Analysis of Highly Efficient Adsorption of Au(S₂O₃)₂ ^3- by Calcined Cu/Fe Layered Double Hydroxides

One of the main problems affecting the application of gold thiosulfate leaching is the difficulty in recovering gold from the leaching solution. Our previous studies revealed that when using calcined Mg/Al layered double hydroxides (LDHs), the single adsorption capacity of Au(S₂O₃)₂ ^3- can reach 7.76 mg/g. In order to further examine the recovery of Au(S₂O₃)₂ ^3- by various types of LDHs, the divalent metal and trivalent metal ions in LDHs were altered. Also, thiosulfate anions are introduced between the layers of LDHs to reduce the competitive adsorption of thiosulfate ions in the solution. Results show that the calcined LDHs (CLDH) prepared with Cu/Fe-LDHs are the best at adsorbing Au(S₂O₃)₂ ^3-. Compared with Mg/Al-CLDH, the single adsorption capacity reaches 48.6 mg/g. The pseudo-second-order kinetic model is more suitable for describing the adsorption of Au(S₂O₃)₂ ^3- by Cu/Fe-CLDH. The adsorption isotherm fitting experiment indicates that the adsorption by Cu/Fe-CLDH of Au(S₂O₃)₂ ^3- conforms to the Langmuir model. During the process of Cu/Fe-CLDH adsorbing Au(S₂O₃)₂ ^3-, CLDH restored part of the layered structure, and Au(S₂O₃)₂ ^3- was inserted between the layers as a counteranion. Furthermore, the reduction of Au(S₂O₃)₂ ^3- by low-valent iron compounds in the adsorbent promoted the process of Cu/Fe-CLDH adsorbing Au(S₂O₃)₂ ^3-.