Analysis of chemical species for trace metals in near-shore sediment by sequential leaching method

Abstract

Sediments samples from the Gulf of Thailand collected during March-April 1985 were analyzed for geological, mineralogical and geochemical properties. A representative from each group of sediments was chosen. The sequential extraction methods were investigated and the developed method was tested with the representatives of these groups. It was found that both type and strength of extractants were very important. The strength of the extractants must be strong enough to liberate metals from sediments into the solution. However, the ratio of sediment : extractant must be optimized. The sequence and concentration of extractants found from this study to be suitable and efficient for the Gulf sediments are (1) exchangeable, carbonate and sorbed fraction : NaOAc (1.0 M) + HOAc, pH 5.0; (2) oxyhydroxides fraction : NH2OH∙HCl (1.0 M) + Na-citrate (0.175 M), pH 5.0; (3) organic bound fraction : acidified H2O2; pH 2.0; and (4) residual fraction : HF-HNO3-HClO4 , respectively. The optimum sediment : extractant ratio is 1 : 20. Cd, Cr and Zn are distributed among the non-residual fractions as follows : Cd exchangeable, carbonate and sorbed > oxyhydroxides ≥ organic bound Cr organic bound > exchangeable, carbonated and sorbed ≥ oxyhydroxides Zn organic bound > oxyhydroxides > exchangeable, carbonate and sorbed