Solid residue derived from thermochemical degradation of vegetal biomass, generally named biochar, is currently under study for its potential agronomic value as soil amender and fertilizer. Feedstock pre- treatments aiming to a partial demineralization of the biomass could promote the development of char porosity by inducing modifications of the chemical and physical characteristics of the feedstock. In the present paper three different methods of feedstock demineralization have been applied on Arundo donax samples. Steam assisted pyrolysis of raw and demineralized Arundo donax has been carried out in aproper experimental apparatus up to 873 K, at pressure P=5×105 Pa and heating rate HR=5 K/min. Acomparison of the chemical and physical properties of produced chars and energetic content of gaseous phase has been evaluated for its possible use as fuel to sustain biochar production itself.