Dissolution kinetics of malachite in ammonia/ammonium carbonate leaching

The leaching of oxide copper ore containing malachite, which is the unique copper mineral in the ore, by aqueous ammonia solution has been studied. The effect of leaching time, ammonium hydroxide, and ammonium carbonate concentration, pH, [NH₃]/[NH₄⁺] ratio, stirring speed, solid/liquid ratio, particle size, and temperature were investigated. The main important parameters in ammonia leaching of malachite ore are determined as leaching time, ammonia/ammonium concentration ratio, pH, solid/liquid ratio, leaching temperature, and particle size. Optimum leaching conditions from malachite ore by ammonia/ammonium carbonate solution are found as ammonia/ammonium carbonate concentrations: 5 M NH₄OH+0.3 M (NH₄)₂CO₃; solid/liquid ratio: 1:10 g/mL; leaching times: 120 min; stirring speed: 300 rpm; leaching temperature: 25 °C; particle size finer than 450 μm. More than 98% of copper was effectively recovered. During the leaching, copper dissolves as in the form of Cu(NH₃)₄⁺² complex ion, whereas gangue minerals do not react with ammonia. It was determined that interface transfer and diffusion across the product layer control the leaching process. The activation energy for dissolution was found to be 15 kJ mol⁻¹.     

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.     

柠檬酸铅在柠檬酸钠溶液中溶解行为

通过氧化铅与柠檬酸反应制备了柠檬酸铅,考察了溶解时间、溶解温度、柠檬酸钠浓度和柠檬酸加入量对柠檬酸铅在柠檬酸钠溶液中溶解率的影响.结果表明：温度、柠檬酸钠浓度及柠檬酸加入量是主要影响因素,升高温度和提高柠檬酸钠浓度可显著提高柠檬酸铅溶解率;温度和溶解率呈正线性关系,拟合的线性方程为Y=0.76+0.63T;加入柠檬酸则对柠檬酸铅溶解有抑制作用.     

Racemization of ketorolac in aqueous solution

The racemization of ketorolac was studied in aqueous buffered solution at 25 and 80 degrees C and analyzed in detail with respect to the catalytic species in solution. The reaction has a U shaped pH rate profile at 80 degrees C with the pH of maximum stability occurring in the region of pH 3.0-7.5. A T90 value of 8 months was observed for a 1.5% (R)-ketorolac tromethamine solution at pH 7.4 and 25 degrees C. Additionally, the data shows that alternative salt forms are necessary in order to prepare a stable single isomer formulation. Alternative buffers, in particular phosphate buffer, provide formulations exhibiting a T90 greater than 2 years.     

Equilibrium reaction of pyrazolodiazepinones in aqueous solution

This study of the behavior of some pyrazolodiazepinones in aqueous solution at near ambient temperature indicated that they form stable equilibrium mixtures consisting of ring and opened forms. Under isothermal conditions, mixtures are produced whose composition is dependent on pH and may vary from that corresponding to essentially complete ring opening to complete closure. Ring closure equilibrium constants were calculated, and the influence of methyl substitution was determined. Substitution of a methyl group for an amido hydrogen in the open form results in a fivefold increase in this constant. Methylation of the terminal amino group, however, did not cause a corresponding increase and may not significantly affect equilibrium.     

Photodegradation products of levofloxacin in aqueous solution

The photodegradation of levofloxacin (DR-3355, CAS 100986-85-4), the S-(-)-isomer of ofloxacin, was investigated. Levofloxacin in aqueous solution was exposed to near ultraviolet light (peak wavelength 352 nm) for 16 h at room temperature. Nine degradation products (P-2-P-10) were isolated from the reaction mixture by preparative high performance liquid chromatography. The structures of these compounds were deduced from their NMR, MS, UV and IR spectra and optical rotations. The elucidated structures showed that all of these degradation products were analogues altered at the N-methylpiperazine moiety of levofloxacin.     

Dissolution kinetics of zinc silicate (hemimorphite) in ammoniacal solution

The influence of ammonia-ammonium ratio, specific surface area of particles, associated anions, temperature and total ammonia concentration on the dissolution kinetics of zinc silicate (hemimorphite) has been investigated in ammoniacal solutions. The results show that the initial dissolution rate increases with the specific surface area, temperature and total ammonia concentration. The associated anions have a significant influence on the zinc extraction from hemimorphite due to their different complexing affinity with zinc ion. SEM analysis shows that cleavage of hemimorphite appears during dissolution. The silica formed in the dissolution process is absorbed back and covers some active sites of the particles. The Elovich equation typifies the dissolution behavior of hemimorphite in ammoniacal solution with an activation energy of 57.6 kJ/mol which is characteristic for a chemically controlled process.     

Thermal stability of sodium hyaluronate in aqueous solution

Since its identification 60 years ago as a ubiquitous component of the body of mammals, hyaluronic acid has been widely studied, primarily in the fields of medicine and biology. On the other hand, our research has dealt with hyaluronic acid as a chemical intermediate in the synthesis of novel lubricious coatings, and in this connection data were needed on stability of aqueous solutions of the polymer over a range of temperatures from 25-100 degrees C. The investigation reported here provides that information, obtained by exposing samples in sealed ampules in baths at controlled temperatures and determining the resulting change in viscosity of the solutions. Data of this kind have not previously been reported on sodium hyaluronate freed from the proteins and other organics normally associated with the polymer in its natural environment.     

Stability of 5-aminolevulinic acid in aqueous solution

OBJECTIVE: To assess and contrast the role of interventional therapy for two types of cavitating pneumonias: lung abscess and necrotizing pneumonia. MATERIALS AND METHODS: We retrospectively reviewed the imaging, interventional therapy, and outcome of 14 children seen between February 1987 and January 1996 with lung abscess and 9 with necrotizing pneumonia. All children were treated with antibiotics prior to intervention. Pulmonary parenchymal fluid was percutaneously aspirated from ten lung abscesses and three necrotizing pneumonias. Percutaneous catheters drained five lung abscesses. Pleural drainage was performed for three lung abscesses and eight necrotizing pneumonias. RESULTS: All 14 children with lung abscesses had positive Gram stains of the pulmonary fluid; 13 cultures were positive. All 14 defervesced within 48 h of intervention. None developed a bronchopleural fistula. All nine necrotizing pneumonias were presumed to be sequelae of prior pneumonia. Streptococcus pneumoniae was the only organism as documented by pleural fluid latex fixation in three patients, gram stain in two, and culture in only one. Seven of these children developed pneumatoceles, five developed bronchopleural fistulae, and three required long-term chest tubes for persistent pneumothoraces. CONCLUSION: Aggressive interventional therapy can be diagnostic and therapeutic in the infected lung abscess. Interventional therapy can be harmful in postinfectious necrotizing pneumonia.     

Dissolution of Cu2S in aqueous edta solutions containing oxygen

The mechanism of the reactions taking place in the heterogeneous system: synthetic polydispersive Cu₂S-ethylediaminetetraacetic acid (EDTA)—O₂—H₂O has been investigated. The partial pressure of oxygen and pH of the solution were found to exert a significant effect on the process kinetics. The dissolution rate does not depend, in practice, on the agitation rate and the EDTA concentration exerts an influence only at higher partial oxygen pressures.Dissolution of Cu₂S in aqueous EDTA solutions proceeds in two steps with the formation of CuS as an intermediate. In acid and neutral solutions the final products of dissolution are elementary sulphur and Cu(EDTA)^2- complex ion. The activation energy ΔE = 10.4kJ/mol (2.4 kcal/mol) suggests a diffusion controlled process. In alkaline solutions sulphur is oxidized to the sulphate ion and the dissolution process is kinetically controlled, ΔE = 41.4 kJ/mol (9.9 kcal/mol).     

Solubility of uranous sulfate in aqueous sulfuric acid solution

To provide important thermodynamic data for use in uranium hydrometallurgy, solubilities of uranous sulfate were determined as a function of free acid concentration and temperature. Two sets of experiments were performed in this study. One set was the precipitation experiments of uranous sulfate crystals, in which concentrated uranous sulfate solution was mixed with sulfuric acid solution of suitable concentration. The other set was the dissolution experiments of uranous sulfate crystals in aqueous sulfuric acid solutions. It is noteworthy that good agreement exists between the solubilities determined by the two methods. At elevated temperatures, say, 363 K, the presence of free sulfuric acid is required to avoid precipitation of uranous hydroxide resulting from the hydrolysis of uranous sulfate. Generally speaking, however, an increase in free sulfuric acid concentration results in a slight decrease in uranous sulfate solubility. The elevation of solution temperature causes a decrease in solubility of uranous sulfate. It should be noted that the solid uranous sulfates equilibrated with saturated solutions at 298 K were U(SO₄)₂ 2H₂O in dilute sulfuric acid solution and U(SO₄)₂ 4H₂O in concentrated sulfuric acid solution, while those at 333 K and 363 K were mainly U(SO₄)₂ 4H₂O. Formerly Director, Mining and Ore Processing Division, Ningyo-toge Works, Power Reactor and Nuclear Fuel Development Corporation, is Director, Ningyo-toge Nuclear Service Company, Tomata-gun, Okayama Prefecture 708-06, Japan.     

Reactivity of aliphatic peptides toward hydroxyl radicals in aqueous solution

Dextrostix is now widely used as a method of screening for hypoglycemia of the newborn. There has always been some anxiety about its accuracy for estimating very low blood sugars; this is important, since symptomatic hypoglycemia of the newborn does not usually occur until the blood glucose falls below 20 mg/dl. In 1970 a reflectance meter was introduced which would measure the colour of the strip electronically. The aim of this study was to assess the accuracy of the meter and its reliability in estimating hypoglycemia. The study was continued to investigate a new model of the reflectance meter which superseded the original one. In the pilot study using the original model, blood samples were taken from 46 babies. Readings of the Dextrostix were made by two independent observers and compared with a reading taken on the reflectance meter. These estimations were later compared with blood glucose measured by the glucose oxidase method. the meter showed a marked tendency to overestimate the blood glucose: 44 out of 46 samples were overestimated (Fig. 1, 2). In the second series 180 cord blood samples were collected. Because the intention was to study very low levels of blood glucose, the samples were allowed to stand at room temperature for several hours to allow glycolysis to occur. Again, readings were taken by two independent observers and compared with the readings taken on the new Dextrostix-Eyetone meter. The blood glucose was measured on each of the samples. There was a strong correlation (r = 0.8877, p less than 0.00005) between the blood glucose values and the readings taken from the meter, with no tendency towards overestimation (Fig. 3). A similar correlation (r = 0.8533, p less than 0.00005) was seen for the observers' readings and the chemical method, although there was a tendency to underestimate blood glucose (Fig. 4). When the meter gave an estimate of more than 20 ml/dl, in no case was the actual blood glucose in the profoundly hypoglycemic group of less than 10 mg/dl. When estimated by eye there was one case in which the blood glucose was only 7 mg/dl but the observer had estimated the result of 30 mg/dl. In order to avoid any possibility that a blood glucose was less than 20 mg/dl, it is necessary to take action on any estimate below 40 mg/dl on a Dextrostix. Despite this, Dextrostix remains a very useful method of screening for neonatal hypoglycemia, whether assessed by eye or with the new Dextrostix-Eyetone meter. the meter does give better results than estimating Dextrostix by eye, but the difference was never statistically significant.     

液相脉冲放电制备纳米Ni-P合金粉工艺

采用液相脉冲放电技术,通过改变脉冲电压、放电次数、Ni²⁺浓度、pH值,以及加入稀土添加剂(LaCl₃、NdCl₃)等途径,研究了制备工艺中各因素对Ni-P合金粉的结构、形貌、粒径以及对Ni²⁺转化率的影响.结果表明,脉冲能量是影响Ni-P合金粉粒径和Ni²⁺转化率的主要因素,提高脉冲电压或增加放电次数,Ni-P合金粉平均粒径明显减小,而Ni²⁺转化率增大.聚焦光束反射测量仪(FBRM)实时监测结果表明,在放电过程中Ni-P合金粉的形核、生长速率显著大于放电结束之后的形核、生长速率.加入LaCl₃、NdCl₃能使Ni-P合金粉粒径减小,LaCl₃质量浓度为0.1g·L·时制得的Ni-P合金粉平均粒径为156nm,NdCl₃质量浓度为0.05g·L^-1时其平均粒径为72nm.     

High-resolution 1H-NMR studies of monomeric melittin in aqueous solution

High resolution 1H-NMR at 360 MHz was used to characterize monomeric melittin in aqueous solution. The monomeric form of melittin was found to prevail at 3 mM concentration, pH 3.0, and temperatures between 30 and 90 degrees C, both in the absence of salt and with 6 M guanidium chloride. From comparison with model peptides and studies of the effects of 6 M guanidium chloride and variable temperature on the NMR parameters it was concluded that monomeric melittin is predominantly in an extended flexible form, with the fragments 5--9 and 14--20 more highly structured than the rest of the amino acid sequence. The appearance of a second, low abundant form of monomeric melittin, which is in slow exchange on the NMR time scale with both the more abundant monomeric conformation and aggregated melittin, was attributed to cis-trans isomerism of the peptide bond Leu-13--Pro-14.     

On crack closure of precipitation hardened steels in aqueous solution

Fatigue crack propagation tests were carried out in air and in a 3.5 pct NaCl aqueous solution under cathodic potential of −0.85 V (Ag/AgCl) for aged-hardened high strength steel (Ni−Al−Cr−Mo−C steel). the emphasis in the study was placed on the crack closure behavior of age-hardened materials in air and in the NaCl aqueous solution. The degree of crack closure in air was dependent on the behavior of plastic deformation such as inhomogeneous or homogeneous slip under mixed modes I and II. The underaged material containing coherent precipitates with the matrix had a higher crack opening load in air, compared with the overaged steel containing incoherent precipitates with the matrix. The degrec of crack closure of the underaged material in the NaCl aqueous solution was lower than that in air and was similar to that of overaged materials in the NaCl aqueous solution. It was shown that the decreased crack closure level for the underaged material resulted from accelerated fatigue crack growth under mode I due to hydrogen embrittlement in the aqueous solution.     

Solubility prediction of malachite in aqueous ammoniacal ammonium chloride solutions at 25 °C

The solubility of malachite in the presence of ammonia, ammonium chloride and their mixed solution is calculated by a geochemical modeling code and is measured in a series of dissolution experiments using synthetic malachite at 25 °C. The simulated results show a good agreement with the experimental data gained at 25 °C. The predicted and experimental results indicate that the precipitate CuO limits the copper solubility in aqueous ammonia and Cu(OH)_1.5Cl_0.5 in aqueous ammonium chloride. For a mixed solution containing ammonia and ammonium chloride, highest copper solubility can be achieved by adjusting the [NH₃]/[NH₄Cl] ratio to about 2:1. The thermodynamic model presented rationalises the interactions between the different components and predicts the influence of changes in the concentration of ammonia and ammonium chloride on the copper solubility of malachite.