Chemical weathering

Chemical weathering is the break-down of rocks or minerals by chemical processes operating at the atomic and molecular levels. New substances frequently form during chemical weathering. Solution, silicate hydrolysis and oxidation are some examples of chemical weathering.

1. Solution

is the process through which minerals and rocks dissolve in water. Carbonic acid formation:

H2CO3 + CO2 = H2CO3

and subsequent solution (or dissolution) of calcium carbonate:

CaCO3 + H2CO3 = Ca2+ + 2HCO3

is an example of solution that affects the carbonate alkalinity, buffering capacity and pH of water.

2. Silicate hydrolysis

is the breakdown of silicate rocks to yield cations, alkalinity, silica and clay minerals:

primary silicate + H2O + CO2 = clay + cations + HCO3 + SiO2

3. Oxidation

is the loss of an electron from an element. Oxidation usually results in the formation of an oxide. Pyrite oxidation in acid sulphate soils gives rise to acid drainage in the coastal zone.

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