Effect of the carbonaceous matter deposition on the textural and surface properties of complex carbon-mineral adsorbents prepared on the basis of palygorskite

Natural palygorskite spent in adsorption process of paraffin purification w as used for the preparation of carbon-mineral adsorbents. The waste materia l containing 10.88% w/w carbonaceous matter was treated in three ways: (1) direct pyrolysis at 400 degreesC with a suitable temperature programme; (2) preliminary hydrothermal modification (200 degreesC, 8 h, 13.5 atm.) and t hen thermal treatment as in method 1 and (3) preliminary thermal (400 degre esC) and then chemical treatments (boiling in 3% Na2CO4 solution), next hea ting at 500 degreesC (10 min). The carbon-mineral adsorbents prepared in th is way included 3.07, 3.37 and 2.18% C w/w, respectively. These were determ ined the following characteristics of the prepared adsorbents: porous and c rystal structure parameters, as well as, chemical composition, carbon depos it topography on the mineral matrix surface and adsorption heat of the test substances. It was stated that thermal acid hydrothermal treatments did no t cause significant changes in the parameters of natural palygorskite porou s structure, Such changes are caused by the presence of carbon deposit on t he mineral matrix whose topography and morphology depend on the type of tre atment used for the prepared palygorskite. Carbon deposit is located mainly in mesopores diminishing their volume. At the same time, a number of narro w pores of a radius equal to about 1.9 nm increases compared with the initi al palygorskite. Carbon deposit blocks the strongest adsorption/catalytic c entres partially or completely and as a result adsorption heat of the test substances (n-hexane, dichloromethane, tetrachloromethane) on the carbonise d adsorbents decrease with the increase of carbon deposit amount in the com plex adsorbent. 8 2001 Elsevier Science B.V. All rights reserved.