Effect Of High Oxygen Pressure Research Articles

EFFECT OF PRESSURE ON GOLD CYANIDE LEACHING

Although the effect of high oxygen pressure on gold recoveries at elevated slurry temperatures was previously investigated, the sole effect of the pressure at ambient temperatures on cyanide leaching with the presence of nearly enough oxygen for the cyanide reactions to occur has not been found to be studied. This research work was carried out with the objective of investigating the effect of pressure on the recovery of gold from an oxide gold ore and flotation tailing (Carbon in leach (CIL) feed) samples during cyanide leaching process at room temperature. Pressure cyanidation experiments were run in a batch autoclave under different air and nitrogen gas pressures, and pH conditions. Atmospheric bottle roll leach tests for 24 and 8 hours resulted in 90.5% and 66.4% gold recoveries, respectively, whereas 8 hours batch autoclave leach tests under 90 psi air pressure resulted in 88.8% gold recovery from oxide ore samples. Flotation tailing samples leached under atmospheric and under 90 psi air pressure for 8 hours resulted in 16.8% and 34.5% gold recoveries, respectively.

Effect of high oxygen pressure annealing on superconducting Nd1.85Ce0.15CuO4 thin films by pulsed laser deposition from Cu-enriched targets

We show that the quality of Nd1.85Ce0.15CuO4 films grown by pulsed laser deposition can be enhanced by using a non-stoichiometric target with extra copper added to suppress the formation of a parasitic (Nd, Ce)2O3 phase. The properties of these films are less dependent on the exact annealing procedure after deposition as compared to films grown from a stoichiometric target. Film growth can be followed by a 1 bar oxygen annealing, after an initial vacuum annealing, while retaining the superconducting properties and quality. This enables the integration of electron-doped cuprates with their hole-doped counterparts on a single chip, to create, for example, superconducting pn-junctions.

Perturbed Angular Correlations Studies in the HgBa2CaCu2O6+δ high-TC Superconductor

The electric field gradients at Hg-199m nuclei have been measured via the perturbed angular correlation (PAC) technique, allowing a full characterization of the Hg neighborhood charge distribution at high oxygen doping on the Hg planes. The PAC technique has been applied to investigate the effect of high oxygen pressure during the measurement. Polycrystalline HgBa2CaCu2O6+delta (Hg-1212) samples have been annealed at 152 bar pressurized oxygen. The influence of oxygen pressure during the experiment was then investigated by measuring the samples at atmospheric pressure and under 152 bar oxygen pressure. The present set of PAC experiments shows that at high oxygen concentrations there is a non-uniform oxygen distribution. Moreover, the Hg environment is not free from oxygen and the results hint to a new type of ordering.

Auger electron spectroscopy study of copper binding states in YBa 2Cu 3O 7−x monocrystals: effect of high oxygen pressure

The Cu L 3M 45M 45 Auger transitions were compared for the oxides CuO and Cu 2O and for YBa 2Cu 3O 7− x monocrystals as grown or annealed at 400°C under 60 atm oxygen pressure. An indication of the presence of copper in other binding states than in copper oxides was found for the YBa 2Cu 3O 7− x monocrystals. Deconvolution of the Cu L 3M 45M 45 spectra allows a clear distinction between copper in the oxidized monocrystal and copper in a non-oxidized monocrystal. Gaussian components found for the superconducting oxide can be interpreted by considering the presence of two copper sites containing two different copper(II) binding states, or copper(II) andcopper(III) binding states. It is also probable that the variations in the L 3M 45M 45 line shapes for YBa 2Cu 3O 7− x and the shifts observed for this transition indicate the mixing of Cu 3d levels with O 2p states.

Increased axonal excitability during exposure to hyperbaric oxygen

The effect of high oxygen pressure on neural function was studied in the isolated nervous system of the cockroach. Intracellular and extracellular action potentials were recorded from single giant axons during exposure to 7 ATA (atmosphere absolute) (1 ATA = 0.1 MPa) of oxygen. Axonal excitability was measured as changes in stimulus strength-duration relationship. Initially, a transient increase in the rheobase current was observed followed by a significant decline to 75% of air control values. This decrease was accompanied by a parallel increase in the membrane time constant. The results demonstrate that hyperbaric oxygen increases axonal excitability. Such changes are consistent with the epileptogenic properties of high oxygen pressure.

Inhibitory effect of high oxygen pressure on potassiuminduced activation of pyruvate dehydrogenase and glucose metabolism in rat brain slices

The effects of high oxygen pressure on pyruvate dehydrogenase (pyruvate: lipoate oxidoreductase (decarboxylating and acceptor-acylating), EC 1.2.4.1) activity, tissue concentration of ATP, and CO 2 production from glucose were studied in rat brain cortical slices. The increase in pyruvate dehydrogenase activity and the lowering of cellular ATP, occurring during potassium-induced depolarization at 1 atm of oxygen, were reversed by increasing the oxygen pressure to 5 atm. When brain slices were incubated at 1 atm oxygen with [U- 14C]glucose, a high potassium medium approximately doubled the production of 14CO 2. Oxygen at 5 atm abolished this potassium-dependent increase in 14CO 2 production with no significant effect on glucose oxidation in normal Krebs-Ringer phosphate medium. Adding 4 atm helium to 1 atm oxygen did not interfere with the ability of potassium ions to activate pyruvate dehydrogenase, lower ATP, or increase glucose oxidation. The results show that toxic effects of hyperbaric oxygen, not manifest in “resting” tissue, may be revealed during stress such as potassium depolarization. The site of the toxic effects of oxygen is probably the cell membrane where excess oxygen appears to interfere with the action of the sodium pump, calcium transport or other processes stimulated by increased concentrations of extracellular potassium.

Effects of intermittent hyperbaric oxygen on guinea pig lung elastin and collagen

The effect of high oxygen pressure on collagen and elastin turnover in lung parenchyma tissue was studied in guinea pigs. Three groups of animals was used. One group (I) was given a clinically excessive exposure of 3 h daily for 9 days of 3 ATA oxygen. A second group (II) was given 3 ATA compressed air on the same schedule, and a third (III), a control, was given the same handling conditions only. Collagen and elastin which amounted to 10.45 and 4.62 mg, respectively, per 100 mg dry defatted parenchymal tissue was labeled with [14C]proline injected ip. Connective tissue protein turnover was estimated by labeling half of each group before exposure (a); effects on biosynthesis were determined by labeling the other half postexposure (b). No differences in hydroxyproline specific activity of collagen fractions or elastin were found with respect to either biosynthesis or turnover. Alveolar wall length-tension measurements were not changed. Since exposures were in excess of those used for treatment of gas gangrene, ischemic burns or wound healing, these results suggest that the metabolism of lung connective tissue is unaffected by the short-term exposure to hyperbaric oxygen.

Effect of high oxygen pressure on brain norepinephrine and serotonin turnover

The effect of high oxygen pressure on the in vivo turnover of NE in mouse and rat brain, and the turnover of 5-HT in mouse brain was investigated. Turnover of NE and 5-HT was determined by steady-state kinetic methods. In mice, synthesis of NE was inhibited by the administration of α-MPT. In rats NE turnover was determined from the decline in intracisternally administered H 3NE. Steady-state kinetic methods also were used to determine 5-HT turnover in mice, utilizing probenecid to block the transport of 5-HIAA. In these studies, 100% oxygen at 1 and 3 atmospheres had no effect on either NE turnover in mice and rats or 5-HT turnover in mice. These studies suggest that changes in NE and 5-HT turnover do not appear to be implicated in the onset of oxygen-induced convulsions.

Effect of high oxygen pressure on ground squirrels in hypothermia and hibernation: Popovic, V., R. Gerschman, and D. L. Gilbert. Amer. J. Physiol., 206: 49–50, 1964

Effect of high oxygen pressure on ground squirrels in hypothermia and hibernation: Popovic, V., R. Gerschman, and D. L. Gilbert. Amer. J. Physiol., 206: 49–50, 1964

EFFECT OF HIGH OXYGEN PRESSURE ON GROUND SQUIRRELS IN HYPOTHERMIA AND HIBERNATION.

The protective role of hypothermia has been demonstrated in barometric depression or hypoxia, in X irradiation, after intoxication with carbon monoxide or after intoxication with other substances, after severe hemorrhage, hyperuremia, or insulin shock. In the present work ground squirrels (hibernators) in three different metabolic states (euthermia, hypothermia, and hibernation) were exposed to 6 atm of pure oxygen and their survival was measured. The hibernating ground squirrels exposed to 6 atm of pure oxygen lived for over 18 hr, the hypothermic ground squirrels for over 6 hr, and the euthermic ground squirrels for a half-hour only. The oxygen consumptions of ground squirrels in three different physiological states—in hibernation, in hypothermia, and in euthermia—were in the proportion of 1:12:40, while the survival times of these animals show an inverse correlation of 33:13:1. Thus it appears that the lowering of body temperature has a protective role against high oxygen pressure mainly because of a decreased metabolism.

The Effect of High Oxygen Pressure on the Respiratory Metabolism of Pea Seeds

The time course of the changes in concentration of certain of the intermediates of the Krebs cycle (and derivatives of these intermediates) in the mature pea seed during the inhibition of respiration by high oxygen pressure has been studied. The results support the conclusion that the primary effect of high oxygen pressure is an inhibition of the oxidation of citric acid by the Krebs cycle. Aconitase appears to be the most likely site of inhibition. In the later stages of treatment there appears to be a slowing of the rate of glycolysis either as a consequence of the primary inhibition or due to direct inhibition of other enzymes. The highest rate of citrate accumulation observed in this work would allow 50 per cent, of the aerobic carbon dioxide output of the pea seed to be derived from the Krebs cycle.

Effect of high oxygen pressure on the protective action of cystamine and 5-hydroxytryptamine in irradiated rats.

BOTH the oxidized disulphide, cystamine (—S—S—) and its corresponding sulphydryl amine, cysteamine (—SH) are excellent radioprotective agents in vivo 1. If rats, protected by the latter reduced substance, respire pure oxygen under pressure (4–5 atmospheres absolute) at the time of irradiation, the protective action is completely reversed2,3 and this result also applies to cysteine. Our own findings have shown that this reversal also applies to the pharmacologically active amines, histamine and adrenalin, and largely to 5-hydroxytryptamine (vide infra). The lessening of the radioprotective action of these reducing agents by an increased oxygen pressure in tissue fluids may be due to the inactivation of additional —SH and reducing groups supplied to the body, or due to an increase in physical solution and diffusion of oxygen so provided, in overcoming the anoxaemia caused by either decreased oxygen-carrying capacity of haemoglobin (for example, with paraaminopropiophenone3), or by smooth muscle constriction in bronchioles or arterioles resulting from pharmacological action (for example, 5-hydroxytryptamine4). However, the protective disulphide, cystamine (—S—S—), is reduced to cysteamine (—SH), in vivo 5 and in vitro 6, and increased oxygen pressure in vivo may be expected to lessen its protective action, if the latter depends on the reduction of cystamine in tissues, to produce available —SH groups, or promote pharmacological activity, both of which tend to result in intracellular anoxia.