Preparation Of Bamboo Shoot Shell Biochar By Torrefaction And Its Adsorption Properties Of Cr(?) From Aqueous Solution

Technetium(⁹⁹Tc)is a radioactive metal element with long half-life.Tc???has the strong mobility and high solubility in aqueous solution,which has a potential pollution risk for water environment.The common immobilization method of Tc???is the reduction of Tc???to sparingly soluble Tc???by reducing materials.The redox behavior of Tc???is similar with Cr???.Biochar has great potential as a immobilization material of Tc???,due to its surface reducibility.In this paper,biochar derived from torrefaction of hemicellulose-rich bamboo?Acidosasa longiligula?shoot shell was used to adsorb Cr???as a no radioactivity surrogate for Tc???from aqueous solution.The torrefaction process of bamboo shoot shell was described by using torrefaction intensity,and the relationships of the physicochemical properties of bamboo shoot shell and torrefaction intensity were also studied in detail.Combining torrefaction intensity index model and its rate of change model,elaborated the torrefaction mechanism of bamboo shoot shell.The effects of environmental factors were investigated by batch adsorption.The adsorption kinetics,adsorption equilibrium and thermodynamic behavior of Cr???on biochar were studied,and the adsorption mechanism of biochar for Cr???were investigated.The main conclusions were as follows.?1?With the increasing of torrefaction intensity,the hemicellulose component of bamboo shoot shell was gradually decomposed,and the mass yield of biochar gradually decreased,while the ash content,pH value,point of zero charge and hydrophobicity of biochar increased.Meanwhile the surface functional groups of biochar increased,showing that the adsorption ability of bamboo shoot shell enhanced when torrefaction intensity was lower than 4.421.?2?The torrefaction intensity index model and its rate of change model were suitable to research the torrefaction process of bamboo shoot shell.?3?The hydroxyl,carboxyl and lactonic group were main Cr???adsorption sites on biochar surface and the electrostatic interaction and redox mechanism were mainly involved adsorotion mechanism in the adsorption process.?4?The optimal adsorption conditions were:adsorbent dosage:3 g·L-1;solution pH value:1.0;contact time:12 h;solution temperature:40 0C.The maximum Cr???adsorption capacity of biochar was 102.77 mg·g-1.?5?The adsorption kinetics of Cr???onto biochar could be well-defined by the pseudo-second-order model.The adsorption process was controlled by film diffusion.Compared with Langmuir model,Freundlich model and Temkin model described the adsorption equilibrium better.The adsorption Cr???onto biochar was a multilayer,heterogeneous chemical adsorption process.?6?The adsorption thermodynamic parameter of ?C0 value was negative,indicating that the adsorption was spontaneous.The positive value of ?H0 indicated that adsorption was endothermic.The positive value of ?S0 suggested the increased randomness at the solid-solution interface after Cr???adsorption.