Experimental studies of the efficiency of electroflotation recovery of poorly soluble lanthanum compounds from aqueous solutions

Features of electroflotation recovery of poorly soluble lanthanum compounds from aqueous solutions containing sodium salts were experimentally determined and studied for the first time. The role was identified that anionic, cationic, and nonionic surfactants added to various supporting electrolytes (sulfate, chloride, carbonate, nitrate) play in the efficiency of electroflotation recovery of poorly soluble lanthanum compounds. The possibility of electroflotation recovery of lanthanum hydroxide with an efficiency of 95–99% was experimentally and theoretically substantiated.     

Determination of Cadmium and Lead in Sea Water after Extraction Using Electrothermal Atomisation. Minimisation of Interferences from Co-Extracted Sea Salts

Abstract

Interferences from small amounts of sea salt in the determination of cadmium and lead were investigated. Test samples were made to mimic solutions obtained after extraction of sea water for trace metal analysis. Sea salt concentrations in the range 0–400 mg/l were investigated. Background absorption from this salt was high but easily minimised through the addition of nitric acid (2 % v/v). Sensitivity reductions due to the salt were considerable and varied from one graphite tube to the other. This problem was overcome by the addition of 1000 mg lanthanum per litre of sample. The positive effect of the lanthanum matrix modification is thought to be due to a change of the graphite tube surface.     

A Simple Liquid Chromatographic Method for Quantitative Extraction of Hydrophobic Compounds from Aqueous Solutions

Abstract

We are reporting a rapid, high-capacity liquid chromatographic method for quantitative extraction and concentration of hydrophobic compounds from biological fluids and aqueous solutions. Samples are injected into commerically-available cartridges (Sep-Pak C^18R) containing a microparticulate, reversed phase packing which retains hydrophobic compounds. Inorganic salts and organic hydrophilic contaminants are removed with a water wash. Hydrophobic compounds are eluted quantitatively with minimal volumes (～5 ml) of organic solvents. As demonstrated with radiolabeled taurocholate, thin-láyer chromatography, enzymatic fluorimetry and capillary gas chromatography, complete recovery of bile salts from large volumes of urine, serum, amniotic fluid and hydrolysis reaction mixtures was achieved at flow rates up to 20 ml/min. A single cartridge concentrated approximately 50 mg of either taurocholate or the more polar bile salt, taurolithocholate sulfate. The technique is simple and applicable to the isolation of a wide range of hydrophobic compounds from aqueous solutions.     

Sorption of lanthanum ions by natural clinoptilolite tuff

The equilibrium and kinetics of sorption of lanthanum ions on natural clinoptilolite tuff are studied. It is demonstrated that sorption of lanthanum ions from diluted solutions occurs in micropores of clinoptilolite, and from concentrated solutions in the mesoporous structure of tuff. The main capacity of zeolite tuff is found in the secondary porous structure. The sorption of lanthanum ions is limited by diffusion in tuff grains. Lanthanum ions are regularly distributed in the tuff phase and interact with the Brønsted centers of large clinoptilolite cavities.     

Kinetics of thorium(IV) and lanthanum(III) extraction from aqueous salt solutions with composite material based on trialkylamine and polymeric support at various temperatures

The kinetics of thorium(IV) and lanthanum(III) extraction from aqueous salt solutions with a composite material based on trialkylamine and a polymeric support at 293.15–333.15 K was studied. The mass transfer coefficients were found, and the apparent activation energy of the extraction reaction was estimated.     

The study of thiophene adsorption onto La(III)-exchanged zeolite NaY by FT-IR spectroscopy

Zeolites NaY and LaNaY (ion-exchanged with aqueous lanthanum nitrate solution) were used as adsorbents for removing organic sulfur compounds from model gasoline solutions (without and with toluene) and fluid catalytic cracked gasoline in fixed-bed adsorption equipment at room temperature and atmosphere pressure. The adsorptive selectivity for organic sulfur compounds was significantly increased when Na(+) ions in zeolite NaY were exchanged with lanthanum ions. IR spectra of thiophene adsorption indicate that thiophene is adsorbed onto La(3+) ions via direct S-La(3+) interaction and Na(+) ions via pi-electronic interaction for La(3+)-exchanged zeolite NaY, but only via pi-electronic interaction with Na(+) ions for NaY. The amount of adsorbed thiophene on La(3+)-exchanged zeolite Y was slightly decreased by coadsorption of benzene, but greatly reduced on NaY. The adsorption of thiophene via interaction with La(3+) on La(3+)-exchanged zeolite Y is hardly replaced by benzene coadsorption. The direct S-La(3+) interaction might be the essential reason for the evidently improved adsorptive selectivity of LaNaY for removing organic sulfur compounds from solutions containing large amount of aromatics.     

The application of polypropylene membranes for production of fresh water from brines by membrane distillation

Scaling and wettability of hydrophobic membranes were studied during the membrane distillation applied for the production of fresh water from the concentrated salt solutions. The studies were performed with the use of membrane modules in which the capillary membranes from polypropylene were assembled. A saline ground water containing several sparingly soluble salts was used as a feeding solution. The presence of such compounds caused an intensive surface and internal scaling. Due to the scaling, a partial wetting of the membrane walls and the permeation of salts into distillate were observed. These phenomena were eliminated for the membranes with thicker walls when the amount of deposit was limited by a periodic rinsing of the module with water. During this study, the feed was concentrated up to the supersaturation state, which caused a salt crystallization on the membrane surface, and as a consequence, the permeate flux was reduced to zero. In this case, the internal scaling can be limited using the capillary membranes with a net covering their surface.     

An improvement study on the closed chamber distillation system for recovery of renewable salts from salt wastes containing radioactive rare earth compounds

In this paper, an improvement study on the closed chamber distillation system for recovery of renewable salts from salt wastes containing radioactive rare earth compounds was performed to determine optimum operating conditions. It was very important to maintain the pressure in the distillation chamber below 10 Torr for a high efficiency (salt recovery >99 %) of the salt distillation. This required increasing the salt vaporization and condensation rates in the distillation system. It was confirmed that vaporization and condensation rates could be improved controlling the given temperature of top of the condensation chamber. In the distillation tests of the salt wastes containing rare earth compounds, the operation time at a given temperature was greatly reduced changing the given temperature of top of the condensation chamber from 780 to 700 °C.     

Thermal-Decomposition Chemistry of Modified Lead-Titanate Aquo-Diol Gels Used for the Preparation of Thin Films

Lead-titanate gels and thin films modified with calcium, lanthanum or samarium have been prepared by chemical solution deposition (CSD) methods. Lead acetate, titanium di-isopropoxide bis-acetylacetonate and 1,3-propanediol were used for the synthesis of Pb-Ti-sols. Calcium, lanthanum or samarium were added to these sols as acetates or nitrates dissolved in water. The solutions were dried to obtain the gels or spin-coated onto platinised silicon substrates to obtain the films. Thermal decomposition of the gels was followed by means of simultaneous thermogravimetric and differential-thermal analysis (TGA/DTA) coupled with evolved gas analysis (EGA). Infrared (IR) analysis of the gels helped to identify the compounds formed during the thermal decomposition. Crystal structure and microstructure of the films were observed by grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). These analyses indicated that the structure and microstructure of the modified-lead-titanate thin films are related to the thermal decompositions of the corresponding gels. It was inferred from these studies that the decomposition sequence is linked to the type of modifier, Ca, La or Sm, and to the precursor salt (acetate or nitrate) used for the incorporation of the modifier into the Pb-Ti-sol.     

Phase relations in the lanthanum nitrate (copper nitrate)-poly(vinylpyrrolidone)-water systems

Room-temperature isothermal sections of the phase diagrams of lanthanum nitrate-poly(vinylpyrrolidone)-water and copper nitrate-poly(vinylpyrrolidone)-water systems were studied. The following features were found: a wide region of homogeneous water-polymer solutions, liquid-liquid phase separation field, and a three-phase region in which two liquids coexist with salt crystals. In the lanthanum nitrate system, liquid-liquid phase separation has a lower critical solution point (polythermal sections were studied); in the copper nitrate system, it has an upper critical solution point. The type of diagram for unstudied systems is predicted based on the analysis of polymer-salt phase diagrams.     

Deep desalination of water by evaporation through polymeric membranes

Transport properties and structural features of a number of already known and new types of polymeric membranes in desalination of aqueous salt solutions by membrane distillation and pervaporation were studied. The possibility of obtaining distilled water in a single stage by pervaporation from dilute or concentrated aqueous salt solutions was examined for the example of membranes fabricated from celluloses of varied origin (wood, cotton, bacterial).     

On the Determination of the Hold-Up Time in Reversed Phase Liquid Chromatography

Abstract

The determination of the hold-up time in reversed phase liquid chromatography has been studied extensively for the mobile phase system methanol-water. Hold-up times obtained by static methods, linearization of homologous series and so-called “unretained compounds” are discussed and mutually compared. Several n-alkyldimethylsilyl bonded phases have been used for this investigation.

A rough estimate of the hold-up time can be obtained by using components of the mobile phase or highly concentrated salt solutions, but only for mobile phase compositions around 60% (v/v) methanol. Hold-up times accurate to 1% can be obtained over the complete range of mobile phase compositions from the linearization of net retention times of homologous series.     

Extraction of Gold from ores and concentrates by leaching with the use of cyanides and alternative reagents

The problems associated with gold mining are considered from the standpoint of application of heap leaching, a method for gold recovery. Data on the kinetics and mechanism of gold dissolution in cyanide and alternative solvents [thiocarbamide solutions containing Fe(III) ions and hypochlorite-chloride bromine-bromide, iodine-iodide, and copper-thiosulfate solutions], which make it possible not only to improve the working efficiency in gold mining, but also to lessen the contamination of the environment with highly toxic compounds.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1585–1604.Original Russian Text Copyright © 2004 by Kozin, Melekhin.     

Enhanced copper surface protection in aqueous solutions containing short-chain alkanoic acid potassium salts

The ability of dissolved potassium monocarboxylate salts to produce surface passivation and to inhibit aqueous corrosion of copper was studied. The electrochemical measurements indicate that the inhibiting efficiency of these compounds, with a general formula Cn-1H2n-1COOK or CnK (n=3...12), is dependent on the hydrocarbon chain length. The inhibiting efficiency was higher for a longer hydrocarbon chain of n-alkanoic acid. The degree of copper protection was found to increase with an increase in n-alkanoic acid potassium salt concentration; the optimum concentration of potassium dodecanoate (C12K) in sulfate solutions was found to be 0.07 M. The protective layers formed at the copper surface subsequent to exposure in various n-alkanoic acid potassium salt solutions were characterized by contact angle measurements, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared reflection spectroscopy. Pronounced copper protection was attributed to the growth of a protective film on the copper surface, containing both copper oxides and copper carboxylate compounds. It is suggested that the organic molecules enhance copper protection by covering copper oxides with a thin and dense organic layer, which prevents water molecules or aggressive anions from interacting with the copper surface.     

液膜萃取法回收磷酸体系中的微量镧

通过斜率分析法研究了P204和TOPO从磷酸体系中液液萃取微量镧的反应机制和热力学,推测出一种可能的反应历程和萃合物结构,得到萃取反应式和反应的平衡常数K=104.502,焓变ΔH=-13.02 kJ.mol-1,自由能ΔG=-25.686 kJ.mol-1,熵变ΔS=0.0425kJ.(mol.K)-1。在液液萃取反应机制研究的基础上,采用液膜萃取法进行磷酸体系中微量镧的富集回收研究,考察了载体P204(2%～10%w/w)和TOPO(1%～10%w/w)、表面活性剂磺化聚丁二烯LYF(1%～10%w/w)、内萃取剂HCl(1～5 mol.L-1)和水乳体积比A/O(2:1～7:1)对液膜萃取收率及稳定性的影响。在最优条件下,可回收94.10%～95.94%的镧,并且膜溶胀率为8%～17%,破损率为0.45%～1.93%,能够维持较好的液膜稳定性。研究结果对磷酸中的微量稀土镧回收利用具有一定的参考价值。     

Methods for the extraction of microplastics in complex solid,water and biota samples

The widespread distribution of plastics, their persistence and ability to act as a vector of toxic chemicals has rendered them concerning emergent pollutants. The quantification of these contaminants is highly relevant for the evaluation of anthropogenic impacts on aquatic and terrestrial ecosystems and dependent of the efficacy of methods to separate microplastics from environmental matrices. Little information is available about the microplastic extraction methods on complex samples – i.e. samples with multiple types of matrices. Herein, methods for the separation of microplastics from complex samples are summarized and discussed based on their advantages and drawbacks focused on a comparative analysis of their efficiency on organic matter removal, polymer recovery and preservation of plastic integrity. The efficiency on microplastic recovery and organic matter reduction, as well as the examination of the effects of treatments on plastics are closely linked to the density and digestion approaches selected, the polymer features and the environmental matrix analyzed. High-density salt solutions are more effective for density separation, while oxidative methods have recurrently shown better rates of organic matter reduction (particularly in vegetal-rich samples) and plastic recovery, with little impact on plastics, while 10 % KOH has been described as highly efficient in samples containing animal organic matter. This comparative analysis highlights the benefits and limitations of different approaches for the analysis of microplastics in complex samples which may be helpful for the optimization and harmonization of the methods.     

The Oxidation of Organo-Boron Compounds Using Electrochemically Generated Peroxodicarbonate

Peroxodicarbonate represents a green and largely underexplored oxidizer generated electrochemically from aqueous carbonate solutions. Through state-of-the-art electrolyzer technology, highly concentrated solutions have now become accessible. These were successfully employed as green oxidizer in deborolative hydroxylations. A plethora of phenols and alcohols have thus been synthesized in up to 99 % from organoboron compounds using only green and non-toxic solvents. This transformation was successfully scaled-up to multi-gram batch sizes.     

Reduction of matrix effects in ICP-MS by optimizing settings of ion optics

The effect of ion optics settings on the degree of suppression of analyte signals due to the presence of different basic elements in a sample solution, such as manganese, copper, indium, lanthanum, hafnium, and lead, was investigated on an example of an XSeries II inductively coupled plasma mass spectrometer. The effect of atomic mass and the concentration of the matrix element on the optimum values of ion optics settings and the change in the analyte signals was studied. It was shown that a decrease in the potential of the extractor lens to ?300 V can significantly reduce the matrix effect. As an example, the results of determining impurity elements in solutions containing up to 1 g/L of lanthanum were obtained using standard settings of the spectrometer with a reduced voltage on the extractor. It was shown that the optimization of ion optics settings enables the use of more concentrated solutions, thus reducing the detection limits for elements by several times.     

Solid phase extraction of lanthanum on modified low-polar sorbents

The preconcentration of lanthanum has been studied on low-polar sorbents modified with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one, including hexadecylsilica, hyper-crosslinked polystyrene, polyvinylidene difluoride F2M, and activated carbon. The coefficients of reagent and the lanthanum distribution have been calculated under dynamic conditions. The leaching of the attached reagent from the sorbent surface has been investigated. The recovery of lanthanum with modified and nonmodified sorbents has been compared. The efficiency of lanthanum desorption with nitric acid and ethanol has been studied.