Journal of Ecology and Rural Environment ›› 2020, Vol. 36 ›› Issue (1): 106-114.doi: 10.19741/j.issn.1673-4831.2018.0853

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Adsorption of Lead and Cadmium on Biochars Produced From Agroforestry Wastes

JI Meng-yuan1,2, HU Yi-wen1, LIANG Cheng1,2, SANG Wen-jing1,2, LI Deng-xin1   

  1. 1. Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China;
    2. Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention(LAP3), Shanghai 200433, China
  • Received:2018-12-20 Published:2020-01-17

Abstract: The adsorptions of Pb2+ and Cd2+ in aqueous solutions by biochar derived from salix, straw and corn stalk at pyrolysis temperature of 500℃ were evaluated. The characteristics of adsorbent were mainly observed by scanning electron microscope (SEM), specific surface area analyzer and Fourier transform infrared spectroscopy (FTIR), and the effects of initial pH, ionic strength of Na+ and Ca2+ and adsorbent dose in sorption experiments were further investigated. Results show that the alkali and ash content of the 3 biochars were salix straw biochar (SWB) > corn stover biochar (CB) > rice straw biochar (SB), and all the surfaces of the 3 biochars contained large number of oxygen-containing functional groups. The adsorption kinetics and adsorption results indicate that when the pH was set between 3 to 6, the adsorption efficiency of biochar to Pb2+ and Cd2+ increased with the increase of pH value, and the adsorption efficiency to Pb2+ decreased with the increase of ionic strength in the solution. While the adsorption efficiency of SWB on Cd2+ increases with increasing ionic strength. In addition, the adsorption kinetic results of SWB, CB and SB to Pb2+ and Cd2+ met quasi-secondary kinetics, and the correlation coefficient R2 was greater than 0.99, indicating that the biochar adsorption rate is mainly determined by the chemical adsorption mechanism. Moreover, the adsorption isotherm model of Pb2+ and Cd2+ show that the adsorption of Cd2+ was suitable to be described by both Langmuir and Freundlich isothermal equation, while the adsorption of Pb2+ was only well simulated by the Langmuir isothermal equation, indicating that the adsorption mechanism of Pb2+ by biochar was similar to that of monolayer adsorption law, but the adsorption process of Cd2+ showed multi-molecular layer adsorption mechanism.

Key words: agroforestry wastes, biochar, Pb, Cd, adsorption characteristics

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