Optimization of Silver Recovery from Used Radiograph Films (URF) via Sodium Hydroxide Stripping
Author : Roco, Joshua Bon Ariza
Major Adviser : Laurio, Michael Vincent O.
Major Co-Adviser : Migo, Veronica P.
Committee Members : Alfafara, Catalino G.; Guerrero, Gino Apollo M.
Year : 2016
Month : June
Type : Thesis
Degree: BS
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Abstract
This study focused on the recovery of the residual silver from used radiograph films (URFs) via sodium hydroxide stripping by conducting factorial and response surface experiments. Initially, 100 g of 4 x 4 cm² URF samples were found to have 0.5845 grams of silver at 30.91 % purity based on the AAS and XRF analyses, respectively. At 95 % confidence level, results from the 2ᵏ full-factorial experiment showed that sodium hydroxide concentration, reaction temperature, and contact time were significant in the recovery process. Further, a quadratic model was found to conform the central composite experimental design with significant effects of NaOH concentration, temperature, time and the quadratic effects of concentration and time. The response surface model was used for numerical optimization. From 46 possible solutions, the selected condition was 90 °C, 1.75 M and 194 seconds based on highest percent recovery and lowest NaOH concentration. Experimental verification showed 69.69 % silver recovery with a reasonable difference of 12.62 % from the predicted value. At these conditions, preliminary cost analysis showed that the recovery process costs ₱ 54.72, with profit of ₱ 39.26 per kilogram of film processed.
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