Abstract:

The aim of this article is to research the ecomineralogical development by investigating the adsorption of iron oxide minerals for phenol and dissolved organic matter (DOM). The multiple mechanisms of surface adsorption associated with the iron minerals can coexist, mainly depending on the solution chemistry as well as the natural and physicochemical properties of adsorbates and minerals. The adsorption study was conducted by batch equilibrium techniques. The results showed that the adsorption of goethite and hematite for phenol is weak in acidic and mild acidic media, and that the phenol adsorption isotherms can be fitted well by Langmuir equation with a correlation coefficient of R>0985. Therefore, the phenol adsorption was subjected to a surface physical adsorption model, whereas the sorption of goethite for the DOM was stronger along with the DOM sorption fractionation. The DOM sorption fractionation was controlled simultaneously by multimechanisms in acidic and neutral media, mainly including “surface ligand exchange”, “hydrophobic force”, and “van der Waals forces” models. Moreover, the DOM sorption isotherms can be fitted well by linear and Freundlich equations with correlation coefficients, R>092, but not by Langmuir equation ascribed to low concentration of DOM used in this article. The effect of the mineral surface charge on adsorption was significant, especially when pH of the solution neared pHpzc (pH for point of zero charge); the phenol and the hydrophobic DOM molecule and/or fraction can preferentially adsorb onto iron oxide minerals because of the decrease in thickness; even the binding of the water film over the iron minerals disappear.  However, the phenol adsorption can be impacted more significantly because of its simple adsorption model, therefore, its pHdependence adsorption curve showed a peak value at pH 78 near the pHpzc. In general, surface complexation reaction of iron oxides can occur especially in acidic and mild acidic media. However, under the condition of pH 75 or so of this study, though the surface ligand exchange may have been still functional, the predominant adsorption mechanisms of DOM onto goethite would be mainly based on the “hydrophobic force” and “van der Waals forces” models. Moreover, the adsorption isotherm of DOM was almost linear (Freundlich equation fitting constant n=102), accounting for the importance of the later two types of adsorption models in the DOM adsorption. Of course, the surface sorption reactions of iron oxide minerals play an important role in regulating immobility and fate of pollutants and natural organic matter in red soils that contain low content of organic matter but high content of iron oxide minerals.

Key words:

adsorption; phenol; dissolved organic matter; mineral