Characteristics and mechanisms of phosphate adsorption onto basic oxygen furnace slag.
ABSTRACT The adsorption characteristics of phosphate adsorption on the basic oxygen furnace (BOF) slag were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and phosphate adsorption process of the BOF slag, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity from 4.97 to 3.71 mgP/g slag when the solution pH was increased from 2.0 to 13.0 and phosphate initial concentration was 50 mg/L, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as NO(3)(-), SO(4)(2-) and Cl(-), onto BOF slag reveal that BOF slag can selectively adsorb phosphate ions. The insignificant effect of NO(3)(-), SO(4)(2-) and Cl(-) on phosphate adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of NO(3)(-), SO(4)(2-) and Cl(-) suggests that phosphate replaced the functional groups from the surface of BOF slag which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO(4)(3-) and total calcium, magnesium and aluminum concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.
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ABSTRACT: Phosphate was captured from aqueous solutions by cationic metal-EDA complexes anchored inside mesoporous silica MCM-41 supports (Cu(II)-EDA-SAMMS and Fe(III)-EDA-SAMMS). Fe-EDA-SAMMS was more effective at capturing phosphate than the Cu-EDA-SAMMS and was further studied for matrix effects (e.g., pH, ionic strength, and competing anions) and sorption performance (e.g., capacity and rate). The adsorption of phosphate was highly pH dependent; it increased with increasing pH from 1.0 to 6.5, and decreased above pH 6.5. The adsorption was affected by high ionic strength (0.1 M of NaCl). In the presence of 1000-fold molar excess of chloride and nitrate anions, phosphate removal by Fe-EDA-SAMMS was not affected. Slight, moderate and large impacts were seen with bicarbonate, sulfate, and citrate anions, respectively. The phosphate adsorption data on Fe-EDA-SAMMS agreed well with the Langmuir model with the estimated maximum capacity of 43.3 mg/g. The material displayed rapid sorption rate (99% of phosphate removal within 1 min) and lowering the phosphate content to approximately 10 microg/L of phosphorus, which is lower than the EPA's established freshwater contaminant level for phosphorus (20 microg/L).Environmental Science and Technology 03/2010; 44(8):3073-8. · 5.23 Impact Factor
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ABSTRACT: a b s t r a c t Phosphorus removal was a crucial aspect in controlling eutrophication problem of water pollution. Zirco-nium oxide was a suitable adsorbent for phosphate removal due to its good adsorption efficiency, but it suffered from the separation inconvenience. In this paper, magnetic Fe–Zr binary oxide was synthesized and used as adsorbent for removing phosphate from aqueous solution. The adsorbent was characterized by energy dispersive analysis system of X-ray, scanning electron microscopy (SEM), infrared spectrum (IR), X-ray powder diffraction (XRD) analysis and BET surface area measurements. The results showed that kinetic data followed a pseudo-second-order model and equilibrium data were well fitted by the Langmuir model. The maximum adsorption capacity was 13.65 mg P/g at pH 4. The adsorption mecha-nism was mainly derived from ion-exchange of zirconium species and partly originated from magnetite species of Fe–Zr binary oxide. The main advantages of magnetic Fe–Zr binary oxide adsorbent consisted in its separation convenience and highly efficient reusability compared to the other adsorbents.Chemical Engineering Journal. 01/2011; 171:448-455.