Tuesday, 8 November 2005
5

Amendment Effects on pH and Salt Content of Bauxite Residue.

James Ippolito, Edward Redente, and Kenneth Barbarick. Colorado State University, CO St. Univ.-Soil & Crop Sci., C127 Plant Science Bldg., Fort Collins, CO 80523-1170

Bauxite residue, a waste product from the refining of bauxite to alumina, contains excessive Na and an elevated pH. We investigated the use of four chemical amendments to reduce bauxite residue pH and Na content, and to improve soil characteristics for reclamation purposes. A control (no addition) or gypsum, acidic gypsum, sulfuric acid, and elemental sulfur were thoroughly mixed with bauxite residue at rates to reduce the exchangeable sodium percentage (ESP) to 5%, with or without an equivalent of 90 Mg ha-1 wood chips for aeration. Materials were placed in separate 32-L containers, leached with water, and 8 separate pore volumes collected. All treatments were replicated three times. Pore volumes 1 through 5, and 8 were analyzed for pH, Na, Ca, Mg, and sodium adsorption ratio (SAR). The acidic gypsum and acidic gypsum + wood chips treatments significantly lowered the pH, leached the greatest amount of Na, Ca, and Mg for all pore volumes, and lowered the SAR as compared to other treatments. At the end of the experiment we analyzed the 0-15-cm and 15-30-cm depths for Na, Ca, Mg, SAR, ESP, pH, and electrical conductivity and compared values to the control. For all treatments the Na content and ESP were reduced by an order of magnitude, Ca and Mg content increased, pH was reduced, and SAR was reduced by several orders of magnitude. Overall, the acidic gypsum and the acidic gypsum + wood waste treatments showed the most promise for reducing bauxite residue pH and Na content.

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