3538 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
MICP-Co-Disposal Cementation
Formation of the hybrid MICP-co-disposed waste frac-
tions were prepared according to the protocol previously
described (Hajee et al. 2023). In summary, the approach
included propagating Sporosarcina pasteurii in ATCC ®1376
ammonia-yeast medium consisting of 20 g/L yeast extract,
10 g/L ammonium sulphate, and 0.13 M pH 9 Tris buffer
until a cell density of 1 × 109 cells/mL was obtained. This
was used to inoculate the bioreactors for 24 h. Thereafter,
a fresh batch of cementation solution (pH 8) comprised
of 1 M urea, 0.5 M CaCl2, and 3% ATCC ®1376 media
was thereafter prepared daily and used to irrigate the co-dis-
posed bioreactors to initiate the microbially-induced calcite
presentation according to the mechanisms presented in the
following equations (Castro-Alonso et al. 2019):
CO(NH2)2 +H2 → NH2COOH +NH3 (1)
NH2COOH +H2O→NH3 +H2CO3 (2)
H2CO3 ↔HCO3– +H+ (3)
NH3 +2H2O → 2NH4++ 2OH– (4)
HCO3–+ H+ +2NH4+ +2OH →
CO32– +2NH4+ +2H2O (5)
Ca2+ +Cell → Cell−Ca2+ (6)
Cell−Ca2+ +CO32– → Cell−CaCO
3 (7)
Bioreactor Monitoring and Effluent Analyses
The three 60 mL bioreactors containing the blended con-
figuration of WR and FW at a ratio of 3:2 were placed
in bench-scale incubator. The first bioreactor was inocu-
lated via irrigation, where the S. Pasteurii allowed to dis-
perse through the bioreactor over a period of 24 hours
(IRR-BLND). The second bioreactor was inoculated via
agglomeration, where the coal waste was agglomerated
with the S. Pasteurii culture, mixed, and then packed into
the bioreactor (AGG-BLND). The third bioreactor was
not inoculated (UNINOC-BLND). Following a 24-hour
period of inoculation and acclimatization, the bioreactors
were irrigated with 20 mL of cementing solution daily
for 60 days. The daily effluent was analyzed in terms of
volume, pH, and redox potential. Additionally, the Fe2+,
Fe3+, and total iron concentration was determined using
the 1,10-phenanthroline assay (American Public Health
Association 1976). Finally, the cell concentration was
determined using a Helber Cell Counting Chamber with
a Leica DM500 compound microscope at 100× magnifica-
tion (Leica Microsystems, Switzerland).
Synthetic Acid Rain Experiment
Bioreactor Setup
After the 60-day cementing period, any irrigant in the head
space of the bioreactors was removed and the bioreactors
were left to air dry for a further 60 days. An additional bio-
reactor was then packed (CONTROL-BLND). This biore-
actor did not undergo the cementation process and served
as the negative control to the ARD prevention test.
Synthetic Acid Rain
A synthetic acid rain (SAR) solution was prepared using
a mixture of HNO3 and H2SO4 (1:3), since SO42− and
NO3− are the major components that form acid rain due to
SO2 and NOx emissions from fossil fuels (Du et al. 2020),
and adjusted to pH 4,5 using deionized water. A pH of 4,5
was selected as it is the pH of acid rain in the Mpumalanga
region where the coal waste samples were obtained.
Bioreactor Monitoring and Effluent Analyses
For the ARD prevention tests where the robustness of the
MICP co-disposal strategy relative to the negative control
was evaluated, the bioreactors were irrigated weekly with
20 mL of SAR for a period of 90 days. The same efflu-
ent analyses were conducted as in the cementing period
to determine the discharged volume, pH, redox potential,
Fe2+, Fe3+, total iron concentration, and cell concentration.
In the case of bioreactors where no effluent was observed
due to restricted flow effected by MICP, the irrigant present
in the head space was removed and the pH was measured.
RESULTS &DISCUSSION
MICP-Co-Disposal Cementation
The three bioreactors used at this stage of the experiment
were the bioreactor inoculated with S. Pasteurii via irriga-
tion (IRR-BLND), agglomeration (AGG-BLND), and the
control bioreactor that was not inoculated (UNINOC-
BLND). The purpose of the cementation phase was to
generate calcite in the co-disposed reactors and assess the
differences observed between the inoculation methods,
prior to exposing them to synthetic acid rain.
Effluent Flow and pH During Cementation
Table 2 shows the sealing day and average pH obtained
from the bioreactors after the 60-day cementing period.
The bioreactors were thought to be sealed due to cal-
cite formation via MICP. As can be seen in Table 1, the
inoculated IRR-BLND and AGG-BLND displayed similar
sealing times, whereas the uninoculated UNIOC-BLND
did not seal at all, which supports the hypothesis that the
MICP-Co-Disposal Cementation
Formation of the hybrid MICP-co-disposed waste frac-
tions were prepared according to the protocol previously
described (Hajee et al. 2023). In summary, the approach
included propagating Sporosarcina pasteurii in ATCC ®1376
ammonia-yeast medium consisting of 20 g/L yeast extract,
10 g/L ammonium sulphate, and 0.13 M pH 9 Tris buffer
until a cell density of 1 × 109 cells/mL was obtained. This
was used to inoculate the bioreactors for 24 h. Thereafter,
a fresh batch of cementation solution (pH 8) comprised
of 1 M urea, 0.5 M CaCl2, and 3% ATCC ®1376 media
was thereafter prepared daily and used to irrigate the co-dis-
posed bioreactors to initiate the microbially-induced calcite
presentation according to the mechanisms presented in the
following equations (Castro-Alonso et al. 2019):
CO(NH2)2 +H2 → NH2COOH +NH3 (1)
NH2COOH +H2O→NH3 +H2CO3 (2)
H2CO3 ↔HCO3– +H+ (3)
NH3 +2H2O → 2NH4++ 2OH– (4)
HCO3–+ H+ +2NH4+ +2OH →
CO32– +2NH4+ +2H2O (5)
Ca2+ +Cell → Cell−Ca2+ (6)
Cell−Ca2+ +CO32– → Cell−CaCO
3 (7)
Bioreactor Monitoring and Effluent Analyses
The three 60 mL bioreactors containing the blended con-
figuration of WR and FW at a ratio of 3:2 were placed
in bench-scale incubator. The first bioreactor was inocu-
lated via irrigation, where the S. Pasteurii allowed to dis-
perse through the bioreactor over a period of 24 hours
(IRR-BLND). The second bioreactor was inoculated via
agglomeration, where the coal waste was agglomerated
with the S. Pasteurii culture, mixed, and then packed into
the bioreactor (AGG-BLND). The third bioreactor was
not inoculated (UNINOC-BLND). Following a 24-hour
period of inoculation and acclimatization, the bioreactors
were irrigated with 20 mL of cementing solution daily
for 60 days. The daily effluent was analyzed in terms of
volume, pH, and redox potential. Additionally, the Fe2+,
Fe3+, and total iron concentration was determined using
the 1,10-phenanthroline assay (American Public Health
Association 1976). Finally, the cell concentration was
determined using a Helber Cell Counting Chamber with
a Leica DM500 compound microscope at 100× magnifica-
tion (Leica Microsystems, Switzerland).
Synthetic Acid Rain Experiment
Bioreactor Setup
After the 60-day cementing period, any irrigant in the head
space of the bioreactors was removed and the bioreactors
were left to air dry for a further 60 days. An additional bio-
reactor was then packed (CONTROL-BLND). This biore-
actor did not undergo the cementation process and served
as the negative control to the ARD prevention test.
Synthetic Acid Rain
A synthetic acid rain (SAR) solution was prepared using
a mixture of HNO3 and H2SO4 (1:3), since SO42− and
NO3− are the major components that form acid rain due to
SO2 and NOx emissions from fossil fuels (Du et al. 2020),
and adjusted to pH 4,5 using deionized water. A pH of 4,5
was selected as it is the pH of acid rain in the Mpumalanga
region where the coal waste samples were obtained.
Bioreactor Monitoring and Effluent Analyses
For the ARD prevention tests where the robustness of the
MICP co-disposal strategy relative to the negative control
was evaluated, the bioreactors were irrigated weekly with
20 mL of SAR for a period of 90 days. The same efflu-
ent analyses were conducted as in the cementing period
to determine the discharged volume, pH, redox potential,
Fe2+, Fe3+, total iron concentration, and cell concentration.
In the case of bioreactors where no effluent was observed
due to restricted flow effected by MICP, the irrigant present
in the head space was removed and the pH was measured.
RESULTS &DISCUSSION
MICP-Co-Disposal Cementation
The three bioreactors used at this stage of the experiment
were the bioreactor inoculated with S. Pasteurii via irriga-
tion (IRR-BLND), agglomeration (AGG-BLND), and the
control bioreactor that was not inoculated (UNINOC-
BLND). The purpose of the cementation phase was to
generate calcite in the co-disposed reactors and assess the
differences observed between the inoculation methods,
prior to exposing them to synthetic acid rain.
Effluent Flow and pH During Cementation
Table 2 shows the sealing day and average pH obtained
from the bioreactors after the 60-day cementing period.
The bioreactors were thought to be sealed due to cal-
cite formation via MICP. As can be seen in Table 1, the
inoculated IRR-BLND and AGG-BLND displayed similar
sealing times, whereas the uninoculated UNIOC-BLND
did not seal at all, which supports the hypothesis that the