Underestimation of phosphorus fraction change in the supernatant after phosphorus adsorption onto iron oxides and iron oxide–natural organic matter complexes
Jinlong Yan
,
Tao Jiang
,
Ying Yao
,
Jun Wang
,
Yuanli Cai
,
Nelson W. Green
,
Shiqiang Wei
DOI:10.1016/j.jes.2016.08.005
Received April 13, 2016,Revised August 06, 2016, Accepted August 09, 2016, Available online September 08, 2016
Volume 29,2017,Pages 197-205
The phosphorus (P) fraction distribution and formation mechanism in the supernatant after P adsorption onto iron oxides and iron oxide–humic acid (HA) complexes were analyzed using the ultrafiltration method in this study. With an initial P concentration of 20 mg/L (I = 0.01 mol/L and pH = 7), it was shown that the colloid (1 kDa–0.45 μm) component of P accounted for 10.6%, 11.6%, 6.5%, and 4.0% of remaining total P concentration in the supernatant after P adsorption onto ferrihydrite (FH), goethite (GE), ferrihydrite–humic acid complex (FH–HA), goethite–humic acid complex (GE–HA), respectively. The < 1 kDa component of P was still the predominant fraction in the supernatant, and underestimated colloidal P accounted for 2.2%, 55.1%, 45.5%, and 38.7% of P adsorption onto the solid surface of FH, FH–HA, GE and GE–HA, respectively. Thus, the colloid P could not be neglected. Notably, it could be interpreted that Fe3 + hydrolysis from the adsorbents followed by the formation of colloidal hydrous ferric oxide aggregates was the main mechanism for the formation of the colloid P in the supernatant. And colloidal adsorbent particles co-existing in the supernatant were another important reason for it. Additionally, dissolve organic matter dissolved from iron oxide–HA complexes could occupy large adsorption sites of colloidal iron causing less colloid P in the supernatant. Ultimately, we believe that the findings can provide a new way to deeply interpret the geochemical cycling of P, even when considering other contaminants such as organic pollutants, heavy metal ions, and arsenate at the sediment/soil–water interface in the real environment.
