Removal of Hexavalent and Total Chromium from Aqueous Solution by Avocado Shell Eliseo Cristiani-Urbina1,*, Alma Rosa Netzahuatl-Muñoz1,2, María del Carmen Cristiani-Urbina3 1
Escuela Nacional de Ciencias Biológicas, IPN. Prolongación de Carpio y Plan de Ayala s/n. Colonia Santo Tomás. México, D.F., 11340, México. firstname.lastname@example.org 2 Universidad Politécnica de Tlaxcala. Av. Universidad Politécnica No. 1. Colonia San Pedro Xalcaltzinco. Tepeyanco, Tlaxcala, 90180, México. 3 Universidad Autónoma de Chiapas, Campus I. Boulevard Belisario Domínguez km 1081 s/n. Tuxtla Gutiérrez, Chiapas, 29000, México The main aim of this work was to evaluate the potential of Hass avocado (Persea americana Mill var. ‘Hass’) shell to remove hexavalent chromium [Cr(VI)] and total chromium from aqueous solutions. Results showed that avocado shell removed Cr(VI) by two different mechanisms: chromium biosorption and bioreduction of Cr(VI) to Cr(III). The capacity for removing Cr(VI) and total chromium gradually increased as the contact time proceeded, reaching values of 101.81 and 61.67 mg g-1 respectively, after 120 h. The opposite behavior was observed concerning the volumetric rates of Cr(VI) and total chromium removal. The pseudo-second order model adequately described the kinetic process of chromium biosorption by avocado shell, which suggests that this process chiefly occurs as a result of chemisorption.
Chromium compounds are environmental pollutants occurring in soil, water and industrial effluents because they are widely used in many industrial activities. Although chromium has several oxidation states, chromium compounds mainly occur in the environment as trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium. Cr(VI) is highly toxic, mutagenic, carcinogenic and teratogenic. Cr(III) is much less toxic and mutagenic than Cr(VI), but long-term exposure to high Cr(III) concentrations may cause allergic skin reactions, cancer and DNA damage. The World Health Organization has established drinking water guidelines for total chromium of 0.05 mg l-1. Therefore, the removal or reduction of Cr(VI) to Cr(III) is nowadays recognized as a key process for the detoxification of Cr(VI)-contaminated water and wastewater. In comparison with the conventional methods for the removal of heavy metals from wastewater, the biosorption process offers potential advantages such as low operating cost, minimization of the volume of chemical and/or biological sludge to be disposed of, high efficiency in detoxifying very diluted effluents, and so on (Hajar, 2009). Biosorption utilizes the properties of certain kinds of inactive or dead biomass to bind
and accumulate heavy metals by different mechanisms. A number of biomaterials have been tested in order to remove Cr(VI) from aqueous solutions. The main aim of this work was to evaluate the potential of Hass avocado shell, a biowaste from the avocado processing industry, to remove hexavalent and total chromium from aqueous solution. Furthermore, the kinetics of chromium biosorption by Hass avocado shell is described.
2. Material and Methods
2.1 Preparation of the biomaterial Shells of Hass avocado (Persea americana Mill var. ‘Hass’) were used as biosorbent for the biosorption of chromium ions from aqueous solution. Avocado shells were washed thoroughly with distilled deionized water and then dried in an oven at 60 ºC for 24 hours. Subsequently, they were milled and the resulting particles were screened using ASTM standard sieves. The fraction with particle size 0.3-0.5 mm was used in the Cr(VI) and total chromium removal experiments carried out in this study. An average rejection rate of 35% was obtained during the sieving process. 2.2 Batch experiments Batch experiments were conducted in 500 ml Erlenmeyer flasks with a working volume of 100 ml. 0.1 g of the biomaterial was brought into contact with Cr(VI) aqueous solution with a concentration of 102 mg Cr(VI) l-1 at pH 2.0 ± 0.1. The flasks...
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