4.3 gold adsorption
The results of the 8 h Au adsorption study involving both the activated carbonised macadamia shells and commercially available carbonised coconut shells are summarised for comparative purposes in Table 3. Fig. 2 presents the logarithmic plots of D[Au]tc/[Au]ts as a function of time for both the activated carbonised macadamia shells and commercially available carbonised coconut shells. Both plots exhibit linear behaviour, with the values of k’ and n being based on the slopes and y-intercepts of the curves of best fit (Eq. (8)). These values are listed in Table 3; inspection of these values reveals that the macadamia based activated carbon n value is close to unity for activation temperatures in the range of 800–1000 C. The CO2 activated macadamia based k0 value reaches a maximum of 23.4 h-1 at 1000 C, while the activated coconut shell based carbon reached a maximum value at 14.5 h-1. The increase in the k0 value with increasing activation temperature is generally consistent with the increase in surface area, see Tables 2 and 3. A comparison of Au adsorption data is made between activated macadamia based carbon and coconut based carbon at the activation temperatures of 1000 C and 1100 C over a 40 h period in Fig. 3. The data indicates that the Au adsorption capacity of activated macadamia shell based carbon is comparable with that of activated coconut shell based carbon.