Fig. 5 plots the binary adsorption data for the Group 1B metals: copper, silver and gold. The experiments were conducted using equimolar solutions of Au(III)/Cu(II) and Ag(I)/Cu(II) solution
at room temperature for different solution pH.
Fig. 5a and b shows that silk sericin and chitosan did not adsorb gold or copper at pH 1 and above pH 3, precipitations occurred.
It can be seen from Fig. 5a that silk sericin did not adsorb copper over the entire range of pH of the experiment, and the adsorb gold gradually increased to 0.6mmolg−1 at which point all the gold was removed from the solution.
Fig. 5b shows that gold adsorption on chitosan behaves in a similar manner as silk sericin (cf. Fig. 5a), and only trace amount of copper was adsorbed (i.e., 0.02mmolg−1).
Fig. 5c shows that silver and copper ions were not adsorbed by silk sericin over pH range of 1–3, while chitosan adsorbed both metal ions from the binary solution as shown in Fig. 5d. The binary adsorption study shows the silk sericin adsorbed only gold, whereas chitosan can adsorb all three metals depending on the experimental situation.
Also, it is possible to recover gold and regenerate the adsorbent by a simple acid wash. Table 2 lists the gold adsorption and separation on a number of adsorbents reported in the literature