The weathering characteristics of rock containing pyrite sometimes have serious influences on its environment since the oxidation of pyrite (FeS2) generates acid drainage, resulting in accelerated rock weathering and the discharge of heavy metals into the environment. Pyrite is a common and abundant sulfide mineral and it is oxidized upon exposure to oxygen at the earth’s surface. Such accelerated weathering of rock can degrade its mechanical properties and therefore menace the stability of rock structures such as slopes and tunnels. The evaluation of the physical properties of rocks and the chemical composition of the drainage were evaluated by leaching tests using a double soxhlet extractor for one month in the laboratory. Three groups of biotite gneiss were used for the soxhlet extraction experiment: Group A:<0.1 % of pyrite; Group B: about 5 % of disseminated pyrite; Group C: about 6 % of vein type pyrite. Groups A and B showed no significant quick absorption ratio after one month experiment but Group C showed about a 10 % increase in value. The uniaxial compressive strength of the three groups decreased about 20%, 10 % and 45 % for Groups A, B and C, respectively. The mechanical properties of the samples and the chemical composition of the drainage indicate that the oxidation of pyrite contained in the samples accelerated weathering, resulting in the deterioration of the mechanical properties of rocks and the possibility of discharging heavy metals and acid into the environment.


Natural weathering cannot be generally recognized due to its slow rate, whereas we sometimes find that rock containing pyrite FeS2) which has been exposed to the atmosphere is considerably weathered in a relatively short period.

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