The removal of phosphate ions from aqueous solution by fly ash, slag, ordinary Portland cement and related blends

• Published in: Cement and concrete research Vol. 32; no. 12; pp. 1889 - 1897
• Main Authors: Agyei, N.M., Strydom, C.A., Potgieter, J.H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-12-2002
• Subjects: Adsorption; Fly ash; Frumkin isotherm; OPC; Phosphate ions; Slag; Phosphate ions; Slag; Fly ash; OPC; Adsorption; Frumkin isotherm
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/S0008-8846(02)00888-8

Phosphate ions have been removed from aqueous solution by fly ash, slag, ordinary Portland cement (OPC) and related cement blends. The rate and efficiency of PO
4
3− removal were found to increase in the order: fly ash, slag, OPC, apparently mimicking the order of increasing percent CaO in the adsorbents. Blending OPC with fly ash or slag evidently results in diminished PO
4
3− removal efficiency. Better removal was obtained at higher solute concentration, acidic pH and higher temperature. The effect of particle size and the speed of mixing were found not to be significant. A first-order kinetic model was used to obtain values for overall sorption rate constants and intraparticle diffusion constants. The Frumkin isotherm was found to be the appropriate equation for modelling isotherms from the experimental adsorption data, and values have been obtained for the isotherm constants. A 400-mg/l PO
4
3− (as P) solution was fed at a steady velocity of 2.0 cm/min through a 2.0-cm fixed-bed column (at pH 9.0 and 25 °C), and breakthrough curves were constructed to obtain estimated adsorption capacity values of 32, 60, 75, 78 and 83 mg PO
4
3−/g adsorbent for fly ash, slag, OPC+fly ash, OPC+slag and OPC, respectively.