Chemostat-controlled selective leaches of model soil phases – the hydrous manganese and iron oxides. Part 1

Selective leaching of synthetic Mn and Fe oxide phases were examined using a Chemostat to control the system temperature, pH and/or Eh. Reaction conditions for the selective dissolution of model phases of Mn oxide (birnessite, ‘MnO 2 ’), amorphous Fe oxyhydroxide (ferrihydrite, Fe(OH) 3 . x H 2 O) and crystalline Fe oxide (hematite/goethite, Fe 2 O 3 /FeOOH) were optimized, concomitant with the behaviour of their dopant metals Cu, Pb and Zn. The pure oxide phases, as well as model compounds doped via coprecipitation with Cu, Pb and Zn, each to a concentration of 1000 ppm with respect to the mass of the oxide phase, were employed. Quantitative dissolutions of the target model phases were achieved within relatively short reaction times (within 15 min) for the purpose of high throughput field procedures. A limited study of three soil samples collected from a Pb–Zn–Ag mining province in northern Queensland, Australia was conducted employing the leach conditions found to provide optimal selectivity.