Extraction studies of uranium(VI) and thorium(IV) with tributylphosphine oxide

Clay minerals occur widely in nature and play a very important role in agriculture, mineral recovery and chemical manufacturing. Among the many properties which affect clay behaviour, water binding and ion exchanging appear to be the most important. The study of the cation exchange capacity of soils is of great theoretical and practical importance since the CEC determines in many ways the behavior of nutrients, chemical amendments, and many toxic compounds entering the sols. Sorption interactions with montmorillonite and other clay minerals in soils are potantially important mechanisms for attenuating the mobility of heavy metal cations through the subsurface environment. In this work the cation exchange capacity (CEC) of montmorillonite from west Anatolia, and sorptions with montmorillonite for attenuating the mobility of uranium were studied. The CEC value was found to be 77 meq/100 g montmorillonite. The relative importance of test parameters e.g., contact time, particle size, pH and U(+6) aqueous speciation was determined. The results show that sorption on montmorillonite is a funtion of pH depending strongly on the aqueous U(+6) species. It reaches a maximum at near neutral pH(pH}7). At low and at high pH solutions the sorption values of uranium are poor. These sorption values were attributed to the formation of aqueous U(+6) carbonate complexes in alkaline conditions and the ionexchange process between UO₂ ⁺² species and interlayer cations on montmorillonite in acidic solutions.     

Extraction of copper(II) and nickel(II) by nopinoquinone dioxime

In the research for a selective extractant for nickel a strained dioxime, β-nopinoquinone dioxime, has been studied in its extraction properties for copper(II) and nickel(II). Spectroscopic investigations (ESR and NMR) showed that both copper and nickel are extracted as a N,N-coordinated chelate. The extraction studies showed that the use of strained instead of aliphatic dioximes makes the extraction more convenient because of the higher extraction rate, but the selectivity for nickel above copper disappears.δ-nopinoquinone dioxime is easily converted into its furazan by treatment with 1N NaOH. This furazan is a rather weak ligand without significant extraction capacities.     

Extraction of copper(II) and nickel(II) by long-chain aliphatic dioximes

In the search for a selective nickel extractant symmetric dialkyl dioximes have been studied in the extraction of copper and nickel ions from ammoniaca     

Column separation and preconcentration of copper(II), lead(II) and zinc(II) from seawater

Summary The sample of seawater (51) is freed from solid particles, buffered at pH 5.6 and percolated through a column filled with ED₃A. After sample passage 15 ml 1 M hydrochloric acid solution are pumped through the column to dissolve the concentrated ions. The final measurement using flame atomic absorption is carried out in the hydrochloric acid solution. The total labour time is less than 15 min. The standard deviations (4 analyses) for the determination of Cu, Pb and Zn (in the normal concentration range of 2–6 g · l^–1) were 2–5%, 5% and 1–10%, the recoveries 100%, 102% and 104%, respectively. A concentration coefficient of 300–500 was obtained.On leave from Lisbon University, Portugal     

Extraction of Pd(II) by some petrochemical products from nitrate media

Liquid-liquid extraction of divalent palladium by solutions of Diesel oil (D.O.) and gas oil II (G.O.II) in benzene and lacquer petroleum from nitrate media has been studied. Palladium in concentrations of ∼10⁻³M is very effectively extracted by dilute solutions of extraction reagents and the distribution of palladium is almost independent of the acidity and nitrate concentration of the aqueous phase. Of other common salts, chlorides, thioeyanates and nitrites affect the palladium distribution. In many cases high concentrations of salts completely suppress the extraction of palladium. The rate of palladium extraction by dilute solutions of extractants is relatively small. Some substances such as dimethyl sulfoxide (DMSO) were found to accelerate the extraction. Palladium extraction from nitric acid media also has been studied from the points of view of chemical and radiation stability. Diesel oil was found to be a more stable extraction reagent in acid media than gas oil II.     

Simultaneous removal of copper(II), lead(II), zinc(II) and cadmium(II) from aqueous solutions by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were used successfully for the removal of heavy metals from aqueous solution. Characterization techniques showed the carbon as nanotubes with an average diameter between 40 and 60 nm and a specific surface area of 61.5 m² g^?1. The effect of carbon nanotubes mass, contact time, metal ions concentration, solution pH, and ionic strength on the adsorption of Cu(II), Pb(II), Cd(II) and Zn(II) by MWCNTs were studied and optimized. The adsorption of the heavy metals from aqueous solution by MWCNTs was studied kinetically using different kinetic models. A pseudo-second order model and the Elovich model were found to be in good agreement with the experimental data. The mechanism of adsorption was studied by the intra-particle diffusion model, and the results showed that intra-particle diffusion was not the slowest of the rate processes that determined the overall order. This model also revealed that the interaction of the metal ions with the MWCNTs surface might have been the most significant rate process. There was a competition among the metal ions for binding of the active sites present on the MWCNTs surface with affinity in the following order: Cu(II) > Zn(II) > Pb(II) > Cd(II).     

Synthesis of copper(II) oxide hydrosols

A procedure is developed for the synthesis of copper(II) oxide hydrosols. It is shown that the main parameters that govern the reproducibility of the synthesis results and the aggregation stability of synthesized hydrosols are the temperature of copper(II) nitrate hydrolysis and the concentration of a peptizing agent. Dispersed phase particles are shown to have a cylindrical shape with a prevailing length-to-diameter ratio of approximately 2.7.     

Adsorption of copper(II), cadmium(II), nickel(II) and lead(II) from aqueous solution using biosorbents

Three types of agricultural waste, citrus maxima peel (CM), passion fruit shell (PF) and sugarcane bagasse (SB), were used to produce biosorbents for removing the heavy metal ions of copper(II), cadmium(II), nickel(II) and lead(II) from a pH 5.0 solution. The properties of biosorbents were characterized using scanning electron microscopy (SEM), zeta potential analyzer, Fourier transform infrared (FTIR) spectroscopy, elemental analyzer and tests of cation exchange capacity (CEC). The result indicated that the selected biosorbents possess rich carboxyl (COOH) and hydroxyl (OH) groups to produce a complexation with the heavy metals. Moreover, the negative surface charge of the biosorbent might adsorb the metal ions through the ion exchange. All of the adsorption isotherms indicated that L-type characters represented complexation and ion exchanges that were the adsorption mechanisms of biosorbents toward heavy metals. Biosorbents with higher oxygen content might generate high adsorption capacities. The adsorption capacities of CM and PF, estimated from the fitting to the Langmuir isotherm, are similar to those reported by others regarding biosorbents.     

Extraction of copper(II) and nickel(II) by cyclic trioximes and cyclic furazan oximes

The extraction properties of 1,2,3-cyclopentanetrione trioxime (H₃CPT) and its furazan, and of 4-t-butyl-1,2,6-cyclohexanetrione trioxime (H₃BHT) and its furazan are described. H₃CPT was found to be too soluble in water and was therefore of no use in extraction but H₃BHT was satisfactory. The extracted copper and nickel chelates of H₃BHT precipitate by agglomeration caused by intermolecular hydrogen bonding and/or coordination of the third oxime group. This precipitation blocked back extraction. The furazan oximes derived from these trioximes did not form copper or nickel chelates under extraction conditions.     

Extraction of Ni(II) from nitrate media by Di-n-octylphosphinic acid dissolved in toluene

The extraction of Ni(II) from nitrate media of ionic strength 1.0 mol dm⁻³ by di-n-octylphosphinic acid (HR) in toluene solution has been studied over a range of pH and reagent concentrations. The data have been analysed both graphically and numerically to determine the stoichiometry of the extracted complexes and their extraction constants. Evidence was found for the formation of both NiR₂(HR)₄ (log K₂₄ = −9.14±0.06) and NiR₂(HR)₂ (logK₂₂ = −7.35±0.10), the former being the predominant species although the latter is important at low reagent concentrations and high pH values.     

Coulometric production of sulfhydryl reagents Titrations of lead(II) and copper(II)

The efficiency of generation of 1-propanethiol and thiophenol from the electrodes Ag/AgSR (R=Pr,Ph) was tested. Coulometric titrations of lead(II) and copper(II) with electrically generated sulfhydryl reagent are reported. The reaction between copper(II) and sulfhydryl ions was studied.     

Fluorescence-based detection of nitric oxide in aqueous and methanol media using a copper(II) complex

The quenched fluorescent intensity of a copper(II) complex, 1, of a fluorescent ligand, in degassed methanol or aqueous (buffered at pH 7.2) solution, was found to reappear on exposure to nitric oxide. Thus, it can function as a fluorescence based nitric oxide sensor. It has been found that the present complex can be used to sense nanomolar quantities of nitric oxide in both methanol and pH 7.2 buffered-water medium.     

Nickel(II) hexamethyleneiminedithiocarbamate complexes with triphenylphosphine or tributylphosphine

A series of square-planar nickel(II) hexamethylenedithiocarbamate complexes with heterogeneous coordination spheres of composition [NiX(hmidtc)Y] · nCHCl₃ [X = Cl, Br, I or NCS; hmi = C₆H₁₂, dtc = S₂CN^–; Y = PPh₃ or PBu₃, n = 0,1] have been synthesized and characterized by elemental analyses, i.r. and u.v.–v.i.s. spectroscopy, magnetochemical and conductivity measurements, and by thermal analysis. X-ray structures of [NiCl(hmidtc)(PPh₃)] · CHCl₃ and [NiBr(hmidtc)(PPh₃)] · CHCl₃ have been determined.     

Adsorption of lead(II) and copper(II) on activated carbon by complexation with surface functional groups

The adsorption of lead(II) and copper(II) on an activated carbon (Filtrasorb 300, Chemviron) was characterized assuming that it takes place by formation of complexes with functional groups, present in the activated carbon. Their concentration and conditional adsorption coefficients were determined for each metal by titration of the carbon in suspension in aqueous phase, at constant acidity, with the metal itself. For each titration point, the concentration of the metal in the solution phase after equilibration was determined, and the data were processed by the Ruzic linearization method, to obtain the concentration of the active sites involved in the sorption, and the conditional constant. The effect of the pH was also examined, in the range 4-6, obtaining that the adsorption increases at increasing pH. The protonation and adsorption constants were determined from the conditional adsorption coefficients obtained at the different acidities. The concentration of the active sites is 0.023 and 0.042 mmol g⁻¹, and the protonation constants are 1.0×10⁶ and 4.6×10⁴ M⁻¹ for Pb(II) and Cu(II). The corresponding adsorption constants are respectively 1.4×10⁵ and 6.3×10³ M⁻¹. All the parameters are affected by a large uncertainty, probably due to the heterogeneity of the active groups in the activated carbon. Even if so, these parameters make it possible a good prediction of the adsorption in a wide range of conditions. Other sorption mechanism can be set up at different conditions, in particular at different pH, as it has been demonstrated in the case of copper(II).     

Extraction of heterometal ruthenium(II) complexes by diphenyl(dibutylcarbamoylmethyl)phosphine oxide from nitrate-nitrite solutions

The synergistic extraction of [RuNO(NO₂)₄OH]^2? by diphenyl(dibutylcarbamoylmethyl)phosphine oxide (L) in the presence of nonprecious metal cations (M²⁺) is studied; the extraction occurs on the account of the formation of heterometal complexes [RuNO(NO₂)₄OHML_m] (M = Zn, Cu, Co, Ni) due to the addition of M²⁺ to ruthenium through the oxygen atoms of the OH and NO₂ groups and the bidentate coordination of L to M²⁺. The extraction constants for Ru/M complexes and ML_n(NO₃)₂ are determined. The variation in the extraction constants with changing M (Co, Zn, Cu > Ni) does not agree with the Irwing-Williams row, unlike the extraction with monodentate PO-containing extractants (Zn > Cu > Co > Ni). The feasibility of ruthenium extraction in the form of Ru/M complexes from complex nitrate-nitrite solutions is demonstrated.     

Formation of copper(II), zinc(II), silver(I) and lead(II) ferrocyanides

The factors influencing the formation of metal hexacyano-ferrate(II) complexes have been examined and the experimental conditions leading to formation of M(2)Fe(CN)(6), and K(2)M(3)[Fe(CN)(6)](2) have been studied, where M is Cu(II) or Zn(II); Ag(I) yields Ag(4)Fe(CN)(6). and KAg(3)Fe(CN)(6) and Pb(II) yields only Pb(2)Fe(CN)(6). Measurements made at constant ionic strength obtained by addition of K(2)SO(4) show how the potassium ion affects the stabilization of the complexes. The free energy changes and K(sp) values for the complexes have been calculated.