| Attributs | Valeurs |
|---|
| type
| |
| Is Part Of
| |
| Subject
| |
| Title
| - Rock−Water InteractionsControlling Zinc, Cadmium, and LeadConcentrations in Surface Watersand Sediments, U.S. Tri-StateMining District. 2. GeochemicalInterpretation
|
| has manifestation of work
| |
| related by
| |
| Author
| |
| Abstract
| - We have studied principle rock−water interactions thatcontrol trace metal concentrations in a complexgeochemicalenvironment containing multiple contaminants and multiplesolid phases by combining kinetic and thermodynamicevaluation of the water chemistry with spectroscopicanalysesof the sediments. This approach allows the number ofgeochemical reactions needed to model and predict tracemetal mobility over a range of natural settings to begreatlyconstrained. In the U.S. Tri-State Mining District(Kansas−Missouri−Oklahoma) the most important geochemicalinteractions are degassing of CO2(g)-rich waters; theshort-term uptake and release kinetics of zinc, cadmium, andlead; competition between iron oxyhydroxides andcarbonatesfor zinc, cadmium, and lead; and catalysis of sulfidedissolution by iron in near-neutral waters. In our fieldstudy,degassing of CO2(g) waters is responsible for therangeof pH measured at each site over the 1-year field study.Tracemetal release and uptake kinetics by iron oxyhydroxidesand carbonates are driven by changes in pH. Aqueousmetal concentrations and pH of pond water and streamwaterin contact with high-iron sediments suggest thatoxidation−reduction reactions involving iron accelerate sphaleritedissolution kinetics in near-neutral waters. This studyclearlyshows that zinc is preferentially partitioned intosecondaryzinc hydroxide or iron oxyhydroxide, but in the samesediments cadmium is not. Cadmium is the most mobileelement because it dissolves from sulfide and is takenup by calcite only in waters with pH > 7. Lead istakenup by carbonate or iron oxyhydroxide and is extremelyinsoluble in these near-neutral waters. To accuratelypredicttrace metal mobility in complex environments, laboratorystudies are needed to quantify competition effects amongmultiple metals for carbonate and iron oxyhydroxide phasesand to quantify reaction rates of metal release and uptakefrom sulfides and secondary phases in the presence ofdissolved iron.
|
| article type
| |
| is part of this journal
| |
