CO2 capture with solid sorbents is one of the most promising options for reducing the consequences of climate change when large amounts of CO2 are emitted into the atmosphere. The present study explores the possible use of macroalgae industrial waste, algae meal (AM), and its carbonised (AMP) to prepare activated carbons by means of MOH and K2CO3 activation in two different devices (an electrical conventional and a multimode microwave furnace) for CO2 capture and for the separation or concentration of gas mixtures. The adsorbents obtained, at 750 degrees C, with a low weight ratio of KOH:AM (0.5:1), show in most cases a high specific surface area-BET (up to 1982 m(2)/g). These materials are mainly microporous (Vmicropore > 80%) with a certain degree of mesoporosity and contain a significant amount of nitrogen. The adsorbents were subjected to a CO2, CH4 and H-2 adsorption process at high pressure, showing a better selectivity towards CO2, than towards CH4 and H-2. This suggests they could be used for capturing CO2 in pre-combustion processes or separating/concentrating mixtures of CO2/CH4 in natural gas feeds for use as fossil fuel. Some of the adsorbents proved to be more effective in adsorbing CO2 than one of the commercial activated carbons used as reference (Chemviron Filtrasorb F400). (C) 2014 Elsevier B.V. All rights reserved.