Abstract:

Objective: This paper was carried out to explore the adsorption performance of the Pinus massoniana nano-lignocellulose aerogel adsorbent for Cr³⁺/Cu²⁺/Pb²⁺/Ni²⁺, and clarify the related mechanisms of P. massoniana bark and nano-lignocellulose aerogel adsorbing heavy metal ions, with aims to make better use of agricultural and forestry waste P. massoniana bark to prepare low-cost and easy-to-industrial biomass adsorption materials, and to lay a theoretical foundation for its large-scale application. Method: The extracted dry sample was treated with p-toluenesulfonic acid solution for 1 hour under the conditions of heating and stirring in a water bath at 80℃. Then the reaction materials were filtered and filter residue was dialyzed. The filter residue sample was homogenized 20 times by a microfluidizer to obtain nano-lignocellulose samples. The samples with a solid content of 2% were frozen at-20℃ for 120 min, and then freeze-dried to obtain aerogel samples. The adsorption properties of the aerogel were studied, including the maximum q_e of heavy metal ions as Cr³⁺, Cu²⁺, Pb²⁺ and Ni²⁺, the isothermal adsorption characteristics, adsorption thermodynamics and adsorption kinetics. Result: The maximum q_e of different heavy metal ions of Cr³⁺, Cu²⁺, Pb²⁺ and Ni²⁺ were 132.7, 130.4, 186.7 and 123.4 mg·g^-1, respectively. The adsorption of Cr³⁺ on P. massoniana bark nano-lignocellulosic aerogel was consistent with the Temkin isothermal adsorption(R²=0.990 1), and it was a non-uniform monolayer adsorption. The adsorption thermodynamic characteristics indicated that the adsorption process of Cr³⁺ was accordant with the thermodynamic law, with R²=0.992 9. Moreover, the process was a non-spontaneous composite adsorption, and the promotion effects of the increasing temperature on the adsorption process and the inhibition effects of the exothermic reaction on the adsorption process may even cancel each other out. At the same time, the adsorption of Cr³⁺ on the nano-lignocellulosic aerogel of P. massoniana bark was accordant with the pseudo-second-order kinetic model(R²=0.991 0), the adsorption rate of Cr³⁺ was mainly affected by chemical interaction rather than material transport steps, especially the process of chemical sharing or covalent bond exchange between the two. Conclusion: The nano-lignocellulosic aerogel of P. massoniana bark prepared from cheap biomass-mass pine bark can be used as an effective adsorbent for heavy metal ions, showing an ideal adsorption capacity. The conditions involved in static adsorption experiments are also relatively simple. Therefore, it can be experimentally popularized to some extent. The development of the adsorbents can also promote the resource utilization of low-cost biomass. The adsorption performance of P. massoniana bark and nano-lignocellulose aerogel is stable and reliable, and the performance is expected to be improved by optimizing the processes. However, both of the above two points need to test their effectiveness based on large-scale or even pilot-scale experiments, so further to guide the process optimization to obtain better performance of aerogel as a heavy metals ion adsorbent.

Key words: Pinus massoniana bark, nano-lignocellulose, aerogel, heavy metal ions, adsorption