Sedimentable polyethyleneimine-modified yeast residue enhances the selective adsorption of Pd(II) by altering isoelectric point

Modifying the surface of microorganisms is a common method for increasing microbial adsorption capacity although further treatment of the microorganisms is required to facilitate the use. However, only a few studies have explored how to simultaneously achieve selective adsorption ability and convenient separation. In this paper, the maximum Pd(II) adsorption capacity on polyethyleneimine (PEI)modified Pichia pastoris residue (PEI-PR) was achieved at a PEI:glutaraldehyde (GA) ratio of 4:1. An adsorption kinetics study showed that PEI-modified biomass (PEI-PR) reached adsorption equilibrium within 180 min, and the adsorption conformed to the pseudo-second-order model. Using the Langmuir adsorption isotherm, the maximum adsorption capacity for Pd(II) at pH 3 was found to be 587.67 mg center dot g(-1) of dry weight. After five adsorption-desorption cycles, PEI-PR could maintain 90.35% of its initial adsorption capacity. Moreover, PEI-PR showed satisfactory selectivity to Pd(II) in simulated multi-metal solution. The selective adsorption efficiency of PEI-PR was mainly due to the introduction of a large number of amino and imino groups onto the surface of the biomass through PEI modification, which caused the increase of the isoelectric point from 4.64 to 9.46. At a pH value lower than its isoelectric point, PEI-PR became protonated and thus was positively charged. As a result, it could only undergo electrostatic adsorption with negatively charged Pd(II) chloride complex ions, rather than with other positively charged metal ions. The adsorption complex could be separated from the solution via sedimentation. This research presents a new approach for preparation of microbial adsorbent with selective adsorption capacity and can conveniently be separated from a solid-liquid mixture. It is a green approach for efficient microbial adsorption and recovery of Pd(II). (c) 2023 Elsevier B.V. All rights reserved.