Efficiency of rice husk ash to adsorb chromium(VI) using the Allium cepa toxicity test.

Adsorption is widely used in the treatment of effluents and contaminated water. However, the removal of the pollutant alone does not ensure that the effluent can be safely discharged in the environment. Controlling effluent toxicity may become an important tool to ensure that the quality of the treated effluent is compatible with that of the receiving water body. In this sense, this study evaluated the efficiency of rice husk ash (RHA) to adsorb chromium(VI) using the Allium cepa toxicity test. Adsorption was assessed based on the variables adsorption time, initial concentration, and pH. The data obtained were fitted the pseudo-second-order and the pseudo-first-order models, and the Langmuir and Freundlich isotherms. Kinetic analysis indicated removal rates between 43 and 100%. All data were best fitted by the pseudo-second-order model. Also, pH 1 and pH 2 data were best fitted by the Freundlich and Langmuir isotherms, respectively. In the Allium cepa test, pH 2 solutions were toxic. At pH 7, the Alium cepa test confirmed the efficiency of chromium(VI) adsorption by RHA, ensuring acceptable germination index values.