The effect of exchangeable cations in clinoptilolite and montmorillonite on the adsorption of aflatoxin B1

Abstract

The adsorption of aflatoxin B1 (AFB1) by cation-exchanged clinoptilolite zeolitic tuff and montmorillonite was investigated at 37ºC and pH 3.8 from an aqueous electrolyte having a composition similar to that of gastric juices of animals. Bothminerals were exchanged from the natural form to the sodium form and then to the Cu2+, Zn2+ and Co2+-rich forms. The cation exchange was different for the different cations, but in all cases the exchanges were larger on montmorillonite than on clinoptilolite. The degree of exchange on montmorillonite was 76 % for copper (from a total of CEC 0.95 meq/g, Cu2+ -0.73 meq/g) and 85 % for zinc and cobalt. Under the same conditions (concentration, temperature, pH, contact time), the degree of exchange on zeolitic tuff was 12 % for Cu2+ (from a total CEC of 1.46 meq/g, Cu2+ -0.17 meq/g), 8 % for Zn2+ and 10 % for Co2+. Both groups of mineral adsorbents showed high AFB1 chemisorption indexes (cα). For the montmorillonite forms, cα ranged from 0.75 for the Cu-exchanged montmorillonite to 0.89 for the natural Ca-form, 0.90 for the Zn-exchanged form and 0.93 for the Co-exchanged montmorillonite. The adsorption of AFB1 on the different exchanged forms of clinoptilolite gave similar values of cα for the Cu and Ca forms (0.90) and values of 0.94 and 0.95 for the Zn- and Co-exchanged form. The impact of the mineral adsorbents on the reduction of essential nutrients present in animal feed (Cu, Zn, Mn and Co) showed that the Ca-rich montmorillonite had a higher capability for the reduction of the microelements than the Ca-rich clinoptilolite.

Keywords

• clinoptilolite
• montmorillonite
• cation exchange
• adsorption
• aflatoxins