Sorption of metal ions to unoxidized tailings

Nelson, H.
M.Sc. Thesis
M.Sc. Thesis, Dept. of Chemistry, Umeå University


One environmental problem from old mining activities, as well as today’s mining, is leakage of acidity and heavy metals from sulfide-rich tailings and waste rock dumps. The tailings is oxidized in contact with oxygen and generates acidic drainage water with high content of metals and sulfate. 90-95 % of the metals dissolved during oxidation are, however, secondarily retained in the unoxidized zone of the tailings. Sorption within the unoxidized tailings is one of several processes that control the mobilization of dissolved metals.


The objectives of this work have been to study how parameters like pH and presence of iron ions at high concentrations affect the sorption processes, and to determine the metal sorption capacity within the unoxidized tailings in impoundment 1 in Kristineberg.


Series of laboratory experiments with zinc(II), copper(II) and arsenic(III) added to the tailings show clear sorption edges where sorption increases with pH. Zinc is sorbed to the tailings at higher pH than copper and arsenic.


Experiments including trace metal ions (zinc, copper and lead) and high concentrations of iron(II) ions indicate that the uptake of these trace metals is affected by the iron. The iron is totally sorbed at pH >5 and the sorption of the trace metals is shifted towards higher pH compared with single metal systems.


The tailings’ total capacity to sorb zinc(II) and copper(II) were studied at pH 8. Much more metal ions were associated with the solids than can be explained by adsorption. Precipitation is probably one of the other processes involved.



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