Study On The Sorption Of Heavy Metal Ions On Montmorillonite And Its Modified Samples

Montmorillonites, which were derived from different areas and their inorganic modified samples, were used in this paper as sorbents to study the sorption properties of cobalt, lead and thorium on the different samples. The montmorillonites and their modified samples were characterized by XRD, FT-IR, N2-sorption and desorption methods in detail. Effect of pH, fulvic acid, ionic strength and other parameters on the metal ions sorption to the clay minerals were investigated, and the sorption mechanism of the three heavy metal ions on different materials was also discussed by using different sorption models. The sorption performances of lead ion on silicon dioxide and alumina were also studied in this thesis as a comparison.The results of the thesis indicate that the spacing, specific surface area, and hole volume of inorganic modified samples augment markedly as compared with the untreated montmorillonite. The sorption of metal ions on Montmorillonites derived from different areas and their inorganic modified samples were different. Fulvic acid has good strong complexation ability to metal ions. Effect of ionic strength on the sorptin of cobalt is not obvious, whereas a slight effect of ionic strength on the sorptin of lead at low pH values is found. At acid conditions, the influence of pH value have intense effect on lead and thorium ions' sorption is apparently and little effect of pH on cobalt ion sorption is achieved. At the range of pH 5-8, pH value have intense effect on sorption of the three metal ions on the solid sorbent is strongly influenced by pH, i.e., the sorption of the three metal ions increases markedly, it presented at sorption rate ascend;At alkali conditions, the sorption of the three metal ions on the sorbent surface is mainly attributed to surface precipitation and about 95% of the initial metal ions is sorbed on solid surface. Sorption of the three metal ions is not influend by pH values. However, the precipitated lead on sorbent surface begins to dissolve at pH>10 and the sorption of lead decrease with increasing pH.At the condition of pH<8, the dominated sorption mechanism is surface complexation, whereas ion-exchange also contributes to the sorption on montmorillonite, and diffusion sorption mechanism contributes to the sorption on the modified samples, respectively;at pH>8, the sorption of metal ion on the bare montmorillonite is mainly attribute by surface precipitation. In the presence of fulvic acid, the sorption of the three metal ions on montmorillnite-FA hybrids is mainly dominated by surface complexation.