OXIDATION OF DICTYONEMA SHALE IN MAARDU MINING WASTE DUMPS
E. PUURA
Department of Chemical
Engineering and Technology
Royal Institute of Technology
Stockholm, S-10044 Sweden
&
Institute of Geology,
Tartu University
46 Vanemuise, Tartu
51014 Estonia
A. PIHLAK
Institute of Chemical
and Biological Physics
Estonian Academy of Sciences
23 Akadeemia St., Tallinn
12618 Estonia
| Geochemical processes occurring in Maardu mining waste rock dumps, Estonia, are
reviewed on the basis of Estonian practice and recent modelling studies. Oxidation of Dictyonema shale disposed close
to the steep slopes leads to air pollution and destruction of newly formed vegetation during first decades after
disposal. New mineral phases are formed at high temperatures and potential pyritic acidity is eliminated. In central
parts of the dump, low-temperature (below 40 °C) oxidation of pyrite leads to a sequence of geoche-mical reactions in
interaction with dumped material, including conversion of illite to smectite, precipitation of K-jarosite, gypsum and
ferric oxyhydroxide, as well as formation of leachate with high sulphate content and anomalously high Mg/Ca ratio. Hydrochemical modelling showed that low-temperature oxidative leaching of the shale would cause regional surface and ground water contamination with sulphate for centuries. A possibility exists, that limestone buffering capacity becomes locally depleted inside the dump, leading to the breakthrough of acidic and metal-rich waters. Maardu study assists also in development of environmentally friendly technology for shale handling in future. |