Determinación del punto de carga cero y punto isoeléctrico de dos residuos agrícolas y su aplicación en la remoción de colorantes.

Agro-industrial wastes have shown adsorptive properties and therefore can be considered as a potential alternative for the removal of dissolved contaminants present in industrial effluents. The chemical composition of the absorbate`s surface allows it to stablish its capacity to retain certain ionic contaminants. This study, determinates the point of zero charge (PZC) and the isoelectric point (IEP) of two agricultural wastes, rice husks and coconut husk, with the end of establishing the distribution of charges on the surface and subsequently to evaluate their capacity for the removal dissolved anionic or cationic colorants. In order to accomplish this, the study utilized the methods of pH drift and zeta potential varying the pH interval between 2.0 and 11 and maintaining the other variables at a constant. A PZC of 5.40 and an IEP of 9.10 were obtained for the rice husk, and a PZC of 4.61 and an IEP of 9.45 for the coconut husk, indicating a distribution of predominately positive charge on the surface. Further study of this characteristic confirmed its affinity for the removal of ionic colorants. The rice husk showed a removal of 93% of the cationic colorant basic red 46 (RB46) with at a pH higher than 5.0 and a retention of 73% of the anionic red 40 colorant(R40) at pH = 2.0 on rice husks. The determination of the PZC and IEP of the adsorbents allows for the establishment of better conditions for the adsorption of ionic colorants in solution. [ABSTRACT FROM AUTHOR]