The procedure was published by Akhavan et al. (2014). The link to their paper is here: Article Synthesis of graphene from natural and industrial carbonaceous wastes

After the treatment, the mixture was left for gradual evaporation at room temperature, followed by drying at 100 C for 5 h.

I am not sure if the conditions are enough to reduce Fe3+ (aq) to Fe (s) and induce catalytic graphitization of carbon.