Adsorption of Phosphate from Aqueous Solution by Calcination of Silicified Coal: Kinetic and Isotherm Studies

Abstract

Silicified coal (SC) consisting of SiO2 is promising raw material for adsorbent. The present study aimed to utilize the adsorbent of silicified coal bottom ash (SCBA) by calcination of the SC at the temperature of 600, 800 and 1000 oC for 1 hour. The FTIR result showed that the SCBA-600, SCBA-800 and SCBA-1000 had chemical functional groups such as the asymmetric Si-O-Si, the symmetric Si-O-Si and Si-O-Si bond rocking for adsorption of phosphate (PO43−) with the lowest percentage of transmittance of SCBA-1000. The adsorption test showed that a rapid adsorption occurred in the first 10-min of contact time, and it did not change significantly for the rest of contact time until reaching an equilibrium time of 30 min. The PO43− adsorption efficiency and capacity fluctuated over initial PO43− in solution in the range of 60.02–480.29 mg/L. The highest PO43− adsorption efficiency and capacity was at 480.29 mg/L, which was 95.49 % and 45.86 mg/g, respectively using the SCBA-1000. The adsorption kinetic fitted better to pseudo second-order kinetics model (average R2 = 0.999) with the adsorption capacity of 45.454, 45.662 and 45.872 for the SCBA_600, SCBA_800 and SCBA_1000, respectively, and the PO43− adsorption rate was 0.0007, 0.0008 and 0.001 g/mg.min, respectively. The adsorption isotherm followed Langmuir model (average R2 = 0.873) with the adsorption capacity being 2.357, 1.198 and 8.196 mg/g, respectively, and the pore volume being 0.0316, 0.0364 and 0.2103 L/mg, respectively