Silver recovery from spent photographic solutions by a magnetically assisted particle bed

The work presents experimental results on silver cementation from spent photographic fixer thiosulphate solutions by iron in magnetically controlled particle beds. Axial magnetic field created by Helmholtz pair was used. The increase in the fluid flow rate yields an increased silver recovery due to reduction in the external mass transfer resistance irrespective of the particle bed structures used for cementation. The field intensity slightly boosts the silver recovery and results in granular structures appearing at the surface of the deposits. The bed structures when the iron is used as a particle beds in column operation has major role in the efficient performance of the cementation process. With flow rate slightly exceeding the minimum fluidization point in the absence of a field the preferable operating regimes are: a fixed bed (FB) and moderately expanded magnetically stabilized beds (MSB) regimes, both of them with the Magnetization FIRST mode. However, when high flow throughputs are required, the frozen beds with the Magnetization LAST exhibit higher separation efficiencies and higher mass transfer coefficients than those with FB and MSB.