Assessment Of Chromium Pollution At Baula Mines Biology Essay

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The study conducted in and around one of the chromite mine of the Baula reveals that the concentration of hexavalent chromium is found in the water samples. Hexavalent chromium have been found varying between 0.002 to 0.006 ppm in groundwater and 0.008 to 0.036 ppm in mine discharge water. The total chromium have been found varying between 0.002 to 0.007ppm in groundwater and 0.009 to 0.042 ppm in mine discharge water. The goethite rich overburden material at chromite mines is an efficient sink for the chromate anion. Leaching experiments using a saline solution, phosphate solution and tap water showed that phosphate solution release more hexavalent chromium compared to other two solution. These results can be useful in evaluating natural attenuation of fertilizer-derived pollutants in the agricultural land near chromite mines. From the mineralogy it was found that the laterite contains more goethite mineral compared to other minerals. The concentration of chromium is more in laterite than OB and soil. The impacts of chromium on the environment depend on the percentage of chromium in exchangeable fraction. The study shows that percentage of chromium is less in exchangeable fraction and more in residual fraction in baula mine. So the Bioavailability is low and toxicity is less.

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CHAPTER

INTRODUCTION

BACKGROUND

OBJECTIVE

BACKGROUND

Chromium is a member of the transition metals, in group 6. Chromium exhibits a wide range of possible oxidation states. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. From them +6 oxidation state is mobile in water and carcinogenic. In the hexavalent state, chromium exists as oxospecies such as CrO3 and CrO42- that are strongly oxidizing. In solution, hexavalent chromium exists as hydro chromate (HCrO4-), chromate (CrO42-), and dichromate (Cr2O72-) ionic species. The proportion of each ion in solution is pH dependent. In basic and neutral pH, the chromate form predominates. As the pH lowered the hydro chromate concentrate increases. At very low pH, the dichromate species predominate. Hexavalent chromium may exist in aquatic media as water soluble complex anions and may persist in water. Hexavalent chromium is a strong oxidizing agent and may react with organic matter or other reducing agents to form trivalent chromium. The trivalent chromium will eventually be precipitated as Cr2O3.XH2O. Therefore, in surface water rich in organic content, hexavalent chromium will exhibit a much shorter life time. Any hexavalent chromium in soil is expected to be reduced to trivalent chromium which is lost from soil by aerial transport through aerosol formation and surface water transport through run off (www.epa.gov/iris/toxreviews/0144tr.pdf).

There has been an increasing demand for Chromite ores in recent years. In the opencast mining processes, the chromite ore as well as waste rock material are dumped in the open ground without considering the environmental aspects. The result has been damage to the topography and leaching of chromium and other impurities to the groundwater as well as surface water bodies (R.K.Tiwary, R.Dhakate,V.Ananda Rao, V.S.Singh,2005).

OBJECTIVE

To determine the concentration of Total chromium and Hexavalent chromium in Mine water, Ground water, Laterite soil, Agricultural field soil, Overburden in Baula Mines.

CHAPTER

2

LITERATURE REVIEW

CHROMIUM CHEMISTRY

HARMFUL EFFECT OF Cr(VI)

Cr(VI) RETENTION BY MINE OVERBURDEN

LOCATION OF BAULA-NUASAHI COMPLEX

2.1 CHROMIUM CHEMISTRY

Chromium has a unique geochemical behavior in natural water systems. Under strong oxidizing conditions, chromium is present in the Cr(VI) state and persists in anionic form as chromate. Cr(III) is the most common form of naturally occurring chromium, but is largely immobile in the environment. Redox potential Eh-pH diagrams present equilibrium data and indicate the oxidation states and chemical forms of the chemical substances which exist within specified Eh and pH ranges.

Fig 2.1 Eh-pH diagram for Chromium

(Sources: http://www.epa.gov/nrmrl/pubs/625r00005/625r00005.pdf)

The above diagram implies that the boundary separating one species from another is distinct, the transformation is so clear cut. Concentration, pressure, temperature, and the absence or presence of other aqueous ions can all affect which chromium species will exist. A measure of caution must be exercised when using this diagram as site-specific conditions can significantly alter actual Eh-pH boundaries. Under reducing conditions, Cr(III) is the most thermodynamically stable oxidation state. However, Cr(VI) can remain stable for significant periods of time. Cr(III) exists in wide Eh and pH ranges. Cr(III) predominates as ionic (i.e., Cr+3) at pH values less than 3.0. At pH values above 3.5, hydrolysis of Cr(III) in a Cr(III)-water system yields trivalent chromium hydroxy species [CrOH+2, Cr(OH)2+, Cr(OH)3o, and Cr(OH)4-] is the only solid species, existing as an amorphous precipitate (http://www.epa.gov/nrmrl/pubs/625r00005/625r00005.pdf).

2.2 HARMFUL EFFECT OF Cr(VI)

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Chromium(VI) is one of the most toxic water pollutant and is comparatively more toxic than trivalent compounds. Chromium and its compounds are known to cause cancer of the lungs, nasal cavity and paranasals sinus and is suspected of causing cancer of the stomach and larynx. Hexavalent chromium is transported into cells via the sulfate transport mechanisms, taking advantage of the similarity of sulfate and chromate with respect to their structure and charge. Trivalent chromium, which is the more common variety of chromium compounds, is not transported into cells. Cr(III) is considered to be essential to mammals for the maintenance of glucose, lipid and protein metabolism. Chromium can act directly at the site of contact or be absorbed into, or through, human tissue. Chromium (VI) can act as an oxidant directly on the skin surface or it can be absorbed through the skin, especially if the skin surface is damaged. Chromium absorbed into the blood does not accumulate in any organs at significant concentrations. In metabolism studies, injected and ingested chromium was found mainly in the liver, kidneys, and blood. Breathing in high levels of Cr(VI) (>2 μg/m3) containing dust particles in the form of compounds like chromic acid or chromium tri-oxide, can cause irritation to the respiratory system. The permissible limit of Cr(VI) in drinking water is 50µg/L and total Cr is 100µg/L ( www.epa.gov/iris/toxreviews/0144tr.pdf).

Cr(VI) RETENTION BY MINE OVERBURDEN

Chromium is mined as its oxide ore chromite Feo.Cr2O3. Some of the largest opencast mines of india occur in the state of orissa. Generally the chromite ore occure in the form of discontinuous bands and lenses and confined to the altered dunite-peridotite, serpentine has been extensively weathered by atmospheric and percolating ground water. The FeO component of primary minerals like chromite, olivine and serpentine has been oxidized to group of Fe(III) like goethite , Fe2O3.H2O and maghemite, γ- Fe2O3.These are the main constituents of the thick laterite-limonite overburden over the ore body. It is apparent that under the same oxidizing condition Cr(III) in chromite is mobilised into ground water as the hexavalent CrO42- ion.

The overall process can be represented by a reaction of the type:

Chromite + 7/2 O2+ 5H2O= goethite+ 4 CrO42- + 8H+

The situation is favourable for quantitative adsorption of the Cr(VI) anion on the positively charged surface of goethite. The goethite is positively charged as the pH of water is below the ZPC (Zero Point Charge) value of goethite. At ZPC the net charge on the mineral is zero (B.C.Raymahashay,1998).

TABLE 2.2: pH values at Zero point of charge for HFO minerals

Minerals

pH at ZPC

Magnetite,Fe3O4

6.5

Hematite, Fe2O3

5 to 9

Goethite, Fe2O3.H2O

6 to 7

7.3 to 7.8

9.5

Maghemite,γ-Fe2O3

6.7

Amorphous Fe(OH)3

8.5

( Source: Sk. Md. Equeenuddin and B.C. Raymahashay,2008)

LOCATION OF BAULA-NUASAHI COMPLEX

Deposits of chromite in Boula-Nuasahi area of Kendujhar district was discovered in 1942 and mining started from 1943. The area around Nuasahi (210 17' N: 860 20' E) lies at the south eastern fringe of Baula state forest and is connected to S.E railway and N.H.5 at Bhadrak town by an all weather 45 kilometers long metal road passing through Bidyadharpur barrage and Agarpara. The important features of the area include a dam on Salandi river and a barrage at Bidydharpur. In Boula-Nuasahi sector, three mines are in active operation. Here, chromite is mostly lumpy and the wall rock is hard serpentine.Orissa Mining Corporation Limited (OMCL), a State Government undertaking is engaged in mining and processing of chromite ore in Keonjhar district of Orissa. Bangur Chromite mining lease of OMCL is located in Anandpur subdivision of Keonjhar district in Orissa. The total geological reserve of chromite ore in the lease-hold has been estimated to be 2.75 million tonnes (Mt). The mine has been in continuous operation since 1975. Rated production of shall be 0.06 Mt/y. Life of underground mine will be 28years.

CHAPTER

3

SAMPLE COLLECTION

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Generally the overburden which are excavated from mine are dump near to the mine and the overburden samples were collected from that point. The water samples were collected in a plastic bottle of 250ml and the agriculture field soil & overburden samples were collected in a lock polythene.

Precautions were taken

For water sample:

Before filling, the samples bottle were rinsed two or three times with the water being collected, unless the bottle contains a preservative or dechlorinating agent.

The bottles were filled living some space for aeration or mixing.

A record was maintained of every sample collected and to identify every bottle a level was attached to the bottles.

The sampling points were fixed by drawing a map in a notebook.

For soil & overburden sample:

The overburden and soil samples were carefully packed in lock polythenes..

For this Project I have collected samples from:

Bangur underground chromite mine (OMCL)

IMFA opencast mine

2.1 Samples from Bangur underground chromite mine(OMCL)

Overburden samples were collected from different OB dump site. There are 2 overburden sites are present in mine. From OB-1 weathered gabbro and serpentine samples and OB-2 fresh waste rocks were collected.

7 agriculture soil samples were collected from different agriculture field near to the mine.

2 wet laterite samples were collected near to the discharge water from mine.

The water samples were collected from stock water of mine, Discharge water flowing over laterite soil and direct discharge water. Ground water samples were collected from tube well in residential area near to the mine.2 samples from stock water of mine, 2 samples from discharge water flowing over laterite soil and 2 samples from direct discharge water.

2.2 Samples from IMFA opencast mine

2 Dry laterite soil samples were collected from IMFA open cast mine.

CHAPTER

4

METHODS AND MATERIALS

4.1 COLORIMETRIC METHOD

Purpose: This method measures only hexavalent chromium.

Apparatus:

Colorimetric equipment:

Spectrophometer, for use at 540nm, with alight path of 1cm or longer

Separatory funnels. 125-ml. Squibb form, with glass or TFE stopcock and stopper.

Acid washed glass ware

Reagents:

Standard chromium solution: Dissolve 2.8g of K2Cr2O7 in water and dilute to 1000ml.

Nitric acid HNO3 conc.

Sulphuric acid, H2SO4 0.2 N

Phosphoric acid, H3PO4 conc.

Diphenylcarbazide solution: Dissolve 250 mg 1,5-diphenylcarbazide in 50ml acetone.

Procedure:

100ml of solution was taken . 2ml of diphenylcarbazide solution was added into it followed by 0.25ml of H3PO4 and0.2N H2SO4. Mix and stand for 5 to 10 min. A red violet colour was developed. The absorbance of 540nm wavelength was measured by spectrophotometer.

Preparation of calibration curve:

0.1 ppm, 0.2 ppm, 0.005ppm and 0.4 ppm standard solution was prepared from 1000ppm solution. A colour was developed by above procedure. A suitable portion of each coloured solution was transfered to 1cm absorption cell and measure absorbance at 540nm. A calibration curve was constructed by plotting corrected absorbance value against concentration ( Standard Methods, 1985).

Fig 4.1 Calibration Curve

4.2 ATOMIC ABSORPTION SPECTROPHOTOMETRY METHOD

Purpose: This test method covers the determination of dissolved and total recoverable chromium in most waters and wastewaters.

Apparatus:

Atomic Absorption spectrophotometer

Chromium Light Source

Graphite Furnace

Graphite Tubes

Data Storage and Reduction Device

Reagents:

Chromium Solution, Standard (1.0 mL = 0.10 μg Cr)-Dilute 10.0 mL of chromium intermediate solution and 1mL of HNO3 (sp. gr. 1.42) to 1 L with water. This standard is used to prepare working standards at the time of the analysis.

Nitric Acid (sp gr 1.42)-Concentrated nitric acid (HNO3).

Procedure:

For total recoverable chromium, 5 mL HNO3 (sp gr 1.42) was added to each standard and sample. The samples was heated at 95°C and Cool and the sample was filtered through a suitable filter paper. A measured aliquot of sample was injected into the furnace device following the directions as provided by the particular instrument manufacturer.

Calculation:

The concentration of chromium in the sample, in milligrams per liter, was calculated using the calibration curve(Standard Methods, 1985).

4.3 X-RAY DIFFRACTION METHOD

The detailed mineralogy of samples was studied by X-ray diffraction both in bulk powders and oriented slides. The samples were scanned at 1.202θ/min under X-ray diffractometer Model ISO Debyeflex 1001 and 2002, Rich-seifert & Company (Sk.Md.Equeenuddin and B.C.Raymahashay,2008).

DESORPTION EXPERIMENT

In order to estimate the quantity of Cr(VI) can be released under various condition a saline solution NaCl-NaHCO3 was used. In this method, a saline solution of pH 8 and ionic strength 0.3 was prepared by dissolving 1.74 gm of NaCl and 0.05 g of NaHCO3 in 100ml distilled water. 1gm sample was kept in 1% suspension of a saline solution at room temperature for 1,2,3 and 5 days with periodic stirring(B.C.Raymahashay and T.praharaj,1998). Desorption of Cr(VI) was also carried out with KH2PO4 as phosphate was found be competitive for the surface sites and release various anionic pollutants. This situation is critical to evaluate the fertilizer derived pollutants. In this method , 1 gm sample was kept in 0.1M KH2PO4 solution at room temperature for 1,2,3 and 5 days with periodic stirring.Desorption of Cr(VI) was also carried out by Normal tap water.

SEQUENTIAL EXTRACTION OF CHROMIUM

Sample+ 8ml 1M MgCl2 at pH 7(Shaken for 1 h at room temp)

Fraction-1

Exchangeable

Centrifuged at 7000 rpm for 15 min

1

15 min

Fraction-5

Residual

Fraction-4

Organic

Fraction -3

Fe-Mn oxides

Fraction-2

Carbonate

Centrifuged at 7000 rpm for 15 min

Concentrated mixture of HNO3+HCl+HF at 1700c

Centrifuged at 7000 rpm for 15 min

3 ml 0.02M HNO3, 8 ml 30% H2O2(pH 2) heated for 5 h at 850c , then added 5 ml of 20% of CH3COONH4 and shaken for 30 min

Centrifuged at 7000 rpm for 15 min

20ml 0.04M NH2OH.HCl in 25% Na-acetate at pH 2(Shake for 6 h in water bath at 960c)

Centrifuged at 7000 rpm for 15 min

8 ml of 1M Na-acetate adjusted to pH 5 (Shaken for 5 h at room temp)

Figure 4.5 : Scheme of the selective sequential extraction (Tessier et al., 1979)

CHAPTER

5

RESULTS AND DISCUSSIONS

5.1 CHROMIUM IN WATER

TABLE 5.1: Dissolved chromium and pH in mine and ground water

Sample

pH

Cr(VI) (ppm)

Total Cr (ppm)

Mine Discharge water

7.7

0.011

0.013

7.6

0.014

0.015

7.9

0.036

0.042

7.8

0.008

0.009

Ground water

7.5

Nil

Nil

6.7

Nil

Nil

6.7

0.002

0.002

7.2

0.006

0.007

The above table shows the pH, Total chromium, hexavalent chromium in Mine discharge water and Ground water. The pH of Mine discharge water range between 7.6 to 7.9 which is higher than the pH of ground water whose pH range between 6.7 to 7.2. The concentration of Cr(VI) in groundwater range between 0.002 to 0.006ppm which is below than the Mine discharge water. The total chromium in mine water is range between 0.009 to 0.042 which is much higher than groundwater. The amount of Cr and Cr(VI) is below permissible limit. From the above table it is observed that in Total Cr , most of the Cr(VI) are present. This sharp decrease is apparently due to adsorption of Cr(VI) on laterite soil.

5.2 DESORPTION EXPERIMENT

In order to know the amount Cr(VI) adsorbed in laterite soil, desorption experiment was carried out.

TABLE 5.3: Desorption of Cr(VI) from laterite soil into saline, phosphate solution and water

Day

Saline Solution(ppb)

Phosphate Solution(ppb)

Tap water(ppb)

1

21

78

8

2

28

93

12

3

34

115

17

5

46

128

21

The following graph is plotted between Cr(VI) concentration in ppb and leaching period taking different solution like saline solution, phosphate solution and Tap water.

Figure No-5.3: Desorption of Cr(VI) in saline, phosphate solution and tap water at various period

From the above graph it is observed the leaching of Cr(VI) from laterite is gradually increases due to the increase of leaching period.

5.4 MINERALOGY OF LATERITE SOIL

Figure No-5.4 : XRD pattern of laterite sample.

From the above pattern it is observed that the intensity of goethite is more in laterite sample as compared to other mineral.

.

Figure No-5.5: Concentration of Cr

From the above graph it is observed that the concentration of chromium in laterite is much higher than OB and Soil. This is due to the presence of goethite in laterite. The concentration of chromium is much higher than the crustal abundance (126 ppm).

5.6 SEQUENTIAL EXTRACTION OF CHROMIUM

TABLE 5.6: % leached in different fractions

% leached

Sample

Exch

Carb

Fe-Mn

Org

Res

Laterite

0.03

32.17

0.13

0.13

54.65

OB

0.15

0.11

23.09

0.14

58.11

Soil

0.09

0.06

24.55

0.08

66.03

Figure: 5.6

The metals mainly occur in soil and sediments through five major mechanisms, exchangeable, with organic matter, with carbonates, with Fe-Mn, and residual. Metals in exchangeable fraction considered to be most mobile and readily available for biological uptake in environment. The organic fraction represents metals held by complexation, adsorption, and chelation process. Under oxidising condition it release metals bound to those materials. Metals bound to Fe-Mn oxides and hydroxides fraction are unstable under reducing conditions. Metals bound to carbonates are sensitive to pH changes with the lowering of pH being associated with the release of metal cations. The residual fraction contains naturally occurring minerals which may hold trace metals within their crystal lattices and unlikely to be released from the soil and sediments thus it is considered to be chemically most stable and immobilized. Thus the bioavailability is low and toxicity is less. From the above experiment it is observed that the Concentration of Cr is more in residual fraction as compared to other fraction. So the chromium toxicity is less in Baula mines.

CHAPTER

6

CONCLUSIONS

The WHO limit for Cr in drinking water is 50µg/L. On the other hand, preliminary sampling and analysis during the present work showed that the hexavalent chromium was not detectable and total chromium ranged between 0.002 to 0.007ppm in tube wells in baula. This sharp decrease is apparently due to the retention of CrO43-anion on the positively charged surface of fine grained goethite during percolation of ground water through the lateritic cover soil. From XRD pattern it is concluded that the goethite mineral is more in laterite soil compared to other minerals. So the Chromium retention is more in laterite than OB and soil. From Desorption Experiment it is concluded that phosphate release more Cr(VI) than saline solution. The concentration of Cr(VI) decreased progressively with each subsequent desorption and P concentration in soil suspension increased with increasing number of desorptions in the presence of Na+, which clearly indicates the competitive nature of the ion for adsorbed sites.