Adsorption Of Heavy Metals On Bone Char And Its Improvement Of Landfill Liners

Water and soil are contaminated seriously by heavy metals ions in some regions in China, typically the lead. Batch experiments are conducted to study the adsorption behaviors of lead on bone char detailedly. The experimental results show that bone char is a new biological adsorbent whose application prospect is wide and lead ions in aqueous solution can be removed effectively by it. In order to improve the adsorption capacity of landfill liner, bone char is mixed in clay or bentonite as a kind of ameliorant. Transport of lead ions in landfill liner is measured by a series of column model tests. All of the column models are compacted basing on each maximum dry density. Some conclusions are obtained according to the tests and analysis as the above description.1. The bone char is effective to remove lead ions from aqueous solutions. The adsorbing capacity is158.36mg/g when the optimum pH was found to be2-3(Initial concentration200mg/L, S/L=1.0g/L and temperature20℃). The factors including adsorbent dose and initial solution pH were found to have significant effects on the adsorption capacity of bone char. The influence of ion strength can be ignored. The adsorption process is spontaneous and endothermal. The mechanism of Pb(II) adsorption on bone char involved both surface complexation and calcium hydroyapatite (CaHA), Caio(PO4)6(OH)2, dissolution followed by less soluble Pb10(P04)6(OH)2precipitation.2. Langmuir isotherm describes the experimental equilibrium data of Pb(Ⅱ), Cd(Ⅱ), Ni(Ⅱ) and Cu(Ⅱ) well. Kinetic studies showed that the Pb(Ⅱ), Cd(Ⅱ), Ni(Ⅱ) and Cu(Ⅱ) adsorption followed pseudo-second order kinetics well.3. Binary-component and quaternary-component equilibrium studies show that adsorption capacity of Pb(Ⅱ) is far higher than Cd(Ⅱ), Ni(Ⅱ) and Cu(Ⅱ) which suggested the adsorption selectivity of bone char for Pb(Ⅱ). The influence of the Pb(Ⅱ) adsorption on bone char by Cu(Ⅱ) is obvious, while Cd(Ⅱ) and Ni(Ⅱ) is not significant.4. According to the column model tests lasting350days, the transport distance of lead ions through clay liner, improved clay liner, bentonite liner and improved bentonite liner are as follows:4cm,3cm,3cm and2cm. Compared with original liner, the transport of lead ions in the improved liner is delayed owing to the efficient adsorbent capacity of bone char. The diffusion coefficients of liners are follows:for clay,5.9×10-10m2/s; for97%clay plus3%bone char,5.4×10-10m2/s; for bentonite,2.2×10-10m2/s; for97%bentonite plus3%bone char,1.8×10-10m2/s.