| dc.description.abstract | In many cases, it may be possible to recover value (e.g. metals, land) from legacy mine
wastes and tailings when applying leaching-based remediation such as dump/heap leaching or
in-vessel soil washing. However, if the lixiviant used has the potential to cause environmental
damage upon leakage, then this approach will have limited practicability due to actual or perceived
risk. This study focused on comparing the efficacy of organic acids, namely methanesulfonic
(CH3SO3H) and citric (C6H8O7) acid, with mineral acids, namely sulfuric (H2SO4) and hydrochloric
(HCl) acid, for the dissolution of Cu and As from mine tailings. The advantage of the former acid
type is the fact that its conjungate base is readily biodegradable which should thereby limit the
environmental impact of accidental spill/leakage (particularly in non-carbonate terrain) and might
also be directly useful in capture/recovery systems coupled with percolation leaching (e.g., as an
electron donor in sulphate-reducing bioreactors). The operational factors acid concentration,
leaching time, mixing intensity and solid–liquid ratio, were tested in order to determine the
optimum conditions for metal dissolution. HCl, H2SO4, and CH3SO3H typically exhibited a
relatively similar leaching ability for As despite their different pKa values, with dissolutions of 58%,
56%, 55%, and 44% recorded for H2SO4, HCl, CH3SO3H, and C6H8O7, respectively, after 48 h when
using 1 M concentrations and a 10:1 L:S ratio. For the same conditions, H2SO4 was generally the most
effective acid type for Cu removal with 38% compared to 32%, 29% and 22% for HCl, CH3SO3H and
C6H8O7. As such, CH3SO3H and C6H8O7 demonstrated similar performances to strong mineral acids
and, as such, hold great promise as environmentally compatible alternatives to conventional
mineral acids for metal recovery from ores and waste. | en_GB |
