LAUSR

Abstract Use of sewage sludge (SS) and cement kiln dust (CKD) to prepare hydroxyapatite nanoparticles through a chemical reaction between phosphate and calcium ions extracted respectively, from these wastes represents the novelty of this work. The nanoparticles were deposited on the filter cake (FC) remaining after extraction to produce “Hydroxyapatite Coated Filter Cake (HAP-CFC)”. The removal efficiency of tetracycline onto HAP-CFC was surpassed 90% at best conditions of time (2 h), pH 5, and dosage (0.4 g/50 mL) respectively, for 50 mg/L initial concentration of tetracycline at a speed of 200 rpm. The pseudo-second-order model described well the kinetic measurements and, accordingly, depicts that chemisorption will predominate the adsorption process. Also, the Langmuir model was an ideal relationship for describing the adsorption data. The maximum adsorption capacity for tetracycline onto HAP-CFC was 43.5 mg/g and this value had decreased to 41.5 mg/g for mixture of 10% sand and 90% HAP-CFC applied in the column tests. The X-ray diffraction (XRD) analysis proved the precipitation of nano-hydroxyapatite onto FC due to the appearance of new peaks at the 2 θ values of 21.21, 29.76 and 48.86. Also, all characterization tests showed that the electrostatic attraction, intra-particle diffusion and surface complexation are predominant mechanisms for removal of tetracycline onto HAP-CFC. Theoretical predictions of effluent normalized concentrations with measurements for packed bed revealed a propagation delay of plume front, resulting from the reduction of flow rate and inlet concentration with increase of bed height.