Kinetic Aspects of Methylene Blue Adsorption on Blast Furnace Sludge

In this paper the potential of blast furnace sludge (BFS) in methylene blue (MeB) removal from aqueous solutions was studied by following the adsorption of dye. The BFS was used without any modification/activation. The kinetics of adsorption on the sludge was studied in laboratory batch experiments by monitoring the effect of contact time and dye concentration (20-160 mg [L.sup.-1]) on the adsorption capacity at room temperature (293 K) and at natural pH (7 ± 0.5). It was found that the adsorption capacity at equilibrium increased from 10.3 to 70.6 mg [g.sup.-1], as the initial MeB concentration increased from 20 to 160 mg [L.sup.-1]. For analysis of experimental data, three kinetic models were applied: pseudo first-order, pseudo second-order and Weber-Morris intra-particle diffusion model. Results demonstrate that kinetics of dye adsorption on BFS is best described by the pseudo second-order equation ([R.sup.2] ≥ 0.99, F-value=0.86) while fitting to Weber-Morris model has shown that the pore diffusion is not the only rate limiting process in MeB-uptake. Such kinetics can be related to surface characteristics of BFS used: particle diameter [d.sub.p] [less than or equal to] 56 mm, specific area 31.46 [m.sup.2] [g.sup.-1], pore volume 157 [10.sup.-3] [cm.sup.3] [g.sup.-1], and average pore diameter 17.88 nm, mark this industrial by-product as a mesoporous material. Its surface morphology change after MeB adsorption was confirmed by SEM/EDS analyses. The results obtained allow concluding that untreated BFS has the capacity for MeB uptake within the range of concentrations employed and could be considered as potential low cost adsorbent for treating of dye-polluted waste waters. Key words: industrial waste, blast furnace sludge, Methylene Blue, batch adsorption