Comparison of the adsorption characteristics and mechanism of Pb onto four adsorbents derived from edible fungi spent substrate

In this work, the adsorption characteristics and mechanism of Pb(II) onto edible fungi spent substrate (EFSS11EFSS: edible fungi spent substrate.), EFSS modified by NaOH (EFSSM22EFSSM: EFSS modified by NaOH.), EFSS biochar (EFSSB33EFSSB: EFSS biochar.) and EFSS compost (EFSSC44EFSSC: EFSS compost.) in water were studied. All adsorption quantities increased with the increment of solution pH and the reduction of adsorbent dosage. The adsorption of Pb(II) onto four materials followed Langmuir isotherm model and pseudo-second-order kinetic model. The maximum adsorption quantities of EFSS, EFSSM, EFSSB and EFSSC measured 34.57 mg/g, 49.32 mg/g, 77.96 mg/g and 138.02 mg/g, respectively by Langmuir model. The spontaneous order of Pb(II) adsorption onto four materials was EFSSC > EFSSB > EFSSM > EFSS based on their Gibbs free energy changes of −1.208, −2.342, −4.676 and –5.832 kJ/mol, respectively. The results of SEM-EDX, FTIR, XRD and CEC showed that four materials varied greatly in surface structure, they all had amino, hydroxyl, carbonyl and aromatic groups but these groups played distinct roles in adsorption, and the differences in polarity, crystal species, pH change, ash content and cation exchange capacity might also lead to the divergence in adsorption quantities.