Adsorption of ammonium from water solution onto natural and modified palygorskite

This work aims to study ammonium removal in an aqueous solution by adsorption on natural and modified Palygorskite clay to improve water quality. The palygorskite (Pal) is a fibrous natural clay and was modified by acid treatment using 4 N and 6 N HCl solutions to enhance its adsorption capacity toward ammonium. The Pal modified were designated as Pal-Ac4 and Pal-Ac6. The ammonium adsorption isotherms on Pal, Pal-Ac4, and Pal-Ac6 were evaluated, and the effects of modification, pH, and temperature on the adsorption capacity were analyzed. At an equilibrium concentration of 300 mg/L and T = 25 °C, the adsorption capacity of Pal, Pal-Ac4, and Pal-Ac6 was 2.8, 9.2, and 5.3 mg/g, respectively, and the optimal acid treatment was that for Pal-Ac4. The adsorption capacity of Pal-Ac4 increased, reducing the solution pH from 7 to 3, and the maximum adsorption capacity of Pal-Ac4 was 28.5 mg/g at pH 3.