微波场诱导改性磷石膏吸附Cu^(2+),Zn^(2+),Pb^(2+)和Cd^(2+)的动力学与热力学研究

Kinetics and thermodynamics of Cu^(2+),Zn^(2+),Pb^(2+) and Cd^(2+) adsorption onto microwave-preconditioned phosphogypsum

选用微波场诱导改性磷石膏作为吸附剂,采用批式振荡吸附法研究改性磷石膏对重金属离子Cu2+,Zn2+,Pb2+和Cd2+的吸附动力学及吸附热力学特性,提出吸附机理。研究结果表明:微波场改性磷石膏对Cu2+,Zn2+,Pb2+和Cd2+的吸附平衡数据符合Langmuir和Freundlich吸附等温方程,但Freundlich方程能够更好地描述吸附等温线。在改性磷石膏对重金属离子吸附的初始阶段,Lagergren伪一级动力学方程、Lagergren伪二级动力学方程、Elovich方程、粒子内扩散模型均能很好地反映吸附模式,而整个吸附过程则遵循Lagergren伪二级动力学方程,其吸附过程是液膜扩散和粒子内扩散共同作用的结果;Cu2+,Zn2+,Pb2+和Cd2+的平衡吸附量分别为3.937 0,3.993 6,2.627 4和3.319 0 mg/g;微波场改性后的磷石膏对Cu2+,Zn2+和Cd2+的吸附是吸热反应,对Pb2+的吸附为放热反应。

Kinetics and thermodynamics characteristics of Cu2＋, Zn2＋, Pb2＋ and Cd2＋ adsorption onto microwave- preconditioned phosphogypsum were investigated by batch adsorption methods. The results show that the adsorption results fit well both in the Langmuir and the Freundlich model, however, Freundlich equation is more applicable than Langmuir equation. The Lagergren pseudo-first-order kinetics, Lagergren pseudo-second-order kinetics, Elovich equation and intraparticle diffusion model were studied in the process of adsorption. All the four equations, i.e, Cu2＋, Zn2＋, Pb2＋ and Cd2＋ are found applicable in initial stage of adsorption. The absorption of Cu2＋, Zn2＋, Pb2＋ and Cd2＋ on microwave- preconditioned phosphogypsum is in accordance with pseudo-second-order reaction kinetics in the entire stage. The absorption characteristics of metal ions on microwave-preconditioned phosphogypsum are controlled by both film diffusion and particle diffusion. The maximum adsorption capacities are 3.937 0 mg/g of Cu2＋, 3.993 6 mg/g of Zn2＋, 2.627 4 mg/g of Pd2＋ and 3.319 0 mg/g of Cd2＋ onto microwave-preconditioned phosphogypsum. The process of microwave- preconditioned phosphogypsum adsorbing Cu2＋, Zn2＋, Cd2＋ are endothermic reaction, but adsorbing Pb2＋ is exothermic reaction.