Kinetic analysis of the dissolution of natural magnesite in nitric acid

investigated, and the results of a detailed critical analysis are
presented. The reaction system MgCO3-HNO
studied with special regard to the production of pure magnesium
salts. The generalised non-porous shrinking particle model
considering the n-th order liquid-solid reaction was fitted to the
measured kinetic data and the values of apparent activation energy,
EA, and reaction order, n, were calculated. Relatively high values
EA (43.7 and 58.5 kJ mol-1) obtained for both “low” (0.01
and “high” (1-6 M) concentrations of HNO
within the range of values presented by other authors and indicate
that the overall process is controlled by the chemical reaction in the
whole range of reaction conditions considered (temperature from 70
to 100°C and concentration of HNO3 from 0.01 to 6M). This
hypothesis has been confirmed by the calculated values
considerably differ from 1. Until now, it has been assumed in the
literature that n=1 and no attention has been paid to the
mechanism of the intrinsic chemical reaction. In this work, the
value of n=0.22 was calculated for the solutions with “low” HNO
concentration, and n=0.05 was obtained for the concentrated HNO
solutions. These values of n are considerably lower than the value
of n=0.5, predicted by the theory. It is hypothesised that the
decrease in n with increased acid concentration might be related to
the formation of CO2 and its transfer from the liquid to the ga
phase.