Sorption of phosphate from innovative composite material focusing on physicochemical interactions

A modified inorganic bentonite (Zenith/Fe) based on natural bentonite has been evaluated for phosphate uptake under various physicochemical conditions prevailing in natural water bodies. The effects of material fraction size, solution alkalinity, dissolved organic matter (DOM), solution potential (Eh), ionic strength on the adsorption of phosphate on modified bentonite are investigated by bench-scale batch techniques. The role of anions and cations has been also evaluated. Modified inorganic bentonite had the most prominent effect on phosphate ion removal at an alkalinity close to that of soft water (low alkalinity), followed by moderate and hard waters (high alkalinity). Hence the phosphate-adsorption capacity (PAC) followed the order: [soft] > [moderate] > [hard] water. The kinetics of phosphate uptake by Zenith/Fe is influenced by DOM: Phosphate is captured during the first 60 min of adsorption while equilibrium is attained after approximately 120 min. However, the PAC of Zenith/Fe in the presence of DOM (74%) is lower than the PAC onto modified bentonite in the absence of DOM (87%). Metal cations in solution have a positive effect on phosphate uptake by Zenith/Fe. The PAC increased with the increase of cation concentration, following the order: Na+ > K+ > Mn2+ > Mg2+. Contrarily, PAC decreased with the increase of anion concentration following the order: [carbonate] > [chloride] > [sulfate]. In addition, phosphate adsorption was found to be not influenced by ionic strength, suggesting formation of strong inner-sphere complexes. Finally, solution potential does not change the maximum adsorption capacity of modified inorganic bentonite; however, it changes the adsorption rate in the first minutes.