Effect of pH on the simultaneous sorption of Cr(III) and Cr(VI) by magnetic nanomodified lettuce roots in aqueous medium.

The incorrect disposal of industrial effluents containing potentially toxic metals is of great concern for the environment and humans. Among these pollutants, chromium is a metal present most commonly as Cr(III) and Cr(VI). Although rarely found in nature in its hexavalent form, it has been contaminating effluents due to anthropogenic actions such as incorrect disposal of industrial waste. This work conducts a study of the effect of pH on the remediation of aqueous matrices using in natura (LR) and nanomodified (LR-NP) lettuce as a biosorbent material in the simultaneous removal of Cr(III) and Cr(VI) species. The assessment of pH was performed based on the pHPZC to evaluate the best parameters of the individual and simultaneous sorption of Cr(III) and Cr(VI) species. With the solutions' pH variation, the oxidation and reduction process was observed between these species, which start to present different molar fractions. The optimal pH values ​​obtained within the range of 1 to 6, established by the pHPZC, were 6 for Cr(III), 1 for Cr(VI), and 2 for the simultaneous removal testes, with the percentage of Cr retention in the best pH conditions around 50 to 80% with Cr(VI) exhibiting the best adsorption results.