Showing papers on "Dissolution published in 1972"

Selective Dissolution of Manganese Oxides from Soils and Sediments with Acidified Hydroxylamine Hydrochloride

Abstract: Hydrous manganese and iron oxides of soils and sediments are strong scavenging agents for heavy metal ions. Information on heavy metals extracted along with manganese and iron oxides has been used in mineral exploration. But currently used methods do not differentiate metal ions associated with manganese oxides and those associated with iron oxides. Manganese oxides differ from iron oxides in solubility in response to oxidation-reduction conditions, charge characteristics, and the quantity and kind of metal ions scavenged. This paper reports the development of an extraction method for the selective dissolution of manganese oxides from soils and sediments with minimal attack on the coexisting iron oxides, based on the difference in behavior of manganese oxides and iron oxides toward reduction under various conditions. By dissolving manganese oxides and iron oxides separately and determining respective metal ions which are released in the process, the geochemical significance of interelement relationships may be established. Manganese oxides in soils and sediments are found to be readily dissolved by a hydroxylamine hydrochloride (NH₂OH · HCl) solution, leaving the major part of iron oxides in the residue. Although dissolution of manganese oxides is relatively independent of pH (pH 1, 2, and 3) and concentration of the NH₂OH · HCl solution (0.025 to 0.25M), and time of equilibration (15 to 60 min), progressively greater amounts of iron oxides are released with lower pH and higher concentration of NH₂OH · HCl solution, and with longer time of equilibration. A 0.1M NH₂OH · HCl solution prepared in 0.01M HNO₃ (pH 2) dissolves, on the average, 85% of manganese oxides and about 5% of iron oxides from various sediments after equilibrating for 30 min. Dissolution of manganese oxides and of iron oxides from four highly weathered soils by this solution amounts, respectively, to 50% and less than 1%. At pH 2, most heavy metal ions released during the dissolution of manganese oxides will be prevented from forming insoluble hydroxides or basic salts through hydrolysis, and then they can be determined in solution by appropriate analytical methods.

Double Layer Capacitance of Iron and Corrosion Inhibition with Polymethylene Diamines

Abstract: The effect of α,ω‐polymethylenediamines on the corrosion of iron in deaerated was investigated by polarization measurements and colorimetric analysis of solution. The adsorption of these inhibitors at the metal/solution interface was monitored by measurement of the double layer capacitance using the single pulse method. 1,3‐propanediamine was found to be a better inhibitor than ethylenediamine, but no further improvement in per cent inhibition resulted upon increasing the chain length from . Increased inhibitor efficiency for hydrocarbon chains longer than eight carbon atoms was attributed to the concomitant decreased solubility. On a relative solubility basis, the C6‐diamine was more efficient than the C12‐diamine, although both inhibitors produced 90% inhibition at a reduced concentration of 0.1. The double layer capacitance was approximately constant at 21 µF/cm2 for the C2‐ through C8‐diamines, and alternated between 6 and 14 µF/cm2 for the C9‐ through C12‐diamines. The constancy at 21 µF/cm2 suggets that diamines with up to 8 carbon atoms are adsorbed in the same configuration, probably the flat position. The subsequent reduction and alternation in capacitance is believed due to a structuring of the adsorbate similar to that in the bulk where certain physical properties oscillate with carbon number. Colorimetric analysis of solutions with and without additions showed the dissolution rates to be higher than those measured by the polarization technique, possibly due to the "chunk" effect, in which dislodged grains of metal contribute to the total but not faradaic corrosion.

Kinetics of Iron Corrosion in Concentrated Acidic Chloride Solutions

Abstract: The kinetics of active iron dissolution at 25°C has been studied in deaerated 1N and 6N chloride solutions for hydrogen ion concentrations of 0.1–6.0N. For 1N chloride solutions with , the dissolution reaction is described by anodic Tafel slope and electrochemical reaction order with respect to hydrogen ion activity . These parameters are characteristic of a dissolution mechanism in which chemisorbed halide ions interact with adsorbed hydroxyl ions in a two‐electron rate‐determining step. For 6N chloride solutions, this mechanism holds only over a narrower (H+) region up to 0.24N, in which . With increased ; and for , indicating that the hydrogen ion (and no longer the hydroxyl ion) catalyzed the dissolution reaction. A positive value of ensues for synergistic adsorption of hydrogen ions on the halide ion covered surface. A formal detailed dissolution mechanism is proposed, giving and , in agreement with experiment. Alternate dissolution mechanisms including one‐electron transfer schemes are discussed.

Laboratory Dissolution of Plagioclase Feldspars in Water and Organic Acids at Room Temperature

Abstract: Freshly fractured albite, oligoclase, labradorite, bytownite, anorthite, and a high-K variety of plagioclase in particle sizes between 4r[ pm and 150 arm were disolved at roorn temperature in deionized water, 0.01 M acetic and aspartic acids (weakly complexing), and salicylic and citric acids (strongly complexing). Solutes of centrifuged solution were analyzed for pI[, and for Si, Al, Fe, Mg, Ca, Na, and K. Ca-rich plagioclases dissolved in organic a,cids more readily than did Na-rich plagioclases, whereas Na-rich plagioclases were the more soluble in deionized water. AI was preferentially dissolved over Si in particular from Ca-rich plagioclase in complexing acids. Ca was relatively more soluble than was Na in both organic acids and water. The organic solvents, in order of increasing effect of dissolution, were acetic, aspartic, salicylic, and citric acids, which is the order of complexing capacities. Citric acid was more effective t.han other acids in extracting Al and Ca, particularly from Ca-rich plagioclases, presumably because of the formation of Aland Cacomplexes.

Transport-Controlled Deposition and Dissolution of Metals

Abstract: Metal deposition and dissolution usually involve more than a simple discharge or formation of hydrated metal ions. In most practical cases, reactions of complex dissociation or formation occur simultaneously as well as deposition and incorporation of foreign substances (impurities or additives), etc. They all affect the structure and appearance of the deposit obtained. In particular, the shape of the deposit, the surface roughness, and surface coarseness (see Section 2) are found to depend strongly on the path of the flow of the electric current (traditionally termed “primary current distribution”) and the path and rate of flow of the species involved, directly or indirectly, in the electrolytic process. Thus, the last factor has a profound effect on the morphology of the deposit and may be a cause of seemingly unrelated phenomena: (a) Amplification of surface irregularities has been known to appear in electrode processes of high specific rate when deposition is carried out at low concentrations of simple ions in solution.1,2 A special example of such a case is shown in Figure 1.

The Dezincification of Alpha and Beta Brasses

Abstract: The mechanisms of dezincification of single phase alpha and beta brasses were studied using X-ray diffraction, electron microprobe, metallographic, atomic absorption, and electrochemical techniques. The two mechanisms of dezincification which had been previously reported, (1) dissolution of both alloy constituents followed by redeposition of the more noble species, and (2) the selective removal of the less noble constituent, were found to be operative under certain conditions of potential and pH for both alpha and beta brasses. An electrochemical explanation of the circumstances under which dealloying can be expected to occur was developed based on the use of Pourbaix Diagrams.

Dissolution of trioctahedral layer silicates by ammonium oxalate, sodium dithionite–citrate–bicarbonate, and potassium pyrophosphate

Abstract: The effects of NH4-oxalate (pH 3), Na–dithionite–citrate–bicarbonate (pH 7.3), and K-pyrophosphate (pH 10) on various size fractions of biotite, chlorite, muscovite, and illite minerals were investigated. The data showed that the release of mineral cations by the three chemical extractants increased with decreasing particle sizes. The dissolution of layer silicates was slight and gradual in the particle size range of 100–5 μ, increased considerably for 5–2 μ and markedly below 2 μ. In general, NH4-oxalate dissolved the maximum percentage of Fe, Mg, and Al, and K-pyrophosphate extracted the least amount. Approximately 18.8% of original Fe, 15.5% of Mg, and 11.3% of Al were extracted from 0.2–0.08 μ-size biotite by the oxalate procedure. The corresponding values for the same size fraction of chlorite were: 23.2% Fe, 18.5% Mg, and 13.5% Al. In view of the data obtained it is suggested that the use of NH4-oxalate as an extractant for amorphous Fe and Al may have limitations for soils containing trioctahedral ...

Geochemical mechanics for the dissolution, transport, and deposition of aluminum in the zone of weathering

Abstract: Organic acids in the 0-01M concentration range representing amino-, aliphatic, and aro- matic types present in humus dissolve 70-85 ppm A1 from Arkansas bauxite at room temperature, whereas 0-03 ppm is dissolved in water. The species of A1 in aqueous solution, calculated from stability data, range from A13+ at pH 3 and lower, through AI2(OH)24+ at a maximum concentration at pH 4.5, AI(OH) 2+ at a maximum at pH 4.7, AI(OH)2 + at a maximum at pH 6.0, to AI(OH)4- at pH 8.5 and higher. In salicylic acid an Al-Sal + complex occurs between pH 1"5 and 8.5, and is at a maximum at pH 4.2. Solubility of A1 obviously is pH dependent; also because of the vulnerability of organic acids to oxidation, the solubility and transport of A1 is indirectly Eh dependent. Anions that combine with Al include OH- to form bauxite, PO43- to form lateritic phosphate such as the Bone Valley Formation, Fla., and SiO4 4- to form allophane or kaolin as noted in the kaolin synthesis by Linares and Huartes. Spongelike, pisolitic or oolitic structures, and mineral veins in bauxites, lateritic phos- phates, and some flint clays attest to mobilization of Al in solution. Lignites and humus zones associa- ted with laterites are a logical geologic source of these complexing organic solvents. Although Al is inherently mobile, such commonly available precipitating anions render A1 relatively immobile.

Cholesterol dissolution rate in micellar bile acid solutions: retarding effect of added lecithin.

Abstract: In vitro studies on the dissolution rate of cholesterol monohydrate crystals in micellar bile acid solutions showed that the addition of lecithin decreases the dissolution rate even though lecithin increases the equilibrium solubility of cholesterol in these solutions. The reduction in rates caused by lecithin was attributed to a large crystal-solution interfacial barrier. An effective permeability coefficient for the interfacial barrier was calculated to be around 1.5 x 10 -5 centimeter per second for the transport of cholesterol molecules.

A kinetic model for microbial growth on liquid hydrocarbons

Abstract: A kinetic model is presented to explain microbial growth using liquid n-alkanes as substrate. The model is based on the assumption that growth occurs on the soluble alkane and that the metabolite produced by the growing cells helps the dissolution of liquid alkanes in the aqueous medium. Growth curves based on that model fit well with growth data for batch and continuous culture reported by various authors. The model also explains the differences between the relative length of exponential and linear phases of growth reported earlier.

Voluminous oxidation of aluminium by continuous dissolution in a wetting mercury film

Abstract: Aluminium, in its normal passivated state, does not react with mercury, i.e., it is not attacked and does not wet or readily dissolve. When the passivating surface layer is removed from high-purity aluminium, the metal can be easily wetted by mercury and upon exposure to air a spontaneous and rapid growth of a fibrous or ribbon-like product emanates from the wetted surfaces. In this work it was observed that the reaction product had little mechanical strength and readily disintegrated into a molecular-scale powder. It was identified as γ-Al2O3 which even after heating for 48 h at 750° C was still of the order of 60 to 70 A in average particle size. By consideration of the Al-Hg phase diagram, thermodynamic data, and further experimental observations, a mechanism for the phenomenon has been proposed. The probably unique situation which exists at room-temperature in the Al-Hg system enables a spontaneous reaction to take place between the aluminium dissolved in the wetting mercury film and the water vapour and oxygen present in the atmosphere. The influences of several variables on the reaction product morphology and relative reaction rate were investigated. Also, other mercury-metal systems were investigated for possible similar reactions.

The Dissolution of Olivine in Aqueous Solutions of Inorganic Acids

Abstract: The dissolution of olivine was studied in aqueous solutions of inorganic acids at temperatures of 35, 50, and 65°C in order to obtain basic information about the alteration and leaching processes i...