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Evaluation of sulfidic mine tailings solidified/stabilized with cement kiln dust and fly ash to control acid mine drainage

Minerals & Metallurgical Processing , 2008, Vol. 25, No. 4, pp. 185-198

Nehdi, M.; Tariq, A.


Deficient surface disposal systems of sulfidic mine waste often cause severe contamination of surface streams and groundwater reservoirs due to the oxidation of sulfide phases. The subsequent generation of leachates characterized by high acidity and elevated concentrations of toxic elements (commonly known as acid mine drainage) jeopardize the health of contiguous ecosystem. Stabilization/solidification (S/S) is recognized as a promising solution for treating such wastes. S/S processes generally mobilize alkaline and/or cementing materials/additives
that act as neutralizing and/or binding agents. In the present research, industrial byproducts, namely, cement kiln dust (CKD) and Class C fly ash (FAC) have been used as candidate materials along with the partial addition of sulfate-resistant cement (SRC) in the S/S of polymetallic sulfi dic mine tailings (MT). The effectiveness of S/S was assessed by comparing laboratory experimental values obtained from unconfined compressive strength, hydraulic conductivity and leaching propensity tests of S/S samples with regulatory standards for safe surface disposal of such wastes. Despite general regulatory compliance of compressive strength and hydraulic conductivity, some solidified/stabilized-cured matrices were found unable to provide the required immobilization of pollutants.
Solidifi ed/stabilized and 90-day cured mine tailings specimens made with composite binders containing (10%
CKD + 10% FAC), (5% SRC + 15% FAC) and (5% SRC + 5% CKD + 10% FAC) signifi cantly impaired the
solubility of all contaminants investigated and proved successful in fi xing metals within the matrix, in addition
to achieving adequate unconfi ned compressive strength and hydraulic conductivity values, thus satisfying U.S.
EPA regulations. Laboratory investigations revealed that, for polymetallic mining waste, leachate concentrations
are the most critical factor in assessing the effectiveness of S/S technology.