Thermophilic micro-organisms are known to oxidise pyrite and other iron sulphide minerals resulting in the production of acidic ferric sulphate solutions. In this study, the leach liquors generated from such bacterial oxidation were aged through a forced hydrolysis process to yield various iron oxyhydroxides and sulphates. The forced hydrolysis was carried out under a pH range of 1.9 to 9.0. Upon completion of aging, the precipitates generated were characterised using powder X-Ray diffractrometry. The XRD analyses revealed a production of a variety of iron oxyhydroxides and basic iron sulphates. The nature of these precipitates was influenced by the pH conditions used during aging. Jarosite compounds were precipitated under acidic conditions, whilst aging under more basic conditions led to the precipitation of iron oxyhydroxides. These findings may find application in forecasting the phase boundary conditions for Fe(III) precipitation in biogeochemical processes and provide an insight into the tackling of problems associated with the treatment and management of acid mine drainage.