Phosphate Removal from Digested Sludge Supernatant Using Modified Fly Ash
The removal of phosphate in digested sludge supernatant by modified coal fly ash was investigated in this study. Modification of the fly ash by the addition of sulfuric acid could significantly enhance its immobilization ability. The experimental results also showed that adsorption of phosphate by the modified fly ash was rapid with the removal percentage of phosphate reaching an equilibrium of 98.62% in less than 5 minutes. The optimum pH for phosphate removal was 9 and the removal percentage increased with increasing adsorbent dosage. The effect of temperature on phosphate removal efficiency was not significant from 20 to 40 °C. X‐ray diffraction and scanning electron microscope analyses showed that phosphate formed an amorphous precipitate with water‐soluble calcium, aluminum, and iron ions in the modified fly ash.
Simultaneous Removal of NH4+ and PO43‐ at Low Concentrations from Aqueous Solution by Modified Converter Slag
In this study, modified converter slag (CS) was characterized in relation to its physicochemical structure, and used for the simultaneous removal of NH4+ and PO43‐ at low concentrations from aqueous solutions. The effects of contact time, pH, adsorbent dosage, and temperature on the adsorption process were studied in batch experiments. The results showed that the adsorption capacity of modified converter slag was found to sharply increase as a result of modification. The optimum pH is 5‐8. The adsorption process was able to reach equilibrium in 90 minutes. Kinetic data were best described by the pseudo‐second‐order model. The sorption isotherms were a good fit with the Langmuir model. The maximum adsorption capacities of modified converter slag for NH4+ and PO43‐ were 2.59mg/g and 1.185 mg/g, respectively. Thermodynamic studies indicated that the adsorption was a spontaneous and endothermic process. The calculated values of enthalpy change indicated that ligand exchange, chemical reactions, and precipitation are dominating mechanisms of PO43‐ removal, while physisorption and ion‐exchange are major mechanisms of NH4+ removal.
Submicroscopic Structure and Characteristics of Intermediate-Calcium Fly Ashes
The surface and near surface characteristics of alkaline fly ash particles were studied to evaluate the heterogeneous chemistry and structure of ash in order to provide data and understanding of the dissolution behavior of elemental constituents. Fly ash was subjected to a range of chemical weathering intensities in laboratory column experiments. Weathered ash from columns were then analyzed for surface morphology and chemical compositional change. Determinations included chemical characterization by instrumental neutron activation analyses, surface analysis by SEM-EDXA of whole and fractured particles, surface glass analysis by selective dissolution, and mineralogy by powder x-ray diffraction. These data were used to develop a physical model of fly ash particles that describes the heterogeneous distribution of elements on or in a reactive glass hull and in matrix glass and mullite. The model is discussed in terms of elemental partitioning and its application to the mechanistic approach advocated for prediction of leachate composition.