Utilising highly characterised peats to remove cadmium from aqueous solutions

This research investigated the biosorption of cadmium (Cd) from aqueous solutions by six highly characterised peats. Samples of the peats were tested both in unaltered condition and after treatment with hydrochloric acid (HCl) to free up any occupied exchange sites. Other factors tested were sample dose, contact time, mixing temperature, and the concentration and pH of the Cd solution. Desorption studies were also performed, and tests were done to determine whether the peats could be re-used for Cd biosorption. The results indicate that all six peats biosorb Cd from aqueous solution well (36−100 % removal) and that their Cd removal capacities are affected by the various factors that were manipulated. The three factors that had the greatest effects on the Cd removal capacities of the peats were sample dose and the concentration and pH of the Cd solution. The percentage of Cd removed increased as the sample dose increased (16−31 % increase) and as the pH of the Cd solution increased (16−57 % increase). As the concentration of the Cd solution increased, the percentage of Cd removed increased slightly for two of the six peats (1−2 % increase) and decreased for three peats (19−23 % decrease). As the mixing temperature increased, the percentage of Cd removed increased slightly for three of the peats (1−12 % increase) and decreased slightly for the other three (1−5 % decrease). The desorption results showed a 34−71 % Cd recovery rate. Re-used peats were also highly effective at removing Cd, whether or not they had gone through desorption. Two of the six peats were slightly better at Cd removal after treatment with HCl (4−7 % better than untreated peats), while the other four peats worked better in their unaltered states (3−18 % better). As all of the peat types tested can be repeatedly re-used for additional Cd biosorption cycles, their disposal should not create a hazardous waste problem. On the other hand, using peat for any industrial purpose is increasingly disfavoured nowadays, for sustainability reasons. Thus, the results of this study might be used to identify and/or develop materials with properties similar to those of the most effective peats (i.e. artificial peats) for use as biosorbents of Cd. These materials could be agricultural waste products such as soybean or rice hulls, constructed wetlands with living plants similar to those found in the tested peats, or possibly biochar of these living plants