Aflatoxins are mycotoxins formed by strains of the fungi Aspergillus flavus and parasiticus. This research has focused on aflatoxin B1 (AfB₁), due to its extreme toxicity and its carcinogenic activity in animals, in addition to its potential effects in humans. Aspergillus fungi may infect grains in the field or in storage developing aflatoxin especially in corn, peanuts, cottonseed, grain sorghum, millet, Brazil and pistachio nuts, almonds, and other tree nuts and dried fruits (Coulombe, 1991). Clays are materials used as adsorbents or catalysts (Vaccari, 1999). Clay minerals can catalyze a variety of organic reactions occurring on their surface and interstitial space. Clay catalysts are used in organic reactions that take place under acid conditions. The acidity is due to Al³⁺ and Fe³⁺ at the crystal edges, and can be further improved by exchange of the interlayer cations Na⁺+ and Ca²⁺ by Al³⁺ ions by treating the clay with AlCl₃ solution (Gopalpur, 2002). Previous investigations of natural and commercial clays have different AfB₁ sorption capacity ranging from 0.06 - 0.67 mol/kg, yet there is little known about the factors that influence the adsorption and binding of AfB₁ to smectite (Kannewischer, et al., 2005). The objective in this research was to see the aluminum influence on the sorption capacity to explain the possible mechanisms of reactions between AfB1 and the smectite structure. Samples selected for this research from a larger population are montmorillonite 6WY, Ca-bentonite 8TX and bentonite 16MX previously screened for pH, cation exchange capacity (CEC), exchangeable calcium, and clay mineralogy. After the screening process the samples were saturated with aluminum chloride (AlCl₃) at three different concentrations 0.001N, 0.05N, and 0.5N and then characterized as to their AfB₁ sorption capacity using isothermal adsorption. Earlier results showed that the samples had pH of 7.1 for 8TX, 7.6 for 16MX and 9.6 for 6WY. The CEC was 68 cmol/kg and 84 cmol/kg for 8TX and for 6WY. The amount of Ca ions is high for the samples 8TX i.e. 54, cmol/kg and 20 cmol/kg 16MX and 15 cmol/kg for 6WY. All the samples produced smectite XRD peaks. Adsorption capacities of samples saturated with 0.001 N AlCl₃ in all cases had isotherms that did not fit the Langmuir equation well. For the sample 16MX when the isotherm was done with samples in natural condition the adsorption capacity was 0.06 mol/kg. After the AlCl₃ saturation at low Al concentrations, the isotherms did not fit the Langmuir equation very well, however showed an increased in the sorption capacity. In the case of the 6WY sample sorption capacity was 0.29 mol/kg without treatment and with AlCl₃ treatment the median sorption capacity was 0.31 mol/kg. A notable case is sample 8TX, in natural condition the sample sorption capacity was to 0.67 mol/kg and when the sample was saturated with AlCl₃ the sample showed a slight decrease to 0.62 mol/kg. From these observations it is possible to say that the aluminum at different concentrations in sample 6WY did not have any effect on amount AfB₁ sorption. For bentonite 16MX the sorption increased following Al treatment, however the data did not fit the Langmuir equation well. For sample 8TX the data show a decrease in the sorption of AfB₁ following Al treatment. We speculate that replacing Ca by Al may have reduced AfB₁ sorption. References: (1) Coulombe Jr. Roger A. 1991. Aflatoxins Chapter 5 in Mycotoxins and phytoalexins. (2) Raghubir P. Sharma. Dattajrao K. Salunke. CRC Press. USA. Gopalpur Nagendrappa. 2002 Organic Synthesis using Clay Catalysts.Clays for Green Chemistry. Resonance. 1:64-77. (3) Kannewischer Ines, Maria Guadalupe Tenorio Arvide, G. Norman White and Joe B. Dixon. Smectite Clays as Adsorbents of Aflatoxin B1: Initial Steps. 13th ICC Proceeding, Special Issue of Clay Science (Journal of the Clay Science Society of Japan). In press. (4) Vaccari A. 1999. Clays and catalysis: a promising future. Applied Clay Science 14: 161–198.