II) complexes have been studied using experimental methods and quantum-chemical studies. Preferred coordination centers and possible structures of the complexes have been determined. It has been revealed, that the main coordination center for anabasine complexes with both Cu(II) and Zn(II) ions is the piperidine nitrogen atom, while in zinc complexes also the nitrogen atom from the pyridine residue of anabasine is engaged to some small degree. In both systems investigated preferable formation of hydroxo-complexes was observed.

An experimental study of hydroxo complex formation in basic and near-neutral solutions of rare-earth elements and yttrium at 25 ºC

We have studied the hydrolytic behavior of Y3+ and trivalent ions of rare earth elements in aqueous solutions at 25ºC. The stepwise stability constants of hydroxide complexes were measured by spectrophotometry, using m-cresol purple and 1-(2-pyridylazo)-2-naphthol as pH indicators at an ionic strength no more than 0.0005. The results showed that at pH ranging between 6.0 and 11.0 in freshly prepared solutions of REE trichlorides, lanthanides are presented as Ln3+, Ln(OH)2+, Ln(OH)2, and Ln(OH)3. The plots of the formation constants of +0 monohydroxo complexes of 4f n ions M3+ versus atomic number Z deviate from smooth ones and consist of four convex curves. This phenomenon is also observed in normalized spectra of REE concentrations in natural objects and is known as the tetrad effect. The obtained data give an insight into the relationship between REE complex formation and REE fractionation in geochemical processes and can be used for physicochemical modeling of geochemical systems.

Geochemical Association of Ni 2+ , Zn 2+ , Pb 2+ , Ag + , Cu 2+ , and Co 2+ Ions in Natural Pyrite

The natures of competitive adsorption of six metal ions on the natural pyrite surface have been studied with an objective to provide strong foundations towards mode of association/occurrence of trace elements on pyritic surface. Some parameters, for instance, adsorption edge, mechanism, correlation coefficient, monolayer coverage, pH, and thermodynamic parameters, have been considered here. The significant results are the order of increasing trend of adsorption edges which has been found to be Pb2+ < Cu2+ < Ni2+ < Zn2+ < Co2+ < Ag+. Nonuniformity in variation of adsorption edge of a particular metal ion in presence of a second metal ion in solution is evident from the study. However, in case of Ag2+ and Co2+ ions two adsorption edges are observed. These variations have been explained based on the formation of hydroxo complexes which are pH dependent. The competitive monolayer coverage of each metal ion as a function of pH has shown variation in the extent of adsorption. Computed higher correlation coefficient in a binary system indicates retardation in adsorption of metal ion in presence of a second metal ion. Further the adsorption of metal ions on pyrite surface showed exothermic processes due to the spontaneous nature at low temperature. Our study has strongly revealed promising adsorbent characteristics of natural pyrite with considerable geochemical and environmental implications.

Thermodynamics of formation of lanthanide hydroxo complexes in aqueous solutions

Gibbs energies of formation have been determined by conductometric titration for hydroxo complexes of cerium, samarium, europium, erbium, ytterbium, and yttrium. All these elements form monohydroxo complexes; yttrium, erbium, and terbium also form dihydroxo complexes. The Gibbs energies of formation of lanthanide hydroxo complexes from ions have virtually equal values of −47.3 ± 0.6 kJ/mol monohydroxo complexes and −44.5 ± 0.5 kJ/mol for dihydroxo complexes, respectively. These values were used to estimate the Gibbs energies of formation of hydroxo complexes for the entire lanthanide series.

Thermodynamic characterization of the amphoterism of oxides M2O3 (M = As, Sb, Bi) and Their hydrates in aqueous media

Thermodynamic method was used to calculate, taking into account the formation of hydroxo complexes, the effect of the pH value on the molar solubility of M2O3 solid oxides and their hydrates at 25°C and the constants of acid-base equilibria in aqueous media for crystalline oxides and dissolved hydroxides M(OH)3, where M = As, Sb, Bi.

Mercury recovery from aqueous solutions by polymer-enhanced ultrafiltration using a sulfate derivative of chitosan

The sulfatation of chitosan, by reaction with chlorosulfonic acid under controlled conditions, allowed increasing the pH range of chitosan solubility. The biopolymer was characterized using FTIR and <TEX>$^{13}C$</TEX>-NMR spectroscopy, elemental analysis and titration analysis and it was tested for mercury recovery by polymer enhanced ultrafiltration (PEUF). In slightly alkaline conditions (i.e., pH 8) mercury recovery was possible and at saturation of the polymer the molar ratio <TEX>$-NH_2$</TEX>/Hg(II) tended to 2.6. Polymer recycling was possible changing the pH to 2 and the polymer was reused for 3 cycles maintaining high metal recovery. The presence of chloride ions influences metal speciation and affinity for the polymer and "playing" with metal speciation allowed using the PEUF process for mercury separation from cadmium; at pH 11 the formation of hydroxo-complexes of Hg(II) limits it retention. Cake formation reveals the predominant controlling step for permeation flux.

Synthesis of hybrid nanographite particles using fluidized bed system

Nanographite coated with ferromagnetic substances such as iron or iron oxide is a potential material for microwave absorption because of its favorable structural, magnetic, and electrical characteristics. In this paper, deposition on surfaces of acid functionalized and microwave-exfoliated nanographite particles with the use of fluidized bed system is reported. Acid functionalization improves iron adhesion and exfoliation reduces the flake thickness. The parameters influencing the deposition process are considered. It is demonstrated that Faraday’s laws of electrolysis can be used for these systems if the charge transfer from solid cathode to bed particles is uniform. This requirement is satisfied only above some critical values of suspension density, electrolyte concentration, and stirring rate. The optimized values of current density are required for each specific system, as low current density leads to non-uniform deposition with local nucleation, when high a current density induces too rapid nucleation and promotes iron hydroxo complex formation. Deposition time also should be optimized for any specific system, as the expected amount of deposit cannot be formed longer because of side reactions.

Thermodynamic characterization of the amphoterism of hydroxides and oxides of scandium subgroup elements in aqueous media

Effect of the pH value on the molar solubility of solid hydroxides M(OH)3 and oxides M2O3 at 25°C and the constants of acid-base equilibria in aqueous media for crystalline hydroxides and oxides and dissolved hydroxides M(OH)3 (M = Sc, Y, La) were calculated using the thermodynamic method, with the formation of hydroxo complexes taken into account.

Ternary complex formation of Eu(III) with o-phthalate in aqueous solutions

Ternary hydroxo complex formation of Eu(III) with o-phthalate was investigated by potentiometry and fluorescence spectrophotometry. Curves of the equilibrium pH versus the amount of NaOH added showed that the pH value starting to form a Eu(III) precipitate was decreased due to the formation of a ternary hydroxo complex, EuOHL(s) (L = phthalate). The formation of EuOHL(s) was qualitatively confirmed by the enhancement of the fluorescence intensity of Eu(III) in the precipitate with the light absorbed by phthalate, and was quantitatively confirmed by the measurement of the amounts of Eu(III), OH − and phthalate included in the precipitate. The solubility product of EuOHL(s) was determined as p K sp 0 = 15.6 ± 0.4 . Characteristic features in the fluorescence spectra and the solubility product of the Eu(III)–phthalate complex were compared with those of the Eu(III)–PDA (PDA = pyridine-2,6-dicarboxylate) complex. The fluorescence intensity of the EuL + complex of L = PDA was about 11 times stronger than that of L = phthalate. The origin of the difference in the fluorescence intensity is discussed based on the intramolecular energy transfer effect from the lowest triplet energy level of the ligand to the resonance energy level of Eu(III).

The thermodynamic properties of hydroxo compounds and the mechanism of ion flotation for cerium, europium, and yttrium

The pH values of formation of hydroxo complexes and hydrates in solutions of cerium(III), europium(III), and yttrium salts were determined by conductometric titration. The instability constants of hydroxo complexes, solubility products of hydroxides, and Gibbs energies of formation of the compounds specified were calculated. Conclusions about the mechanism of extraction and ion flotation of these metal cations from aqueous solutions were drawn.

Thermodynamic characterization of the amphotericity of oxides and hydroxides of group-IIIA elements in aqueous media

Dependences of the molar solubility of M2O3 solid oxides on the pH of aqueous media at 25°C and also the constants of acid-base equilibria in aqueous media for stable crystalline M2O3 oxides and for crystalline and dissolved M(OH)3 hydroxides (M = In, Al, Ga, In, and Tl) were calculated by the thermodynamic method with account of the formation of hydroxo complexes.

Aqueous Uranium(VI) Hydrolysis Species Characterized by Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy

The speciation of uranium(VI) in micromolar aqueous solutions at ambient atmosphere was studied by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and by speciation modeling applying the updated NEA thermodynamic database. It can be shown that reliable infrared spectra of micromolar U(VI) solutions are obtained abolishing the restrictions of previous spectroscopic investigations to millimolar concentrations and, consequently, to the acidic pH range. A significant change of the U(VI) speciation can be derived from the spectral alterations of the absorption band representing the antisymmetric stretching mode (nu3) of the UO2(2+) ion observed upon lowering the U(VI) concentration from the milli- to the micromolar range at a constant pH 4 value. The acquisition of spectra of diluted U(VI) solutions allows the increase of the pH up to 8.5 without the risk of formation of colloidal or solid phases. The infrared spectra are compared to the results of the computed speciation patterns. Although a complete interpretation of the spectra can not be given at this state of knowledge, the spectral data strongly suggest the presence of monomeric U(VI) hydroxo species already showing up at a pH value > or = 2.5 and dominating the speciation at pH 3. This is in contradiction to the predicted speciation where the fully hydrated UO2(2+) is expected to represent the main species at pH values below 4. At ambient pH, a more complex speciation is suggested compared to the results of the computational modeling technique. The predicted dominance of the UO2(CO3)3(4-) complex at pH > or = 8 was not confirmed by the infrared data. However, the infrared spectra indicate the formation of hydroxo complexes obviously containing carbonate ligands.

Thermodynamic calculation of the solubility of solid hydroxides of group IIIA elements in water and aqueous media

The effect of pH on the molar solubility of amorphous and crystalline hydroxides M(OH)3 and metahydroxides MO(OH), where M is B, Al, Ga, In, or Tl, in aqueous alkaline and acidic media at 25°C was calculated thermodynamically taking into account the formation of hydroxo complexes.