Sorption of precious metals onto chemically prepared carbon from flax shive

The sorption of gold, silver, palladium and platinum chlorides onto a carbonaceous sorbent prepared from flax shive by treatment with hot sulfuric acid is described. The results showed that the rate of sorption followed a first-order relationship with the initial rate described largely by pore diffusion. The sorption of the metal ions followed the Langmuir equation with the calculated monolayer capacities following the order: Au(III)>Pd(II) >Ag(I)>Pt(II)≈ Pt(IV). The sorption process was shown to occur by ion exchange reactions with functional groups on the sorbent. Once the metal ions had been loaded onto the sorbent, they were, except for platinum(IV), reduced by the sorbent to the metal with oxidation of the sorbent generating further ion exchange sites for sorption of the metal ions. This allowed the possibility of recycling the sorbent until significant amounts of the precious metal had been accumulated, thus simplifying the recovery of the metal by combustion of the residual sorbent.