Abstract
The study reports aspects that allowed to correlate structural and redox properties of iron species deposited on clay minerals with the capacity of geomaterials for arsenic removal. Natural ferruginous clays as well as an iron-poor clay chemically modified with Fe(III) salt (ferrihydrite species) were investigated as adsorbents of the arsenate(V) in water. The study, carried out from minerals from abundant Argentinean deposits, was conducted with the aid of different techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM-EDS), Raman Spectroscopy, ICP-AES (Inductively Coupled Plasma) chemical analysis and Temperature Programmed Reduction (TPR). This last technique allowed to detect availability of iron species in oxidic environment with different structural complexity and to determine active sites, accessible for arsenate(V) adsorption. The effect was observed through temperature dependence of the first Fe(III) reduction step (below 570°C) of iron-oxide species. The sequence of reducibility: ferrihydrite > hydrous oxide (goethite) > anhydrous oxide (hematite) > structural iron in clay was in agreement with the availability of iron active sites for the reducing process as well as for the arsenate adsorption. The important role of very high iron content in original samples was also observed. The chemical activation of iron-poor clay by a simple and feasible modification with Fe(III) solutions promoted the deposition of the ferrihydrite active phase with an increase of 2.81% (expressed as Fe2O3) respect to the original content of 1.07%, constituting an accessible and eco-friendly technological alternative to solve the environmental problem of water containing arsenic.
Highlights
A series of innovative and alternative technologies have been developed in last years for dealing different type of environmental problems in worldwide
The iron content ranged between 1.07% and 54.50% for natural clays, whereas for the iron modified sample (MC5) the iron was increased from 1.07% (C5) to 3.88%
The study of thermal reduction behavior of natural clay minerals containing iron, as well as of Fe(III) activated iron-poor species allowed establishing a correlation between iron reducibility and performances as Arsenic adsorbents
Summary
A series of innovative and alternative technologies have been developed in last years for dealing different type of environmental problems in worldwide. Research efforts are done to establish a simple, inexpensive and locally appropriate method to arrive to the 10 ppb As background, recommended by the WHO With this aim the effectiveness of arsenic removal capacity by means of natural Al, Mn and Fe oxide phases was extensively studied, related to the geochemical affinity between arsenate(V) oxoanion and metallic oxide species [5]-[11]. In this sense, iron oxy-hydroxides as goethite, hematite and red mud as well as ferruginous clay minerals are used as adsorbents with different results [7] [8] [10]
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