Study On The Removal Of Heavy Metal Ion Pb²⁺ In Water With Molecular Sieve And Its Adsorption Mechanism

Molecular sieve is a kind of aluminosilicate adsorbent with skeleton structure. It is widelyused in various kinds of water treatment technology due to its high adsorption capacity andselective adsorption performance.The influence of the type of molecular sieve, pH of water, adsorption time, and initialconcentration of Pb2+on removal rate were studied. The results showed that the removalefficiency of Pb2+with4A and13X molecular sieve were significantly higher than that ofMCM-41molecular sieve, the removal rate reached more than90%.The adsorption was inconsistent with the Langmuir adsorption isotherm and Lagergren rate equation2through thematching of adsorption isotherm and kinetics equation,Compared with cation exchange resins and activated carbon, The adsorption rate constant of4A molecular sieve for Pb2+was0.0149g/(mg·s) and the adsorption capacity was595.2mg/g,higher than that of cation exchange resins (0.0005g/(mg·s) and203.3mg/g), and that of activecarbon (0.0019g/(mg·s) and177.3mg/g). The adsorption process was mainly controlled by theliquid film diffusion. The comparison of the adsorption of different valence metal ions showedthat the adsorption rate was inversely proportional to the number of valence. With the increase ofthe valence, the adsorption rate decreased. According to the change of the cation of molecularsieve after adsorption-desorption, the adsorption mechanism can can be mainly attribute to ionexchange adsorption. The results of X-diffraction and scanning electron microscope show thatthe crystal structure and morphology of4A molecular were not changed afteradsorption-desorption. The analysis of Zeta potential showed that there existed physicaladsorption with electrostatic attraction.4A molecular sieve had better settling performance and was suitable for recycling. Theremoval rate of Pb2+was still88.7%after four adsorption-desorption process and the adsorptioncapacity was still493.2mg/g. The concentration of Pb2+in the concentrate after desorption was720.3mg/L. Heavy metal Lead can be reclaimed by the addition of Na2S to generate lead sulfideprecipitation.