Waste carbon powder from pyrolysis of discarded tyre was converted into activated carbon for decolourization of metylene blue (MB). The precursor was activated using ZnCl2 (ZC), recycled ZnCl2 solution from the earlier activation (RC), and irradiated water (MC). Activated carbons were characterized according to surface area and morphology. The values of surface area were recorded as 288, 104 and 113 m2/g for ZC, RC and MC, respectively. The decolourization of MB was observed to have the following order: ZC>MC>RC. The maximum adsorption capacity of MB by ZC was found to be 154 mg/g. Adsorption data for all activated carbons studied obeyed Redlich-Peterson isotherm for which the process could be described as mixed features of Langmuir and Freundlich models. The kinetics data were well- fitted to pseudo-second-order model, suggesting the chemisorption process.