Biosorption of chromium (III) by orange (Citrus cinensis) waste: Batch and continuous studies

Biosorption of Cr(III) and Pb(II) by Schoenoplectus californicus and Insights into the Binding Mechanism

“…Although increasing removal percentages at high doses may be attributed to the availability of a larger quantity of sorption sites [2], a partial aggregation of the biosorbent, which occurs at higher biomass dosages, resulted in a decrease in the effective surface area for metal uptake. Instead, at pH 5 ( Figure 4(a)), in agreement with several authors [3,6,24], it was observed that a decrease in the biosorption capacity and an increase in the removal percentage, with increasing biosorbent dose, were attributed to the availability of a larger quantity of sorption sites and no aggregation of the biosorbent.…”

“…This behaviour can be explained by the strong forces between the metals and the sorbent [2]; fast diffusion onto the external surface was followed by slow pore diffusion into the intraparticle matrix to attain pseudoequilibrium. Furthermore, the faster initial rate may be due to the availability of the uncovered sorption sites of the adsorbent at the beginning [24]. The differences observed in both pH values are because, at pH 7, the predominant reaction is the precipitation, which could occur at different velocities than sorption reactions.…”

“…The band at 1639 cm −1 can be assigned to the C=C benzene stretching ring of lignin; the band at 1514 cm −1 is mainly attributed to N-H deformation in secondary amides due to the protein peptide bond, but can also indicate C=C benzene stretching [23,25,26]. The carboxylate ions resulted in two bands, one at 1430 and the other at 1377 cm −1 , due to the COOsymmetric stretching in the acidic group of polygalacturonic acids, the main component of pectin present in the primary plant cell wall [23][24][25]. The band at 1055 cm −1 was assigned to [26] with cellulose and hemicelluloses, which represent 97% of the structural fibres in S. californicus (see Table 1).…”

“…The presence of the carboxylic hydroxyl and aromatic amines groups on the biosorbent is defined by a broad band approximately 3363 cm −1 , corresponding to -OH and -NH stretching, respectively [23]. The peak at 2921 cm −1 indicates the symmetric or asymmetric -CH stretching vibration of aliphatic acids [24]. The band at 1639 cm −1 can be assigned to the C=C benzene stretching ring of lignin; the band at 1514 cm −1 is mainly attributed to N-H deformation in secondary amides due to the protein peptide bond, but can also indicate C=C benzene stretching [23,25,26].…”

“…An ideal biosorbent should rapidly sorb high concentrations of heavy metals from solutions [6] and reach the pseudo-equilibrium state in a relatively short time. Additionally, this information is necessary to design a sorption processing system because knowing the rate at which the metal uptake occurs will help us to evaluate the performance of biosorption [24]. Taking the previous points into consideration, the effect of contact time on the biosorption of Cr(III) and Pb(II) was studied over the time period of 5 min to 24 h. Figure 3 show the biosorption of both metals as a function of time.…”