South African Journal of Science
versão On-line ISSN 1996-7489
Agroforestry waste presents a problem for disposal and negatively impacts on the environment if left to rot or burn. The aim of this study was to reduce environmental problems associated with agroforestry waste by promoting the innovative use of such waste in the production of activated carbons (ACs) using a low-cost production technique, and ultimately delivering more affordable water and effluent treatment adsorbents. Four varieties of ACs from four different agroforestry materials - pine (Pinus contorta) cones (PC), Abies (Abies cilicica) seeds (AS), maple (Acerginnala) seeds (MS) and peach (Prunuspersica) stones (PS) - were prepared by single-step steam pyrolysis and characterised. The raw materials were evaluated for AC yield while the respective ACs were evaluated on the basis of iodine number, phenol specific area, ash content, pH, moisture content and removal of metal ions, nitrates and sulphates from aqueous solution. The AC yields for PS, PC, AS and MS were found to be 23.0%, 18.0%, 17.8% and 14.6%, respectively. The yield for PS (23%) is within the specified commercial limits of 20% to 40%. The phenol specific areas of the ACs ranged between 381 m2/g and 415 m2/g higher than the commercial lower limit (300 m2/g) generally specified. The ACs also showed the capacity to remove heavy metal ions from their aqueous solutions. Removal of both nitrates and sulphates in raw water was greater than 50%. Although no quantitative analysis has been performed to date, it is envisaged that the production of AC from agroforestry wastes can contribute to the sustainable management of environmental pollution by these residues and the concomitant delivery of cheaper adsorbents.
Palavras-chave : activation; pyrolysis; characterisation; removal; adsorption.