Tải bản đầy đủ - 0 (trang)
III. Application of Various Amendments to Ameliorate Acidic Mine Spoil

III. Application of Various Amendments to Ameliorate Acidic Mine Spoil

Tải bản đầy đủ - 0trang

384



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.

A. TOPSOIL

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



385



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.

C.



SEWAGE

SLUDGE



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



386



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).

D. PAPERMILL

SLUDGE

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).



E. SODIUM

LAURYLSULFATE

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.



387



RECLAMATION OF ACIDIC MINED LANDS



Table I1

Major Plant Nutrient Content of Fly Ash, Sewage Sludge,

Papermill Sludge, and Soil

Fly ash of

bituminous coal'



Sewage

sludgeb

(Yo)



Papermill

sludge'

(q0)



-



0.03-17.6

0.04-6.1

0.008-1.9

0.1-25

0.03-2.0



0.008-2.33

0.0125-0.50



Element

N

P



K

Ca

Mi3



0.1-0.2

1.7-3.2

0.2-4.1

0.1-0.8



0.004-0.85



0.10-14.4

0.09-0.57



Soil"

(VO)



0.02-0.4

0.0005-0.2

0.04-3.0

0.7-50.0

0.06-0.6



'From Capp (1978).

bFrom Halderson and Zenz (1978).

%om Dolar et al. (1972)and Haghiri and Sutton (1982).



Table Ill

Metal Content of Fly Ash, Sewage Sludge, Primary

Papermill Sludge, and Soil'



Element



Fly ash of

bituminous coalb



Sewage

sludgeC



Papermill

sludged



1.22%



Al



127,000



-



As

B

Ba

Cd

co

Cr

cu

Fe

Ga

Hg

La

Mn

Mo

Ni

Pb

sc

Sr

Zn



82



6-230

4-757

21-8,980

1-18

17-99,000

84-10,400

400-90,000

-



36

974

0.3

35

172

132

86,600

100

0.1

99

145

33

11

15

22

794

20



-



33

23

-



36

0.67%



-



18-7,100

5-39

10-3,515

13-19,700

13-27,EOO



'In mg/kg except where noted.

bFrom Adriano et al. (1980).

Trom Halderson and Zenz (1978).

dFrom Haghiri and Sutton (1982).



537



-



22

47

319



Soilb



4-30070

0.1-40

2-100

100-3,000

0.01-7

1-40

5-3 ,000

2-100

O.7-55%

15-70

100-4,000

0.2-5

10-1,000

2-100

10-25

500-4,000

10-300



388



P. SUTTON AND W. A. DICK



F.



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

OF AMENDMENTS

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



Table IV

Recommended Cumulative Limits for Metals of Major

Concern Applied to Agricultural Croplane



Soil cation exchange capacity (cmol/kg)b

Metal

(kglha)



< 5 kg/ha



Cadmium

Copper

Nickel

Zinc

Lead



6



11



140

140

280

560



280

280

560

1,120



5-15 kg/ha



aFrom USEPA (1983).

%oil must be maintained at pH 6.5 or more.



>I5 kg/ha

22

560



560

1,120

2,240



RECLAMATION OF ACIDIC MINED LANDS



389



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.



IV.



SEEDING AND MANAGEMENT OF

AMENDMENT-TREATED SPOIL

A.



LIMESTONE

AND FERTILIZER



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.



390



P. SUTTON AND W. A. DICK



B. MULCHES



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,

1981).



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



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

III. Application of Various Amendments to Ameliorate Acidic Mine Spoil

Tải bản đầy đủ ngay(0 tr)

×