Feasibility of the preparation of effective cheap adsorbents from lignites in rotary kiln

The feasibility to obtain effective cheap adsorbents using rotary kiln technology is studied for three lignites with different composition. The paper analyzes three different aspects, (i) relation between lignite origin and adsorption capacities of 4 nitrophenol, (ii) effect of the mineral matter content (amount and nature of ashes), (iii) pore volume distribution and surface area development. The Lignite characteristics (i.e. water and volatile matter content) influence the pyrolysis behavior and the characteristics of the obtained chats and in consequence, the adsorption capacities. Optimal pyrolysis temperature has been determined for each precursor using a very simple and fast method in laboratory scale. We found temperature between 700 and 850 degrees C. Moreover, we propose a simple thermal post-oxidation treatment which allows to strongly enhance the adsorption capacities. In our case, the higher Volatile matter content, the higher ability to be oxidized leading to an improvement of the adsorption properties. The amount and nature of ashes seems to be a key parameter which positively influences the development of micro and mesoporosities. Moreover we have observed that a high degree of dispersion of mineral matter, and mostly calcium, allows to enhance reactivity of chars. Adsorption of 4 nitrophenol has been performed in batch reactor for all samples. Freundlich and Langmuir equations have been applied to the results. Very high adsorption capacities can be reached with some chars. For all samples which have different lignites precursor, we observed that adsorption capacities are twice more important after post-oxidative treatment. The feasibility of the preparation in rotary kiln of effective cheap adsorbents, starting from lignites has been demonstrated. Semi-pilot scale production of adsorbent having comparable adsorption properties in aqueous phase with commercial product has been realized. (C) 1998 Elsevier Science B.V. All rights reserved.