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 ligni te origin and adsorption capacities of 4 nitrophenol, (ii) effect of t he mineral matter content (amount and nature of ashes), (iii) pore vol ume distribution and surface area development. The Lignite characteris tics (i.e. water and volatile matter content) influence the pyrolysis behavior and the characteristics of the obtained chats and in conseque nce, 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 a llows to strongly enhance the adsorption capacities. In our case, the higher Volatile matter content, the higher ability to be oxidized lead ing to an improvement of the adsorption properties. The amount and nat ure of ashes seems to be a key parameter which positively influences t he 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 h as been performed in batch reactor for all samples. Freundlich and Lan gmuir 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 feasibili ty of the preparation in rotary kiln of effective cheap adsorbents, st arting from lignites has been demonstrated. Semi-pilot scale productio n of adsorbent having comparable adsorption properties in aqueous phas e with commercial product has been realized. (C) 1998 Elsevier Science B.V. All rights reserved.