Mineralogical attenuation for metallic remediation in a passive system for mine water treatment

Passive systems with constructed wetlands have been consistently used to treat mine water from abandoned mines. Long-term and cost-effective remediation is a crucial expectation for these water treatment facilities. To achieve that, a complex chain of physical, chemical, biological, and mineralogical mechanisms for pollutants removal must be designed to simulate natural attenuation processes. This paper aims to present geochemical and mineralogical data obtained in a recently constructed passive system (from an abandoned mine, Jales, Northern Portugal). It shows the role of different solid materials in the retention of metals and arsenic, observed during the start-up period of the treatment plant. The mineralogical study focused on two types of materials: (1) the ochre-precipitates, formed as waste products from the neutralization process, and (2) the fine-grained minerals contained in the soil of the wetlands. The ochre-precipitates demonstrated to be poorly ordered iron-rich material, which gave rise to hematite upon artificial heating. The heating experiments also provided mineralogical evidence for the presence of an associated amorphous arsenic-rich compound. Chemical analysis on the freshly ochre-precipitates revealed high concentrations of arsenic (51,867 ppm) and metals, such as zinc (1,213 ppm) and manganese (821 ppm), indicating strong enrichment factors relative to the water from which they precipitate. Mineralogical data obtained in the soil of the wetlands indicate that chlorite, illite, chlorite–vermiculite and mica–vermiculite mixedlayers, vermiculite, kaolinite and goethite are concentrated in the fine-grained fractions (<20 and <2 μm). The chemical analyses show that high levels of arsenic (up to 3%) and metals are also retained in these fractions, which may be enhanced by the low degree of order of the clay minerals as suggested by an XRD study. The obtained results suggest that, although the treatment plant has been receiving water only since 2006, future performance will be strongly dependent on these identified mineralogical pollutant hosts.Fundação para a Ciência e a Tecnologia (FCT

Das Niedersaechsische Fliessgewaesserschutzsystem. Grundlagen fuer ein Schutzprogramm Einzugsgebiete von Oker, Aller und Leine

With 2 mapsAvailable from TIB Hannover: RA 4507(25,2) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Das Niedersaechsische Fliessgewaesserschutzsystem. Grundlagen fuer ein Schutzprogramm Einzugsgebiete von Weser und Hunte

With 2 mapsAvailable from TIB Hannover: RA 4507(25,3) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Das Niedersaechsische Fliessgewaesserschutzsystem. Grundlagen fuer ein Schutzprogramm Elbe-Einzugsgebiet

With 2 mapsAvailable from TIB Hannover: RA 4507(25,1) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Proc. Natl. Acad. Sci. U. S. A.

Caspases form a family of proteinases required for the initiation and execution phases of apoptosis. Distinct proapoptotic stimuli lead to activation of the initiator caspases-8 and -9, which in turn activate the common executioner caspases-3 and -7 by proteolytic cleavage. Whereas crystal structures of several active caspases have been reported, no three-dimensional structure of an uncleaved caspase zymogen is available so far. We have determined the 2.9-Angstrom crystal structure of recombinant human C285A procaspase-7 and have elucidated the activation mechanism of caspases. The overall fold of the homodimeric procaspase-7 resembles that of the active tetrameric caspase-7. Each monomer is organized in two structured subdomains connected by partially flexible linkers, which asymmetrically occupy and block the central cavity, a typical feature of active caspases. This blockage is incompatible with a functional substrate binding site/active site. After proteolytic cleavage within the flexible linkers, the newly formed chain termini leave the cavity and fold outward to form stable structures. These conformational changes are associated with the formation of an intact active-site cleft. Therefore, this mechanism represents a formerly unknown type of proteinase zymogen activation

Structural basis for the activation of human procaspase-7

Caspases form a family of proteinases required for the initiation and execution phases of apoptosis. Distinct proapoptotic stimuli lead to activation of the initiator caspases-8 and -9, which in turn activate the common executioner caspases-3 and -7 by proteolytic cleavage. Whereas crystal structures of several active caspases have been reported, no three-dimensional structure of an uncleaved caspase zymogen is available so far. We have determined the 2.9-Angstrom crystal structure of recombinant human C285A procaspase-7 and have elucidated the activation mechanism of caspases. The overall fold of the homodimeric procaspase-7 resembles that of the active tetrameric caspase-7. Each monomer is organized in two structured subdomains connected by partially flexible linkers, which asymmetrically occupy and block the central cavity, a typical feature of active caspases. This blockage is incompatible with a functional substrate binding site/active site. After proteolytic cleavage within the flexible linkers, the newly formed chain termini leave the cavity and fold outward to form stable structures. These conformational changes are associated with the formation of an intact active-site cleft. Therefore, this mechanism represents a formerly unknown type of proteinase zymogen activation