Mechanical fragmentation of wheat straw at different plant scales: Pb2+ adsorption behavior and mechanism

Abstract

Wheat straw samples at the plant scale (> 1 mm), tissue scale (100 to 500 μm), and cellular scale (30 to 50 μm) were produced to characterize their microstructure and adsorption properties. The effects of changes in the microstructure and adsorption properties on the adsorption capacity of Pb2+ were investigated. The results implied that specific surface areas and pore volumes in the cellular-scale sample were four to five times larger than at other scales, as superfine grinding destroyed the structure of tissues and cell walls. The crystallinity declined significantly from 53% to 34% with decreasing fragmentation scale. Changes in adsorption properties (point of zero charge, acidic functional groups, and cation exchange capacity) were not apparent. The pseudo-second-order model and Langmuir isotherm model fit the experimental data better than alternate models. The adsorption capacity of Pb2+ increased significantly with decreasing fragmentation scale. The main mechanism improving the adsorption capacity of Pb2+ was intensive complexation owing to an increase in cellulose accessibility to water and enhanced chemical reaction activity of the hydroxyl groups, rather than physical and electrostatic adsorption.