Effect of chitosan and sodium alginate on heavy metal adsorption by natural plant extracts

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To investigate the effects of chitosan (CS) and sodium alginate (SA) on heavy metal ions adsorption by natural plant extract (Pe), different proportions (0%, 10%, 20%, and 50%) of CS and SA were used to modify Pe to prepare CS- and SA-modified Pe (CS-Pe and SA-Pe). The different CS-Pes and SA-Pes were analyzed by different spectroscopic test instruments. The adsorption properties and differences of Cu2+, Pb2+, and Cd2+ under various temperatures, pH, and ionic strengths were studied. Results displayed that (1) characterization showed that CS and SA attached to the Pe surface and altered the morphology of Pe surface. The adsorption of Cu2+, Pb2+, and Cd2+ by different CS-Pes and SA-Pes was better suited to Langmuir model than that to Freundlich model, maintaining the maximum adsorption capacity at 378.01–833.83 (Cu2+), 218.66–531.04 (Pb2+), and 221.46–384.93 (Cd2+) mmol/kg. (2) Higher pH and temperature facilitated the pollutants adsorption by CS-Pes and SA-Pes, which followed a chemisorption mechanism. Heavy metal ions adsorption rose initially and then reduced with increasing ionic strength (peak value at 0.1 mol/L). Thermodynamic parameters presented that the pollutants adsorption was a spontaneous, primarily chemical, and multi-mechanism reaction. (3) Heavy metal ions adsorption by SA-Pes maintained approximately 60–72% of the raw material by triple regeneration. The economy (qm/price) of different modified Pes for heavy metal ions adsorption ranged from 0.97 to 6.41 mmol/¥, and SA-Pe showed the highest economy.