## 3 Results and Discussion  
### Characterization of Bioadsorbents  
African palm fibrillates (OPB) were obtained from the Department of Bolivar-Colombia, as a result of the waste generation during palm oil extraction process. The hulls of hawthorn yarn (YP), cassava (CP), cocoa (CH) and corn residues (CCR). The morphological and compositional characteristics of these materials were analyzed. Figures 1-5 are referring to biomaterials before and after adsorption characterized via SEM analysis coupled with EDS. The heterogeneous surface of the biomaterials can be clearly seen. Most of the biomasses showed a smooth porous structure. According to [PERSON] at al. [40] molecules in the amorphous region contain hydroxyl groups specially for cassava peel. In SEM micrographs before and after adsorption, luminous and non-luminous features are observed, which revealed the presence of organic minerals such as Ca\({}^{2+}\), Mg\({}^{2+}\) and K\({}^{+}\) in the matrix of biomasses [41]. The EDS spectra also confirmed these findings with characteristic peaks attributed to these elements. Before adsorption, no signal was recorded for cadmium ions. Figure 1: EDS spectra and -SEM micrographies for YP: (**a**) before and (**b**) after adsorption. Figure 2: EDS spectra and -SEM micrographies for r OPB: (**a**) before and (**b**) after adsorption. Figure 4: EDS spectra and -SEM micrographies for CP: (**a**) before and (**b**) after adsorption. Figure 3: EDS spectra and -SEM micrographies for CH: (**a**) before and (**b**) after adsorption. As shown in Figures 1a and 3a, the elements C, O, Ca, K and Si were present in greater proportion in the structure of biomaterials, with YP and CH being the most diverse in structure. The higher presence of these mineral parts (revealed by small white spot) is also confirmed by the elemental compositional analysis gathered from the literature. After adsorption, the decrease in K near the 3.3 keV peak, the reduction of Ca by 1.3 keV and its disappearance by 3.4 keV, as well as the disappearance of Fe are observed in the YP; OPB shows a decrease of Ca in 1.3 keV and 3.4 keV and of Si in 1.6 keV; the CH had a decrease of K in 3.3 keV; CCR showed disappearance of Si at 1.9 keV and of K at 3.3 keV; On the other hand, an increase in K was observed in the CP spectrum with the appearance of Cd near 2.8 keV. The aforementioned occurred together with the conservation in most cases of the presence of Ca in the 1.3 keV peak, finding conservation of the variation of the equivalent charges between Cd\({}^{2+}\) and Ca\({}^{2+}\)/K\({}^{+}\), hence, adsorption of Cd\({}^{2+}\) is more competitive for functional groups that resulted in the ion exchange process [42]. The increase of the Si atomic percentage in OPB; P, O and S in CH; Si, P and O in CP; and P, Mg, Al, O and K in CCR, after Cd\({}^{2+}\) adsorption illustrates that the formation of precipitation in the form of calcium sulfate and phosphate on the cell surface, which was observed in SEM micrographs, was another biosorption mechanism probable. Table 1 shows the chemical composition of the bios adsorbents under study, with carbon being the most abundant element in all bioadsorbents, which is typical of lignocellulosic materials due to the presence of lignin, cellulose and hemicellulose, which is why expects a high Cadmium adsorption efficiency, because these polymers are known for the large number of hydroxyl and carboxylic groups that can favor the adsorption of heavy metals [3; 15]. Previous research reports that the presence of OH, COOH and amines groups contribute to the metal ion uptake process in the lignocellulosic matrix of bioadsorbents, which favors interaction with the active centers due to their anionic nature [43; 44]; In the adsorption of Cd\({}^{2+}\) on cocoa mesocarp, it was found that the functional groups involved in the removal process were those that have an oxygen in their structure such as ethers (aromatic, olefinic or aliphatic), esters, amines, hydroxyl, and aliphatic hydrocarbons [45].