Environmental Assessment of Acid Mine Drainage Pollution on Surface Water Bodies around Ngwenya Mine, Swaziland

A. O. Fadiran, C. L. Dlamini, J. M. Thwala

Department of Chemistry, University of Swaziland, Kwaluseni, Swaziland..

DOI: 10.4236/jep.2014.52020                

Abstract

Twenty-three water samples and three “yellow boy” samples were obtained from different water bodies located at the foot of the Ngwenya Mountain on top of which the old Ngwenya Iron Ore Mine is located. The samples were analysed for pH, electrical conductivity (EC), redox potential (ORP) and temperature (T). The dominant Fe species was determined using a UV-VIS spectrophotometer. Selected anions namely: halogens (F^-, Br^-, Cl^-), the nutrients (NO₂^-,NO₃^-,PO₄^3-) and the best indicator for AMD pollution (SO₄^2-) were analysed using Ion Chromatography (IC) while the selected heavy metals, namely: Cr, Mn, Fe, Ni, Co, Cu, Zn, Pb and Cd were analysed using Flame Atomic Absorption Spectrometry (FAAS). The physico-chemical parameters ranges obtained were pH (6.32 - 8.63), EC (11.00 - 585.33 μS/cm), ORP (-93.67 - 79.33 mV) and T (7.60°C - 18.57°C). The levels of the Fe species (ppm) in the water samples were Fe²⁺ (0.56 - 3.17) and Fe³⁺ (0.00 - 0.73). Measured mean anion ranges in ppm were F^- (0.00 - 0.15), Cl^- (1.5 - 11.19),

Keywords

Acid Mine Drainage; Heavy Metal Pollution; Redox Potential; Physico-Chemical Properties; Iron Speciation

It is hypothesized that acid mine drainage from the Ngwenya Mine ore and dumping sites deteriorates the quality of water in their vicinity [16]. Mobility of heavy metals is enhanced by acidic waters rendering them liable to contaminate the environment [17,18] and causing adverse effects on life generally. As a result, acidic waters are a menace to the environment as well as being incapable to carry out its functions well [2,19]. Such water is unsafe for drinking, irrigation, swimming or cooling purposes in industry. The increased acidity interferes with the characteristics of pure water rendering it a poor coolant in the industry and engines. Low-pH water is inhabitable to aquatic fauna and flora and animals in general [12]. The human population around Ngwenya Mine that can be potentially affected by the AMD stands at 11147 as per 2007 report [20].

AMD can develop throughout the mining process [4], that is, in underground workings, waste rock dumps, open pit mine fractures, tailing deposits, ore stockpiles, etc. Once it occurs, the adverse effects can be costly because of high clean-up costs and irreversibility because of lack of available technology [6,21]. Waters with low pH kill all forms of living organisms in them, save only the highly tolerant ones. This leads to poor water quality and release of bad odour due to the decomposing dead organisms. Moreover, in low pH water, heavy metals become soluble and as such are potential contaminants to soils, sediments and terrestrial plants that use such water for growth [9]. Aquatic organisms can also accumulate the dissolved metals in their bodies which eventually are consumed by higher organisms and sequentially causing pollution by biomagnifications. This continues up to the trophic ladder until these metals get into humans and on accumulating beyond maximum contamination limits (MCL) and cause detrimental effects on human health. Heavy metals are systemic toxins with specific carcinogenic, teratogenic, nephrotoxic, neurotoxic and fetotoxic effects [15]. Reproductivity in crops is hindered by watering with acidic water. Quite often, low pH water contains high concentrations of copper ions that interfere with photosynthesis, and thus resulting in poor yields. This eventually negatively affects food security [10].

Furthermore, acidic waters are unsuitable for tourism purposes. The water is corrosive; hence it is not good for swimming. It has bad odour due to the decomposition of dead organic matter which strips off the water of a substantial amount of dissolved oxygen, rendering the waters anoxic. The water is not fit for aesthetics as acidic waters are characterized by an orange-brown colour. This is the colour of ferric hydroxide which is a product of pyrite oxidation. The ferric hydroxide precipitate is called “yellow boy” [22].

Equations (1)-(3) summarize the oxidation of pyrite:

(1)

(2)

(3)

The formation of “yellow boy” removes dissolved oxygen from water [19]. The “yellow boy” is produced in the AMD receiving streams because there is no pyrite to be attacked by the ferric ion. The corresponding stepwise reactions are as follows:

(4)

(5)

(6)

Figure 1 is a typical picture of “yellow boy” produced in one of the tributaries to Mlondozi River which is very close to the mine.

In summary, the influx of acid mine drainage into streams can severely degrade both habitat and water quality. It often produces an environment devoid of most aquatic life and unfit for desired uses. The severity and extent of damage depend upon a variety of factors including the frequency, volume, and chemical nature of the drainage. The size and the buffering capacity of the

Figure 1. The photograph of typical “yellow boy”.

receiving stream are other vital factors. The transport route from the source to the receptor may equally be a determining factor of the extent of damage by the AMD.

2. Materials and Methods

2.1. Description of the Study Area

The study area is the surface water bodies found around the Ngwenya Iron Ore Mine, Swaziland. The streams studied are used by the communities in the study area for domestic purposes, that is, they are the sole providers of potable water in this area. Some of these streams are feeders for the Hawane Dam which supplies water to the capital city of Swaziland, Mbabane. Figure 2 below shows the areas in the vicinity of the Mine and the streams that source their water from the Ngwenya Mountain where the AMD producing mine is located [1].

2.2. Experimental

Water samples were collected from streams and dams around the foot of the Ngwenya Mountain. The sampling points are shown in Figure 3 below. Water samples were collected into 1 L prewashed polyethylene bottles as described elsewhere [1]. They were thereafter placed in a cooler box containing ice blocks and transported to the laboratory.

2.2.1. Physico-Chemical Properties

Upon arrival in the laboratory, about 100 ml of each of the water samples were poured into a small beaker and then quickly analysed for the physico-chemical parameters, namely: pH, temperature (T), redox potential (ORP) and electrical conductivity (EC). These analyses were carried out using electrochemical methods during which WTW Multi 340i probes were used. The pH and the ORP were measured by one probe, the pH-Electrode Sen Tix 41-3, which can be switched from measuring pH to measuring ORP and vice versa. The EC and T were measured by another probe, the TetraCon^R 325. The ORP values were converted to Eh (-log of electron concentration) using Equation (7) below:

(7)

This is addition of the temperature-adjusted potential of the saturated calomel electrode, where T is the measured temperature of the sample in ˚C [23].

The water samples were taken out of the freezer, allowed to defrost and then filtered through 0.45 µm HVLP polymer membrane filter using a Nalgene filter funnel with a V-700 model vacuum pump. The filter funnel and the collecting flask were rinsed first with deionized water three times and then with the next sample to be filtered to avoid cross sample contamination.

Figure 2. Areas around Ngwenya Mine and streams whose source is the Ngwenya Mountain, Source: Central Statistical Office of Swaziland [20].

Figure 3. Sampling points (  ) in areas around the Ngwenya Mine.

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	C. L. Dlamini, A. O. Fadiran and J. M. Thwala, “A Study of Environmental Assessment of Acid Mine Drainage in Ngwenya, Swaziland,” Journal of Environmental Protection, Vol. 4, No. 11B, 2013, pp. 20-26.
[2]	http://dx.doi.org/10.4236/jep.2013.411B003
[3]	S. R. Jennings, D. R. Neuman and P. S. Blicker, “Acid Mine Drainage and Effects on Fish Health and Ecology: A Review,” Reclamation Research Group Publication, Bozeman, 2008.
[4]	R. F. Fuggle and M. A Rabie. “Environmental Management in South Africa,” Juta & Co., Ltd., Cape Town, 2000.
[5]	M. Gosar, “Environmental Impacts of Metal Mining,” RMZ-Materials and Geoenvironment, Vol. 51, No 4, 2004, pp. 2097-2107.
[6]	S. Bega, “No Mine Dump Far Enough, No Corporate Big Enough, by Mariette Liefferink,” FSE Press, 2011.
[7]	A. E. Meadows and A. A. Carpenter, “Acid Mine Drainage and Groundwater Pollution,” Groundwater Pollution Primer, CE 4594: Soil and Groundqwater Pollution. Civil Engineering Department, Virginia Tech., 1997.
[8]	BC Wild and EMCBC, “Acid Mine Drainage: Water and Water Pollution Issues in BC,” Environmental Mining Council of British Columbia, Canada.
[9]	M. Gebrekidan and Z. Samuel, (MEJS), “Concentrations of Heavy metals in Drinking Water from Urban Areas of the Tigray Region, Northern Ethiopia,” Mekelle University, Vol. 3, No. 1, 2011, pp. 105-121.
[10]	R. S. Lokhande, P. U. Singare and D. S. Pimple, “Pollution in Water of Kasardi River Flowing along Taloja Industrial Area of Mumbai, India,” World Environment, Vol. 1, No. 1, 2011, pp. 6-13.
[11]	E. G. Regis, “Assessment of the Effects of Acid Mine Drainage on Mogpog River Ecosystem, Marinduque, Phillippines, and Possible Impacts on Human Communities,” Ph.D. Dissertation, 2006.
[12]	Wikipedia, “Acid Mine Drainage,” 2002
[13]	D. K. Niyogi, W. M. Lewis Jr., and D. M. McKnight, “Effects of Stress from Mine Drainage on Diversity, Biomass and Functions of Primary Producers in Mountain Streams,” Department of Zoology, University of Otago, Dunedin, 2002
[14]	H. Tutu, E. M. Cukrowska, V. Dohnal and J. Havel, “Application of Artificial Neural Networks for Classification of Uranium Distribution in the Central Rand Goldfield, South Africa, and Assessment,” Environmental Modelling, Vol. 10, No. 2, 2005, pp. 143-152.
[15]	http://dx.doi.org/10.1007/s10666-005-0214-x
[16]	E. U. Etim and G. U. Adie, “Assessment of Toxic Heavy Metal Loading in Topsoil Samples within the Vicinity of a Limestone Quarry in South Western Nigeria,” African Journal of Environmental Science and Technology, Vol. 6, No. 8, 2012, pp. 322-330.
[17]	Tuberose, “Heavy Metal Toxicity,”
[18]	www.Tuberose.com/Heavy_Metal_Toxicity.html
[19]	M. Jopony and F. Tongkul, “Acid Mine Drainage at Mamut Copper Mine, Sabah, Malaysia,” School of Science and Technology, Universiti Malaysia Sabah, Kota Kinabalu, 2009.
[20]	M. C. Jung, J. S. Ahn and H. Chon, “Environmental Contamination and Sequential Extraction of Trace Elements from Mine Wastes around Various Metalliferous Mines in Korea,” Geosystem Engineering, Vol. 4, No. 2, 2001, pp. 50-60.
[21]	http://dx.doi.org/10.1080/12269328.2001.10541168
[22]	E. Galan, M. I. Carretero and J. C. Fernandez-Caliani, “Effects of Acid Mine Drainage on Clay Minerals Suspended in the Tinto River (Rio Tinto, Spain). An Experimental Approach,” Clay Minerals, Vol. 34, No. 1, 1999, pp. 99-108. http://dx.doi.org/10.1180/000985599546118
[23]	J. Earle and T. Callaghan, “Impacts of Mine Drainage on Aquatic Life, Water Uses and Man-Made Structures,” Department of Environmental Protection, Harrisburg, 1994.
[24]	Central Statistical Office of Swaziland, “Population for Selected Areas around Ekupheleni (Ngwenya Mine) by Sex,” 2007.
[25]	L. Donnely, “No Quick Fix for Acid Mine Drainage,” Mail and Guardian, 2011.
[26]	Wikipedia, “Acid Mine Drainage,” 2002.
[27]	J. M. Bigham, O. H. Tuovinen, K. S. Brady and T. J. Logan, “Iron Speciation in Acid Mine Effluents: Chemical and Microbial Controls,” Department of Agronomy and Microbiology, The Ohio State university, Columbus, 1984.
[28]	C. Afriyie-Debrah, K. Obiri-Danso and J. H. Ephriam, “Effect of Acid Mine Drainage on Creeks or Streams in a Mining Community in Ghana and Treatment Options,” 2010 International Conference on Environmental Engineering and Applications (ICEEA), 10-12 September 2010, pp. 285-290.
[29]	E. Mswane, “Determination of Levels of Inorganic Anions in Water and Sediments of the Black Mbuluzi River along the Mhlume-Simunye Sugar Plantations in Swaziland,” M.Sc. Final Year Research Report, University of Swaziland, Kwaluseni, 2007.
[30]	N. F. Gray, “Water Quality Problems and Solutions,” John Wiley, New York, 1994, pp. 118-132.
[31]	A. D. O’Sullivan, R. Conlon, B. Moran and M. Otte, “Characterisation of Constructed Wetland Substrates by Chemical Sequential Extraction and X-Ray Diffraction Analyses,” Biology and Environment: Proceedings of the Royal Irish Academy, Vol. 105B, No. 2, 2005, pp. 87-94.
[32]	http://dx.doi.org/10.3318/BIOE.2005.105.2.87
[33]	A. Concas, C. Ardau, A. Cristini, P. Zuddas and G. Cao, “Mobility of Heavy Metals from Tailings to Stream Waters in a Mining Activity Contaminated Site,” Chemosphere, Vol. 63, No. 2, 2006, pp. 244-253.
[34]	http://dx.doi.org/10.1016/j.chemosphere.2005.08.024
[35]	S. Singh, S. Lal, J. Harjit, S. Amlathe and H. C. Kataria, “Potential of Metal Extractants in Determination of Trace Metals in Water Sample,” Advanced Studies in Biology, Vol. 3, No. 5, 2011, pp. 239-246.