A major problem encountered in dump leaching operations is the plugging of both the dump and the piping by precipitated iron compounds. Bureau of Mines research to obtain basic data on agitation leaching and dump leaching methods has shown that the addition of organic chelating reagents can significantly enhance the lixiviant permeability through the ore and the concentration of the metal values in the liquor. For example, the addition of 5 g/l citric acid (ca) to a conventional sulfuric acid lixiviant almost doubled the fluid flow rate through 5-cm-diameter laboratory columns containing copper ore. After 185 h of percolation leaching, the metal concentrations with (and without, in parentheses) ca were 1.7 (1.5) G/l cu, 200 (70) ppm mn, 160 (40) ppm al, and 6 (3) ppm carbon monoxide. The enhancement of metal concentrations with chelating reagents such as ca was confirmed by determining the solubility of several metal ions as functions of ph and chelating reagent concentration. When ferric ions became insoluble at ph values above 3, the concentrations of other ions also decreased. The addition of chelating reagents kept iron, as well as the other dissolved metals, in solution even at ph values as high as 5. Citric acid was a more effective chelating reagent than gluconic acid, oxalic acid, or sodium lignin sulfonate.