Clay biopolymers matrix (fungi or bacteria and montmorillonite) to improve the uranium uptake: adsorption isotherms models

M. OLIVELLI; G. CURUTCHET; R. TORRES

Budapest

Conferencia; 5th Mid-European Clay Conference (MECC2010); 2010

Uranium is heavy metal, with noticeable toxicity associated with nuclear energy processes and acidic mine drainage. It reaches water from natural and man-made sources representing a risk not only for human but also for environment. Conventional sorption techniques for heavy metals removal from wastewaters are not useful due to the great volumes treated and the low concentration of pollutants. Biosorption is an alternative process where different types of biomass allow concentrating heavy metals from diluted solutions. Among the biomass described until now bacteria, algae and fungi were the most used to Uranium uptake. Fungal biomass had the advantage of being easily and low cost generated. The main technological drawback in biosorption processes is getting a suitable immobilisation of the biomass to obtain efficient biofilters. A methodology to increase biosorption surface and retain biomass is to generate clay biopolymers matrix. Montmorillonite (MMT) clays have optimal characteristics to be used as innocuous sorbents, with the advantage to be able also to complex all kind of organic as well as inorganic compounds on its surface. In this study, two fungi: Aphanocladium sp., Acremonium sp., and the acidophilic bacteria Acidithiobacillus ferrooxidans were used as micro organisms growth on MMT (in P5 and K9 saline media, respectively). The Uranium adsorption isotherms on all MMT/systems studied were fitted to Langmuir, Freundlich, Tempkin, Redlich-Peterson, and Toth models, in order to determine monolayer coverage of adsorbate over homogeneous adsorbent surface; heterogeneous system; indirect adsorbate/adsorbate interactions; homogeneous/heterogeneous system and systems with submonolayer coverage, respectively. MMT/micro organisms systems and Uranium adsorbed on MMT/micro organisms systems were characterized by specific surface area determined by water vapour adsorption (Sw) and XRD (analysis of the reflection peak d(001).   Specific surface area (Sw) indicates differences from -5% to +50% for MMT in P5 and K9 saline media, respectively. While the different microorganisms growth on MMT evidenced only around 5-10% difference respect to the Sw value of MMT. All MMT/micro organisms systems showed higher maximum Uranium adsorption that those obtained from micro organisms or MMT alone. Adsorption isotherms for MMT+ Aphanocladium sp fitted with Freundlich model while MMT+ Acremonium sp. and MMT+ Acidithiobacillus ferrooxidans fitted with Toth adsorption model, indicating the presence of heterogenous and submonolayer coverage, respectively..  The XRD analysis of the reflection peak d(001) performed on MMT and MMT/micro organisms indicated: intensity decrease and interlayer space collapse with the micro organisms presence respect of that of raw MMT. This behaviour was mainly produced by the different saline growth media or an interlayer water displacement by the micro organism entrance in the interlayer space. Uranium adsorption shift the MMT reflection peak d(001) around 3.5Å, indicating an Uranium entrance in the interlayer clay space.