Investigação da reatividade e da cinética de dissolução do metacaulim em ácido sulfúrico (Investigation of reactivity and dissolution kinetics of metakaolin in sulfuric acid)

A study about reactivity and dissolution kinetics of metakaolin was carried out using kaolin for paper coating derived from the Rio Capim region, Para state, northern Brazil. The kaolin was burned at 600, 700, 800, 900 and 1000 oC during 2 h in order to obtain metakaolin, followed by leaching with sulfuric acid at constant temperatures within the 50-95 oC ± 3 oC range. In the leachings, amounts of sulfuric acid corresponding to 10% above the stoichiometric values were used with respect to aluminum present in the material. Samples were collected in predetermined intervals every 15 min until a total time of 3 h, which were subjected to aluminum analysis by the EDTA titrimetric method. The results showed that the reactivity of burned kaolin decreased with the increase of burning temperature and that the dissolution kinetics of aluminum from metakaolin obtained by burning at 700 oC followed the methods of homogeneous reaction used: integral method, method of half-lives and method of initial rates. 96.25 kJ/mol of activation energy was found as well as leaching reaction of the first order with respect to aluminum from metakaolin and the first order with respect to acid concentration. Researches carried out previously, using one of the reagents with excess above 90% and models of heterogeneous reaction, are consistent with the data found in this paper developed with only 10% excess.