HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hahne, H. C. H. Articles by Kroontje, W. Search for Related Content PubMed Articles by Hahne, H. C. H. Articles by Kroontje, W. Agricola Articles by Hahne, H. C. H. Articles by Kroontje, W.

Significance of pH and Chloride Concentration on Behavior of Heavy Metal Pollutants: Mercury(II), Cadmium(II), Zinc(II), and Lead(II)¹

ABSTRACT

Calculations were performed (i) to assess the degree to which Hg(II), Cd(II), Zn(II), and Pb(II) complex with hydroxyl and chloride ions and (ii) to evaluate the significance of such complexation in natural systems. Results indicate that both the hydroxy and chloride complexes may contribute to the mobilization of these heavy metal ions in the environment.

Hydrolysis of Hg(II) becomes important at pH values above 1 whereas Pb(II), Zn(II), and Cd(ll) hydrolyze above pH 5, 7, and 8, respectively. Chlorides complex with Hg(II) at chloride concentrations above 10^–9M (35 x 10^–6 ppm). HgCl₂ forms above 10^–7.5M Cl^–(1.1 x 10^–3 ppm), and HgCl₃^– and HgCl₄^2- formation occurs above 10^–2M Cl^–(350 ppm). The MCl⁺ species of Zn(II), Cd(II), and Pb(II) appear at chloride concentrations above 10^–3M (35 ppm), and MCl₂ complexes occur above 10^–2M (350 ppm Cl^–). The respective MCl₃^– and MCl₄^2- species become important above 10^–1M Cl^–(3,500 ppm).

Hydrolysis and chloride complexation of these heavy metal ions are important factors affecting the solubility of the sparingly soluble salts of these metal ions. This is most pronounced for mercuric salts.

Intrinsic solubilities of the metal-ion hydroxides allow for 160 ppm Zn(II) and 107 ppm Hg(II) to be soluble as complexed Zn(OH)₂ and Hg(OH)₂, respectively. These values are higher than calculated solubilities based on solubility products.

An example of the competition between hydroxy and chloride complexes shows that at pH 8.5 and a chloride concentration range of 350–60,000 ppm, Hg(II) and Cd(II) are mainly complexed by chlorides. Zn(II) and Pb(II), under these conditions, are predominantly in the form of hydroxy complexes.

Key Words: movement of heavy metals • hydrolysis • salt accumulation • water quality

¹ Contribution from the Agronomy Dep., Virginia Polytechnic Inst. and State Univ., Blacksburg 24061.

² Graduate Research Assistant, now Chief Professional Officer, Soils Research Institute, Pretoria, Republic of South Africa; and Professor of Agronomy, Virginia Polytechnic Inst. and State Univ.

Received for publication August 25, 1972.

This article has been cited by other articles:

				D. A. Spears An investigation of metal enrichment in Triassic Sandstones and porewaters below an effluent spreading site, West Midlands, England Quarterly Journal of Engineering Geology and Hydrogeology, May 1, 1987; 20(2): 117 - 129. [Abstract] [PDF]