Received 30 January 2016; accepted 15 April 2016; published 18 April 2016

ABSTRACT

The rare earth elements (REE) are of great interests due to wide industrial applications. In the present work, geochemistry of REE in the contaminated pond sediment of Ambagarh Chowki, central India is described. The concentration (n = 24) of La, Ce, Pr, Nd, Eu, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th and U was ranged from 16 - 119, 41 - 163, 4.1 - 28, 16 - 99, 0.7 - 2.7, 3.2 - 18, 2.7 - 16, 0.4 - 2.3, 2.2 - 13, 0.4 - 2.4, 1.1 - 6.1, 0.2 - 0.8, 0.9 - 4.8, 0.13 - 0.70, 6 - 25 and 0.46 - 1.86 mg/kg with mean value of 42 ± 9, 89 ± 13, 9.4 ± 1.9, 34 ± 7, 1.2 ± 0.2, 6.3 ± 1.2, 5.4 ± 1.0, 0.8 ± 0.1, 4.2 ± 0.8, 0.8 ± 0.2, 2.0 ± 0.4, 0.3 ± 0.1, 1.6 ± 0.3, 0.24 ± 0.04, 11 ± 2 and 1.14 ± 0.13 mg/kg, respectively. The concentration ratio of ∑LREE/∑HREE, La/Y and Th/U are discussed. The spatial distribution and sources of the REE are described.

Keywords:

Rare Earth Element, Sediment, Geochemistry, Sources

1. Introduction

The rare earth elements (REE) including actinide have wide industrial applications in several fields i.e. nuclear energy as fuel and modifier, organic synthesis as catalyst, ceramics as coloring agents, X-ray tubes as phosphors, etc. [1] [2] . The distribution of REE in various environmental materials i.e. soil and sediments was reported [3] - [13] . Recently, the health hazards of the REE were highlighted [14] [15] . The environment of the Ambagarh Chowki block, central India is seriously contaminated with As and heavy metals [16] . In this work, the geochemistry of the REE in pond sediments of Ambagarh Chowki block, Rajnandgaon district, central India is described.

2. Materials and Methods

2.1. Study Area

Arsenic and other heavy metals are deposited in the environment of Ambagarh Chowki block, Rajnandgaon district, Chhattisgarh, India over area »3000 km⁻². The Ambagarh Chowki block falls in a tribal belt with population of ≈0.1 million. This block covers 155 villages and towns which suffering with serious health hazards due to contamination of the environment with toxic elements. In this work, 24 ponds lie in different 11 villages (locations) of Ambagarh Chowki block were selected for the investigation of the REE contamination (Figure 1).

2.2. Sampling

The composite surface sediment sample (0 - 10 cm) was collected from five points in the equal ratio from each pond as prescribed in literature [17] . For the depth profile studies, the samples at the depth profile of 0 - 10, 10 - 20 and 20 - 30 cm of the Bhadsena pond was collected.

2.3. Analysis

The samples were dried, crushed and sieved out the particles of size ≤ 1 mm. A 0.25 g of each sediment sample was digested with 8 ml aqua regia in the closed microwave vessel for 15 min. An aliquot of the extract was diluted with deionized water for the further analysis. The Thermo Fisher ICP-OES and ICP-MS (Polish Geological Institute, NRI, Central Chemical Laboratory, and Warsaw) were employed for analysis of the elements. The NCS DC 73382 CRM sediment sample was used for the quality control. The background levels of the REE reported in the upper earth crust were used for computation of the enrichment factor (E_f) by using following equation [18] .

where, X_s, Al_s, X_e and Al_e are concentrations of metal and Al in the soil and earth crust, respectively.

3. Results and Discussion

The sediment was found to be colored from light brown (LBr) to dark brown (DBr), Table 1. The pH value of the extract was ranged from 6.5 - 8.1 with mean value of 7.2 ± 0.2.

3.1. Concentration of Elements

The concentrations of 49 elements in 24 pond sediments are shown in Tables 1-4. The concentration of elements i.e. Fe, Al, Ca, Mg, K, Mn, Ti, Na, P, S, Ba, V, Zn, Cu, As, Ni, Cr, Co, Sr, Pb, Rb, Ga, Li, Be, Mo, Ag, Cd, Sn, Sb, Cs, Bi, Th, U, Sc, Y, La, Ce, Pr, Nd, Eu, Sm, Gd, Tb, Dy, Ho, Er, Tm, Tb and Lu was ranged from 25,400 - 65,900, 11,800 - 34,700, 1500 - 16,100, 1500 - 30,200, 1200 - 4500, 256 - 1660, 62 - 735, 90 - 830, 90 - 570, 50 - 790, 88 - 304, 29 - 166, 32 - 100, 28 - 89, 10 - 53, 19 - 340, 24 - 1298, 9 - 76, 10 - 69, 10 - 40, 12 - 46, 7 - 15, 5 - 18, 0.9 - 3.4,0.14 - 1.32, 0.07 - 2.36, 0.05 - 0.39, 0.8 - 2.6, 0.27 - 0.97, 0.5 - 2.2, 0.10 - 0.30, 6.1 - 25, 0.5 - 1.9, 3.0 - 25, 11 - 61, 16 - 119, 41 - 163, 4.0 - 28, 16 - 99, 0.7 - 2.7, 3.2 - 18, 2.7 - 16, 0.4 - 2.3, 2.2 - 13, 0.4 - 2.4, 1.1 - 6.1, 0.15 - 0.83, 0.9 - 4.8 and 0.13 - 0.70 mg/kg with mean value of 44842 ± 5133, 23813 ± 2819, 5133 ± 1418, 6850 ± 2581, 2708 ± 243, 759 ± 158, 254 ± 79, 355 ± 93, 268 ± 45, 285 ± 81, 196 ± 21, 84 ± 16, 63 ± 7, 52 ± 6, 22 ± 5, 75 ± 30, 177 ± 118, 30 ± 7, 26 ± 6, 23 ± 3, 26 ± 3, 11 ± 1, 12 ± 2, 1.6 ± 0.2, 0.63 ± 0.14, 0.67 ± 0.23, 0.13 ± 0.03, 1.5 ± 0.2, 0.44 ± 0.05, 1.2 ± 0.2, 0.15 ± 0.03, 11 ± 2, 1.1 ± 0.1, 11 ± 2, 20 ± 4, 42 ± 8, 42 ± 8, 89 ± 13, 9 ± 2, 34 ± 7, 1.2 ± 0.2, 6.3 ± 1.2, 5.4 ± 1.0, 0.77 ± 0.15, 4.2 ± 0.8, 0.8 ± 0.2, 2.0 ± 0.4, 0.27 ± 0.05, 1.6 ± 0.3 and 0.24 ± 0.04 mg/kg, respectively. Among them, the highest concentration of Fe was marked. They occurred in following decreasing order in the sediment: Fe < Al < Mg < Ca < K < Mn < Na < S < P < Ti < Ba < Ce < Cr < V < Ni < Zn < Cu < La < < Nd < Co < Sr » Rb < Pb < As < Y < Li < Ga » Th » Sc < Pr < Sm < Gd < Dy < Er < Yb » Be < Sn < Eu » Cs < U < Tb » Ho < Ag < Mo < Sb < Tm < Lu < Cd » Bi.

3.2. Concentration of REE

The concentration of the LREE (i.e. La, Ce, Pr, Nd, Eu and Sm) and HREE (i.e. Gd, Tb, Dy, Ho, Er, Tm, Yb

and Lu) was ranged from 82 - 431 and 8 - 46 mg/kg with mean value of 182 ± 30 and 15 ± 3 mg/kg, respectively. The ratio of LREE/HREE and Lu/Y was found to be in the range of 9 - 18 and 14 - 56 with mean value of 12 ± 1 and 27 ± 4, respectively. The concentration of REE and LREE/HREE and Lu/Y ratio were found to be higher than values reported in river sediments of the other regions of the World [3] - [11] .

The concentration of Th and U in the sediments (n = 24) was ranged from 6.1 - 25 and 0.46 - 1.86 mg/kg with mean value of 11 ± 2 and 1.14 ± 0.13 mg/kg, respectively. The Th/U ratio was ranged from 6 - 28 with mean value of 11 ± 2. The concentration of actinide elements in the studied area was found to be comparable to values reported in soil of other regions of the country [12] [13] (Figure 2).

3.4. Spatial Variations and Sources

The sediment samples were collected from 24 ponds which situated in 11 locations (i.e. villages) of Ambagarh Chowki block. The content of the REE in the pond sediments of 11 locations are shown in Figure 3. The highest content of the REE in the pond sediment of Bhadsena was observed. The REE content in sediment was found to increase as the depth profile was increased from 0 - 30 cm, may be due to geogenic origin and less binding with organic components of the sediment, Figure 4.

The correlation matrix of the REE is summarized in Table 5. All REE inclusive of Eu, Th and U are correlated well in the sediment, indicating origin from the similar sources likely to geogenic origin. They were partially correlated with elements i.e. Be, K, Rb, Cs, Mo, As, Sb, Bi, Sn, and Ag. Their negative correlations with elements i.e. Na, Mg, Ca, Ba, Sr, Al, Ga, V, Cr, Fe, Mn, Co, Ni, Cu, Zn, Cd and Pb were observed.

3.5. Enrichment

The E_f value for Sc, Y, La, Ce, Pr, Eu, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th and U in the sediment was ranged from 0.8 - 4.2, 1.5 - 9.4,1.7 - 13, 1.4 - 12, 1.7 - 13, 1.6 - 9,1.7 - 12, 1.6 - 12, 1.9 - 13, 1.6 - 11,1.6 - 11, 1.6 - 9, 1.4 - 9, 1.4 - 9, 1.4 - 8, 1.1 - 7, 1.1 - 11 and 0.4 - 3 with mean value of 2.5 ± 0.4, 4 ± 1, 6 ± 1, 5 ± 1, 5 ± 1, 4

± 1, 5 ± 1, 5 ± 1, 5 ± 1, 4 ± 1, 4 ± 1, 4 ± 1, 3 ± 1, 3 ± 1, 3 ± 1, 3 ± 1, 4 ± 1 and 1.7 ± 0.3, respectively. They were moderately enriched in the sediment. Their highest enrichments were marked in sediment of the Bhadsena village.

4. Conclusion

The REE were moderately enriched in all ponds and their enrichments were found to decrease as the mass number of the REE was increased. The concentration of all REE in the sediment was increased vertically, may be due to origin from the rock weathering. Their highest contents were marked in the sediment of Bhadsena village, Rajnandgaon, India.

Acknowledgements

We are thankful to the Alexander von Humboldt Foundation, Bonn for financial support to one of author: KSP. Our sincere thanks are also extended to the UGC, New Delhi for awarding Rajiv Gandhi Scholarship to students: BLS, KPR and SR.

Cite this paper

Bharat Lal Sahu,Keshaw Prakash Rajhans,Shobhana Ramteke,Khageshwar Singh Patel,Irena Wysocka,Irena Jaron, (2016) Geochemistry of Rare Earth Elements in Sediment of Central India. Journal of Environmental Protection,07,705-714. doi: 10.4236/jep.2016.75063

References

NOTES

^*Corresponding author.