Journal of Scientific & Industrial Research

Vol. 59, October 2000, pp 822-828

Characteristics of the Iron Ore Tailing Pond Effluent in India and its Management

M K Ghose* and P K Sen**

Centre of Minin g Environment , Indi an School of Mines, Dhanbad 826 004

**Metallurgical and Engi neering Consultants Limited, Ranchi 834 002

Received: 22 February 2000; accepted: OS May 2000

Nature and behaviour of iron ore taili ng cfllucnt is discussed . One iron ore mine in Eastern India is selected for the st udy. Study sites are described. Physico-chemical characteri st ics of the effluent are discussed. Methodo logy adopted for the sampling and analysis of the cflluent is described and results arc analysed. It is observed that most of the TSS and hea vy metal constituents are being removed in the tai ling pond, as such provision of tai ling pond is a must. But it does not oivc the full guarantee of enviro nmental compliance due to the di scharge of decanted effluent. It is worth whi le to rec;ver the decanted water to recycle it in the plan t. The main pollutants in the crtluen t arc TSS and Fe. A scheme is proposed for the removal of the contaminants. By recycling the raw water in take is reduced by 50 m3/h which causes less surface water pollution.

Introduction

Tailings are ground rock parti c les that a re produced during ore bene fi c iati on and di sposed in slurry form . The iron ores many- a- times contai n so little metal that almost 32 per cent of the ore ex tracted ends up as tailings . The fine tailings generated are usually di sposed off in tailing ponds. By the end of this century in India the es timated iron ore producti on would be 85 m tonnes/y generating 27 m tonnes/y of tailings for which safe disposal by way of containment in tailing ponds are needed to be planned 1• Surface water contro l measures are prime factors for safety of tailing pond e mbankment against floods . As noted by Scog lund and Hanson2

, water inputs and outputs are var iab le and hi ghly sensitive to a number of factors that are often very difficult to es timate within reasonable degree of accu racy. Seepage from the impoundment must be contro ll ed both during operating life and after the c losure o f the dam 1

• Whenever poss ible the efflu ent is decanted from pond and returned to the benefi c iation plant for reuse and sometimes let out to the natural stream.

*Author for correspondence

The phys ical and chemical nature of the effluent coming out of beneficiation plant , depends on the type of ore be ing treated, the milling operati ons used to benefic iate the ore, and the water content in the efflu ent. Matte r of serious concern in this regard is the direct di scharge of tailings into rivers ' . Another cause of pollution of surface water is the di scharge of excess supernatant effluent into a wa ter course. In ferrous mining sector, whic h gene rates huge ta il ings vo lume needs huge land space for accommodating thi s residual product. This accumu lated waste product ultimate ly could be the resource, a ft e r the ava ilabl e rich resou rces are fully exploited . The present study is carried out to determine the characteristics of tailing pond effluent which can be recyc led from the tailing dam or to be discharged to the environment and the treatment if any needed to improve the quality.

Nature and Behaviour of Iron Ore Tailing Effluent

No nati ona l plan or des ign of ta ilings d isposa l can be carried out without an appreciation of the physical nature and chemical characteri sti cs of the liquid benefici ation plant effl uent4 The physico-

GHOSE & SEN: IRON ORE TAILING POND EFFLUENT 823

chemical properties of the material dictate on the most fundamental level the type of disposal facility required and the degree of conservation in its design , consi stent with the hazards posed by the material s. Understanding of tailing effluent involves knowledge of the processes through which they are produced. While tailings characteristics vary over wide ranges the type of ore being processed usually al lows for some reasonably valid generalisations about the general nature of the effluent. Ritce/ has laid emphasis on effluent treatment for environmental control.

Physico-chemical Characteristics of Effluent

The tailings are disposed off to tailing ponds for containment. The surface area of the pond remains semi-dry up to great extent, except for the area near decantation tower. The tailing slime after the disposal moves in the down gradient direction toward s the decantation tower and during this process the settlement takes place. The coarser particles settle down near the inlet point and the relatively fine

.,. . ~c. KOIRA o

~\\ , .

\\ TENSA fl ~

BARSUA

material settles at longer distances. The water with finest particles reaches near the decantation area, known as decant pond and accumulates over there. Finally the decanted water comes out of the tailing pond as an effluent. In this type of tailing pond design the weir level of decantation tower is gradually rai sed as the pond gets fi lled up. In some ponds of the same design the spill channel is provided for carrying storm water and an effluent. For extracting the decanted effluent during dry season, a cunnetle (small channel) is provided in the spill way in which a weir is a lso provided, which is to be gradually raised as the pond gets filled up. For most of the tailing dams the average slope of settled tailings is 0.5 to 2.0 per cent for initial several hundred feet. At more di stance points the slope may become flatterer to as little as 0. I per cent. Particle size sorting that occurs along the settled tailings has been studied in the laboratory by Kelay et al. 6 and Jerabek and Hartman7

. The partic les are transported along the settled tailings surface by si ltation and rolling8

. Tailing pond of the study area i the tailing pond of this type, where a spill channel is

Figure I -Location map of Barsua iron ore mines

824 J SCIIND RES VOL 59 OCTOBER 2000

provided . The deposition of the finer particles and the pond area near decantation tower of tailing pond are relative simple processes of vertical settling. The effluent quality coming out from a tailing pond depends on the proper distribution of tailing slurry and efficiency of the decantation arrangement provided in the tailing pond, particle size distribution, specific gravity,and settling behaviour.

Description of the Study Sites

The iron ore mine under study is situated at an elevation of 790-910 m in Toda forest. It is 68 km from Rourkela , having latitude 21 °50'N and longitude 85°8'E. The location map is given in Figure I . The mines' crushing and ore handling plant became operational in 1961. A decade later, beneficiation plant comprising washing and jigging units was developed into system. In 1981 , wet re-screening facilities were added to control undersize product. No tailing pond was provided initially with the beneficiation plant. At a later stage, in order to minimize the pollution of Kurhadi river, temporary tailing pond was constructed, followed by construction of permanent tailing pond at the same site.

The existing tailing pond, originally designed to handle 4-5 y slime disposal, was utilised to its maximum capacity. As such to increase its capacity and to keep it effective till 1990 and beyond, a proposal was forwarded, in 1984, for creating additional storage capacity for 5-6 y by increasing the height of existing tailing dam. The tailing pond was originally designed with dam's top level of 410.5m. The spillway level was kept at 406 m. To augment the capacity of tailing pond to raise the height of existing dam an idea of two stages of 5 m each was conceived. The tailing level was gradually built-up by raising the weir level of the decanting tower. Except during rains, most part of the tailing pond used to remain dry and settling of the tailing used to take place during its flow towards the decanting tower. Figure 2 shows the water and tailing slime flow diagram for the iron ore mines. In order to assess the characteristics of the effluent, samples we:re collected and analysed.

Materials and Methods

Equal volumes of samples were co llected hourly in a washed plastic container and mixed at the end of the sampling period at each of the sampling locations. Composite effluent samples were collected from

LOSSES 20 m 3/h 160 m3/h

140 m3/h

680 m3/h WATER + J1GG1NG LOSSES

·100 m /h CLARIFIER

LOSSES 80 m3/h WATER

+ 82 TONS/h {50m3/h) SLIME

( I I I I

oo I w~ I ~ffi I <~ I t:< o~ I I I TREATMENT RECYCLE PUMP I L- ..J PLANT HOUSE I t L -- -{ = ]- - 60 m 3/h _j

DISCHARGE DURING MONSOON

82 TONS { SO m3/hl SLIME

. RETURN BY GRAV!TV

/

//

/

160 m3/h

WATER PUMP HOUSE EL 1550 M

3 PUMPS EACH 320 m 3/ h 3 PUMPS EACH 80 m 3/ h

( 2 WORKING +1 SlAND 8Y)

INTERMEDIATE PUMP HOUSE EL 1400 M

3 PUMPS EACH 100 m3/ h { ·2 WORKING + 1 STAND BY )

INTAKE PUMP HOUSE EL 1240 M -- 3 PUMPS EliCH 100 m 3/ h

( 2 WORKING+ 1 STANO 3Y)

Figure 2- Water and tailing slime fl ow diagram for Barsua iron ore processing plant

GHOSE & SEN: IRON ORE TAILING POND EFFLUENT 825

nallah which contained the tailing pond decanted water once in a month round the year. Samples were preserved and brought to the laboratory for analysis. Temperature, pH and DO were measured at site . Preservation methods were limited to pH control, chemical addition, refrigeration and freezing. Samples were analysed as per methods laid down in Standard Methods9

. Fe, Mn, AI, Cu and Zn were analysed by Atomic Absorption Spectrophotometer (AAS), make- Shimadza, Model 680. Cr, Mo, Ni and Cu were measured by Induced Coupled Plasma (ICP), make-Shimadzu, Model I 003.

Results and Discussion

Effluent quality of the iron ore mine under study was determined from two locations, one from the decant pond out let, (EB I) and another from a nallah which carried the decant' pond over- flow (EB2). As can be seen from from Table 1 the results of EB I and EB2, TSS range from 50-165 mg/1 and 81-212 mg/1 respectively . Fe content varies from 10-33 mg/1 and 16.2-36.9 mg/1 respectively . Samples were collected from the feed to the tailing pond (B8) and the results are given in Table 2. It is observed that there is substantial reduction in TSS and Fe content in the

effluent as compared to the values of feed to the tailing pond ., which shows the effectiveness of tailing pond in holding the pollutants. The TDS of effluent is found to ri se, as compared to the tailing samples (B8). The rise in the value of TDS in effluent, confirms the leaching characteristics of tailings. The higher standard deviation in the case of TSS , confirms the larger variation in tailing discharge.The presence of Cr, Cu and AI reveals that effluent mostly carry the iron ore rejects, a substantial part of which is being retained in tailing pond as pollutants to the surface water bodies . From the results of the effluent sample it is observed that the effluent sample mostl y contributes the iron oxide as suspended matter. Other metals are also present as oxides along with the suspended matter. Fe and Mn content in di ssolved form was also found in higher proportion and exceeded the permiss ible limit as prescribed by Pollution Control Board. The reported max imum results of other operational tailing ponds showed Fe-3 mg/1 and Mn-0.8 mg/1 (ref. 10). Other constituents in the effluent sample were reduced to great extent, in comparison to the tailings sample. Thus it provides the efficiency of tailing pond as a water pollution control unit in tailing disposal system.

Table I - Physico- chemical char teristics of effluent of Barsua iron ore mine

Parameters Unit EB I (spillway EB2 (D/S of spillway)

Range Mean so Range Mean so pH 6.5-7.3 6.2-7.2

Temperature oc 18-32 18-32

DO mg/1 4.9-5 .9 5.22 0.3 1 4.5-5 .6 5.0 0.34

TSS 50-165 79.00 3 1.1 8 81 -212 121.75 40 .65

TDS 51-62 55.0 1 3.28 75-106 88.0 9.9

Chloride 10-22 15.00 3.44 15-26 18.04 3.38

Hardness 8- 16 11 .75 2.34 28-46 33.84 5.8

Sodium(Na) 0.6-1.2 0.82 0.18 1.0-1.7 1.26 0.25

Potassium(K) 0.3-0.6 1 0.45 0. 10 0.2-0.5 0.47 0.1 8

lron(Fe) 10-33 15.80 6.84 16.2-36.9 23 .24 6.97

Manganese(M) 0.2-0.72 0.34 0.16 0.4-0.98 0.56 0.19

Chromium(Cr) Tr.o.008 Tr-o.007

Cobalt(Co) Tr-o.008 Tr-o.007

Nicke;(Ni) Tr-o.015 Tr-o.025

Copper(Cu) 0.015-0.051 0.025 0.01 0.025-0.065 0 .. 037 0.012

Molybednum(Mo) 0.37-1.24 0.59 0.26 0.6-1.6 0.92 0.3 1

Aluminium(AI)

Zinc (Zn) 0.005-0.022 0.012 0.005 0.014-0.039 0.022 0.008

COD 8- 15 11 .42 2.02 15-36 22 6.56

826 J SCI IND RES VOL 59 OCTOBER 2000

Table 2- Physco-chemical characterisation of tailing slime

Parameters Unit 87 (Thickener over flow) B8(Tailing slime from nullah)

Range Mean

pH 5.5-6.8

Temperature oc 18-30

TSS mg/1 2.8-6.6 4.93

TDS 48-61 53 .58

Chloride 14.2-18 16.23

Hardness 15 .8-23 18.48

Sodium (Na) 061-1.45 1.09

Potassium(K) 0.28-0.75 0.57

Iron (Fe) 0.61-1.38 1.11

Manganese(Mn 0.006-0.1 5 0.011

Chromium(Cr) 0.94-2.23 1.7

Cobal t(Co) 0.04-0. 1 O.Q75

Nickle(Ni) 0.17-0.41 0.3

Copper(Cu) 0.43- 1.0 I 0.76

(Molybdenum)(Mo) 0.03-0.08 0.06

Alumi nium(A l) 0.021-0.049 0.04

Zinc(Zn) 0.26-0.61 0.46

COD 13-18.2 15 .89

Management of Effluent Water

The studies carriedout for the pollutants present in effluent from tailing pond indicate that main pollutants are TSS and iron. For proper management of water pollution due to effluent discharged from tailing ponds of iron ore mines the recycling method for effluents shou ld be adopted. From technological point of view, it is always feasibl e to provide a recycling pump station at the downstream of the spill channel/decant system after segregating the storm water flow . Depending on the effluent quality from the tailing pond and the quality of the process water needs, certain treatment facilities for removal of suspended so lids, iron or other constituents may be called for, before the recycling step. Tailing pond effluent cauld preferably be recycled without creating any pollution problem in the downstream water bodies.

Treatment Methodology

For decanted effluent from tailing pond the following unit p~ocesses for treatment may be adopted:

so Range Mean so 5.8-6.8

-17-32

1.14 50-184 124.1 46.65

4.13 44.55 47 .75 3.65

1.4 I Cl-17 . 1 14.2 1 2.22

2.29 12-19.8 15.68 2.14

0.25 1.4-5.8 3.97 1.41

0. 17 0.7-2.4 1.73 0.58

0.24 I 0.0-39.3 26.02 9.75

0.003 0.12-0.42 0.29 0.11

0.38 16.9-62.3 42.0 15.78

0.02 0.77-2 .8 1.91 0.72

0.07 3.08- 1 l.32 7.64 2.87

0.17 7.69-28.3 19.1 6.87

0.014 0.61-2.26 1.53 0.55

0.008 0.38-1.39 0.94 0.35

0.1 4.61-16.98 11 .45 4.3

l.32 18-28 21.75 3.11

• Cascade aeration (Taking advantage of the level difference available at site from the spi ll channel to the existing nallah)

• Chlorination by addition of calcium hypo­chloride soluti on.

• Sedimentation m clarifier or horizontal sett ling tanks.

• Addition of polymer flocculant followed by filtration .

• Disposal of sett led solids from sedimentation process to tailing pond.

• Disposal of filter wash to tailing pond.

The decent water from the cunnet of spillway presently is being discharged to a nall ah located on the downstream side of the dam. With the second stage construction of spi llway, about 7 m fa ll will be avai lab le up to the general ground level around the nallah. In the proposed scheme, it is envisaged to provide aeration to the decanted water by taking it through a concrete cascade channel and utili se the draft avai lab le. After aeration step the water is proposed to be taken through a feed channel to a

GHOSE & SEN: IRON ORE TAILING POND EFFLUENT 827

CALCIUM HYPO-CHLORITE

WATER

---;r--1 r:--_C.,. "'"-'"'"'" IIJI~ ~~~~ ~ TAILINv ___ / . ·--===: SOLUTION TANK

~c:~~~ DAM~"-~QND-9 .

ui'c~- 5 ~'~'~' -~'" -~'-'!~~'- ---=-------~+~-=~-. . I PRESS FILTER (OPTIONAL!

BACKWASH WATER

FEED CHANNEL SLUDG~ -=-::= =:_ W-J •

TO TAILINv POND

~---- TREATED WATER FOR DISCHARGE OR RECYCLE

TAIL1Nv POND

Figure 3 -Proposed scheme for treatment of tailing pond decanted e ffluent

clarifier. Apart of the iron will get precipitated by aeration process . In order to remove the remaining iron from dissolved state, chlorination by dosing clac ium hypochlorite solution is proposed, for which a solution making tank and dozing arrangement are to be made. Depending on the analyses report , actual precipitated iron may get removed in the cl arifier. If ca lled for pol yelectrobyte dozing may be introduced before clarification inorder to increase the settlement efficiency . However, to remove remaining fine suspended solids, it is further proposed to pass the clarified wate r through pressure filter. Sometimes, it may be necessary to inj ect polyelectrolyte before the c larified water available should be of high quality and cauld be used for process cooling or other process uses. By carrying out the bench-scale tests, it may be feasible to avoid the filtration step before the water is recyc led/di sposed off.

The s ludge removed from the underflow of clarifier and filter wash water can easily be disposed off to the tailing pond by prodding suitable pumping facility. Figure 3 shows the proposed scheme for removal of suspended solids and iron .

Quantity and Quality of Effluent After Treatment

By adopting the above menti oned treatment , it will become feas ible to meet the regul atory limits for di scharge to inl and surface water. The ta iling pond under study is receiving 130 m3/h of tailing s lime out of which dry tailings are 50 m3/h . After the clarification in tailing pond about 60 m3/h water may be recovered after decantati on. In view of thi s, proposed treatment plant capac ity may be fixed at 60 m3/h . The proposed scheme if adopted and used for recycling process water the drawal of raw water from the river can be reduced from 200 m3/h to 150 m3/h ,

without affecting the present water balance, as well as improving the quality of surface water in Kurhadi nver.

Conclusions

Provision of tailing pond for containment does not guarantee the environmental compliance due to di scharge of decanted effluent causing pollution of surface water. After the tailings are deposited in the tailing pond the mean iron content in the effluent came down to 15.8 mg/1 and 30.31 mg/1 and for suspended solids from 79.0 mg/1 and 151.61 mg/1, respectively . For proper management of tailing effluent, recycling of decanted effluent is to be adopted. Treatment for the remova l of Fe and TSS is also needed . The proposed scheme if adopted, the Fe and TSS will be removed and by recycling as the process water the raw water intake from the river can be reduced from 200 m3/h to 150 m3/h and sati sfactory water balance can be maintained .

Acknowledgement

The financi al support g iven by Steel Authority of India Ltd . Is gratefully acknowleged.

References

Sen P K & Ghose M K, Siting of Tailing Pond for Safe Di sposal of Tai lings from Iron Ore Beneficiation Plants- A Case Study. Min e Tech India , 18 (I and 2) (1997) pp 63-67.

2 Seoglund T & Hanson W, Water Balance and Tail ing Deposition Aspects of C losed System Tailing Basin. Min Congr J, ( 1979).

3 Ghose M K & Kumar Ashok, Impact on Surface Water Quality Due to the Disposal of Coal Washery Effluents and

828 J SCIIND RES VOL 59 OCTOBER 2000

Dispersion Profile of Pollutants in Damodar River, Asian Environ 1 Phillippines, 15 (I) ( 1993) pp32-40.

4 Ghose M K & Kumar Ashok, Removal of Suspended Solids from Coal Washery Effluents, Indian 1 Environ Health, 35(3) ( 1993) pp 232-234.

5 Ritcey G M, Tailing Management (Elsevier Science Publishing Company Inc., New York), 1989.

6 Kelay C, Busch R & McDonald M, Seepage £environmental Analysis of the Slime Zone of a Tailing Pond, US Bureau of Mines, RI 7939, 1974.

•

7 Jerabek F & Hartman H, Investigations of Segregation and Compressibility in Discharged Fill Slurry, Trans SME,( 1965).

8 Vick S G, Planning Design and Analysis of Tailing Dams, (John Willey & Sons, New York) 1983.

9 American Public Health Association (APHA), Standard Methods for Examination of Water and Wastewater, edited byE Arnold et al. 18'h ed. (Washington, DC) 1992.

I 0 KaleY G, Satyanarayan S, Patinker A G, Kaul S N & Rao K H, An Apprisal of Impact of Iron Ore Mining on the Surface and Ground Water Quality - A Case Study, Indian 1 Environ Protect, 15(8 1) ( 1995).