Extracting Vanadium, Molybdenum, and Tungsten from Acidic Solutions via Adsorption on Modified Montmorillonite

Resumo

The possibility of extracting vanadium, molybdenum, and tungsten compounds from acidic media via adsorption is demonstrated. Highly dispersed layered aluminosilicates, modified with a cationic surfactant (didecyldimethylammonium chloride), are used as sorbents. Interactions between the cationic surfactant and the sorbent’s surface are confirmed by means of spectroscopy. It is established that the sorbent is modified through immobilization of the didecyldimethylammonium chloride molecules in the interlayer space of the sorbent. It is observed that the sorbent’s surface acquires a positive charge as a result of modification, allowing adsorption of polyoxoanions of vanadium, tungsten, and molybdenum from solutions. Spectroscopic and thermodynamic investigations show that the interaction between the vanadium and the active centers of the sorbent was due to the formation of ionic associates and corresponded to physical adsorption. Because of the similarities between the chemical properties of vanadate, molybdate, and tungstate ions, their adsorption on a surface of modified montmorillonite is governed by a similar mechanism. Experimentally determined limiting adsorption values of vanadium, molybdenum, and tungsten are 1.65, 1.96, and 1.21 mmol/g, respectively, which corresponds to a 94–95% degree of extraction. It is established that the optimum conditions of isolation are found at рН 3.4 for vanadium, pH 4.0 for molybdenum, and pH 4.5 for tungsten, due to the different forms of their polyoxoanions in solutions.