Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.12, pp.1189-1196, 2011 Printed in the USA. All rights reserved
Phosphorus Degradation Capability of Aspergillus terreus on Nigeria’s
Agbaja Iron Ore
C.N. Anyakwo
and O.W. Obot
Department of Metallurgical and Materials Engineering, Federal University of Technology,
Owerri, Nigeria. Email:
Department of Mechanical Engineering, Faculty of Engineering, University of Uyo,
Nigeria. Email:
A microbial fungus - Aspergillus terreus was used to degrade phosphorus in Nigeria’s Agbaja
iron ore in the laboratory. The ore was first crushed to very tiny particles, screened using
Shital test kits and 1.00/0.50mm, 0.50/0.25mm and 0.25/0.125mm particle size fractions were
selected for the experiment. The microbes, obtained from the nascent remains on the ore
environment, were cultured, used to inoculate 1g of sterile ore samples in 250ml conical
flasks containing 100ml of equally sterile malt extract broth media and left to stand. At
weekly interval, the samples were removed, treated through series of chemical reactions and
ammonium phospho-molybdate precipitate was obtained. This was back-titrated with 0.1 N-
HCl to determine the amount of phosphorus left in samples and consequently, the amount
removed. Findings reveal that A. terreus is capable of degrading the ore samples. pH
monitoring reveals that the P degradation process proceeded in a culture media of increasing
acidity. It is recommended to further study the chemistry of the mixture of culture media, ore
samples and microbes to find parameters that favour the degradation process.
Key words: Ore, microbes, screening, broth, degradation, accumulation, inoculation
The Nigeria’s Agbaja iron ore reserve analyzed 47.5%Fe [1]. It remains the country’s largest
reserve [2] but had long been abandoned due to the fact of very high phosphorus content
variously estimated by researchers as 0.76 – 2.13% [1, 2, 3]. The mineralogy of Agbaja iron
ore revealed abundant goethite with minute magnetite. Hematite, pyrite, siderite and chlorite
were also identified [4, 5]. Any successful degradation of phosphorus in the ore to a
metallurgical acceptable level of 0.03 - 0.02% [6] for high quality steels, will have the
potential of transforming the national economy into a boom with quite substantial multiplier
effects in the areas of job creation, wealth creation generally and much specifically in the
downstream sector of iron and steel industry where the global demand for highest quality
products cannot be compromised.
1190 C.N. Anyakwo
and O.W. Obot Vol.10, No.12
Phosphorus is a deleterious inclusion in steel that is responsible for steel brittleness causing it
to fracture and snap at very low stress values, also associated with phosphorus are the
problems of strong primary segregation during solidification of castings and the formation of
high phosphorus brittle streaks between metal grains thereby impeding plastic deformation
[6]. A flurry of research activities into the removal of phosphorus from the Nigeria’s Agbaja
iron ore commenced in the eighties. Researchers predominantly applied the conventional
froth flotation technique for the removal of phosphorus but failed because the phosphorus is
not associated with the gangue but is in bonding with the iron [3, 7, 8]. The effort of
researchers in the use of microbes in mineral processing with its promises of ecologically
friendlier and cleaner environment is widely reported in recent time. For example, using the
bacterium Burkholderia caribensis isolated from a Brazilian high-phosphorus iron ore,
Delvasto et al [9] were able to mobilize between 5-20% of the phosphorus originally
contained in the ore in 21 days of treatment in shake-flask cultures. Similarly in another
work, Aspergillus niger also isolated from the same Brazilian high-phosphorus ore was
employed to remove phosphorus from the same ore and again in 21 days between 13.8-33.2%
was achieved [10]. In the beneficiation of iron ore slime Aspergillus niger and Bacillus
circulans were able to remove alumina with B. circulans and A. niger showing 39 and 38
percents, respectively of alumina removal after 6 and 15 days, respectively of in situ leaching
at 10% pulp density. Also a culture filtrate leaching with A. niger removed 20% alumina at
2% pulp density with 13 day old culture filtrate. B. circulans was more efficient than A. niger
for selective removal of alumina [11]. Earlier on A. niger isolated from Nigeria’s Agbaja
iron ore was used to mobilize phosphorus from the same ore and in 49 days of leaching, 81%,
63% and 68% efficiencies for Mesh 5, Mesh 100 and Mesh 250 grain sizes, respectively were
achieved [12]. In this present research, Aspergillus terreus – a microbial fungus was
mobilized to degrade phosphorus in Nigeria’s Agbaja iron ore for 10 weeks. During this
period the pH of the broth media and the microbial population were monitored on weekly
The iron ore was collected from Agbaja, near Lokoja in Kogi State of Nigeria. Standard glass
wares, heavy equipment, chemicals and disposables used in the degradation of phosphorus
were sourced locally.
1kg of the iron ore was crushed to tiny particles and then screened using Shital Test sieves to
obtain 1.00/0.50mm, 0.50/0.25mm and 0.25/0.125mm particle size fractions.
10 g of each of the iron ore particle size fractions was weighed using Adventurer-AR3130
(with readability 0.001g), placed in 90 ml of sterile water in 250 ml conical flask and then
serially diluted to 10
. Using a pipette, 1 ml from each final dilution was taken to seed 10
sterile Petri dishes and about 20 ml of mineral oil medium at 45
C was added to each seeded
Petri dish, swirled and allowed to stand for 14 days. The growth of colony of microbes was
observed and later sub-cultured in suitable media and then identified as Aspergillus terreus
using the standard manual for fungal identification [13]. These microbes were preserved for
subsequent use in the experiment.
Malt extract broth (MEB) powder was mixed with distilled water in accordance with standard
procedure. 100ml of this was dispensed into 250ml conical flasks. The conical flasks were
sterilized using autoclave at 121
C at 10 psi for 15 minutes. On cooling, 1g of the already
sterilized set of samples was accurately weighed and mixed with each of the 100ml MEB
Vol.10, No.12 Phosphorus Degradation Capability 1191
medium earlier dispensed into the 250ml flasks. A loopful of the broth culture was used to
inoculate each of the flasks aseptically. 2 conical flasks were not inoculated with the test
organisms, and they served as the control.
Finally, a batch of 3 conical flasks representing each of the 3 particle size fractions was
removed for phosphorus analysis weekly. The pH and cells count of the microbes were noted
on weekly basis as well. The samples were treated through series of standard chemical
reactions [14] to obtain ammonium phospho-molybdate precipitate which was back-titrated
with 0.1 N-HCl to determine the amount of phosphorus left in samples and consequently, the
amount removed. The data obtained from above procedure were organized and presented in
Figures 1 – 5.
The result of P degradation activities by A. terreus in MEB medium of Nigeria’s Abaja iron
ore 1.00/0.50mm, 0.50/0.25mm and 0.25/0.125mm in the course of 10 weeks is presented in
Figure 1. The above curve presents a progressive P degradation process from Week 1 to
Week 7 and thereafter the process stagnated from Weeks 7 to 10. In all cases the initial
phosphorus content for all the particle size fractions was 0.89 wt. %. The minimum
phosphorus concentration attained for the particle size fractions of 1.00/0.50mm,
0.50/0.25mm and 0.25/0.125mm used for the experiments are respectively 0.362 wt. %, 0.335
wt. % and 0.406 wt. % at the end of 10 weeks experimental period. As the result shows, the
best degradation took place in 0.50/0.25mm particle size fraction.
1192 C.N. Anyakwo
and O.W. Obot Vol.10, No.12
Figure 2 presents the pH changes during the process of P degradation by A. terreus for 10
weeks across the three particle size fractions. It is observed that the longer the P degradation
duration the more acidic the broth culture in which A. terreus accumulated phosphorus and
other metabolic wastes became. This observation is in consonance with the observation made
by Delvasto et al, 2007 when they dephosphorized a Brazilian iron ore using acidophilic
Aspergillus niger. The reducing pH however, seems to be an advantage as it facilitates the
microbial ability to continuously solublize the ore samples by advancing the leaching frontiers
inwards from the ore periphery. Figure 2 shows that the initial recorded pH values 4.76, 4.75
and 4.76, respectively for the substrates in which A. terreus was steadily degrading P in the
iron ore, which were taken less than an hour after inoculation, quickly reduced to 3.51, 3.53
and 3.52, respectively at the end of Week 1. This observed tendency continued till the end of
Week 10 when the corresponding pH readings recorded 2.94, 2.40 and 2.92, respectively for
the 3 particle size fractions.
Figure 3 presents the growth profile of A. terreus from Week 1 to Week 10. According to this
figure, it is observed that the longer the P degradation duration the lesser the cells population
became in the cultures. It is observed that after the exponential growth period, Weeks 3 - 5,
when the average cells population across the three particle size fractions was 2.241 – 1.069 g
dry weight, the biomass weight gradually dropped to near stagnation from Weeks 8 – 10 when
the average cells was 0.616 – 0.515 g dry weight. It is very probable that the drop in cells
population of the microbes is a direct consequence of having accumulated so much
phosphorus and other associated wastes especially the heavy metals. Even as older
generations die and contaminate the culture with their content, new generations are constantly
produced, though in a long standing medium this replication might be taking place howbeit,
slowly. The microbes have a unique ability to adapt to aggressive environments [15] while
Vol.10, No.12 Phosphorus Degradation Capability 1193
still carrying out their normal functions as long as nutrients are available – in this case, from
the degradation of phosphorus in the ore. It is not surprising therefore that the microbes’
population has not diminished completely in the medium but only continues to reduce.
Figure 4 presents the % P degradation across the ore fractions by A. terreus in malt extract
broth medium for 10 weeks. The % P degraded was calculated using the equation:
the initial weight % phosphorus content in ore
the final weight % phosphorus in treated ore.
62.36% P degradation is observed in 0.50/0.25mm while 59.33% and 54.38% are seen for
1.00/0.50mm and 0.25/0.125mm, respectively. At about Week 7 the progress in P
degradation seems to have peaked and thereafter stagnated till Week 10.
1194 C.N. Anyakwo
and O.W. Obot Vol.10, No.12
Figure 5 presents the average values for % P degraded (Figure 4), the average pH (Figure 2)
and the average biomass weight (Figure 3). In Figure 5 it is observed that the period of
reduced growth activity more or less corresponded with the period of stagnation observed in
the process of P degradation. A noticeable drop in cells population in the lag phase of cell
reproduction was quickly followed by the exponential growth phase and then a much gradual
death phase indicated that not all microbes died at the end of Week 10. And then, of course, a
fungal characteristic reducing pH profile is observed till the end of Week 10. The trend of
Vol.10, No.12 Phosphorus Degradation Capability 1195
activities shows that the biomass curve intersects the % P degraded curve at two points and
then the pH curve intersects the same curve once. The probable explanations are that the first
indicates the ideal P degradation range when the average cell population is substantial enough
to support a maximum degradation. And the second intersection signals the ideal pH point
from where the optimum pH for the process actually begins.
Particularly deserving great thanks are the staff and Heads of Departments of Microbiology
and Chemical Engineering of University of Uyo, Akwa Ibom State. Few names will not fail
to be mentioned and I wish to thank my Supervisor, Engr. (Dr.) C. N. Anyakwo who, actually
not only conceived the work and provided the experimental strategies stage by stage, but also,
brought his knowledge and expertise to bear on the entire work. Engr. Peter Asangausung,
the Senior Technologist in-charge of the Chemical Engineering Laboratory where the bulk of
this work was done, for his resourcefulness, keen interest and constant prayers; Dr. A. O. Ano
of the Nigerian Root Crops Research Institute, Umuahia, Abia state, whose elastic patience
limit was over stretched many times in an unprecedented manner by my over-keeping
borrowed equipment worth millions of naira in order to complete this research.
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