Zeolites and other molecular sieves for chromate remediation

[摘要] Porous solids loaded with redox-active ions were examined for the selective uptake and simultaneous reduction of Cr(VI) from aqueous solution. XRF spectroscopy was used to determine the extent of chromium uptake by molecular sieves: 29.1 mg\(_C\)\(_r\)/g\(_s\)\(_i\)\(_e\)\(_v\)\(_e\) for Mn-loaded AIPO-5. Some systems were templated: TEM confirmed the introduction of mesopores. Mössbauer and EPR spectroscopies characterised oxidation states and site symmetries of metal ions. Fe(II)-loaded molecular sieves were found to be appreciably oxidised (~ 80 %). To increase the fraction of redox-active ions, promising systems were reduced under 500ºC hydrogen flow for 0-24 hours. Fe(II) fraction increased and Fe(0) metal was evolved after 3-6 hours. Fe(0) was found not to increase chromium loadings, and PXRD patterns demonstrated loss in crystallinity with irreversible breakdown of the molecular sieve upon formation of metal clusters. Fe(II) and MN(II) zeolite X samples were highly selective towards Cr(VI), even in mixed solutions, until large numbers of other metal ions were introduced. Competitive ion exchange, complexation and acid treatment were explored for the purpose of extracting Cr(III) and recycling the molecular sieve. Ba(II) and Ag(I) ions showed the greatest promise for chromium extraction.

[发布机构] University:University of Birmingham;Department:School of Chemistry

[关键词] Q Science;QD Chemistry