Humidity Cell Tests: Effect of Air Flow and Cycle Duration in the Quality of Leachates

A factorial experimental design was used for humidity cell tests conducted for 10 cycles on tailings containing 71% pyrite to determine if the rate of air flow (3 and 6 Lmin-1) and cycle duration (14 and 21 days) affected leachate pH, electrical conductivity, and Eh. The tailings composite sample for the tests was taken from Tizapa, a massive sulfide mine located southwest of Mexico City, Central Mexico. The method ASTM D 5744-96 was taken as the basis for the design of the cells with two modifications: 1) air was circulated across the surface of the tailings and 2) water was dropped directly emulating rain on a tailings dam. Examining drainage quality data by cycles indicated the four treatments did not significantly affect the pH, but it was found that the air flow rate had a significant effect in the quality of leachates. The higher air flow delayed acidification, probably due to excessive water loss that inhibited oxidation reactions.