Evidence for a non-GABAergic action of quaternary salts of bicuculline on dopaminergic neurones

Intracellular recordings were made from neurones, presumed to be dopaminergic, in the rat midbrain slice preparation. Bicuculline methiodide (BMI) and methochloride (BMC) reversibly blocked the slow, apamin-sensitive component of the afterhyperpolarization in these cells. The IC50 for this effect was about 26 microM. In comparison, BMC antagonized the input resistance decrease evoked by muscimol (3 microM) with an IC50 of 7 microM. The base of bicuculline was less potent in blocking the slow afterhyperpolarization. SR95531 (2-[carboxy-3'-propyl]-3-amino-6-paramethoxy-phenyl-pyridaziniu m bromide), another competitive GABA(A) antagonist, and picrotoxin, a non-competitive GABA(A) antagonist, also blocked the action of muscimol (IC50s: 2 and 12 microM respectively), but had no effect on the afterhyperpolarization at a concentration of up to 100 microM. Moreover, 100 microM SR95531 did not affect the blockade of the afterhyperpolarization by BMC. This blockade persisted in the presence of tetrodotoxin and was apparently not due to a reduction of calcium entry, suggesting that it involved a direct action on the channels which mediate this afterhyperpolarization. These results strongly suggest that quaternary salts of bicuculline act on more than one target in the central nervous system. Thus, the involvement of GABA(A) receptors in a given effect cannot be proven solely on the basis of its blockade by these agents.     

Role of pH on the adsorption of xanthate and dithiophosphinate onto galena

In the concentrators of a Mexican mining company has been observed that the pH of the flotation has a significant effect on the galena recovery: the increase of pH from 7.5 to 9.5 in the Pb/Cu flotation circuit, resulted in a decrease of about 10% of lead recovery. In the present investigation, experimental models and techniques were developed to study the effect of pH on xanthate and di-isobutyl dithiophosphinate adsorption onto galena. The results obtained by UV / Vis spectroscopy showed that once galena surface has been slightly oxidised by the dissolved oxygen of the aqueous suspension, adsorption of both surfactants increases significantly, being adversely affected by the increase of pH from 5.5 to 9.5. Microflotation measurements performed for both surfactants support these findings. Thermodynamic simulation of the system suggests that the observed behaviour is due to the nature of the solid species formed on the galena surface at the particular pH: lead sulfate (PbSO₄) under neutral and slightly acid conditions, and the basic sulfate (2PbO·PbSO₄) under neutral and slightly alkaline conditions, as well as to their respective solubility. Infrared spectrometry confirmed the occurrence of sulfate onto galena particles, with a higher concentration for the acid pre-conditioning compared to the alkaline pre-conditioning.     

Adsorption of dichromate ions on the red mud surface

The possibility of using a red mud (waste of alumina production) as a sorbent of dichromate ions from aqueous solutions is studied. A method for the activation of red mud by hydrochloric acid is proposed. The dependences of the amount adsorbed of dichromate ions on the pH and initial concentration of aqueous solutions are studied.     

Direct electrowinning of lead from galena concentrate anodes

The results of an investigation of the electrowinning of lead directly from a galena concentrate compact anode employing an acetate bath as the electrolyte are reported. The effects of graphite content in the compact electrode, bath composition, time of electrolysis, temperature of the bath, current density and compaction pressure were studied on a laboratory scale to optimize operating conditions. An electrode containing 6.25% graphite, compacted at 238 MN m^?2 for 5 min, resulted in 70% current efficiency for the dissolution of lead according to the reaction PbS → Pb²⁺ S⁰ + 2e in a bath of ammonium acetate (0.5 M), acetic acid (0.35 M) and lead acetate (0.1 M) when electrolysed at 333 K with a current density of 110.5 A m^?2. The results have formed the basis of a pilot plant design.     

Model for the ferric chloride leaching of galena

A shrinking core model for the FeCl₃ leaching of galena (PbS), which accounts for the microstructure previously observed during this process, is presented. The microstructure is characterized by two distinct product layers—PbCl₂ in direct contact with the PbS core and S^o above the PbCl₂ layer. Rate equations for the evolution of the three solid phases and the PbS leaching conversion are derived for the case of flat plate geometry appropriate for the reaction of massive galena fragments. In the case of rate control by diffusion of the lead chloride reaction products through the S^o layer, the system is shown to exhibit parabolic behavior as long as the S^o layer is built up primarily at the PbCl₂-S^o interface. For the mechanism considered in this study, negative deviation from parabolic behavior is observed to increase as the amount of S^o forming at the external S^o-solution interface rises. When the system is controlled by surface reaction kinetics, the model predicts linear rates under all circumstances.     

The dissolution of galena in ferric chloride media

The dissolution of galena (PbS) in ferric chloride-hydrochloric acid media has been investigated over the temperature range 28 to 95 °C and for alkali chloride concentrations from 0 to 4.0 M. Rapid parabolic kinetics were observed under all conditions, together with predominantly (>95 pet) elemental sulfur formation. The leaching rate decreased slightly with increasing FeCl₃ concentrations in the range 0.1 to 2.0 M, and was essentially independent of the concentration of the FeCl₂ reaction product. The rate was relatively insensitive to HCl concentrations <3.0 M, but increased systematically with increasing concentrations of alkali or alkaline earth chlorides. Most significantly, the leaching rate decreased sharply and linearly with increasing initial concentrations of PbCl₂ in the ferric chloride leaching media containing either 0.0 or 3.0 M NaCl. Although the apparent activation energy was in the range 40 to 45 kJ/mol (∼10 kcal/mol), this value was reduced to 16 kJ/mol (3.5 kcal/mol) when the influence of the solubility of lead chloride on the reaction rate was taken into consideration. The experimental results are consistent with rate control by the outward diffusion of the PbCl₂ reaction product through the solution trapped in pores in the constantly thickening elemental sulfur layer formed on the surface of the galena.     

The kinetics of leaching galena with ferric nitrate

The kinetics of leaching galena with ferric nitrate as oxidant has been studied. Experimental results indicate that the rate of galena dissolution is controlled by surface chemical reaction. Rate is proportional to the square root of the concentration of ferric ion. The addition of more than one mole/liter sodium nitrate decreases reaction rate. With nitrate additions below this concentration, rate either remains constant or is slightly enhanced. An activation energy of 47 kJ/mol was measured, and rate is proportional to the inverse of the initial size of galena particles. These results are explained in terms of mixed electrochemical control. The anodic reaction involves the oxidation of galena to lead ion and elemental sulfur, and the cathodic reaction involves the reduction of ferric ion to ferrous ion.     

The leaching of galena in ferric sulfate media

The leaching of galena (PbS) in ferric sulfate media was investigated over the temperature range 55 °C to 95 °C and for various Fe(SO₄)_1.5, H₂SO₄, FeSO₄, and MgSO₄ concentrations. Relatively slow kinetics were consistently observed; in most instances, the 1-2/3α-(1−α)^2/3 vs time relationship, indicative of a diffusion-controlled reaction, was closely obeyed. The diffusion-controlled kinetics were attributed to the formation of a tenacious layer of PbSO₄ and S⁰ on the surface of the galena. The generation and morphology of the reaction products were systematically determined by scanning electron microscopy, and complex growth mechanisms were illustrated. The leaching rate increased rapidly with increasing temperature, and the apparent activation energy is 61.2 kJ/mol. The rate increases as the 0.5 power of the ferric ion concentration but is nearly independent of the concentration of the FeSO₄ reaction product. The rate is insensitive to H₂SO₄ concentrations <0.1 M but increases at higher acid levels. The presence of neutral sulfates, such as MgSO₄, decreases the leaching rate to a modest extent.     

The leaching of galena in cupric chloride media

The kinetics of dissolution of galena (PbS) in CuCl₂-HCl-NaCl media have been investigated using the rotating disk technique. Rapid nonlinear kinetics are observed over the temperature range 45 °C to 90 °C and for NaCl concentrations from 0 to 4.0 M. The leaching rate is in-dependent of CuCl₂ concentrations >0.1 M but increases with increasing concentrations of either HC1 or NaCl. The leaching rate decreases with the accumulation of either the PbCl₂ or CuCl reaction product in the leaching medium but is insensitive to the disk rotation speed. The apparent activation energy for the rate controlling process is 33 kJ/mol, and this value falls to about 15 kJ/mol when interpreted as a dissolution rate for PbCl₂, whose solubility increases with temperature. The above observations are shown to be consistent with rate control by the outward diffusion of the PbCl₂ and CuCl reaction products through the solution trapped in the pores of the constantly thickening elemental sulfur layer which forms on the surface of the galena. CANMET, Energy, Mines, and Resources Canada, 555 Booth Street, Ottawa, ON, K1A 0G1, Canada.     

Kinetics of galena leaching in hydrochloric acid-chloride solutions

This article presents a series of studies on the nonoxidative leaching of galena with hydrochloric acid in the presence of a metallic chloride. A systematic study was carried out using a succession of metallic chlorides with cations of different valencies in an attempt to generalize the leaching behavior of these solutions. The reaction order for leaching galena, in terms of the mean ionic activity of HCl, is 3/2 over a wide range of concentration. The addition of soluble chlorides to a HCl solution increases the leaching rate of the galena by augmenting the mean ionic activity of the acid. A reaction order of 3/2 for the mean HCl activity in the solution is maintained for solutions in which the acid concentration is constant and the metallic chloride varies, as well as for the opposite situation. Therefore, the only activity that must figure in the kinetic equation is that of the HCl. The activation energy (58.5 kJ/mole) is independent of the chloride used to increase the activity of the hydrochloric acid. The same is true for the Arrhenius prefactor.     

Kinetics of galena dissolution in ferric chloride solutions

A leaching investigation of galena with ferric chloride has been carried out as a function of concentration of ferric chloride and sodium chloride, temperature, and particle size. Three size fractions were considered in this investigation, namely, 48 × 65, 35 × 48, and 28 × 35 mesh. The concentration ranges of ferric chloride and sodium chloride used in this investigation were 0 to 0.25 M and 0 to 3 M, respectively. The reaction rate mechanism has been discussed in terms of a shrinking core model developed for cubic systems. Mass transport of ferric chlorocomplex through the product sulfur layer appears to be responsible for establishing the overall leaching rate under most of the conditions used in this investigation. The apparent activation energy for the leaching of 28 × 35 mesh galena with 0.1 M FeCl₃, 1 M HC1, and 3.0 M NaCl was found to be about 8.05 kcal/mol (33.7 kJ/mol), which was partially contributed by diffusion and partially by the heat of reaction of the formation of ferric chlorocomplexes. Rate of dissolution at both 50° and 90 °C is greatly affected by ferric chloride concentration up to 0.2 M and is essentially constant with ferric chloride concentration above this value.     

The effect of chloride ion on the ferric chloride leaching of galena concentrate

Previous investigations of the ferric chloride brine leaching of galena concentrate have shown that additions of chloride ion result in accelerated dissolution rates. The current study has provided the necessary information to extend and modify these previous results by incorporating the important effect of chloride ion on the dissolution kinetics. As part of this study the solubility of lead chloride in ferric chloride-brine solutions has been determined and results indicate that additions of either FeCl₃ or NaCl increase the PbCl₂ solubility. This is attributed to the effect of complexing on the level of free chloride ion. In addition, the dissolution kinetics of elemental lead and lead chloride were also determined and compared with the kinetics of PbS dissolution. It is significant that the rate of dissolution of PbCl₂ decreases as the concentration of Cl⁻ is decreased and as the concentration of dissolved lead increases. These results along with SEM examination of partially reacted Pb shot show that solid PbCl₂ forms on the surface long before the bulk solution is saturated with lead. The PbCl₂ is proposed to form by a direct electrochemical reaction between Cl⁻ and PbS prior to the formation of dissolved lead. The reaction was determined to be first order with respect to Cl⁻ and closely obeys the following kinetic model based on a rate limiting charge transfer reaction at the surface: The model is in excellent agreement with experimental results up to about 95 pct reaction as long as the solubility of PbCl₂ is greater than about 0.051 M. Where these conditions are not met, deviation from the surface reaction model occurs due to the extremely slow dissolution rate of PbCl₂. Therefore the effect of Cl⁻ on the brine leaching of PbS is attributed to two factors, the direct reaction of Cl⁻ with the pbS surface and the effect of Cl⁻ on the dissolution rate of PbCl₂. The overall dissolution process is viewed as occurring in three stages; in the first stage the reaction is controlled by the surface reaction and described by the model above, then as solid PbCl₂ is produced the diffusion of Cl⁻ would be equal in importance with the surface reaction,i.e, the second stage. As the reaction proceeds further, a shift in the rate-limiting step from surface reaction to product layer or pore diffusion occurs, the third stage. Thus the rate-determining step would no longer be just the surface reaction as observed experimentally at longer reaction times. The practical implications of these results for the processing of a complex sulfide concentrate using sequential, selective, or total leach approaches are also discussed.     

Effect of particle size distribution on recovery of coarse chalcopyrite and galena in Denver flotation cell

Abstract

The flotation recovery by particle size of single mineral chalcopyrite and galena was studied in a Denver flotation cell, using sodium dicresylthiophosphate (DTP) and sodium isopropyl xanthate (SIPX) as collectors and polypropylene glycol (PPG) as a frother. The study was extended to very coarse particle size (up to 1·6 mm). Froth stability was also measured in parallel to the batch flotation tests, in a specifically designed froth stability column, following the Bikerman approach. It is shown that particles up to 850 μm can be floated successfully, provided they are liberated and hydrophobic. However, the recovery of both chalcopyrite and galena was strongly influenced by the overall particle size distribution, decreasing sharply as the fraction of fines (?106 μm) in the feed also decreased. Rheology measurements showed negligible differences in pulp viscosity, and therefore in the collection zone hydrodynamics, between the different conditions tested. Froth stability, on the contrary, decreased as the feed particle size distribution became coarser. Correlation was found between the amount of fines in the pulp, froth stability and flotation recovery. The recovery of mineral particles is critically dependent on froth stability, which in turn is highly influenced by the overall particle size distribution of the feed material. For these reasons, the study also suggests that it is not possible in batch flotation to determine the rate and recovery of the coarse particle size fractions floating them independently from the fine size fractions.

Dans une cellule de flottation de Denver, on a étudié la récupération par flottation en fonction de la taille de particule d’un minéral unique de chalcopyrite ou de galène, en utilisant du dicrésyle thiophosphate de sodium (DTP) et de l’isopropyle xanthate de sodium (SIPX) comme agents collecteurs et du polypropylène glycol (PPG) comme agent moussant. On a étendu l’étude à la taille de particule très grossière (jusqu’à 1·6 mm). On a également mesuré la stabilité de la mousse en parallèle aux essais de flottation discontinue, dans une colonne de stabilité de la mousse spécialement conçue, d’après l’approche de Bikerman. On montre que l’on peut faire flotter avec succès des particules ayant jusqu’à 850 μm, à la condition qu’elles soient libres et hydrophobes. Cependant, la récupération, tant de la chalcopyrite que de la galène, était fortement influencée par la distribution globale de la taille de particule, diminuant sévèrement à mesure que la fraction de particules fines (?106 μm) dans l’alimentation diminuait. Les mesures de rhéologie montraient des différences négligeables dans la viscosité de la pulpe et ainsi dans l’hydrodynamique de la zone de collection, parmi les différentes conditions évaluées. Au contraire, la stabilité de la mousse diminuait à mesure que la distribution de la taille de particule de l’alimentation devenait plus grossière. On a trouvé une corrélation entre la quantité de particules fines dans la pulpe, la stabilité de la mousse et la récupération par flottation. La récupération des particules minérales dépend, de façon critique, de la stabilité de la mousse qui, à son tour est hautement influencée par la distribution globale de la taille de particule du matériel d’alimentation. Pour ces raisons, l’étude suggère également qu’il n’est pas possible, en flottation discontinue, de déterminer la vitesse et la récupération des fractions de taille de particules grossières, en les faisant flotter indépendamment des fractions de taille fine.     

The thermal behavior of mechanically activated galena by thermogravimetry analysis

The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA) at the heating rate of 10 K min⁻¹ in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T _di) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface area (S _G), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time, but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed.     

Influence of solid state properties on ferric chloride leaching of mechanically activated galena

The reaction of mechanically activated galena with ferric chloride solution was investigated in the concentration range [Fe³⁺] =0.01–0.6 M at temperatures between 303 and 338 K. The mechanical activation lasting 5–30 min was carried out in a planetary mill. It has been found that this reaction is sensitive to the microstrains produced in the structure of galena during grinding as well as to the concentration of Fe³⁺ in the solution. The influence of Fe³⁺ concentration is in operation practically only in the region [Fe³⁺] < 0.2 M.     

Kinetic effects of particle-size and crystal dislocation density on the dichromate leaching of chalcopyrite

Relatively pure, polycrystalline samples of Golden, New Mexico and Transvaal, South Africa chalcopyrite were ground and polished to fit into a density-compatible titanium alloy sandwich assembly and shock loaded (the Golden at 1.2 GPa, the Transvaal at 18 GPa peak pressure). The recovered samples were examined in the transmission electron microscope and observed to contain roughly 10³ and 10⁴ times more dislocations respectively than the natural, unshocked materials which contained roughly 10⁷ cm⁻². These materials were ground to three size fractions and leached in an acid-dichromate lixiviant at 50 and 70 °C (323 and 343 K). Corresponding size fractions were prepared from the unshocked material and leached for comparison; and these experiments were extended to a range of temperatures up to 90 °C (363 K) using a Bingham Canyon, Utah chalcopyrite. An unambiguous effect of dislocations was observed at the largest size fraction leached at 50 °C (323 K): the reaction rate constant increased from 1.44 × 10⁻³ to 1.62 × 10⁻³ to 2.73 × 10⁻³ min⁻¹ for dislocation densities increasing from roughly 10³ cm⁻² to 10¹¹ cm⁻². A linear relationship in the leaching rate was observed between 25 and 60 °C (298 and 333 K) and the activation energy was calculated to be approximately 12 kcal/mol (50 kJ/mol). Above 60 °C (333 K) a conspicuous rate decrease was observed. This was related to a densification of the sulfur product layer, which at 50 °C (323 K) was a loose, porous precipitate while at 90 °C (363 K) it was a continuous, tenacious, glassy coating on the chalcopyrite particles. In addition, and more importantly, the high-temperature decline in leaching rate was inferred to be associated with adsorption of Cr(VI) ion which decreases with increasing temperature. The anomalous and unpredictable behavior of chalcopyrite leached in acid-dichromate lixiviant was therefore observed to be related to variations in a surface chemisorption mechanism as well as variations in the nature of the sulfur reaction product layer. These effects also mask the influence of crystal defects and other surface-related crystallographic effects in leaching.     

The thermal behavior of mechanically activated galena by thermogravimetry analysis

The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA) at the heating rate of 10 K min⁻¹ in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T _di ) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface area (S _G ), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time, but the lattice distortions (ɛ) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed.     

Post treatment of silane and cerium salt as chromate replacers on galvanized steel

A complex film on hot-dip galvanized steel sheet (HDG) was prepared by immersing the sheet in 0.1wt.% Ce(NO3)3 solution and 5vol.% silane solution in turn. The corrosion protection of the complex film was evaluated by potentiodynamic linear polarization(LPR), electrochemical impendence spectra (EIS) and natural salt spray (NSS) tests and compared with that of single cerium film and silane film. The results showed that, the presence of these films on the zinc coating hindered corrosion reaction by reducing the rate of both anodic and cathodic reaction in the corrosion process, and the corrosion protection of the complex film was much better than that of single cerium film or silane film and closed to that of chromate film, because the polarization resistance Rp and electrochemical impendence were increased markedly. Microstructure and chemical composition of these pretreated films were also investigated by scanning electron microscopy (SEM) and AES.