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III. Application of Various Amendments to Ameliorate Acidic Mine Spoil
P. SUTTON AND W. A. DICK
materials and leaching of the acid (Kohnke, 1950). This may require many
years for some areas (Knabe, 1964). In areas with lower quantities of pyritic
materials, the leaching treatment has proven successful (Riley, 1973).
Proper amendment applications, however, achieve rapid vegetative cover.
Prior to application of amendments to spoil, extensive grading often is
conducted to shape the area to be reclaimed so that it will be more suitable
for a specified use and to allow application of the amendments to be accomplished via conventional types of equipment. Grading and shaping a
spoil bank should reduce water runoff and erosion (Struthers and Vimmerstedt, 1965) while increasing infiltration and the removal of salts and
acids by leaching (Riley, 1973). Grading, however, will also result in compaction and may expose new unweathered pyrite-containing materials
which will temporarily increase acid mine drainage. If establishment of
vegetation to control erosion and improve aesthetics are the primary objectives of a particular reclamation project, consideration should be given to
plans that will require limited or no grading. This would eliminate exposure
of unweathered pyrite while simultaneously reducing one of the costly items
(i.e., grading) in reclamation of abandoned mine lands.
Covering spoil with topsoil can be used to establish vegetation. Sutton
(1979) covered a toxic spoil (PH 2.4) with 5, 10,15,20, and 25 cm of pH 6.5
soil material. Vegetative cover was established and maintained over 11
growing seasons when the soil depth was 15 cm or greater. Plant roots,
however, had only begun to penetrate the spoil below the soil cover to a
depth of approximately 0.65 cm, indicating changes in the untreated spoil
are rather slow. Limestone mixed into the surface of the spoil before a topsoiling operation should speed up root penetration (Barnhisel et al., 197,5;
Vogel, 1975). This would be an important consideration if shallow layers of
soil cover are applied or if steep slopes were to be covered. Root penetration
between the soil cover and spoil would reduce the possibility of the cover being removed by sliding.
When topsoil is used to cover toxic spoil the nutrient status can be determined by a soil test. Based on this information the approximate quantity of
nutrients required for good plant growth can be calculated. However, plant
root growth is limited to the soil cover material (Sutton, 1979), which is a
much smaller volume than that generally exploited by plants. As a result,
the recommended rates of application of plant nutrients based on traditional soil tests may underestimate the needs of plants growing on the
reclaimed spoil. If good topsoil or A-horizon material is available, the
growth medium for plants will also be improved in organic matter content
RECLAMATION OF ACIDIC MINED LANDS
and structure. In many areas, however, most of the cover material available
will be subsoil or a mixture of B- and C-horizon materials.
Studies where power plant fly ash has been used to establish vegetation
on toxic spoils have been summerized by Capp (1978). Six stripmine sites
with pH ranging from 2.6 to 4.7 were treated with fly ash at rates of 830 to
4430 tonslha. After 1-10 years the pH at these sites ranged from 5.0 to 7.5
and the condition of vegetation was rated to good except in one case in
which it was rated fair. The treatments had a surface effect only and the
layers below the fly ash-treated material remained extremely acid.
The principal effect of adding large quantities of fly ash is the neutralization of acid, although not all fly ash materials are alkaline in reaction
(Plank and Martens, 1973). With the exception of N, fly ash also contains
many of the elements for plant growth (Table 11). Boron, Mo, Zn, P, and K
in fly ash are available to plants and can be used to correct deficiencies of
these elements (Plank and Martens, 1973; Martens and Beahm, 1976). Toxic amounts of BoyMo, Se, and soluble salts, however, may pose a serious
constraint to the application of fly ash on spoil for the purpose of
establishing vegetation (Adriano et al., 1980). Severe toxicity symptoms in
plants were observed when large amounts of fly ash (224 to 448 tonslha)
were applied to stripmine areas (Bennett, 1971). The toxicity was attributed
primarily to excess B in the fly ash. Before a fly ash is selected for use in
reclamation of a toxic spoil the plant nutrients, soluble salts, and acidity
should be determined and evaluated in relation to plant growth and the
chemistry of the area to which it will be applied.
Large quantities of sewage sludge have also been used to establish vegetation on toxic spoils (Hill et al., 1979; McCormick and Borden, 1973; Montague and Hill, 1976; Peterson and Gschwind, 1973; Lejcher, 1972; Sutton,
1979; Haghiri and Sutton, 1982). The plant nutrient content of sewage
sludges is highly variable but is generally sufficient in N and P and limiting
in K (Halderson and Zenz, 1978; Jewell, 1982). Application rates required
to ameliorate toxic spoils (50-500 tonslha) will also supply more plant
nutrients than are required for plant growth (Table 11). A result of the combination of high application rates and high N content is the formation of
nitrates at levels which may exceed accepted pollution standards. The
possibility of combining lower rates of sludge treatment with lime and other
P. SUTTON AND W. A. DICK
organic residues to create a medium suitable for revegetation, thus reducing
the nitrate leaching hazard, has been suggested by Urie et al. (1982).
A sludge by-product of the papermill industry has been tested as an
amendment for establishing vegetation on toxic spoils and has provided excellent results (Hoitink and Watson, 1982; Hoitink et al., 1982; Haghiri and
Sutton, 1982). Papermill sludges contain large amounts of basic cations and
plant nutrients (Tables I1 and 111). However, they also contain high levels of
readily decomposable organic matter which can be beneficial in altering the
physical and chemical properties of the toxic spoil but have an inhibitory effect on the amount of plant-available N. Dolar et al. (1972) reported that
sludges with a C/N ratio greater than 20:l will likely result in N immobilization.
A mixture of primary and secondary sludges applied at rates of 56-336
tons/ha (dry weight basis) to a spoil containing 0.82% sulfur and a pH of
2.6 was found to inhibit seedling emergence initially (Hoitink et al., 1982).
However, the erosion control provided by the papermill sludge was excellent even without the use of a mulch cover. Although seedling emergence
was delayed, eventually a complete cover of vegatation was established.
With composted papermill sludge, delay in seedling emergence was not
observed (Haghiri and Sutton, 1982).
The bacterium Thiobacillus ferrooxidans accelerates acidification of
pyritic material and significantly increases acid production (Kleinman,
1980). The use of the anionic detergent sodium lauryl sulfate (SLS) as a
bactericide can reduce this acid production by 60-90% (Kleinmann and
Erickson, 1982). The rate of SLS required to inhibit acid formation in a
pyrite-containing spoil will vary among spoils depending on the amount of
SLS that is sorbed. Sufficient SLS must be added to the spoil to overcome
the sorption capacity of the spoil for SLS so that it will interact with the T.
ferrooxidans in the soil solution or surrounding the pyrite-containing particles. Sodium lauryl sulfate is water soluable and will be rapidly lost from
the spoil under field conditions. To overcome this problem, formulations of
SLS in a slow-release matrix have been developed. By using these materials,
acid production in toxic spoils can be controlled for a time period long
enough for establishment of a vegetative cover.
RECLAMATION OF ACIDIC MINED LANDS
Major Plant Nutrient Content of Fly Ash, Sewage Sludge,
Papermill Sludge, and Soil
Fly ash of
'From Capp (1978).
bFrom Halderson and Zenz (1978).
%om Dolar et al. (1972)and Haghiri and Sutton (1982).
Metal Content of Fly Ash, Sewage Sludge, Primary
Papermill Sludge, and Soil'
Fly ash of
'In mg/kg except where noted.
bFrom Adriano et al. (1980).
Trom Halderson and Zenz (1978).
dFrom Haghiri and Sutton (1982).
P. SUTTON AND W. A. DICK
COMBINATION OF AMENDMENTS
When materials such as sewage sludge, power plant fly ash, and papermill
sludge have been used to ameliorate acidic spoils, relatively high rates of
these materials have been applied. Frequently the high rates are required to
raise the pH of the spoil to a level suitable for plant growth. It may be more
economical to apply a combination of limestone and other amendments,
thereby reducing the quantity of the material to be transported. However, if
sufficient supplemental amendments such as limestone are not added to
neutralize the acid produced by additional oxidation of the pyrite, the spoil
will again become toxic to plants (Sutton, 1970, 1983). Further research to
evaluate the use of combinations of amendments for vegetation establishment is needed.
G . METALCONTENT
A major concern when applying high rates of amendments, especially industrial sewage sludges, is the addition of heavy metals that may accumulate in the food chain or in surface and subsurface waters. The metal
content of fly ash, sewage sludge, papermill sludge, and soils (Table 111)
depends primarily on the source from which the material was derived. The
amounts of potentially toxic metals added to a spoil can be controlled by
limiting the rates applied at any one time. If the land use after reclamation is
to be for agricultural production or animal grazing, agricultural sludge
utilization practices and restrictions should be followed (Table IV). If toxic
spoil is to be vegetated primarily for erosion control, a single application of
Recommended Cumulative Limits for Metals of Major
Concern Applied to Agricultural Croplane
Soil cation exchange capacity (cmol/kg)b
< 5 kg/ha
aFrom USEPA (1983).
%oil must be maintained at pH 6.5 or more.
RECLAMATION OF ACIDIC MINED LANDS
sludge at a rate sufficient for rapid establishment of a vegetative cover is
desirable because of economic reasons.
Although little information is available, some concern has been expressed
about the fate of certain organic compounds such as trihalomethanes and
dioxin that may be present in sludges. Additional research is clearly needed
to assess the organic compounds that are contained in sludges and their
behavior in the environment.
SEEDING AND MANAGEMENT OF
Application of limestone and plant nutrients, in addition to those contained in the primary amendment, are often required before seeding can
take place. This is especially relevant when fly ash and sodium lauryl sulfate
are used as primary amendment. The rate of limestone required to adjust
the spoil pH to a proper level for vegetative establishment may be difficult
to determine because (1) methods to determine the neutralization potential
of the amendment cannot be rapidly conducted or are inaccurate and (2)
both the active and total potential acidity of the spoil material must be
known (Barnhisel, 1977). A laboratory procedure which estimates the lime
requirement based on the total potential acidity of spoil material has been
developed by Smith et al. (1974). The acid estimates are obtained from total
pyritic sulfur contents without differentiation of pyritic types, which may
vary in reactivity. If the amendment material produces a cover that essentially seals the spoil from oxygen or inhibits acid production via other
means, it is not necessary that sufficient neutralizing power be added to the
spoil to counteract all the potential acidity in the vegetative rooting zone.
The type of limestone added to spoil is of importance as spoils with a high
concentration of sulfate ions, limed with dolomitic limestone, may limit
plant establishment and growth due to the high soluble salt levels that result
from the solubility of MgSO, (Evangelou and Thom, 1984).
The amount of fertlizer require is usually determined on the basis of standard soil tests and the potential of the amendment to supply essential plant
nutrients. Availability of N in an organic amendment, for example, may require that the amendment be mineralized. The rate of mineralization is thus
as important consideration in determining the total amount of plantavailable nutrients to be applied at time of seeding.
P. SUTTON AND W. A. DICK
Mulches serve as a soil protectant and enhance plant establishment (Kay,
1978). The soil is protected by reducing raindrop impact, by reducing water
flow and soil movement by trapping sediment on the sites, and by increasing
water infiltration. Mulches enhance plant establishment by holding seed
and fertilizer in place, retaining moisture, preventing crusting, and modifying temperatures of the soil.
The type and rate of amendment, the depth of mixing, and the time of
seeding all influence the need for a mulch. Hoitink et al. (1982), for example, found that when 221 tons/ha of papermill sludge were used as a soil
amendment, a mulch was not necessary for controlling erosion before
vegetation became established. Frequently, however, sites are seeded immediately after site preparation has been completed, which may not
necessarily coincide with the recommended seeding dates for the area. A
mulch will provide protection for germinating seedlings and increase the
chances for survival under less than favorable conditions.
Types of mulches available for use in land reclamation are organic
materials, rock, and chemicals. The most commonly used materials are
organic, such as residues from agricultural and wood-processing industries
(Vogel, 1981). The effectiveness of an organic mulch is roughly related to
the size and shape of the particles. Long, narrow particles are superior to
finely ground products. Rates of application for straw and hay mulches
should be 3.0-4.5 tons/ha (Vogel, 1981). If erosion control is a primary
concern, between the time of seeding and establishment of vegetation
rates as high as 8.0-10 tons/ha may be required. A crimper is commonly
used to anchor straw mulches so that they will not be removed by wind.
Recommended rates of application for bark and wood chips for most
seedlings is 85-115 m3/ha (0.95-1.3 cm deep). Where soils are droughty or
the effective rooting zone is shallow, rates of 115-190 m3/ha (1.3-1.9 cm
deep) are recommended for greater conservation of soil moisture (Vogel,
Myer et al. (1972) reported crushed stone, gravel, and wood chip mulches
showed great potential for erosion control on steep barren slopes, especially
where conventional methods might not be satisfactory. For slopes of 20%,
224-448 tons/ha of stone and gravel or 34-56 tons/ha of wood chips provided excellent soil stabilization. Erosion could be controlled much better
with 2.5 cm of stone and gravel and a slightly deeper wood chip mulch than
5.2 tons/ha of straw.
Soil stabilizers are organic and inorganic chemical products that are applied in water solutions to soil surfaces to stabilize the soil against wind and
water erosion (Vogel, 1981). These materials are designed to coat and