Selective recovery of silver ions from aqueous solutions using modified silica beads with Adogen 364

In this work, a method to prepare new adsorbents for the recovery of silver ions was studied. Cheap silica beads for industrial use were obtained and silanized with dichlorodimethylsilane after pretreatment with hot water to increase the silanol contents, followed by immobilization of Adogen 364 (a mixture of trialkyl tertiary amines, Witco Co), a commercial solvent extractant that has a good affinity with silver ions. This sample, designated as K2WDA, was proven to be effective for the adsorption of silver ions from aqueous solutions with fast adsorption rates where sodium nitrate was added as a complexation agent to increase the adsorption capacity of the basic extractant. The adsorption capacity of K2WDA at pH 5 was 0.125mmol g(-1) and corresponded to the proposed mechanism that silver ions adsorb on the functional group with a 1:1 molecular ratio. Selectivity for silver ions in synthetic plating wastewater containing CU2+ and Ni2+ ions was excellent due to thermodynamic stability. In addition, 80% of the silver ions adsorbed could be recovered with sodium thiosulfate solution rather than acids and the solution was concentrated more than 10 times compared with the original solution. For practical application, a semi-batch reactor was considered and numerical modeling was performed. (C) 2002 Society of Chemical Industry.