The function of acid-activated sepiolite clay was evaluated for use in the clarification of apple juice. Optimizing the clarification process was done using response surface methodology (RSM) considering juice turbidity as a response. The efficiency of sepiolite in terms of clarification was compared to that of bentonite and a combination of these fining agents with gelatin and silica gel at optimal conditions. The conditions of 0.05% clay concentration at a temperature of 50°C for 7 h were deemed optimal in terms of juice clarification. The present results showed that treatment of sepiolitegelatin-silica gel was the most active fining agent with 99.7% reduction in apple-juice turbidity. The rate of turbidity, the viscosity, the total phenolic contents and the colour changes were fitted to first-, zero-, first- and zero-order kinetic models, respectively.

The kinetics of dissolution of Amazonian metakaolin in hydrochloric acid (HCl) was studied using the ‘Shrinking Core Model’ for spherical and ‘flat plate’ particles of constant size. The Amazonian kaolin was calcined at 700°C for 2 h. The calcined samples (metakaolins) were leached in an HCl solution with 5% excess at 70, 80 and 95 ± 3°C for 3 h. Samples were collected every 15 min and subjected to Al analysis by the EDTA titrimetric method. Experimental data showed that the spherical morphology produced a better fit with respect to the regression coefficients. The activation energy of the reaction was 90.6 kJ/mol. The chemical process is a first-order leaching reaction. The results of the present study are consistent with those from previous research on this topic, which used HCl with an excess of >90%.