U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 1 of 3--Contamination From Hard-Rock Mining, Water-Resources Investigation Report 99-4018A

Partitioning of Zinc between Dissolved and Colloidal Phases in the Animas River near Silverton, Colorado

By Laurence E. Schemel, Marisa H. Cox, Briant A. Kimball, and Kenneth E. Bencala

This report is available in pdf format): schemel2.pdf 62KB

ABSTRACT

Partitioning of zinc (Zn) between dissolved and colloidal phases was studied in the upper Animas River. Most of the Zn was dissolved in the water column, but a variable fraction of the total Zn was associated with aluminum (Al)- and iron (Fe)-rich colloidal particles. Colloids were supplied to the river by tributary creeks that drain areas with natural sulfide mineral deposits and debris from abandoned mines. The fraction of the total Zn that was in the colloidal phase increased with pH in the river, indicating the possibility of adsorption by colloidal Al and Fe. The influence of pH was confirmed in laboratory experiments in which larger fractions of the total Zn were associated with the colloids when pH was increased in samples from the river. The effect of increasing pH was greatest in the sample with the highest concentration of colloidal Al and Fe. The total concentration of colloidal Al and Fe appeared to be a factor limiting the adsorption of Zn during the late summers when the samples were collected. Our results indicate adsorption of Zn would be greater downstream where the pH increases in the river and perhaps during spring when concentrations of colloidal Al and Fe are higher.