PHOSPHORUS SORPTION DURING IRON(II) OXIDATION IN THE PRESENCE OF DISSOLVED SILICA

摘要

This study investigated the interactions of P and Si with ferrous-derived Fe oxides under conditions simulating natural systems. Iron oxides were formed from the oxidation of Fe(Il) at pH 7.0 under a CO_2/air mixture. Phosphate and/or silicate were either present during the oxidation of Fe(lI) or added 24 h after the Fe(ll) had oxidized and the solid had formd Oxidation of Fe(II) in the presence of P resulted in very high initial P sorption densities; however. much of this sorbed P was subsequently released into solution. probably as a result of coagulation and crystallite growth of the Fe oxide. If Si was present as well during Fe(Il) oxidation, initial P sorption densities were very high and almost all of the sorbed P remained in the solid phase. The formation of Fe(ll)-derived Fe oxide in the presence of Si and P resulted in a very effective sink for P. This solid may have applications in wastewater treatment and important implications for P chemistry in the natural environment. The presence of Si during Fe(II ) oxidation at molar rations of 0.36 Si/Fe or higher promoted the formation of ferrihydrite, an Fe oxide with a high specific surface area and a high concentration of reactive surface sites. Coagulation and crystallite growth of the ferrihydrite were inhibited by the Si, thereby limiting the release of P over time. When P was added 24 h after solid formation, the sorption capacity of the mixed Fe Si oxide was greater than the pure Fe oxide but. in both cases. sorption densities were much less than when P and Si were both present during solid formation Competition of Si and P for Fe oxide sorption sites appeared to he less important to P sorption than the influence of Si on Fe oxide mineralogy. at least under the experimental conditions studied.