Adsorption of silver(I) and gold(III) on resins derived from bisthiourea and application to retrieval of silver ions from processed photo films

Various resins were synthesized through polymerization of bisthiourea (BS) with formaldehyde at different molar ratios. The uptake behaviour of the resins towards Ag(I) and Au(III) from their aqueous solutions was studied. The results showed that the total uptake of both Ag(I) and Au(III) increases as the content of bisthiourea in the matrix increases. The resin synthesized from a 2:1 mixture of bisthiourea and formaldehyde showed maximum uptake capacity of 8.25 and 3.63 mmol/g for Ag(I) and Au(III), respectively. The adsorption data were interpreted based on the metal ion species formed at different pHs and from the data on surface charge of the resin obtained from zeta potential measurements. The adsorption of Ag(I) and Au(III) on the resin followed the Langmuir model and the adsorption parameters were calculated. The resin showed noticeably higher efficiency compared with commercial resins towards the recovery of silver from processed photo films.