Active asteroids constitute a new class of Solar System objects that show dynamical behavior as the main belt asteroids but cometary appearance, i.e., they display coma and tail features. Since the discovery of P/1996 N2 (Elst-Pizarro), and mostly with the help of the current sky surveys, about 20 active asteroids have been identified. The activation mechanisms are, however, not always fully understood. Mass losses are being attributed, among other mechanisms, to ice sublimation, impact, or rotational disruption, or to a combination of those processes. Since 2010, we have undertaken a long-term program of observations with the Gran Telescopio Canarias (GTC), a 10.4-m telescope at La Palma Observatory (Spain). Since then we have characterized the dust environment of a sizable number of such objects with dust tail models. In this talk, we describe the approach used to retrieve the dust physical parameters from image datasets, the underlying approximations, and how this technique can shed some light on the physical mechanism(s) responsible of the dust loss from those objects.