A mechanistic insight into enhanced and selective phosphate adsorption on a coated carboxylated surface

Abstract

Trimesic acid (benzene-1,3,5-tricarboxylic acid, TMA) coated on basic alumina surface showed a significant and selective adsorption of phosphate from aqueous solution. Focus has been given on the selective adsorption and recovery of phosphate from a wide pH range solution which is the major drawback of phosphate removal in the known literature methods. TMA coated alumina exhibited high adsorption efficiency even with low phosphate concentration (∼1.0 mg/L) as well as low pH (∼1.0). Moreover, probable mechanism of high and consistent phosphate immobilizing capacity throughout a broad pH range (pH ∼ 1.0–8.0) is discussed in detail. Adsorbed phosphate could be desorbed completely from adsorbent surface by treating with high alkaline solution. Discussion of adsorption process with two kinetic models revealed a fast kinetic rate and preference of second order model. A competitive study with other anions (chloride, nitrate and bromide) exhibited a high selective removal of phosphate over other anions. Influence of pH and temperature were also studied. Adsorption followed Langmuir isotherm model mostly and was thermodynamically favorable at even higher temperature (50 °C).