Sorption of heavy metals on a chitosan-grafted-polypropylene nonwoven geotextile

摘要

This work describes the development of an environmental friendly functionalized polypropylene nonwoven geotextile (PP) in order to trap heavy metals in sediments and sludges. Chitosan was chosen as the sorbent because of its ability to trap heavy metals, of its natural origin (from shells), and of its low cost. PP was first functionalized with acrylic acid using a cold plasma process, in order to bring some reactive carboxylic functions onto the surface. Chitosan was then covalently grafted on the acrylic acid modified polypropylene. The functionalized surfaces were characterized by FTIR (Fourier Transform InfraRed) and chitosan was thus proven to be grafted. The ability of the functionalized textile to trap heavy metals was then investigated. Copper was chosen as the model heavy metal, and artificial solutions of CuSO_4 were prepared for the experiments. Sorption studies among the concentration of copper in polluted solutions at 20°C were carried out with PP-g-AA-chitosan (Polypropylene-grafted-Acrylic acid-chitosan) in order to evaluate the maximum of absorption of this surface: the textile can chelate copper increasingly with the initial copper concentration until 800 ppm where it reaches a plateau at about 30 mg/L. The effects of pH and of the ionic strength (absorption in a NaCl containing solution) were finally investigated. The trapping of Cu~(2+) decreases slowly when the ionic strength increases. For a seawater-like NaCl concentration of 30g/L, the textile still chelates about 20 mg/L of Cu~(2+). Finally, the optimum pH to trap the maximum amount of copper was determined to be 4.75, which corresponds to the optimum pH for the solubility of the chitosan.