C. Basualto

Comparative studies on polyelectrolyte complexes and mixtures of chitosan-alginate and chitosan-carrageenan as prolonged diltiazem clorhydrate release systems.

The aim of this work was to evaluate the possibility of using mixtures and/or polyelectrolyte complexes from both chitosan-alginate and chitosan-carrageenan as prolonged drug release systems. Different dissolution profiles were obtained by changing the polymer matrix system (chitosan-alginate or chitosan-carrageenan) and the method used to include these polymers into the formulation (physical mixture or polyelectrolyte complex). Drug dissolution profiles from the matrices have been discussed by considering the swelling behavior of the polymers used. The swelling behavior of the chitosan-carrageenan and chitosan-alginate systems was analyzed by using the Hopfenberg model which permits to separate the diffusional contribution, kf, from the relaxational contribution, kr, involved in solvent penetration/sorption in glassy polymers. The chitosan-alginate system is better than the chitosan-carrageenan system as prolonged drug release matrix because the drug release is controlled at low percentage of the polymers in the formulation, the mean dissolution time is high, and different dissolution profiles could be obtained by changing the mode of inclusion of the polymers. Good agreement between td and kf/kr values for the system chitosan-alginate was found, which means that the swelling behavior of the polymers controlled the drug release from the matrix. In the case of the system chitosan-carrageenan, the high capacity of carrageenan promotes the entry of water into the tablet and therefore the main mechanism of drug release would be the disintegration instead of the swelling of the matrix.

Application of hollow-fiber supported liquid membranes technique to the selective recovery of a low content of copper from a Chilean mine water

Abstract This communication describes the application of a hollow-fiber-type solid supported liquid membrane technique to the selective recovery and enrichment of copper from a Chilean mine water. The membrane extractor works by impregnating the porous structure of solid support with an organic film containing a selective salicylaldoximic extractant. Using a relatively low concentration of carrier extractant, a high degree of copper recovery was performed by the liquid membrane technique. The stripping flux of copper from membrane to receiving strip liquor was greatly influenced by the oximic carrier concentration and slightly by the sulfuric acid concentration utilized as stripping agent. No traces of all contaminant ions were detected in the resulting copper strip product solution. These results show the feasibility of separation and enrichment of copper using this liquid membrane technique. A bigger recovery of metal could be attained using a pilot-scale extractor whose design is the subject of current further work.

The solvent extraction separation of molybdenum and copper from acid leach residual solution of Chilean molybdenite concentrate

Abstract A procedure for recovery and separation of molybdenum (VI) and copper (II) from acid leaching residual solution of Chilean molybdenite concentrate by solvent extraction is studied. The process for the recovery of metals was carried out in three stages: 1. 1) Leaching of molybdenite concentrate with nitric acid produced “in situ” by reaction of sodium nitrate and sulfuric acid. The dissolution process at 80°C was effective, yielding a solid phase constituted mainly of MoO 3 and a residual solution. 2. 2) From this solution, molybdenum was extracted with PC-88A, a non-specific alkylphosphonic extractant. It was determined that the extraction is highly efficient around pH 0.8, since cationic species of Mo(VI), feasible to be extracted by PC-88A, are predominant in such pH region. No co-extraction of others metals was observed at the pH of molybdenum recovery. This metal was stripped by ammonia to give an enriched aqueous phase containing 36 g/L. 3. 3) Copper may then be effectively extracted from the resulting molybdenum extraction raffinate with LIX-864, a commercial chelation hydroxy oxime extractant. An optimum pH of 1.9 was determined for copper extraction. From loaded solvent, this metal is easily stripped with copper-containing concentrate sulfuric acid solutions to give a pregnant solution suitable for final recovery of metal by electrolysis.

Extraction of molybdenum by a supported liquid membrane method.

This is a report on the extraction of molybdenum(VI) ions using a supported liquid membrane, prepared by dissolving in kerosene, the extractant Alamine 336 (a long-chain tertiary amine) employed as mobile carrier. A flat hydrophobic microporous membrane was utilised as solid support. Appropriate conditions for Mo(VI) extraction through the liquid membrane were obtained from the results of liquid-liquid extraction and stripping partition experiments. The influence of feed solution acidity, the carrier extractant concentration in the organic liquid film and the content of strip agent on the metal flux through membrane were investigated. It was established that maximal extraction of metal is achieved at a pH 2.0 if sulphuric acid is used in the feed solution and at a pH value over 11.0 if Na(2)CO(3) is used as strip agent. Moreover, the molybdenum extraction through membrane is enhanced when a 0.02 mol l(-1) content of the amine carrier in the organic phase is used. The present paper deals with an equilibrium investigation of the extraction of Mo(VI) by Alamine 336 and its permeation conditions through the liquid membrane, and examines a possible mechanism of extraction.

Study of the influence of the pH media dissolution, degree of polymerization, and degree of swelling of the polymers on the mechanism of release of diltiazem from matrices based on mixtures of chitosan/alginate.

ABSTRACT The dissolution profiles of formulations based on mixtures of chitosan/alginate depend on the pH. It is possible to distinguish two processes: (a) a fast kinetic drug release up to 180 min, where the pH value changes from 1.17 to 2.21 and the drug released is controlled by the degree of polymerization and the quantity of chitosan in the formulation; (b) a low kinetic drug release between 210 and 480 min, where the pH value changes from 5.52 to 8.72 and the drug release from the matrix is controlled by the interpolymeric complex. In all formulations the order of release, according to Peppass model in the range of fast kinetic drug release, was between 0.5 and 1.0. The mechanism of release was non-fickian diffusion, which corresponds to a coupling mechanism of diffusion and relaxation of the polymer.

Extraction of cadmium from aqueous solutions by emulsion liquid membranes using a stirred transfer cell contactor

It is studied the extraction of cadmium(II) ions from acidic aqueous solutions using a stirred transfer cell-type emulsion liquid membrane (ELM) prepared by dissolving in kerosene, with D2EHPA (an alkylphosphoric acid) as mobile carrier and Span-80 as surfactant. The ELM allowed efficient metal transport from the feed solution to the stripping liquor in experiments carried out at 25 oC. The significant variables on cadmium transport through the membrane were extractant concentration and metal content in the feed metal-donor solution. Concentration of HCl as stripping agent affected only the initial metal extraction rate but not the extraction extent. The surfactant content used in this study stabilized the membrane adequately, but the use of a higher content produced a smaller initial extraction rate due to higher interfacial resistance. The experimental results suggest the possibility of recovering or removing valuable or toxic metals from dilute aqueous solution in an extractor based on emulsified liquid membranes.

Cr(VI) sorption behavior from aqueous solutions onto polymeric microcapsules containing a long-chain quaternary ammonium salt: kinetics and thermodynamics analysis.

This work studies the adsorption of Cr(VI) ions from an aqueous acid solution on hydrophobic polymeric microcapsules containing a long-chain quaternary ammonium salt-type extractant immobilized in their pore structure. The microcapsules were synthesized by adding the extractant Aliquat 336 during the in situ radical copolymerization of the monomers styrene (ST) and ethylene glycol dimethacrylate (EGDMA). The microcapsules, which had a spherical shape with a rough surface, behaved as efficient adsorbents for Cr(VI) at the tested temperatures. The results of kinetics experiments carried out at different temperatures showed that the adsorption process fits well to a pseudo-second-order with an activation energy of 82.7 kJ mol(-1), confirming that the sorption process is controlled by a chemisorption mechanism. Langmuirs isotherms were found to represent well the experimentally observed sorption data. Thermodynamics parameters, namely, changes in standard free energy (DeltaG(0)), enthalpy (DeltaH(0)), and entropy (DeltaS(0)), are also calculated. The results indicate that the chemisorption process is spontaneous and exothermic. The entropy change value measured in this study shows that metal adsorbed on microcapsules leads to a less chaotic system than a liquid-liquid extraction system.

Separation of Cu(II) and Mo(VI) from Mine Waters Using Two Microporous Membrane Extraction Systems

This is a report on the separation and recovery of Cu(II) and Mo(VI) ions from two Chilean mine waters using two hollow fiber-type microporous liquid membrane extraction systems. LIX-860 (a salicylaldoxime) and Alamine 336 (a long-chain tertiary amine) were used as carrier extractants for copper and molybdenum, respectively. The measurements of the permeation of these metallic ions through the liquid membrane indicate that the selective transport of Cu(II) produced in respect to iron, arsenic, and aluminum in the experiments resulted from a sulfuric acid leach residual solution. The copper permeation is enhanced at pH 2.8 and when the concentration of LIX-860 in the organic phase was increased. Molybdenum and rhenium were efficiently separated from copper and iron metals, which were obtained from a nitric acid leach residual solution, by a liquid membrane prepared using Alamine 336 as the carrier compound. The membrane extractor consisted of two coupled reactors (one for extraction and one for stripping). Circulation of the organic solution between the modules gave a quite good performance for the extraction step and a deficient behavior in the stripping stage. This problem was resolved by using an extraction system which operates with only one module and by impregnating the pores of the hollow fibers used as the solid support with the organic solution. The feed and strip solutions are circulated on opposite sides of the fibers. The experimental results indicated the feasibility of separation and recovery of metals from diluted mine waters by using this membrane technology.

Membrane transport of copper with LIX-860 from acid leach waste solutions☆

Abstract A membrane transport process is described. The process was developed for use in the recovery of copper from nitric acid leach residual solutions. The flux and the extraction extent of copper with 5-dodecylsalicylaldoxime dissolved in Kermac 500-T (an industrial diluent) were measured at 30°C by using a membrane extractor made of a holow fibre. The content of carrier extractant in the wall of the porous fibre presented the biggest influence on metal extraction rate and its extractability. The results were explained by a diffusion model which considers that the extraction chemical reaction would occur at the inner interface of the liquid membrane, taking account that diffusion of copper-oxime complex through the membrane would be the rate-controlling step.

STUDY OF THE SOLVENT EXTRACTION OF THE LIGHTER LANTHANIDE METAL IONS BY MEANS OF ORGANOPHOSPHORUS EXTRACTANTS

In recent years there has been a great demand for rare earth metals because of their unique physical and chemical properties as new constituents for electronic, optical and magnetic devices. Because oftheir extremely similar chemical and physical properties, it is very difficult to separate them. A study ofsolvent extraction oflighter lanthanide metal ions with a family of organophosphorus extractants, commercially known as D2EPHA, PC88A, CYANEX 272 and CYANEX 301, was made. In general it was found that praseodymium ions were extracted with all the extractants, while in decreasing order neodymium, cerium and lanthanum were extracted less efficiently. Moreover, the D2EHPA and PC88A showed higher extraction efficiencies over the whole pH range used, but they did not allow an effective separation ofREE ions. Furthermore, with CYANEX 301 some degree ofseparation ofthe metal ions was achieved, but the extraction efficiencies were comparatively lower. On the contrary, using the CYANEX 272 extractant, medium efficiencies of extraction were achieved, but with a lower ability to separate the REE ions.