Melanterite (Fe²⁺SO₄·7H₂O) is one of the most common oxidation products of pyrite. Field observations in mine sites indicate that melanterite is associated with acidic waters. However, simple dissolution of melanterite, without oxidation of Fe2+ to Fe3+, can not generate AMD because the hydrolysis of Fe2+ is not able to significantly lower the water pH. Laboratory dissolution experiments modelled with PHREEQC have shown that trace amounts of Fe3+ contained in melanterite in the range of 0.16—0.20 wt.% are sufficient to significantly lower the pH of very dilute interacting waters as a consequence of Fe3+ hydrolysis. In the field, the rapid dissolution of Fe3+ -bearing melanterite by rain water may thus generate AMD and also provide a supply of Fe3+ for subsequent sulphide oxidation. These results should be taken into account when evaluating the impact of AMD on the environment and planning its treatment.
AMD generation from dissolution of secondary metal sulphates
FRAU, FRANCO;CIDU, ROSA;
2011-01-01
Abstract
Melanterite (Fe²⁺SO₄·7H₂O) is one of the most common oxidation products of pyrite. Field observations in mine sites indicate that melanterite is associated with acidic waters. However, simple dissolution of melanterite, without oxidation of Fe2+ to Fe3+, can not generate AMD because the hydrolysis of Fe2+ is not able to significantly lower the water pH. Laboratory dissolution experiments modelled with PHREEQC have shown that trace amounts of Fe3+ contained in melanterite in the range of 0.16—0.20 wt.% are sufficient to significantly lower the pH of very dilute interacting waters as a consequence of Fe3+ hydrolysis. In the field, the rapid dissolution of Fe3+ -bearing melanterite by rain water may thus generate AMD and also provide a supply of Fe3+ for subsequent sulphide oxidation. These results should be taken into account when evaluating the impact of AMD on the environment and planning its treatment.
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