Cr (III) Removal Capacity in Aqueous Solution in Relation to the Functional Groups Present in the Orange Peel (Citrus sinensis)

Abstract

Bioremediation is a pollutant removal method that has had a great boom due to the diversity of agroindustrial waste that can be used for this purpose, and that has shown having great efficiency and profitability in the adsorption of heavy metals, such as Pb, Cu, and Co. Based on the above, the present work carried out kinetic and equilibrium studies of bioadsorption of Cr (III) using orange peel (OP) as adsorbent, previously treated with methanol, water, and a water–methanol mixture at different pH (0.91, 1.78 and 2.72), and at 30 °C, finding that the adsorption capacity at equilibrium increases with increasing pH, having a maximum of 55 mg g−1 at pH 2.72—under these conditions, lower adsorption energy was used to remove Cr (III). In addition, it was determined that there are no external mass transfer limitations. An isoelectric point analysis indicated that the adsorption is not carried out by electrostatic forces and a FTIR study of the functional groups of OP showed a decrease in the main functional groups (pectin, cellulose, and lignin, among others), which is directly related to the adsorption capacity of the bioadsorbent.

3,5-Dinitrosalicylic Acid Adsorption Using Granulated and Powdered Activated Carbons

“…Also, it can be observed that this energy increases with the decrease in temperature for both adsorbents, which allows us to mention that less energy is required to remove this nitroaromatic compound from the solution when the temperature increases [32,33]. Langmuir's model indicates that the removal of this pollutant is a favorable process (0 < RL <1), this is directly related to the shape of the isotherms [28,34,35] presented in Figure 1.…”

“…Also, it can be observed that this energy increases with the decrease in temperature for both adsorbents, which allows us to mention that less energy is required to remove this nitroaromatic compound from the solution when the temperature increases [32,33]. Langmuir's model indicates that the removal of this pollutant is a favorable process (0 < R L <1), this is directly related to the shape of the isotherms [28,34,35] presented in Figure 1. The study of the removal of sulfosalicylic acid and DNS, using GAC treated with commercial oxidative methods at different temperatures, found that the best fit model is that of Langmuir [21], presenting a great adsorption capacity.…”

“…Taking the coefficient of determination (R 2 ) and the normalized standard deviation (∆q%) as criteria to choose the best fit, it was found that regardless of the temperature for both adsorbents, the best fit is that of SIPS, which indicates that the adsorption is performed on the surface in more than one layer; Furthermore, when determining the parameters of this model, the value of n s is greater than 1, which implies that adsorption is a physical process [28][29][30]. This result is also obtained with the Freundlich model, since n > 1 implies that the adsorption of DNS in GAC and PAC takes place on the surface of the adsorbents [24,28,31,32]. Additionally, the adsorption energy (E) obtained with the DR model is less than 8 kJ/mol, confirming that physical adsorption is the mechanism with which DNS is adsorbed in AC.…”

“…This behavior is due to the active adsorption sites that have been exhausted or blocked by the variety on the surface of both adsorbents. In addition, the increase in the removal percentage can be assumed by the reduction of the adsorbate-adsorbent ratio with the increase of the adsorbent concentration [12,28,39]. DNS removal using GAC and PAC also shows an increase with temperature, obtaining a removal percentage of 64, 74.6, and 86.6% at 25, 35, and 45 • C, respectively, for GAC.…”

“…The analysis of the external and intraparticle mass transfer process can have a significant effect on the adsorption of DNS, since the information obtained in Tables 5 and 6 indicate that the limitations due to transport of matter could be present in the removal of DNS, which makes it necessary to carry out an analysis of this phenomenon [36]. Figure 4a is constructed using the external diffusion model as a basis, where it can be seen that for GAC there is a straight line at the experimental points for up to 6 h of contact in the adsorption process, which indicates the possibility that there is control by external mass transfer in the process at any temperature [28]; this type of behavior is similar to that reported in the literature for the adsorption of organic matter components from ship waste [13]. Figure 4b shows the representation of the experimental data obtained for PAC in the adsorption of DNS, where a straight line was observed at 1 h of contact with the adsorbent.…”