A removal of different metals using both acid reflux and the microwave assisted digestion method was investigated. As a carbon material multi-walled carbon nanotubes synthetized on iron, cobalt and iron-cobalt catalysts without support were applied. The amount of metal particles after purification was determined using a thermobalance and it was found that microwave heating improved the efficiency of purification, especially at elevated pressure. Similar removal degrees of catalyst particles were achieved using the acid reflux method for 24 h and microwave heating for 15 min at 20 at regardless of the kind of metal. Raman measurements indicate that all the obtained samples were characterized with a high ratio of peak IG/ID intensities which confirms a good quality of the materials. (C) 2014 Published by Elsevier B.V.