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 was used for the preparation of carbon-mineral adsorbents. The waste material containing 10.88% w/w carbonaceous matter was treated in three ways: (1) direct pyrolysis at 400°C with a suitable temperature programme; (2) preliminary hydrothermal modification (200°C, 8 h, 13.5 atm.) and then thermal treatment as in method 1 and (3) preliminary thermal (400°C) and then chemical treatments (boiling in 3% Na2CO3 solution), next heating at 500°C (10 min). The carbon-mineral adsorbents prepared in this way included 3.07, 3.47 and 2.18% C w/w, respectively. These were determined the following characteristics of the prepared adsorbents: porous and crystal structure parameters, as well as, chemical composition, carbon deposit topography on the mineral matrix surface and adsorption heat of the test substances. It was stated that thermal and hydrothermal treatments did not cause significant changes in the parameters of natural palygorskite porous structure. Such changes are caused by the presence of carbon deposit on the mineral matrix whose topography and morphology depend on the type of treatment used for the prepared palygorskite. Carbon deposit is located mainly in mesopores diminishing their volume. At the same time, a number of narrow pores of a radius equal to about 1.9 nm increases compared with the initial palygorskite. Carbon deposit blocks the strongest adsorption/catalytic centres partially or completely and as a result adsorption heat of the test substances (n-hexane, dichloromethane, tetrachloromethane) on the carbonised adsorbents decrease with the increase of carbon deposit amount in the complex adsorbent.