The valorisation of animal wastes by pyrolysis has shown to be of interest, due to the versatility of the main compound of char, hydroxyapatite (HAP), which can be used in catalysis, electrochemistry, and adsorption. The utility of HAP depends to a great extent on its textural properties, which can be developed by chemical activation, through gasification reactions. In the present work thermogravimetric analysis coupled to mass spectrometry was used to gain insight into the reactions occurring during the chemical activation of pork bone char with different agents: H3PO4, H2SO4, NaOH and K2CO3. Moreover, the role of each activation reagent in the enhancement of porosity was determined. The treatment with H2SO4 resulted in a highly microporous material, suitable to be used in gaseous pollutant adsorption. Chemical activation with NaOH and K2CO3, on the contrary, led to a more equilibrated increase of micro- and mesoporosity, resulting in a hierarchical porous material, with an excellent potential for applications as electrode, in gas storage, catalysis and energy storage. Regarding H3PO4, it was extremely aggressive under the operating conditions used, since it removed almost all the porous structure of HAP. These results are useful to optimize the preparation method of HAP, in order to configure a material with the desired textural properties.