Steam- or carbon dioxide-activated carbons from almond shells: physical, chemical and adsorptive properties and estimated cost of production

series of steam- or carbon dioxide (CO2)-activated, granular activated carbons (GACs) were made from almond shells using six di€erent activation or activation/oxidation conditions for each series. Unoxidized/oxidized pairs of GACs were compared among treatments and to two commercial GACs in order to determine the relative value of the carbons. Comparative terms included yield, surface area, attrition, surface charge, copper ion (Cu2‡) uptake, adsorption of a mixture of six polar and non-polar organic compounds and an estimated cost of carbon production. Of the six conditions investigated for steam activation, two treatments consisting of a 1 h pyrolysis at either 700°C or 800°C, followed by a 2 h activation at 800°C with the introduction of water at a rate of 7.0 ml/min were the best overall performing unoxidized/oxidized pairs in terms of copper ion or organics adsorption, respectively. Of the six conditions investigated for carbon dioxide activation, a treatment consisting of a 1 h pyrolysis at 700°C, followed by a 2 h activation at 800°C using a 75% CO2/25% N2 gas mixture was the best overall performing unoxidized/oxidized pair. Our estimated costs of production indicate that steam-activated, unoxidized and oxidized carbons appear to be the most economical GACs to manufacture and also the most economical for removal of copper ions and organic compounds.