The Use Of Limestone, Lime And MnO2 In The
Removal Of Soluble Manganese From
Acid Mine Drainage
Author(s)
A. Aguiar, G. Xavier & A. Ladeira
Abstract
Acid mine drainage (AMD) is one of the main environmental issues faced by the
mining industry. The acid mine water generally contains metals above the
permissible discharging levels. Manganese is particularly present in this effluent
and its removal is notoriously difficult due to its high solubility over a wide
range of pH. While most of the metals precipitate at a pH below neutrality, the
pH necessary for manganese precipitation is very high, above 10. Most systems
that effectively remove this element from mine waters use the oxidation of Mn
(II) followed by precipitation at an elevated pH. Precipitation consumes a great
amount of lime, which implies high operational cost. Besides, the process
generates a large amount of sludge containing metals which have to be disposed
of. The objective of this study is to optimize the removal of manganese by using
a laboratory prepared acid solution and an acid effluent from Poços de Caldas
uranium mine (Brazil), in order to achieve the Mn permitted level for
discharging (<1mg/L) and to reduce the amount of sludge generated. The
precipitation process has been studied using lime, limestone and a nonconventional
catalyst/adsorbent (MnO2 residue). The results obtained showed
that both lime and limestone are effective in the removal of Mn in a pH higher
than 10. However, there is a slight difference between the two reagents and lime
shows a better performance. The volume of precipitate generated by the addition
of lime was 50% smaller than that obtained when limestone was used. The use of
the non-conventional material made the removal of almost 100% of the Mn
possible as the concentration of manganese was reduced from 140mg/L to
<1mg/L at a pH near neutrality (6.8 to 7.2). The final effluent complies with the
recommended value for manganese discharge.
Keywords: manganese, acid mine drainage, precipitation, manganese oxide.
Keywords
manganese, acid mine drainage, precipitation, manganese oxide
Related Book
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