Study On Adsorption Of Lead And Cadmium In Wastewater By Modified Diatomite

Diatomite can be modified by CaCO3, MnO2 and Mg(OH)2, and it’s adsorption performance can be improved. In this paper, these three modified diatomite adsorption characteristics of Pb2+ and Cd2+ were studied; the adsorption of Pb2+ and Cd2+ adsorption isotherm model, adsorption thermodynamics and adsorption kinetics model were analysed, the conclusions were as follows:1. Modified material characterization results indicated that the surface of modified diatomite wrapped modified substances, not very evenly distributed, also found that many of the pores have modified substances. There were many micropores between the modified particles with diatomite, its specific surface area increased, beneficial adsorption; after modification, the modified substances characteristic absorption peaks appeared; after modification, silica diffraction peak decreased, the modified crystal structure characteristic diffraction peaks appeared, indicating the successful modification.2. CaCO3, MnO2 and Mg(OH)2 modified diatomite adsorption of Pb2+ and Cd2+. With the increasing of pH, the remove rate and the adsorption capactiy was enhanced. When the pH was 5, Pb2+ removal rate was 95.51%,92.15% and 95.56%, the adsorption capacity was 99.33mg/g,95.84mg/g and 99.38mg/g, respectively. When the pH was 6, Cd2+ removal rate was 78.56%,75.48% and 80.05%, the adsorption capacity was 81.70mg/g,78.50mg/g and 83.25mg/g. respectively. Removal rate increased with the initial concentration decreases adsorption capacity was increased. When the initial concentration was 500mg/L, the Pb2+ removal rates was 43.25%, 39.17% and 45.18%, the adsorption capacity was 216.25mg/g,195.85mg/g and 225.90 mg/g, respectively. The Cd2+ removal rate was 36.12%,35.78% and 38.92%, the adsorption capacity was 180.60mg/g,178.90mg/g and 194.60mg/g, respectively. With the increment of the sorbent dosage the remove rate was enhanced and the adsorption capactiy was decrease.When the dosage was lg/L, the Pb2+ removal rate was 99.14%,97.22% and 99.72%. Adsorption capactiy was 99.14mg/g,97.22mg/g and 99.72mg/g. respectively.The Cd2+ removal rate was 85.72%,82.48% and 88.64%. Adsorption capactiy was 85.72mg/g,82.48mg/g and 88.64mg/g, respectively.3. Langmuir model was consistent with the modified diatomite for Pb2+ and Cd2+ adsorption isotherm. The adsorption process was an endothermic reaction, was spontaneous, the confusion of the adsorption process was increased, the high temperature and low concentration favored the absorption. Adsorption was physical adsorption. The time to reach equilibrium adsorption of Pb2+ and Cd2+ by modified diatomite was 60min and 90min, respectively. Adsorption kinetics was consistent with the pseudo-second-order kinetic model.