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Mobility Through Soils of Certain Heavy Metals in Geothermal Brine Water¹

ABSTRACT

Geothermal energy conversion studies in agricultural areas of the Imperial Valley of southern California pose several questions with regard to potential accidental spill of brine water onto the land. Some of the geothermal brine waters (GBW) contain > 30% total dissolved solids, mainly as NaCl, CaCl₂, and KCl, as well as several heavy metals such as Zn, Pb, Cu, and Cd. An investigation was undertaken to determine the mobility of Cd(II), Cu(II), and Zn(II) present in GBW through five agricultural soils. Columns of soils were leached with GBW collected from a well near the Salton Sea in California. The concentrations of Cd(II), Cu(II), Pb(II), and Zn(II) in the effluent were compared with their original concentrations to determine amounts of adsorption or retention in the soils. Heavy metal determinations also were made on whole soils before and after treatment. An estimate of the extent of Cl^– complexation with the metals was made from thermodynamic stability constants by use of the computer program GEOCHEM. Significant quantities (50–100%) of all heavy metals studied were complexed with Cl^–. None of the soils adsorbed Cu(II) from the GBW, while Cd(II) was apparently removed from some soils. All soils adsorbed some Pb(II) and Zn(II), but after passing 10 pore volumes of solution their capacity for adsorption was negligible. A combination of mass action and Cl^– complexation most likely caused the high mobility of Cd(II), Cu(II), Pb(II), and Zn(II) in the GBW.

Key Words: cadmium • copper • lead • zinc • heavy metals • metal-chloride complexes • distribution ratio • geothermal energy

¹ Contribution of Dep. of Plant and Soil Biology, University of California, Berkeley, CA 94720.

² Professor of Soil Chemistry and Staff Research Associates, respectively.

Received for publication April 20, 1981.