Uptake of lead by carbonaceous adsorbents developed from tire rubber

The adsorption of lead in aqueous solution by discarded tire rubber (TR) and by carbonaceous adsorbents (CAs) prepared from it by thermal and chemical treatments is studied. TR was heated at 400 or 900 °C for 2 h in N2 atmosphere or treated chemically with H2SO4, HNO3, H2SO4/HNO3, HCl, NaOH, HCl-NaOH or NaOH-HCl for 24 h. TR and CAs were characterized physico-chemically with regard to their texture, elemental composition and surface chemistry. The adsorption of lead was studied, mainly from the kinetic standpoint, using 4×10−3 mol L−1 Pb2+ solutions at initial pH 2.0, 5.7 and 12.6. TR is practically a non-porous material. The heat treatment of TR mainly develops meso- and macroporosity. The effect on macroporosity is stronger when HNO3 and H2SO4/HNO3 are used. For all adsorbents, the adsorption of lead is not measurable when adsorptive solution at pH 2 is used. With an increase of pH from 5.7 to 12.6, the kinetics of adsorption becomes faster and the amount of lead adsorbed significantly increases. For the solution at pH 12.6 and an adsorption time of 8 h, the adsorption percentage is 36 wt% for TR. For the CAs prepared by heat treatment of TR, it is higher than 50 wt%. For longer adsorption times, the kinetics is much slower for the product of TR treatment with HNO3. However, the corresponding adsorption percentage is as high as 93 wt% for an adsorption time of 264 h. TR and the CAs, in particular the product heated at 400 °C, are good adsorbents to be used in the rapid removal of a significant amount of lead from aqueous solution.