At low pH values, e.g. under the influence of humic
acids in humid tropical climates, aluminum is more
soluble than iron and selective leaching of A1
3+ will
produce iron-rich laterites. Aluminum hydroxide can
be dissolved at low (acidic) or high (basic) pH values
and may reprecipitate as aluminum oxide, which has a
lower iron content and is thus a higher grade aluminium source (bauxite).
a
b
c
Fig. 3.12 (a, b) Weathered granite (North of Kampala, Uganda) showing different stages of weathering. (c) Concentric –
spheroidal weathering in a basic intrusive rock. Weathering is much faster in the absence of quartz
108
K. Bjørlykke
acids in humid tropical climates, aluminum is more
soluble than iron and selective leaching of A1
3+ will
produce iron-rich laterites. Aluminum hydroxide can
be dissolved at low (acidic) or high (basic) pH values
and may reprecipitate as aluminum oxide, which has a
lower iron content and is thus a higher grade aluminium source (bauxite).
a
b
c
Fig. 3.12 (a, b) Weathered granite (North of Kampala, Uganda) showing different stages of weathering. (c) Concentric –
spheroidal weathering in a basic intrusive rock. Weathering is much faster in the absence of quartz
108
K. Bjørlykke