E. Mylona et al., Inhibition of acid generation from sulphidic wastes by the addition of small amounts of limestone, MINER ENG, 13(10-11), 2000, pp. 1161-1175
Limestone addition is a commonly applied technique to prevent acid generati
on from sulphidic wastes containing 1-10% S. In the present paper, the effe
ctiveness of small amounts, lower than the stoichiometric requirement, of t
his alkaline additive in inhibiting acid generation from a pyrite concentra
te material is studied. Long term laboratory column tests were conducted on
a partially oxidised pyrite concentrate, where limestone was added by thor
oughly mixing. The amount of alkaline additive ranged front 6.4 to 29% wt.
corresponding to 5-30% of the stoichiometric quantity. The performance of t
he pyrite-limestone mixtures was evaluated by monitoring the drainage quali
ty of the columns, Furthermore, a detailed geochemical characterisation of
the column solid residues was performed after a monitoring period of 270 da
ys. The effect of secondary oxidation-neutralisation products on the hydrau
lic conductivity of material was also examined. Dissolution of previously f
ormed oxidation products occurred in the control column during the monitori
ng period, resulting in the release of a significant amount of Fe, Zn, Mn,
Cd, As and SO4 and to a lesser extent Pb. However, due to the presence of s
econdary products, further oxidation of pyrite particles was delayed, The e
xperimental results slowed that homogeneous mixing of pyrite with limestone
amounting to only a fraction of the contained acidity inhibited the genera
tion of acidic drainage and significantly reduced the dissolved amount of m
etals and sulphates for a test period of 270 days. Under the alkaline condi
tions prevailing in the limestone amended columns, secondary precipitation
of ferric hydroxides and gypsum occurred. A ten-fold decrease of hydraulic
conductivity was observed for the material amended with 207 kg CaCO3/t, cor
responding to 15% of the contained acidity. (C) 2000 Elsevier Science Ltd.
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