## 3 Results and Discussion
### Bio-Adsorbent's Physicochemical Properties  
Previous authors determined the individual composition of the avocado peel and seeds of the same variety as those used in the present study [93; 94; 95]. The composition of avocado seeds previously had a wide range of parameters. Among these, 52.7-54.1% were water, 97.7-98.8% organic matter, 2.4-8.4% protein, 0.5-17.4% total fat, 27.5-29.7% carbohydrates, approximately 4% crude fiber, and vitamin A, vitamin C, phytosterols, triterpenes, vitamins K, B5, B6, and E, potassium, and folic acid were minority components. The peel is composed of 65.7-76.9% water, 93.4-99.3% organic matter, 1.5-7.42% protein, 11.0-13.7% total fat, 6.9-46.59% crude fiber, and around 16.24% carbohydrates; also, it contains bioactive compounds such as chlorophylls, carotenoids, and phenolic compounds.  
In the present study, a mixture of avocado peel and seed waste from the oil extraction process was used. This bio-adsorbent showed a water content between 7.63-7.76%, similar to the reported by [PERSON] and [PERSON] [96] in seed flour of avocado dried by oven at 60 \({}^{\circ}\)C with values between 7.94-9.28%.  
Regarding the mineral content (ashes), our bio-adsorbent had between 8.82-8.92%, while [PERSON] and [PERSON] [96] reported lower values (2.22-2.33%). It has been observed that low mineral content favors contaminant adsorption processes since adsorbents can only provide a finite number of binding sites on their surface, reducing their removal capacity when there are other minerals adsorbed [83; 97].  
The real and apparent density of the bio-adsorbent was between 0.96-0.98 g/mL and 0.295-0.323 g/mL, respectively, and showed a porosity between 0.630-0.712 g/mL. No previously reported values have been found for avocado peel and seeds biomass. Higher apparent density values favor the biosorption of metal ions [98]. Regarding porosity, studies have shown that the porous structure of the bio-adsorbents with a higher specific surface area will favor the diffusion of metal ions [99]. The solution of the studied bio-adsorbent has a pH of 5.1 \(\pm\) 0.0. In the bio-adsorption of metals from wastewater, the degree of ionization of the adsorbate molecules and the presence of the functional groups on the adsorption surface depend on this, which is a determining factor in the efficiency of theprocess [43]. [PERSON] et al. [100] verified the effect of pH on the retention of Pb in avocado peel biomass, determining that the percentage of cationic Pb removal increased with increasing pH due to the efficient exchange of cations with H\({}^{+}\) ions of carboxylic functional groups present on the surface of the adsorbent as it can affect the adsorbent's surface charge. In the present study, the percentage of the highest adsorption was tested between a pH of 2 and 10, and the maximum retention was found at a pH value of 5 in all cases. The pH of the aqueous medium also influences the metal species distribution and functional group dissociation on active sites [83]. Moreover, the adsorption efficiency of the adsorbents depends on the degree of ionization of adsorbate molecules, and the surface properties of the adsorbent depend on the pH of the solution [43].