The capacity of adsorbent recycled from microwave thermal treatment to remove a synthetic dye, Rhodamine 6G, from a water bath, was examined. The acidified, dewatered sludge was microwave heated for 1–4 min. Batch adsorption tests were conducted on this sludge at various pH values and solution temperatures. Equilibrium of dye adsorption was obtained in 30 h. Three kinetic models—pseudo first-order, pseudo second-order and intra-particle diffusion—were applied to elucidate the adsorption kinetic data. Experimental results indicate that higher adsorption efficiency could be derived at higher pHytemperature levels. Moreover, the sample treated for 1 min by microwaves adsorbed more dye than did the sample so treated for 4 min. Sludge samples were also characterized to interpret the experimental findings. Energy cost analysis demonstrated the feasibility of the present microwave process.