Abstract
Characteristics of refused materials are prerequisite information
required to determine the strategic reclamation of extreme land
degradation in post-tin mining areas. The objective of the study was to
evaluate mineralogical, chemical, and physical properties and heavy
metals of spoil and tailing as the basis for reclamation measures. Seven
representative soil profiles were made and sampled to a depth of 130 cm
for various soil analyses. Results showed that tin mining has
drastically altered the soil texture from sandy clay loam under native
conditions to loamy sand and sand under post-tin mining. Mineralogical
constituents of refused materials were mainly mineral resistant to
chemical weathering, consisting of predominant quartz with small amounts
of tourmaline, opaque, zircon and garnet. Total X-ray fluoresce (XRF)
elemental analysis showed extreme high SiO2 content
(92-96%) associated mainly with quartz mineral, and extremely low
oxides of Ca, Mg, P, K and S (< 0.2% altogether). This
suggests all nutrients are severe problems for crops. Type of total
heavy metals showed the Cr2O3 was high
in sandy tailing (204 - 286 mg kg-1), while the SnO
was low (0 -153 mg kg-1) and they were preserved in
the structure of host minerals, thereby the health risk is negligible.
Based on many serious constraints of soils, the strategic reclamation to
recover soil productivity and ecological function was the building up
soil organic matter, establishing “pot planting point” technique,
complete fertilizer application, and selection of crops with an ability
to fix N nutrient from the atmosphere, and adaptive to low soil
nutrients.
KEYWORDS: Post-tin mining, soil characteristics, heavy metals,
tailing, spoil, strategic reclamation
Mining left the legacy of environmental problems attributed by disposal
of refused materials. Global land use for mining between 1976 and 2000
is cumulatively about 3,700,000 ha or about 0.2% of earth’s land
surface (Barney, 1980). Mines produce large amounts of refused-materials
because the ore constituent of the total volume of the mined materials
occurs only in a small fraction (Duhka and Adriano, 1997). For tin
mining, the separation of tin ores, the heavy sand fraction (density
> 4 g cm-3), from the clay, silt and
light sand fractions leads to the dumping of large amounts of spoils and
tailings, and their cumulative amounts increase with time. The disposal
of tailings is a major environmental issue that has become more serious
with the increased exploration for metals and the exploitation of lower
grade mineral deposits (Ozkan and Ipekoglu, 2002).
Southeast Asian countries (Indonesia, Malaysia, Thailand and Myanmar)
produced 9.6 million tonnes of tin, equivalent to 54% of the world’s
tin production since 1800 (Schwartz et al., 1995). In 2017, Indonesia is
the second larger world producer (50,000 metric tonnes) of tin after
China (100,000 metric tonnes) with total world production of 290,000
metric tonnes (USGS, 2018). Further, tin world reserve is 4,800,000
metric tonnes in which China and Indonesian reserves are 1,100,000 and
800,000 metric tons, respectively (USGS, 2018). The major locations of
tin producer in Indonesia are Bangka, Belitung and Singkep islands. Open
pit mining of tin is destructive due to the complete removal of
vegetation and topsoil. In addition, tin mining processes involving the
dispersion and washing to separate heavy sand fraction of ores from
refused materials could result huge piles of sandy tailing. The large
idle bare land (abandoned tailings or waste piles) is massively
occurred. The high economic return from tin mining activities are not
reconciled with the existing environmental management.
In this study, tailing was referred to dumped materials left over after
the process of separating the valuable heavy sand fraction ores from the
uneconomic light sand fraction. Likewise, spoil was referred to an
accumulation of displaced earthy material or other waste material
removed during mining or excavation. Refused materials (e.g. spoils,
tailings and slime) are mine’s byproducts accumulated from the
excavation, washing, concentration or treatment of ground ores to
extract valuable ores. The Bangka island has been exploited for tin
since 1711 (Ko, 1986), resulting a widespread of huge spoil and tailing
disposal as the extreme threat to the environment. Hence,
characterization of spoil and tailings in terms of chemical, physical,
mineralogical properties and heavy metal contents should be done to
obtain reliable information as a basis for reclamation measures.
Generally, mining is considered to be one of the most significant
sources of heavy metal contamination (Acosta et al., 2011; Dudka and
Adriano, 1997; Fryer et al., 2006). Ores and mineral extraction have
inflicted serious environmental damage, especially in the heavy metal
pollution (Acosta et al., 2011; Komnitsas and Modis, 2006; Zhou et al.,
2007). Metals of major interest in bioavailability studies, as listed by
the U.S. Environmental Protection Agency (EPA), are Al, As, Be, Cd, Cr,
Cu, Hg, Ni, Pb, Se, and Sb (McKinney and Rogers, 1992). Heavy metals
such as Pb, Zn, Cd, Hg and Cr generally refer to metals and metalloids
having densities greater than 5 g cm-3 (Oves et al.,
2012). Li et al., (2014) reviewed the soil heavy metal pollution from
mines in China and concluded that the mean concentrations of As, Cd, Cr,
Cu, Ni, Pb, Zn, and Hg in soils are higher (varying from 0.4 to 36.5
times greater, depended on a heavy metal type) than the Grade II
environmental quality standard for soils in China. The geochemical flux
explained the lithological origin of potential toxic elements (As, Cd,
Co, Cr, Cu, Fe, La, Mn, Ni, Pb, Sc, Th, V) (Pinto et al., 2017)
Mineralogical composition plays a crucial role in understanding native
nutrient sources for crops and heavy metals both short and long-term
period of time. However, mineralogical composition of refused materials
has been ignored in post-tin mining areas, and more attention is given
to chemical properties and heavy metals. Hence, we investigated mineral
composition of refused materials deriving from different parent
materials in post-tin mining areas and relating the minerals to soil
chemistry, nutrients and heavy metals. The objective of the study was to
evaluate mineralogical constituents, particle sizes, chemical and
physical properties and heavy metal contents of refused materials in
post-tin mining areas as the strategic basis for reclamation of soil
productivity and ecological function.
2 MATERIALS AND METHODS
Study site and field samplings
The study areas locate in Bangka Island, Kepulauan Bangka Belitung
province, Indonesia between X 626183 -Y 9757090 and X 632834 -Y 9752946
UTM grid, Zone 48 M with the elevation of 27 to 60 m above sea level.
The areas were selected based on their lithological type that represents
most of the post-tin mining areas in Kepulauan Bangka Belitung province.
Lithologically, Bangka Island occurred on granite and sandstone parent
rocks. The granitoid plutons of the Indonesian Tin Islands was Triassic
age (193-251 Ma) (Aleva,1985; Ko, 1986). It was expected that the
similarity in lithology of the areas would produce a similar property of
tailings and spoils. The process of tin mining and deposition of refused
material were mainly gravitational separation without any chemical
treatment. The companies having tin mining land concession extracted the
tin-host ores by dry-excavating of soils and the underlain deposit
layers, mostly down 5 to 50 m. The companies used conventional
bulldozers, loaders and haulers for the excavation of deposit ores. The
separation of non-tin layer sediment such as white clay was directly
dumped as a spoil, during the excavation. Hydraulic mining by spraying
the ore deposits associated soils to form a slurry and pumped to the wet
separation (concentrator) facility. The slurry was then passed through
sequences of cyclones and separator in which clays, silts, and some very
fine sands (collectively referred to as slimes) were separated
gravitationally from the sand fractions. The heavy mineral sand of ores
(particle density > 4.0 g/cm3) was
further separated from the light sand fraction by cyclones water. The
refused fractions consisting of light sand were dumped as tailings.
The characteristics of spoils (mostly a mixture of native soil, light
sand and white clay) and sandy tailing piles of post-tin mining were
assessed and evaluated as a basis for reclamation measures. Tailings and
spoils deriving from sandstone and have been mined from 2000 to 2015
were represented by two sandy tailing profiles (TBB1 and TBB2), and a
spoil profile (TBB3). The topsoil of TBB3 profile consisted of initial
native soil with some tailing (0-30 cm), while the underlying layers
consisted of a mixture of white clay and sandy tailing. For tailings
resulting from granite materials and mining from 1960 to 1998 were
represented by TBB6 and TBB7 profiles. The native soil profiles adjacent
to post-tin mining areas were included for each type of parent materials
(TBB4 for sandstone, and TBB5 for granite materials) as a comparison to
spoils and tailings. We excavated a soil profile with the dimensions of
100 × 200 × 120–130 cm (width × length × depth) for morphological
property observation and soil sampling. We collected a composite soil
sample for each soil layer from all sides of the profile; the sample was
thoroughly mixed prior to subsampling ~1 kg for
mineralogy, chemical and heavy metal analyses.