[Effects of different temperatures biochar on adsorption of Pb(II) on variable charge soils]

Effects of incorporation of the biochars generated from rice straw and peanut straw at different temperatures on soil pH and Pb(II) adsorption were investigated with two variable charge soils. The soil pH increased by 1.04-3.00 units, and the increase in soil pH increased with the rise of pyrolysis temperature of the biochar. Results from adsorption isotherm experiments indicated that the incorporation of the biochar enhanced the adsorption of Pb(II) by two soils. The adsorption of Pb(II) was increased by 12.6% -57.6%, when the initial concentration of Pb(II) is 2 mmol x L(-1). The adsorption also increased with rising pH. Freundlich and Langmuir equations can be used to fit the adsorption isotherms of Pb(II), but the Freundlich equation fitted the adsorption data better, the r-values are above 0.94. Soils incorporated with peanut straw char have a greater adsorption capacity for Pb(II) than these incorporated with rice straw char as predicted by the parameters of k and Q(m) in Freundlich and Langmuir equations, respectively. The biochars generated at 400 degrees C have a greater enhancement on Pb(II) adsorption by soils than 300 degrees C and 500 degrees C. Desorption results showed that the desorption of Pb(II) for the treatments with biochar added was greater than that for the control, but the amount of desorbed Pb(II) was much lower than that of adsorbed Pb(II). These results suggested that the enhanced adsorption of Pb(II) by incorporation of the biochars involved at least two mechanisms: electrostatic adsorption and non-electrostatic adsorption.