Multi-element removal from road-deposited sediments using weak hydrochloric acid

Abstract

Dilute HCl is a widely applied partial digestion procedure in geo-environmental investigations. Concentrations of HCl from 0.07 to 12 M have been applied to digest solid media, either shaken at room temperature ("cold") or heated to temperatures of 80–95 °C ("hot"). From an exhaustive literature survey, 0.5 M HCl was selected as the most appropriate single leach partial digestion procedure for examining potentially contaminated road-deposited sediments (RDSs). Both cold and hot HCl treatments were examined using objective criteria to identify the leach that produced the most environmentally meaningful data. The treatments were judged according to minimal breakdown of the aluminosilicate lattice and/or liberation of refractory-associated fractions of Al, Cr, and Fe; high recoveries for suspected contaminants (Cu, Pb, and Zn); and contaminant concentrations independent of clay content, organic C content, carbonate content, and cation exchange capacity. Based on all criteria, the cold 0.5 M HCl procedure was identified as superior to the hot HCl treatment. The cold treatment showed limited removal of Al, Cr, and Fe from the residual fraction, with the hot treatment having three- to sevenfold greater removal efficiencies. This suggests significant breakdown of structural lattice and liberation of elements from fractions not generally considered environmentally important. Hot HCl removed quantitative amounts of Cu and Zn from the road sediments, indicating structural release. The greater structural breakdown associated with hot HCl is a major disadvantage for studies examining bioavailability. All data point to the superiority of a cold HCl leach for geo-environmental contaminant studies. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00254-002-0598-8