Lithium has two stable isotopes. Natural variation in the lithium isotope ratio can be used for tracing natural and anthropogenic sources of lithium to water.
Lithium (Li) is an alkali metal which has a small ionic radius but the hydrated ionic radius is much larger and has an affinity for octahedral sites within the lattice of clay minerals; it is also involved in surface reactions of clay minerals.
Lithium has two stable isotopes. Natural variations in the lithium isotope ratio may become useful for tracing natural and anthropogenic sources of lithium to water.
Lithium is measured by inductively coupled plasma mass spectroscopy (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES). Its value as a tracer is enhanced since analytically it is relatively easy to determine.
Lithium is a geogenic element, being rare in polluted waters, and is contributed to groundwaters by time-dependent water-rock interaction and it forms an important tracer element. The enrichment in lithium by water-rock interaction is best expressed by the Li/Cl; (Li/Cl)/Cl, or Li/Na ratios. Lithium may be derived particularly from biotite and other primary minerals (or where these are present in sedimentary rocks).
It follows that in young or dilute groundwaters lithium concentrations are low and any enrichment above say 10 μg/l in stream or dilute groundwaters may indicate an anomalous origin. The Li/Cl concentration in sandstone and other non-carbonate aquifers may increase with residence time. In the East Midlands aquifer (Edmunds and Smedley, 2000) this increase is linear with radiocarbon age and may be used as a semi-quantitative residence time tracer, which may be used to extend and give confidence to age estimations beyond the radiocarbon detection limit.
Strong enrichment may be found in some granitic rocks with concentrations in the mg/l range and lithium is also enriched in many thermal waters where it has been proposed as a geothermometer.
Salinization of groundwater and origins of brines are sometimes highly complex, especially important in semi-arid area. Various minor and trace element such as (Li, B, Br) coupled with ionic ratios are used to characterize the origin of salinization.
Also the elevated mobility of lithium is thought to be related to temperature and it is found high concentration of lithium in thermal waters. So it is a good tracer for use in geochemical investigation of hydrothermal systems (Fouillac and Michard, 1981).
The concentration of lithium in water also depends on the water-rock contact time and lithium is used as an indicator of the residence time.
- Brondi, M., Dall'aglio, M.D. and Vitrano, F., 1973. Lithium as pathfinder element in the large scale hydrochemical exploration for hydrothermal systems. Geothermics, 283(142-153).
- Chan, L.H., Gieskes, J.M., You, C.F. and Edmond, J.M., 1994. Lithium Isotope Geochemistry of Sediments and Hydrothermal Fluids of the Guaymas Basin, Gulf of California. Geochimica Et Cosmochimica Acta, 58(20): 4443-4454.
- Edmunds, 1986. Lithium mobility and cycling in dilute continental waters. Pp 183-187 in Extended Abstracts of Water-Rock Interactuion (WRI-5) Symposium. Orkustofnun, Reykjavik.
- Edmunds, W.M. and Smedley, P.L., 2000. Residence time indicators in groundwater: the East Midlands Triassic sandstone aquifer. Applied Geochemistry, 15(6): 737-752.
- Fouillac, C, and Michard, G., 1981. Sodium/lithium ratio in water applied to geothermometry in geothermal reservoirs. Geothermics, 10, 55-70.
- Sanchez-Martos, F., Pulido-Bosch, A., Molina-Sanchez, L. and Vallejos-Izquierdo, A., 2002. Identification of the origin of salinization in groundwater using minor ions (Lower Andarax, Southeast Spain). Science of the Total Environment, 297(1-3): 43-58.
- General information on lithium isotopes: USGS Periodic Table - Lithium
- Sahoo, S.K., and A. Masuda, (National Institute of Radiological Sciences, Japan), Precise determination of lithium isotopic composition by thermal ionization mass spectrometry in natural samples such as seawater.