We compute the mass and composition of dust produced by stars with masses in the range 1 M _ { \odot } \leq M \leq 8 M _ { \odot } and with a metallicity of Z = 0.001 during their AGB and Super AGB phases .
Stellar evolution is followed from the pre-main sequence phase using the code ATON which provides , at each timestep , the thermodynamics and the chemical stucture of the wind .
We use a simple model to describe the growth of the dust grains under the hypothesis of a time–independent , spherically symmetric stellar wind .
Although part of the modelling which describes the stellar outflow is not completely realistic , this approach allows a straight comparison with results based on similar assumptions present in the literature , and thus can be used as an indication of the uncertainties affecting the theoretical investigations focused on the dust formation process in the surroundings of AGB stars .

We find that the total mass of dust injected by AGB stars in the interstellar medium does not increase monotonically with stellar mass and ranges between a minimum of 10 ^ { -6 } M _ { \odot } for the 1.5 M _ { \odot } stellar model , up to 2 \times 10 ^ { -4 } M _ { \odot } , for the 6 M _ { \odot } case .
Dust composition depends on the stellar mass : low–mass stars ( M < 3 M _ { \odot } ) produce carbon–rich dust , whereas more massive stars , experiencing Hot Bottom Burning , never reach the carbon–star stage , and produce silicates and iron .
This is in partial disagreement with previous investigations in the literature , which are based on synthetic AGB models and predict that , when the initial metallicity is Z = 0.001 , C–rich dust is formed at all stellar masses .
The differences are due to the different modelling of turbulent convection in the super–adiabaticity regime .
Also in this case , like for other physical features of the AGB , the treatment of super–adiabatic convection shows up as the most relevant issue affecting the dust–formation process .

We also investigate Super AGB stars with masses 6.5 M _ { \odot } \leq M \leq 8 M _ { \odot } that evolve over a ONe core .
Due to a favourable combination of mass loss and Hot Bottom Burning , these stars are predicted to be the most efficient silicate–dust producers , releasing [ 2 - 7 ] \times 10 ^ { -4 } M _ { \odot } masses of dust .

We discuss the robustness of these predictions and their relevance for the nature and evolution of dust at early cosmic times .