XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3537
containing bioavailable arsenic, copper, and lead, extend to
diseases that cause damage to the brain, lungs, kidney, liver,
and other vital organs (Jaishankar et al. 2014). Thus, much
research has been conducted on preventing or mitigating
ARD. Prevention focuses on preventing conditions that
promote ARD from arising, and involve techniques such
as pH control via waste segregation and alkaline additives
(Bäckström et al. 2011), sulfide removal and isolation via
conditioning of mine wastes (Ait-Khouia et al. 2021), bac-
terial control via bactericides (Zhang and Wang 2017), and
limiting or preventing oxidant ingress via encapsulation,
water covers, and co-disposal (Kuyucak 2002 Kotsiopoulos
and Harrison 2017).
Co-disposal shows promise as a suitable approach for
ARD prevention (Kotsiopoulos and Harrison 2015). It
involves the blending of acid-producing mine wastes with
a neutralizing or acid-consuming material. Co-disposal has
shown significant ARD prevention potential in a range
of mine wastes (Demers et al. 2008), particularly for coal
mine waste (Kotsiopoulos and Harrison 2017 Mjonono
et al. 2019 Qureshi et al. 2021). Additionally, the packing
configuration of the co-disposed material may yield ben-
efits in terms of limiting the exposure of the mine waste to
aqueous and gaseous oxidants. In a previous study, we inte-
grated microbially-induced calcite precipitation (MICP)
with co-disposal, which used calcite generated from bacte-
ria to improve the physical and chemical properties of the
co-disposal system. Using the hybrid MICP-co-disposal
method, calcite was successfully formed in all coal bioreac-
tors packed in the blended and layered configuration using
acid generating coal waste rock and low sulphur fine coal
waste tailings however, the blended configuration showed
a higher calcite content in the lower half of bioreactors
compared to the layered (Hajee et al. 2023). Consequently,
the MICP protocol was once again used to generate calcite
in the blended co-disposed coal bioreactors, to establish the
efficacy of the application in mitigating ARD. The blended
columns were subjected to aggressive acidic conditions for
two 90-day periods with continuous monitoring to deter-
mine the performance of this hybrid system.
MATERIALS AND METHODS
Coal Sample Characterization
The coal waste rock (WR) and coal fine waste (FW) used in
this study was obtained from coal mines in Mpumalanga,
South Africa. The classification of the coal waste using the
acid base accounting (ABA) tests as outlined by Skousen
(Skousen et al. 2002), showed that the WR was potentially
acid forming while the FW and the blended configuration
of 3 parts WR to 2 parts FW (3WR:2FW) were classified as
non-acid forming (Table 1, Mjonono et al. 2019).
Bioreactor Setup
Three 60-mL syringes were packed in the 3:2 WR:FW
blended packing configuration where the WR and FW
were mixed and incrementally added into the bioreactor so
as to avoid segregation (Figure 1).
Table 1. Acid and base accounting results for the waste rock (WR), fine waste (FW), and blends of the two materials
Sample
Acid Neutralising Capacity,
KgH
2 SO
4 /Tonnes Nett Acid Producing Potential
ARD
Classification Sulfur, %
WR 29,51 10,88 PAF 1,32
FW 56,55 -41,21 NAF 0,50
3WR:2FW 32,04 -2,28 NAF 0,97
Source: Mjonono et al. 2010
Figure 1. Schematic of the blended bioreactor packing
configuration
containing bioavailable arsenic, copper, and lead, extend to
diseases that cause damage to the brain, lungs, kidney, liver,
and other vital organs (Jaishankar et al. 2014). Thus, much
research has been conducted on preventing or mitigating
ARD. Prevention focuses on preventing conditions that
promote ARD from arising, and involve techniques such
as pH control via waste segregation and alkaline additives
(Bäckström et al. 2011), sulfide removal and isolation via
conditioning of mine wastes (Ait-Khouia et al. 2021), bac-
terial control via bactericides (Zhang and Wang 2017), and
limiting or preventing oxidant ingress via encapsulation,
water covers, and co-disposal (Kuyucak 2002 Kotsiopoulos
and Harrison 2017).
Co-disposal shows promise as a suitable approach for
ARD prevention (Kotsiopoulos and Harrison 2015). It
involves the blending of acid-producing mine wastes with
a neutralizing or acid-consuming material. Co-disposal has
shown significant ARD prevention potential in a range
of mine wastes (Demers et al. 2008), particularly for coal
mine waste (Kotsiopoulos and Harrison 2017 Mjonono
et al. 2019 Qureshi et al. 2021). Additionally, the packing
configuration of the co-disposed material may yield ben-
efits in terms of limiting the exposure of the mine waste to
aqueous and gaseous oxidants. In a previous study, we inte-
grated microbially-induced calcite precipitation (MICP)
with co-disposal, which used calcite generated from bacte-
ria to improve the physical and chemical properties of the
co-disposal system. Using the hybrid MICP-co-disposal
method, calcite was successfully formed in all coal bioreac-
tors packed in the blended and layered configuration using
acid generating coal waste rock and low sulphur fine coal
waste tailings however, the blended configuration showed
a higher calcite content in the lower half of bioreactors
compared to the layered (Hajee et al. 2023). Consequently,
the MICP protocol was once again used to generate calcite
in the blended co-disposed coal bioreactors, to establish the
efficacy of the application in mitigating ARD. The blended
columns were subjected to aggressive acidic conditions for
two 90-day periods with continuous monitoring to deter-
mine the performance of this hybrid system.
MATERIALS AND METHODS
Coal Sample Characterization
The coal waste rock (WR) and coal fine waste (FW) used in
this study was obtained from coal mines in Mpumalanga,
South Africa. The classification of the coal waste using the
acid base accounting (ABA) tests as outlined by Skousen
(Skousen et al. 2002), showed that the WR was potentially
acid forming while the FW and the blended configuration
of 3 parts WR to 2 parts FW (3WR:2FW) were classified as
non-acid forming (Table 1, Mjonono et al. 2019).
Bioreactor Setup
Three 60-mL syringes were packed in the 3:2 WR:FW
blended packing configuration where the WR and FW
were mixed and incrementally added into the bioreactor so
as to avoid segregation (Figure 1).
Table 1. Acid and base accounting results for the waste rock (WR), fine waste (FW), and blends of the two materials
Sample
Acid Neutralising Capacity,
KgH
2 SO
4 /Tonnes Nett Acid Producing Potential
ARD
Classification Sulfur, %
WR 29,51 10,88 PAF 1,32
FW 56,55 -41,21 NAF 0,50
3WR:2FW 32,04 -2,28 NAF 0,97
Source: Mjonono et al. 2010
Figure 1. Schematic of the blended bioreactor packing
configuration