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Iron oxide(FeO)coated by natural organic matter(NOM)is ubiquitous.The associations of minerals with organic matter(OM)significantly changes their surface properties and reactivity,and thus affect the environmental fate of pollutants,including nutrients(e.g.,phosphorus(P)).In this study,ferrihydrite/goethite-humic acid(FH/GE–HA)complexes were prepared and their adsorption characteristics on P at various p H and ionic strength were investigated.The results indicated that the Fe O–OM complexes showed a decreased P adsorption capacity in comparison with bare Fe O.The maximum adsorption capacity(Qmax)decreased in the order of FH(22.17 mg/g)>FH-HA(5.43 mg/g)>GE(4.67 mg/g)>GE-HA(3.27 mg/g).After coating with HA,the amorphous FH–HA complex still showed higher P adsorption than the crystalline GE–HA complex.The decreased P adsorption observed might be attributed to changes of the Fe O surface charges caused by OM association.The dependence of P adsorption on the specific surface area of adsorbents suggests that the Fe O component in the complexes is still the main contributor for the adsorption surfaces.The P adsorptions on Fe O–HA complexes decreased with increasing initial p H or decreasing initial ionic strength.A strong dependence of P adsorption on ionic strength and p H may demonstrate that outer-sphere complexes between the OM component on the surface and P possibly coexist with inner-sphere surface complexes between the Fe O component and P.Therefore,previous over-emphasis on the contributions of original minerals to P immobilization possibly over-estimates the P loading capacity of soils,especially in humic-rich areas.  相似文献
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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.  相似文献
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Molecular weight(Mw) is a fundamental property of humic acids(HAs), which considerably affect the mobility and speciation of heavy metals in the environment. In this study, soil humic acid(HA) extracted from Jinyun Mountain, Chongqing was ultra-filtered into four fractions according to the molecular weight, and their properties were characterized.Complexation of cadmium was investigated by titration experiments. For the first time,Langmuir and non-ideal competitive adsorption-Donna(NICA-Donnan) models combined with fluorescence excitation-emission matrix(EEM) quenching were employed to elucidate the binding characteristics of individual Mw fractions of HA. The results showed that the concentration of acidic functional groups decreased with increasing Mw, especially the phenolic groups. The humification degree and aliphaticity increased with increasing Mw as indicated by elemental composition analysis and FT-IR spectra. The binding capacity of Cd~(2+) to Mw fractions of HA followed the order UF1( 5 kDa) UF2(5–10 kDa) UF4( 30 kDa) UF3(10–30 kDa). Moreover, the distribution of cadmium speciation indicated that the phenolic groups were responsible for the variations in binding of Cd~(2+) among different Mw fractions. The results of fluorescence quenching illustrated that the binding capacity of Cd~(2+) to Mw fractions was controlled by the content of functional groups, while the binding affinity was largely influenced by structural factors. The results provide a better understanding of the roles that different HA Mw fractions play in heavy metal binding,which has important implications in the control of heavy metal migration and bio-toxicity.  相似文献
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