Removal of Ammonia from Aqueous Solution Using Activated Carbons

Abstract

The surface areas of non-activated, activated and modified activated carbons were determined from the adsorption of nitrogen at −196°C and of carbon dioxide at 25°C. The base neutralization capacities were determined from the adsorption of NaOH, Na 2 CO 3 , NaHCO 3 and NH 4 OH. The amount of oxygen combined to the carbon surface was estimated by measuring the pressure of CO and CO 2 obtained on outgassing the carbon sample in the temperature range 300–1000°C. The surface area of activated carbon is not a determining factor in its ammonia adsorption. The surface acidity of the active carbon is a good measure of its capacity for ammonia removal. Ammonia adsorption increases appreciably upon surface oxidation of carbons with oxidizing gases and solutions. The acidic groups on the surface of carbons differ in their strength. Only a fraction of the surface covered by the carbon–oxygen groups is responsible for the capacity of the carbon towards ammonia. Most of the adsorbed ammonia is recovered upon treatment with dilute hydrochloric acid leaving the surface free for successive ammonia adsorption cycles.