Impacts due to Tailings Ponds on Water Quality and Biological Environment: A Case Study

 

S.R Verma¹*, P.R Chaudhari ¹, R.K. Singh¹ and S.R. Wate²

¹EIRA Division, National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440020 (India)

²Director, National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440020 (India)

*Corresponding Author E-mail: sanyogitaverma1@rediffmail.com

ABSTRACT:

 

 

INTRODUCTION:

Mining of basic metal sulphides (Cu, Pb, Zn, Fe) is considered among industrial activities generating serious problems of water resources (Marques et al., 2001). Processing, extraction and beneficiation of ore is an important technique for value addition to the ore before its entry in steel industry because of high content of alumina and silica in trace (Sengupta and Prasad, 1990). However, beneficiation of ore result in the production of an extremely high volume of tailings or slime, the disposal of which constitute one of the most serious environmental challenges to the industry.

 

Tailings ponds are man-made depressions designed for the storage and disposal of tailings from ore beneficiation plant in mining area. These wastes vary from approximately 30% of the mass of ore in case if iron, gypsum and other non-metals. The natural oxidization of tailings under the action of water and atmospheric oxygen generates effluents rich in metal (Gray, 1998) which is a source of nuisance for the nearby water bodies. Tailings are composed of small and uniform particles mainly in the sand and silt categories.  The impacts of tailings dam depend on physico-chemical property of the tailings, particle size and pH. Chemical analysis of waters and soil allows only the identification of potential contaminants but cannot confirm their toxic effect on individuals and populations (Soldner et al., 2004). .

 

 The tailings contain concentration of some heavy metals, which may leach out and pollute rivers and surface water bodies as well as ground water due to seepage.

 

The present work was undertaken to carry out limnological study of tailing pond used for storage of tailings from Iron ore beneficiation plant of Bolani mines (Steel Authority of India Limited) in Orissa, India (Figure 1) with the objective to study the natural biological growth on tailing surface, physico-chemical nature the tailings pond water as well as to select the proper method of stabilization of tailings in tailings pond.

 

Material and Method:

Description of Study Site

The Bolani mine site is located in the Keonjhar district of Orissa (India), bordering on Jharkhand and the study area is shown in Figure 1. The flow diagram of Bolani Iron Ore Beneficiation plant/washing plant indicating material flow and water uses is given in Figure 2. Tailings pond attached to Beneficiation plant was selected for study. In beneficiation plant, the ore is crushed and grinded and then washed with water. Slime water is discharged to tailings pond by gravity due to underflow of thickener through slurry pipelines. Two lines of 350 mm diameter slurry pipeline have been laid down to discharge the slime water into the tailings pond. The thickened slurry containing 50% solids is pumped to tailings pond located at a distance of 3.5Km from beneficiation plant. The Tailings pond area is a shallow natural depression surrounded by natural ridges with two of earthen dams joining hillocks and natural soil stripped off up to 300 m beneath the ground level. The slime holding capacity of the pond will be 1.56 million cubic meters. It is expected that the pond will cater for minimum eight years at the existing slime generation rate taking into consideration annual rainfall of 22 cm (average), evaporation and groundwater recharge.

 

Collection of Samples

The moss crust and algal crust over tailings in tailings pond were scrapped and collected in sampling bottles and preserved with formalin. The samples of overlying water were collected randomly for phytoplankton analysis from four locations viz. A, B, C and D and preserved with Lugol’s iodine. The tailings samples were also collected for further study. The analysis of water, algal and moss crust were carried out using Standard Methods (APHA, AWWA, WPCF, 2003) and (Ward and Whipple, 2004).

 

The data on physico-chemical characteristics of tailings pond water from nearby Karampada tailings pond and Rang- Ring tailings ponds of Kiriburu mine was collected from Bolani mines of Steel Authority of India Limited for comparison purpose.

 

Results and Discussion:

The entire water requirement for the beneficiation plant/Washing plant is made through the Karo River. The water balance diagram for the ore washing plant is given in Figure 3. Total water requirement at each wet circuit is about 900 m3/hr, of which 270 m3 /hr of water is reclaimed through thickener and rest 630 m3/hr is drawn from the make-up water tank. The fines along with water from the Double deck screen i.e. slimes is sent to rake classifier where all the coarser particles are removed and the ore flow goes to thickeners. About 35% of water from the thickener is being recycled to the system and the underflow of thickener slurry is discharged to tailings pond.

 

Tailings Characterization

Iron tailings samples collected from the Bolani Ore washing pond were characterized by Granulometry and chemical quality (Steel Authority of India Limited, 2004) tests. The assay analysis of tailings showed that it contains 53.71 % Fe, 5.24% SiO₂, and 6.25% Al₂O₃. The granulometry analysis showed about 59% of material is below 0.038 mm and is of inferior grade having iron content only 50%. The fraction above 0.038 mm constitutes 41% of material with higher iron content above 56% (Table 1). The mineralogical study by microscopy and XRD technique had shown the presence of iron minerals namely hematite, marmite and goethite and gangue minerals namely gibbsite, Chlorite and Caolite.

 

Table 1 : Characteristics of Iron Ore Tailings of Bolani Mines

Size, mm	% Yield	Fe	SiO2	Al2O3
0.20	3.2	56.69	3.54	4.46
0.15	5.6	57.91	3.61	4.16
0.075	10.8	57.91	3.20	4.61
0.044	10.6	59.58	2.98	4.00
0.038	10.8	87.75	3.69	4.53
0.038	59.0	50.19	5.96	6.73
Composite	100.00	53.71	5.24	6.25

 

Table 2 : Physico-chemical Quality of Tailings Pond Overflow Water

Sr. No.	Parameters	Karampada Tailings Pond*	Rang-Ring Tailings Pond*	Bolani mines New-Tailings Pond
	Temperature	29.7	27.9	23.7
	Colour	34	13	29.1
	pH	7.3	6.7	7.1
	Conductivity	58.4	68.5	59.2
	TDS	28.3	37.5	29.8
	TSS	34	5	7.6
	Total Hardness	10	29.3	22
	Calcium	3.5	8.2	6.3
	Magnesium	0.73	2.13	1.5
	Chloride	6.5	5	28.7
	Sulfate	1	1.5	6
	Phosphate	0.01	0.11	8.6
	Nitrate	0.058	2.5	0.24
	Copper	0.013	0.035	1.3
	Ammonical Nitrogen	0.058	0.223	0.013
	Total Chlorine	0.013	0.083	0.28
	Hexavalent Chromium	0.003	0	0.031
	Total Chromium	0.003	0	0
	Manganese	0.29	0.4	0.006
	Total Iron	0.29	0.28	0.711
	COD	1.8	6	0.424
	Sulfide	0.007	0.013	0.008

All parameters are given in mg/l except Temperature (°C), Colour (Pt-Co Scale) and Conductivity (m S/cm)

Source of data : Bolani mines (Steel Authority of India Limited), Orissa, India

 

Figure 2: Flow Diagram of Bolani Iron Ore Washing Plant

 

Table 3: Phytoplankton Community in Bolani Tailings Pond Water Sample

Ranges of Palmer’s Pollution Index

<15             –                  Oligotrophic or unpolluted water body

15-20         –                  Presence of organic pollution in water body

 >20            –                  Presence of high level of organic pollution in water body

 

 

Quality of Tailings Pond Overflow

Physico-chemical characteristics of overflow of tailings pond of Bolani and those of nearby Karampada and Rang-Ring tailings pond as well as water quality standards are presented in Table 2. Tailings pond water was observed to be slightly acidic to alkaline (near neutral) in nature. pH ranging from 6.7 to 7.3. The conductivity was observed to vary from 58.4 to 68.5 µS/cm. Total dissolved solids varied from 28.3 to 37.5 mg/l showing lower amount of dissolved salts. The total hardness was low and ranged from 10 to 29.3 mg/l which was also very low. All these parameters were below the water quality standards. However, some trace elements like Ca, Mg and F were observed to be present in the water. The ammoniacal nitrogen (0.058-0.223 mg/l) and phosphates (0.01 – 8.6 mg/l) indicate lower amount of nutrient level in the tailing pond water. Heavy metals were also recorded in tailings pond overflow and were observed to be below the water quality standard except Cu, total Fe and hexavalent Cr which were exceeding water quality standard in tailings pond water of Bolani while hexavalent Cr was exceeding in Karampada and Mn exceeding in Kiriburu tailings pond overflow water.

 

Figure 3: Water Balance of Bolani Iron Ore Washing Plant

 

 

The above discussion indicate that the Bolani tailings pond overflow is well comparable with those of tailings ponds in nearby Karampada and Rang-Ring tailing ponds and that its physico-chemical characteristics are within drinking water quality standard except Cu, total Fe and Cr.

 

Biodiversity Associated with Tailings Pond

Terrestrial biodiversity on tailings surface   

The exposed tailings pond surface was not observed to support herbs or shrubs. However, the wet and inundating tailing surface was observed to be covered by dense wooly vegetative growth of Moss. The Moss is very well known to absorb and retain moisture and add organic matter to substratum through death and decay. The root zone of moss was observed to be microbiologically active, supporting worms, fungi, algae, bacteria etc. The nematode worms are phagocytic in nutrition and help in aeration by formation of channels due to their burrowing habit. The fungal mycelia were dominantly present and formed interwoven structure binding the tailings surface firmly. Fungi are saprophytic in nature indicating presence of organic matter in the root zone. A few algal species like Oscillatoria and Chroococcus were also observed at a low concentration. This indicates that micro-organisms are the driving force for ecological succession on tailings surface making it suitable and fertile for the growth of higher plants

 

Aquatic Biodiversity

Tailings pond water in settled zone was observed to be clear and transparent. No fish species or zooplanktons were observed in the tailing pond water. However phytoplankton flora was observed in a very low concentration. The total algal count was observed to range from 6-47 algae/ml which is considered to be negligible. Therefore, phytoplankton population density was very low. The pond water was slightly acidic with presence of many heavy metals as well as limiting nutrients which might be responsible for low algal count. However, presence of diverse trace elements was responsible for presence of a good species diversity i.e. a total of 13 species were recorded from the tailings pond water. Out of which, 3 species belonged to cyanophyceae, 4 species to bacillariophyceae, 1 specie to chlorophyceae, 1 species to euglenophyceae and 1 species to pyrrhophyceae. The observations on phytoplankton community structure are shown in Table 3.  It is observed that most of the water samples were dominated by cyanophyceae (Water samples from locations B, C, D) and water sample from location A was dominated by bacillariophyceae. Palmer’s Pollution Index varing from 1 to 11 indicated the presence of pollution indicator species in low amount leading to transparent, clear pond water.

 

Overall biodiversity of phytoplankton was observed to be good (Total number of species 10). However low plankton diversity was observed at B, C and D locations and marginally higher biodiversity was observed at location A (Shannon Wiener Index - 2.6).

indicating large variations in environmental conditions at different sites in tailings pond.

 

The organic pollution indicator species recorded in the present investigation were Oscillatoria limnetica, Chlorococcum humicola, Navicula sp. and Euglena acus. The clean water indicator species observed were Cymbella microcephala and Stephanodiscus hantzschii. The cumulative total count of organic pollution indicator species is observed to be low as compared to cumulative total count of phytoplankton (Table 4).The algal species namely E. acus (20.75% composition), C. humicolo (13.21%), S. hantzchii (12.26%), Phormidium foveolarum (11.32%), Navicula (8.49%), O. limnetica (5.66%), Chroococcus turgidus (3.77%), C. microcephala  (3.77%), Fragillaria capucina (3.77%) and Peridinium tabulatum (3.77%) were found to be dominant in tailings pond water and  considered to be the indicators  of slightly acidic tailings pond.

 

Ecotoxicological Evalution

A large number of bacteria and fungal mycelia were observed in the root zone of moss growing on tailings surface. A similar observation on the microbial flora of a pond for pyritic tailings was made by (Garcia et al., 1996) from the flotation of a complex polymetallic sulphite concentrate from the southwest of spain. They have observed a diverse microbial community in the tailings pond. This community consisted of heterotrophic micro organisms (bacteria, yeast and fungi), which were present in all the samples. The bacterial population consisted of Thiobacillus ferroxidants along with heterotrophic bacteria such as Acidiphilium and other bacteria of same genus Thiobacillus acidophilus and chemolithotrophic bacteria belonging to Thiobacillus genus. The heterotrophic bacteria thrive on organic matter while chemolithotrophic bacteria have the capacity to oxidize ferrous iron. These organisms carry out complex microbiological transformations in these ponds and determine the quality of water.

 

The status of biological community in tailings pond indicates no toxic impact metals leached from the tailings into the pond water. On the contrary, the nutrients and metals are present at trace concentrations. The presence of phytoplankton community in tailings pond water supports the above observations. These observations lead to the conclusion that the Bolani tailings pond water on disposal would not adversely affect the ecosystem of receiving water bodies and the wildlife dependent on it, which may be due to its near neutral nature and low leachability.

 

 

Ecofriendly Fate of Tailings

The tailings dumps after the filling of tailings dam are amenable for stabilization by developing a vegetation cover over it by the use of organic manures and soil conservation methods. The list of plants suggested in the study for restoration of tailings dumps is presented in Table 5 (Department of Environment, Government of India, New Delhi, 1982).

As Bolani tailings pond has high grade and low-grade tailings which occur in 1:1 ratio, it can be mixed to improve its quality for subsequent pelletization and reuse in steel industry. Analysis of earlier work indicates that beneficiation of iron ore tailings is not difficult, but the beneficiation techniques to be used must be matched to the quality of the ore and must be suitable for the range of products. Prasad et al., 1988 studied the beneficiation of iron ore slime produced from washing plants and tailing ponds of Kiriburu mines by using wet high intensity magnetic separators followed by classification in hydrocyclone. They showed that a concentrate containing 63% Fe and 3.3% alumina could be produced with an overall iron recovery of 56%.  Pradip, 1994 showed that the multi gravity separation is the most promising technique for treating the iron-ore tailings and it is particularly effective for reducing alumina. Other avenues of treating the iron-ore tailingss have also been considered to establish significant beneficiation potentials that cover a wide range of iron ores in India (Rakshit, 1997; Bhattacharya et al.,1997; Bhagat and Dey, 1997; Srivastava et al.,1997)

 

Conclusion:

The present observation is made on tailings pond of Bolani Iron Ore Mines in Orissa (India) with special reference to slimes, pond water quality, biological growth as an indicator of environmental quality. The overflow of Bolani tailings pond was observed to be near neutral with almost negligible phosphate content and presence of metals like Cu, Cr, Mn and Fe at trace levels. However in view of the long term impacts, it is necessary to assess the extent of possible contamination of groundwater using mathematical modeling technique.

 

The biological observations indicate low primary productivity i.e. algal count in pond water. However, the biodiversity of phytoplankton was good. Organic pollution indicator species were also recorded from pond water. The exposed tailing pond surface did not support the growth of herbs or shrubs. However, some area was covered with dense wooly vegetative growth of moss supporting microbiologically active layer of worms, fungi, algae, and bacteria. These observations indicate no ecotoxicological impact of heavy metals in the pond water.

 

The deficiency of nutrients may be responsible for poor biological growth. However, presence of trace minerals and trace nutrients result in good biodiversity of phytoplankton sp. Therefore, the stabilization of tailings, after filling of tailings ponds by establishing vegetation cover would require for nutrient fortification in the form of organic manure. Alternatively, the tailings may be recycled after beneficiation and pelletisation in order to save mineral resources.

 

Acknowledgement:

The authors wish to thank Director, NEERI, Nagpur for providing all the facilities for undertaking field and laboratory studies and encouragement to research work. 

 

References:

1.       APHA, AWWA, WPCF, 2003. Standard Methods for Water Analysis, American Public Health Association, Washington.

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3.       Bhattacharya P. et. al., 1997. National Seminar on Processing of Fines, NML, Jameshdpur, India.

4.       Department of Environment, 1982. National Seminar on Mineral and Ecology, New Delhi. India.

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10.     Prasad, N. et. al., Introduction of new technologies for beneficiation of Indian Hematite ores reduction of losses and increase in their quality. In forceberg E. (ed.) XVI International Mineral Processing Congresss, (1988) 1369.

11.     Rakshit, K. N., 1997. National Seminar on Processing of fines, NML Jamshedpur, India.

12.     Steel Authority of India limited., 2004. Beneficiation and sinter amenability study of iron ore slime of Bolani mines, Project No. 120534.

13.     Sengupta, P. K. and Prasad, N., 1990. Beneficiation of high alumina Iron ores. (In Gupta J. K., Litvinanke, V. L. Vegmann, E. F. (ds). Iron Ore Processing and Blast Furnace Iron making. Oxford .

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15.     Srivastava, M.P. et. al., 1997. National Seminar on Processing of fines, NML, Jamshedpur, India.

16.     Stewart, P. M. et. al., Aquatic Ecosystem Health and Management 3(1) (2000) 179.

17.     Ward and Whipple, 2004. Standard Method of Water Analysis.

 

 

 

 

Received on 30.12.2011         Modified on 12.01.2012

Accepted on 07.02.2012         © AJRC All right reserved