Study On Adsorption Of Pb²⁺ And Cu²⁺ In Polluted Water By Intercalated Montmorillonite

In this paper,the titanium intercalated montmorillonite interlayer（Ti-Imt）materials were preparated through the polymeric hydroxy cationic Ti4+ pillared into the interlayer spaces of purified sodium montmorillonite（Na-mt）by the sol-gel method and under the addition of acidic using butyl titanate as titanium source.The Na-mt and Ti-Imt materials were characterized by X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IRs）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,thermogravimetry（TG-DTA）,the specific surface area analysis,respectively.The adsorption of Pb²⁺ and Cu²⁺ in wastewater by Na-mt and Ti-Imt were determined.The several factors of adsorption of Pb²⁺and Cu²⁺were studied,such as pH value,dosage of adsorbent,adsorption time,adsorbate concentration,temperature et al.Meanwhile,The adsorption mechanism were explaned from the adsorption kinetics,adsorption isotherm and thermodynamic analysis.Based on the above studies,the following conclusions can be drawn:（1）The XRD,FT-IRs,SEM,TEM characterization analysis showed that the Ti-Imt basal spacing（d001）increases to 2.94 nm,the structure is more stable and has a higher thermal stability and clearer lamellar structure.The TG-DTA,specific surface area analysis showed that the particle size of the post-pillared pillar is thinner,the average pore size decreases,the pore volume increases and forms a porous structure material with a large specific surface area.（2）The adsorption of Pb²⁺and Cu²⁺by Na-mt and Ti-Imt showed that the adsorption optimum temperature was 20 °C,the adsorption optimum pH value of Pb²⁺was 5 and the adsorption optimum pH value of Cu²⁺was between 6 and 7.The adsorption process of Pb²⁺ and Cu²⁺ includes ion exchange reaction,surface coordination and H+competitive adsorption.The dosage of adsorbent increase was not conducive to the adsorption reaction.The adsorption of Pb²⁺and Cu²⁺onto Ti-Imt reached equilibrium（t=90min）,the saturated adsorption capacities were 49.52 mg/g and 40.14 mg/g,respectively;and the removal rates were99.03% and 80.27%,respectively.However,the adsorption of Pb²⁺onto Na-mt reached equilibrium（t=180min）,the saturated adsorption capacities and removal rate were 43.35 mg/g and 86.7%,respectively;and the adsorption of Cu²⁺onto Na-mt reached equilibrium（t=120min）,the saturated adsorption capacities and removal ratewere 13.83 mg/g and 27.65%,respectively.（3）The adsorption kinetic of Pb²⁺and Cu²⁺ by Ti-Imt and Na-mt follows the pseudo-second-order equation,and the intra-particle diffusion model is not the only step-controlled step,but also controlled by the diffusion of liquid film and surface adsorption,and the adsorption rate of Ti-Imt is larger than Na-mt.（4）The adsorption isotherm process of Pb²⁺and Cu²⁺by Ti-Imt and Na-mt follows the Langmuir isotherm model.The dimensionless separation constant RL value was between 0 and 1,indicating that the adsorption of Pb²⁺ and Cu²⁺ by Ti-Imt and Na-mt is a more easily adsorption process.（5）The thermodynamic parameters（i.e.,the changes of enthaloy,entropy and Gibbs,free energy）were determined and evaluated.It is indicated that the adsorption of Pb²⁺ by Ti-Imt and Na-mt is a non-spontaneous exothermic process and the adsorption is mainly chemical adsorption.The adsorption process of Cu²⁺ onto Ti-Imt changes of enthaloy and Gibbs,free energy values show that the adsorption is a non-spontaneous exothermic reaction,the adsorption force is dominated by Van der Waals force and the adsorption process is a physical adsorption process based on monolayer adsorption.The main force in adsorption process of Cu²⁺ onto Na-mt is dominated by dentate exchange force,which is a non-spontaneous exothermic reaction and a chemical adsorption process.In addition,The adsorption of Pb²⁺ and Cu²⁺ by two adsorbents entropy change are negative values,indacting that adsorption is a process of entropy reduction.