The solubility of aqueous lead chloride solutions

Data are presented for the solubility of lead in acidic solutions of between 5 and 10 M chloride concentration, present as the salts of copper (II) and either sodium or calcium. Cooling these solutions from boiling point to 20°C precipitates approximately two thirds of the lead as PbCl₂ crystals of >99% purity. The solubility of PbCl₂ is shown to depend upon the activity of the lead and chloride ions in solution, and can be predicted from known thermodynamic constants. This has been tested for solutions containing only one cation, other than lead, at 25°C. This approach accurately predicts the lead solubility in solutions of calcium chloride but needs improving before it can be applied to sodium chloride solutions and hydrochloric acid.     

Gamma-irradiation of malic acid in aqueous solutions

The gamma-irradiation of malic acid in aqueous solutions was studied under initially oxygenated and oxygen-free conditions in an attempt to determine the possible interconversion of malic acid into other carboxylic acids, specifically those associated with Krebs cycle. The effect of dose on product formation of the system was investigated. Gas-liquid chromatography combined with mass spectrometry was used as the principal means of identification of the non-volatile products. Thin layer chromatography and direct probe mass spectroscopy were also employed. The findings show that a variety of carboxylic acids are formed, with malonic and succinic acids in greatest abundance. These products have all been identified as being formed in the gamma-irradiation of acetic acid, suggesting a common intermediary. Since these molecules fit into a metabolic cycle, it is strongly suggestive that prebiotic pathways provided the basis for biological systems.     

Solubility of oxygen in aqueous electrolyte solutions

The solubility of oxygen in a number of aqueous electrolyte solutions was determined using a colorimetric method based on the oxidation of indigo carmine. The effects of changes in electrolyte concentration, temperature and partial pressure of oxygen were investigated.The ratio of the solubility of oxygen in the electrolyte solutions to that in pure water decreases as the concentration of the electrolyte increases but is essentially independent of both temperature (over the range 298–348 K) and the oxygen partial pressure (over the range 0.1–1.0 atm).Empirical relationships for this solubility ratio as a function of the electrolyte concentration and temperature were developed. The predictions made using these relationships are found to be superior to the alternative methods suggested in the literature, particularly for those conditions frequently found in hydrometallurgical systems, namely at high electrolyte concentrations.The significance of changes in the solubility of oxygen in aqueous electrolyte solutions is briefly discussed with particular reference to the hydrometallurgical implications.     

Electrocrystallization of copper in chloride aqueous solutions

An apparatus was built in our laboratory in order to electrolyze a Gokhale solution (CuC10.7N,NaC14N, HC10.5N)for extended periods of time under current densities ranging from 50 to 600 A/m² at temperatures between 20 and 50°C The influence of the diaphragm, temperature, current density and duration of the electrolysis in pure solutions was investigated, and the results were interpreted in terms of current efficiency, overall voltage drop and specific energy consumption. The structure of the deposits was investigated by profilometry, optical micrography, scanning electron microscopy and X-ray diffraction. The structure of the deposits is not significantly different from that obtained in pure sulfuric acid solutions, but it shows an increased tendency to growth of rather large elongated crystals protruding in the electrolyte. Both types are characteristic of deposits obtained at rather low inhibition, according to Fischer’s classification. Formerly Researcher, Université Libre de Bruxelles     

Reverse micellar extraction of antibiotics from aqueous solutions

PURPOSE: We reviewed 1,360 EEG reports for all patients studied in two different neurophysiology laboratories during 1 calendar year to determine whether epileptiform discharges have a hemispheric dominance. METHODS: Both inpatients and outpatients, with or without epilepsy, were included. RESULTS: Ninety-four records (6.9%) demonstrated generalized epileptiform activity. Of 95 EEG reports indicating spikes solely from one hemisphere, spikes arose from the left in 61 and from the right in 34. Among 50 other records with bilateral independent spikes with lateralization, 40 were left hemisphere dominant and 10 were right hemisphere dominant. CONCLUSIONS: These findings raise the possibility that the left cerebral hemisphere may generate focal epilepsy more frequently than the right.     

Dissolution of nickel hydroxide in ammoniacal aqueous solutions

The dissolution of nickel hydroxide in ammoniacal solutions was investigated to develop a new recycling process for nickel-metal hydride batteries. The effects of temperature, total ammonia concentration, and pH of the solution were examined in the range of 30 °C to 60 °C, 3.0 to 5.0 M, and 9.0 to 10.7, respectively. All dissolution-time curves showed sigmoidal shapes, which could be approximately expressed by the Johnson-Mehl-Avrami-Yerofeev-Kolmogrov (JMAYK) equation. The hydroxide particles were pitted, and some of them were broken into fragments in the course of the dissolution. An increase in the surface area of the hydroxide particles due to the formation of pits and fragmentation seemed to be the reason for the acceleration of dissolution in the early stage. The surface area of the hydroxide was measured by the Brunauer-Emmett-Teller (BET) method, and the dissolution rate per surface area was determined. The activation energy for the dissolution was obtained as 100±10 kJ mol⁻¹, which confirmed that the dissolution was controlled by chemical reactions at the hydroxide/liquid interface. The dissolution rate was increased by the increase in ammonia concentration, and the highest rate was observed at pH ca. 10.     

Leaching kinetics of colemanite by aqueous EDTA solutions

The dissolution kinetics of colemanite, a boron-containing mineral, in aqueous disodium EDTA solutions were studied. The effects of concentration and pH of the solution, particle size, and temperature were examined. A decrease in pH and particle size increased the dissolution rate, while an increase in the concentration of the solution and temperature increased the rate. The activation energy and pre-exponential factor were calculated as 50.6 kJ mol^-1 and 5.14 x 10⁷ m s^-1, respectively. Mahir Alkan, Assistant Professor, formerly with Atatürk University, Kazim Karabekir Faculty of Education     

Removal of lead from aqueous solutions by natural phosphate

The removal of lead ions from aqueous solution was studied in batch experiments using natural phosphate (NP). The effects of initial concentration of lead and initial pH of solution were investigated and the mechanism for removal of lead has been suggested. The data obtained from sorption isotherms at different temperatures conformed to the linear form of the Langmuir adsorption equation. The influence of NO₃⁻ and Cl⁻ anions has been evaluated. The effect of varying levels of Cl⁻ has significant influence on the sorption capacity of Pb²⁺, while NO₃⁻ did not. The abundance of natural phosphate, its low price and non-aggressive nature towards the environment are advantages for its utilization in point of view of wastewater and wastes clean up.     

Electrodeposition of lead from aqueous acetate and chloride solutions

Electrodeposition of Pb from electrolyte containing CH₃COONH₄, CH₃COOH, and Cl^- was in-vestigated at 25 ‡C in stirred and quiescent solutions on different substrates: Pb, Cu, Al, and C. The deposited lead from the acetate bath was crystalline and showed a marked tendency to form dendrites. The addition of organic additives, phenol, ethyl alcohol, and gelatine, was found necessary in order to obtain a bright, smooth, and compact lead deposit on Pb and Cu electrode. Even with the additives, dendritic lead was observed on Al and C electrodes. Systematic studies of electrodeposition of Pb from these media—such as investigation of the effect of concentration of chemicals in the electrolyte, the effect of temperature, the effect of current density, and the nature of the subtrates—were carried out. Electrochemical techniques such as cyclic voltammetry, potentiodynamic studies, chrono-amperometry, and chronopotentiometry have been employed to shed light on the nature of the reaction mechanism. The deposit quality and purity was examined by X-ray diffraction analysis, SEM, and Auger spectroscopy. The results were compared with those obtained from a fluoborate bath. The quality of a lead deposit from fluoborate bath proved to be similar to that obtained from acetate bath in the presence of organic additives where the deposit was always of a compact, dense, and smooth form.     

Solvation of human serum albumin in aqueous alkylurea solutions

In order to list the negative emergency laparotomies, the records of 24,494 laparotomies performed from 1950 to 1989 were examined. 211 negative laparotomies were performed over this 40 years period: 49 for abdominal trauma, 42 for supposed intestinal obstruction, 44 for supposed peritonitis or visceral infection, 46 for presumed early post-operative abdominal complications and 30 for gastrointestinal bleeding. Over these 4 decades, the emergency laparotomy rate and negative laparotomy rate remained stable despite changes in the diagnostic tools, in the age of the patients and the frequency of their diseases.     

Thermophysical properties of trehalose and its concentrated aqueous solutions

PURPOSE: To address the lack of fundamental thermophysical data for trehalose and its aqueous systems by measuring equilibrium and non-equilibrium properties of such systems. METHODS/RESULTS: Differential scanning calorimetry (DSC) and dynamic mechanical analysis were used to measure glass transition temperatures of trehalose and its solutions. X-ray diffractometry was used to verify the structure of amorphous trehalose. Controlled-stress rheometry was used to measure viscosity of several aqueous trehalose systems at ambient and sub-ambient temperatures. Over this temperature range, the density of these solutions was also measured with a vibrating tube densimeter. The equilibrium phase diagram of aqueous trehalose was determined by measuring the solubility and freezing point depression. CONCLUSIONS: Our solubility measurements, which have allowed long times for attainment of chemical equilibrium, are substantially different from those reported earlier that used different techniques. Our measurements of the glass transition temperature of trehalose are higher than reported values. A simple model for the glass transition is presented to describe our experimental observations.     

Corrosion behavior of aluminum-boron composites in aqueous chloride solutions

A study has been made of the corrosion behavior of diffusion bonded 2024 aluminum alloy-unidirectional boron filament composites in aqueous chloride solutions. Compared with the 2024 alloy, the composites suffer greater localized corrosion, both in the presence and absence of applied stress, when the environment is in contact with transverse section surfaces (i.e. surfaces containing exposed boron filament ends and diffusion bonds). The electrochemical behavior of such surfaces indicates that the lowered corrosion resistance is not due to galvanic action between the filament and matrix, but results from an increase in the number of anodic sites, the latter being associated with the filament-matrix interfaces and the diffusion bonds between the alloy foils.     

针铁矿吸附水中硫酸根离子的试验研究

利用合成的针铁矿对水中硫酸根离子进行吸附试验。试验表明，吸附量主要受pH值和硫酸根离子浓度影响。通过配位体交换理论，很好地解释了吸附量随pH下降而增加，随硫酸根离子浓度的下降而减少。     

Preparation of hydrogel microspheres by coacervation of aqueous polyphosphazene solutions

A new method of preparing ionically cross-linked polyphosphazene hydrogel microspheres which enables effective control over microsphere size distribution has been developed. The synthesized microspheres can be used in protein delivery and, especially, as vaccine delivery vehicles. A new technique utilizes the ability of aqueous solutions of poly[di(carboxylatophenoxy)phosphazene] (PCPP) to form coacervate microdroplets upon addition of sodium chloride. These microdroplets are then stabilized via polymer cross-linking with calcium ions. It was demonstrated that the method enables efficient microencapsulation of proteins. It was also shown that microsphere size can be controlled through the manipulation of microencapsulation conditions. The process is simple, highly reproducible and generates microspheres with a narrower microsphere size distribution, compared to the previous technologies.