<p>This study investigated the adsorption characteristics of Cr(VI) and methyl orange (MO) onto polyethyleneimine (PEI) cryogels. The morphology and physicochemical properties of this prepared adsorbent were characterized with various techniques. Its adsorption behaviors towards MO and Cr(VI) were systematically investigated. In single-component systems, PEI cryogels exhibited significant adsorption capacities for Cr(VI) (875 mg/g) and MO (1777 mg/g), respectively. In binary systems, the cryogels demonstrated a stronger affinity for Cr(VI) than for MO. Column adsorption studies in single-component systems explored the effects of bed height, flow rate, and inlet concentration using breakthrough curves, with the modified dose–response model proving effective in describing these curves. Moreover, repeated dynamic adsorption experiments highlighted that the cryogels exhibited exceptional reusability. Results from column adsorption in binary systems indicated that the presence of MO did not significantly affect the adsorption of Cr(VI), while the presence of Cr(VI) enhanced the affinity of the cryogels for MO adsorption. The adsorption mechanism of PEI cryogels towards Cr(VI) primarily involved electrostatic attraction and reduction, whereas for MO, it predominantly entailed electrostatic attraction and hydrogen bonding. These findings collectively emphasize the significant potential of PEI cryogels for treating dyeing wastewater.</p>