Effects Of Amounts Of Surface Coatings On The Adsorption Rates Of Cd To Natural Surface Coatings

Natural surface coatings composed of microorganisms, oxideminerals and many other things are the composite solids existingwidely in the natural aquatic environments, and they occur on all kindsof solid surfaces and affect the behaviors of heavy metals significantly.Therefore, the aim of this research work focused on the effects ofamounts of surface coatings on the adsorption rates of Cd to naturalsurface coatings.Freshwater surface coatings were developed in Nanhu Lake, JilinProvince, P. R. China. Glass slides were fixed in the device designedfor collecting surface coatings, then submerged in water at a depth of30cm for 19 days. Concentrations of ferric oxides, manganese oxidesand organic materials in the surface coatings were quantified.Adsorption data of Cd to surface coatings whose amount ranged fromone piece to five pieces was obtained in MMS solutions with thedifferent Cd original concentration (2.0μmol·L-1 and 3.5μmol·L-1).During this procedure, the temperature of the system was maintainedat 25℃and pH at 6.0±0.1. The solution was sampled at certain timesduring the adsorption process. The model of Elovich and doubleconstant kinetic equations were employed to investigate the adsorptionprocess of Cd. Meanwhile, the relation of the amounts of surfacecoatings and the rate of Cd adsorption to natural surface coatings wasanalyzed.The results showed that the amount of surface coatings affectedthe Cd adsorption to surface coatings. When the amount of surfacecoatings ranged from one pieces to three pieces, the Cd adsorption tosurface coatings increased with the amount of surface coatings greatly.When the amount of surface coatings ranged from four pieces to fivepieces, the Cd adsorption to surface coatings increased with theamount of surface coatings less. Therefore, the amount of surfacecoatings could not increase the Cd adsorption infinitely with the sameCd original concentration. Correlation analysis between logC and t showed that there'ssignificant relationship between them. Both the Elovich equation andthe double constant kinetic equation could fit the kinetic data of Cdadsorption to surface coatings whose amount ranged from one piece tofive pieces with the different original concentration. It showed that the rate of Cd adsorption to surface coatingsincreased with the amount of surface coatings. The rate of Cdadsorption to surface coatings increased with the amount of surfacecoatings greatly when there were a few surface coatings. However, theincrease of the adsorption rate was limited when there were moresurface coatings. The result showed that when the initial concentrations of solutionwere defined (2.0μmol·L-1/3.5μmol·L-1), increasing the amount ofsurface coatings was an effective approach to improve Cd adsorption.While the adsorptive rates of per unit surface coatings for Cddecreased with the amount of surface coatings. When the initial...