The flotation waste is a finely milled material, usually less than 2 mm. As a result,
the physical characteristics of the material are appropriate for plant growth: they will
usually have good water retention but are sensitive to erosion by water and wind.
Both types of material are equally deficient in essential nutrients N and P. They can
also be deficient in other nutrients (K, Ca, etc.). The critical issue is the content of
metals. In general terms, it is usually about 1000 ppm (0.1%) of any metal in the
waste to be toxic to plants.
The availability of metal depends on atmospheric factors, pH, and the presence of
different cations and anions. Almost all old and new mining waste have levels of
toxic metal content. If there is pyrite, it will be subjected to atmospheric factors and
will be oxidized to ferric sulfate and H 2 SO 4 . This oxidation can be a rapid process
(at neutral pH initially decreases in a few months to 4.0 or below) or may be a slow
process. If the material also contains carbonates, the acid will be neutralized, but a
large amount of soluble salts will be produced.
In an arid climate, evaporation will concentrate these salts on the surface in the
form of a salt crust. As a result, many metalliferous dumps are impossible for plant
growth and have remained bare, exposed to erosion for many years. However, some
old mining waste dumps can find metal tolerant plants (metalloids) that can grow on
metallic soils. These adaptations may be specific (for a specific metal) or less specific
(broad tolerance to metals).
However, possessing the quality of being tolerant to a plant is not sufficient to
ensure its growth in the mining tailings pond; the increase will depend on the
existence of sufficient nutrients (N and P) and humidity (Sun et al. 2018).
4.11.1 Chemical and Physical Treatments
Physical methods of coating materials such as crushed stone or granulated blast
furnace slag are effective but expensive and are impossible to apply for soft, dry
residues. Chemical methods can be an alternative by using materials that can achieve
temporary stabilization, but they do not provide a permanent solution. They are
temporary solutions that do not provide for biological or landscape rehabilitation of
the land.
Direct Sowing Some inferior tailings dumps (0.1%) with low toxicity, where there
are no acidic or saline problems, use a vegetal carpet installation by direct sowing
and addition of fertilizers. Also mix with lime if the pH is below 5.5. Sowing species
will be grass and legume. On sites with higher metal concentrations, it will be
necessary to use varieties of metal-tolerant plants. As a rule, metal-tolerant species
roots deep into the tailings, escapes the drought, and protects the surface. Since the
tolerance is rather specific, tolerant plants should be found where the tolerance
matches the site toxicity. Tolerable varieties for Pb and Zn produced the fescue
(F. rubra) and the grass of the field (Agrostis tenuis). Legumes are needed to provide
nitrogen by fixing them to the ground. However, they are more sensitive to the
toxicity of HMs than grasses.
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M. Butu et al.
the physical characteristics of the material are appropriate for plant growth: they will
usually have good water retention but are sensitive to erosion by water and wind.
Both types of material are equally deficient in essential nutrients N and P. They can
also be deficient in other nutrients (K, Ca, etc.). The critical issue is the content of
metals. In general terms, it is usually about 1000 ppm (0.1%) of any metal in the
waste to be toxic to plants.
The availability of metal depends on atmospheric factors, pH, and the presence of
different cations and anions. Almost all old and new mining waste have levels of
toxic metal content. If there is pyrite, it will be subjected to atmospheric factors and
will be oxidized to ferric sulfate and H 2 SO 4 . This oxidation can be a rapid process
(at neutral pH initially decreases in a few months to 4.0 or below) or may be a slow
process. If the material also contains carbonates, the acid will be neutralized, but a
large amount of soluble salts will be produced.
In an arid climate, evaporation will concentrate these salts on the surface in the
form of a salt crust. As a result, many metalliferous dumps are impossible for plant
growth and have remained bare, exposed to erosion for many years. However, some
old mining waste dumps can find metal tolerant plants (metalloids) that can grow on
metallic soils. These adaptations may be specific (for a specific metal) or less specific
(broad tolerance to metals).
However, possessing the quality of being tolerant to a plant is not sufficient to
ensure its growth in the mining tailings pond; the increase will depend on the
existence of sufficient nutrients (N and P) and humidity (Sun et al. 2018).
4.11.1 Chemical and Physical Treatments
Physical methods of coating materials such as crushed stone or granulated blast
furnace slag are effective but expensive and are impossible to apply for soft, dry
residues. Chemical methods can be an alternative by using materials that can achieve
temporary stabilization, but they do not provide a permanent solution. They are
temporary solutions that do not provide for biological or landscape rehabilitation of
the land.
Direct Sowing Some inferior tailings dumps (0.1%) with low toxicity, where there
are no acidic or saline problems, use a vegetal carpet installation by direct sowing
and addition of fertilizers. Also mix with lime if the pH is below 5.5. Sowing species
will be grass and legume. On sites with higher metal concentrations, it will be
necessary to use varieties of metal-tolerant plants. As a rule, metal-tolerant species
roots deep into the tailings, escapes the drought, and protects the surface. Since the
tolerance is rather specific, tolerant plants should be found where the tolerance
matches the site toxicity. Tolerable varieties for Pb and Zn produced the fescue
(F. rubra) and the grass of the field (Agrostis tenuis). Legumes are needed to provide
nitrogen by fixing them to the ground. However, they are more sensitive to the
toxicity of HMs than grasses.
118
M. Butu et al.