CHEAP ADSORBENT - PART 1 - ACTIVE COKES FROM LIGNITES AND IMPROVEMENTOF THEIR ADSORPTIVE PROPERTIES BY MILD OXIDATION

In this article, cheap adsorbents were produced starting from two diff erent lignites. About 500 kg of each coal was pyrolyzed in a rotary ki ln at semi-pilot scale. Characterization of the obtained chars are mad e in terms of porosity development, surface functional groups and adso rptive properties determined for both 4-nitrophenol and lead. A post-o xidative treatment at low temperature is proposed in order to improve the adsorptive capacities of the initial chars by the introduction of oxygen containing functional groups, which are widely involved in chem isorption. The conditions of the post-treatment were chosen to be easi ly exported in an industrial process, for example during the cooling s tep. The importance of both lignite characteristics (ashes content, wa ter content) and pyrolysis conditions is demonstrated. The positive ef fect of a simple post-oxidative treatment is shown by a strong increas e in the adsorptive capacities, and correlated to the evolution of the porosities and surface oxygen functionalities. Considering unit area, the properties of our active cokes are similar to those of commercial active carbon, but their specific areas are less developed (about 400 m(2) g(-1)). (C) 1998 Elsevier Science Ltd. All rights reserved.