The Science of the total environment | 12 Aug 2017
Z Shen, Y Zhang, F Jin, O McMillan and A Al-Tabbaa
The adsorption mechanisms of lead (Pb(2+)) on four biochars (SB produced from British hardwood at 600°C and three standard biochars produced from wheat straw pellets at 700°C (WSP700), rice husk at 700°C (RH700) and soft wood pellets at 550°C (SWP550)) were characterised qualitatively and quantitatively, using a combination of chemical and micro-structural methods. Sequential extraction test results show that Pb(2+) was predominantly adsorbed on SB (85.31%), WSP700 (75.61%) and RH700 (85.76%) as acidic soluble fraction, which was potentially bioavailable if applied in soil. The exchangeable fraction for SB, WSP700 and RH700 was low (1.38-4.29%) and their water soluble fraction was negligible (0-0.14%). Micro-structural analysis further investigated this fraction and confirmed the presence of cerussite (PbCO3) on SB and hydrocerussite (Pb3(CO3)2(OH)2) on WSP700, RH 700 and SWP550, suggesting a mechanism of surface precipitation for Pb(2+) adsorption on the biochars. The percentages of Pb(2+) in the form of PbCO3 on SB (82.24%) and Pb3(CO3)2(OH)2 on WSP700 (13.00%), RH 700 (19.19%) and SWP550 (29.70%) were quantified using thermogravimetric analysis (TGA). This study suggests that it is feasible to quantify different adsorption mechanisms of Pb(2+) on biochars, which is important for the practical application of biochar in water and/or soil treatment.
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