Schwertmannite to goethite

Schwertmannite is metastable with respect to goethite, except at very low pH (ca. 3) and in the presence of potassium when jarosite is stable. Schwertmannite, therefore, transforms spontaneously to goethite via solution at 25 °C 

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Fig. 14.14 Change in the concentration of Fe " and sulphate and in pH during the transformation of schwertmannite to goethite in water at 25 °C. Vertical bars indicate one standard deviation (Bigham et al., 1996 with permission).

Figure 9.8. TTT diagrams contoured in the extent of transformation of schwertmannite to goethite based on data from Davidson et al. (2008). (a) When a linear temperature axis is used the contours are curved lines, (b) When a reciprocal temperature axis is used the contours are straight lines.

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