A. Justo

Problems in the dissolution of silicates by acid mixtures

The decomposition of silicate rocks using mixtures of mineral acids has been studied. The conventional acid method of dissolving rocks with hydrofluoric-perchloric-nitric acid mixtures is unsatisfactory when pyrophyllite is present. This mineral is not destroyed by acid attack, whereas other silicates such as mica, kaolinite, quartz, feldspars, smectite and interstratified illite-smectite are decomposed. If the acid attack is carried out in a pressure vessel, pyrophyllite is dissolved completely, but with more difficulty than the other silicate minerals present.

Elaboration and Characterization of the Diazepam-Polyethyleneglycol 6000 Solid Dispersions

AbstractDiazepam-polyethyleneglycol 6000 solid dispersions systems were prepared by melting and solvent methods. These dispersions were characterized using D.T.A., X-Ray diffraction and microscopy. The phase diagram has shown that this system is characterized as a simple eutectic mixture with a eutectic composition of 87% diazepam and 13% P.E.G. 6000. Solubility studies showed a linear increase in drug solubility with the increase of PE.G. 6000 concentration.

Thermal study of diazepam-poly(ethylene glycol) 6000 solid dispersions

Abstract Solid dispersions of the binary system Diazepam-poly(ethylene glycol) 6000 have been prepared and studied by means of DTA and optical microscopy. Thermal analysis suggests that a simple eutectic is formed close to the melting point of pure poly(ethylene glycol) 6000. A Diazepam-poly(ethylene glycol) 6000 phase diagram is proposed, although the precise determination of the eutectic point is tentative, as in other solid dispersion systems. The extrapolated values are 87 wt.% poly(ethylene glycol) 6000 and 13 wt.% of the drug. This is in accordance with Tammans triangle, which is constructed and discussed. The microscopic study of the system has shown how the drug becomes very finely dispersed by the formation of very fine particles during solidification of the melt. All these results are of great pharmacological interest in further studies on dissolution processes.

Mineralogy of soils containing pyrophyllite from southern Spain: isolation and identification of the mineral.

Pyrophyllite in the different horizons of typic Haploxeralf and ultic Haploxeralf soils in the south of Spain and developed on shales was studied. The origin of the pyrophyllite in the soils studied was likely to have been in the parent material because the pyrophyllite was detected in shales of Devonian age. The pyrophyllite was isolated from the rest of the minerals, except rutile, by a method previously developed by the authors. We identified the pyrophyllite as type 1Tc by means of x-ray powder diffraction, differential thermal analysis and thermogravimetry, infrared analysis, scanning electron microscopy, and chemical analysis.

Adsorption of chlordimeform by humic substances from different soils.

We studied the interaction of the cationic pesticide chlordimeform with humic and fulvic acids from different soils. The mechanism of chlordimeform adsorption is essentially a cation exchange reaction. Adsorption is influenced by the origin of the humic substances because of the different content in functional groups. Fulvic acids adsorb in lower proportion than humic acids from the same soil, despite the higher content in functional groups.

Effect of pyrophyllite on the precipitation of aluminium sulphate during the dissolution of aluminosilicates by acid mixtures

The dissolution of silicate rocks with hydrofluoric-sulphuric-nitric acid mixtures has been studied. When the samples contained pyrophyllite in addition to other silicoaluminate minerals, the pyrophyllite was not attacked and part of the aluminium dissolved and separated from the other minerals and was precipitated as aluminium sulphate with different degrees of hydration.