SILVER SORPTION DYNAMICS BY NATURAL ZEOLITES

The present work provides data on sorption of silver ions in concentrations ranging from 10 to 20 mg/l from nitrate solutions. The zeolite tuff sorption properties from the Seredochnoe deposit in Khabarovsk Krai were investigated by the down flow solution method through a column with a fixed sorbent bed. The elution curves method was employed to ascertain the operational mode of the column and its dynamic response. Based on the elution curves, the practical maximum sorption capacity and the capacity before breakthrough for silver ions at the outlet of the sorption column were calculated. The Thomas model calculations revealed that for sorption from a silver nitrate solution with a concentration of 10 mg/l KTh, the sorption capacity was 2.50 and 3.09 ml/mg-min for the 1SD and 2SD columns, respectively. The maximum equilibrium sorption capacity in the first and second columns was found to be 0.63 mg/g. The capacity before breakthrough was calculated to be 0.45 mg/g. Upon doubling the concentration of the stock solution (column 8SD), KTh, 0.725 ml/mg⋅min, the maximum sorption capacity increased to 0.98 mg/g, while the capacity before breakthrough exhibited a value of 0.77 mg/g. The following data were obtained when calculating KAB kinetic coefficients (ml/mg∙min): when sorption from solution with silver content of 10 mg/l, the KAB values were 2.48 and 3.07 ml/mg∙min, while at sorption from solution with silver content of 20 mg/l, the KAB was equal to 0.69 ml/mg-min. The theoretical sorption capacity in the first case is 0.67 mg/g, while in the second case it is 1.08 mg/g. The values of the parameters calculated using the Thomas model and the Adams-Bohart model indicate that both models adequately describe the sorption of silver ions from nitrate solutions in the concentration range of 10–20 mg/l. It is recommended that desorption be carried out with 0.1-0.2 n nitric acid. Under these conditions, concentrates with silver ions content of 22.52 mg/l were obtained using 0.1 n acid. Upon desorption with 0.2 n acid, the silver content was 25.23 mg/l and 105 mg/l. The concentration coefficient for one sorption–desorption cycle was found to be in the range of 2.25–5.25 units.