Effect of advanced milling on carbothermal reduction of pyrolusite
(MnO
2
) by carbonized tea plant waste
Mustafa Boyrazlı, Elif Arancı
€
Oztürk
*
Firat University, Faculty of Engineering, Department of Metallurgy and Materials Engineering, Elazig, Turkey
article info
Article history:
Received 6 March 2019
Received in revised form
11 July 2019
Accepted 31 July 2019
Available online 1 August 2019
Keywords:
Advanced milling
Tea plant waste
Carbonization
Carbothermal reduction
abstract
This study examined the effect of advanced milling on carbothermal reduction of oxidized manganese
ore using carbonized tea plant waste as reductant.
For the carbothermal reduction of manganese oxide, the ratios of Mn/Fe, C/(MnO
2
þFe
3
O
4
) and ball/
mixture were 8/1, 2/1 and 10/1, respectively. Samples were subjected to advanced milling in an attritor mill
for 10,15, 20, 30, 60, 90 and 120h. The rotation speed of the mill shaft was 350rpm during the processes
performed in the attritor. DTA-TG, SEM and XRD analyses were carried out to characterize the samples. When
XRD peaks were compared for different grinding times, it was seen that all of the diffraction peaks gradually
decreased in parallel with the increase in grinding time. The DTA-TG analysis of the samples subjected to
mechanical activation for 120 h shows a symmetrical change, which is similar to the Gaussian function. The
activated samples obtained from advanced milling were treated at 1000,1100,1200 and 1300
C for 30, 60, 90
and 120 min in an argon atmosphere. The results of the experimental studies indicate that a 58.76% reduction
occurred in the 120 h advanced milled samples subjected to treatment at 1300
C for 2 h.
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
90e95% of the manganese produced in the world is used as fer-
romanganese or silicomanganese in the iron and steel industry [1].
Ferromanganese is produced by melting ore together with a
carbon-based reductant and flux in either a blast furnace or an
electric furnace depending on the ore composition used. Reduction
grade depends on the grain size, duration, temperature, and the
type and ratio of reductant. Ferromanganese alloys can be used as a
method for controlled addition of manganese during the production
of steel alloys. Depending on the steel quality, steel alloys generally
contain manganese ranging from 0.2 to 2% by weight as it is the
cheapest alloying element among those that enhance some impor-
tant mechanical properties such as strength and elongation [2].
The oxidation states of manganese are MnO
2,
Mn
2
O
3
, Mn
3
O
4
,
and MnO. The degradation of highly oxidized manganese occurs at
high temperatures according to the following reactions.
2MnO
2
¼ Mn
2
O
3
þ 1/2O
2
(1)
3Mn
2
O
3
¼ 2Mn
3
O
4
þ 1/2O
2
(2)
Mn
3
O
4
¼ 3MnO þ 1/2O
2
(3)
The conversion of oxidized phases to one another depends on
the partial pressure of temperature and oxygen. In a study for
Mn
2
O
3
eMn
3
O
4
e MnO system, it has been reported that reaction
(2) occurs between 845 and 1029
C while reaction (3) occurs be-
tween 1248 and 1562
C[3].
Reduction of high manganese oxides by gas starts with the
degradation of MnO
2
in manganese oxide at about 425
C. After-
wards, the reduction of Mn
2
O
3
and Mn
3
O
4
oxides occurs with the
help of reductants such as carbon and carbon monoxide in the
MneCeO system as in the following reactions.
3Mn
2
O
3
þ C ¼ 2Mn
3
O
4
þ CO
DG
¼0:25 0:17T ; kJ =mol 25 1100
C
(4)
3Mn
2
O
3
þ CO ¼ 2Mn
3
O
4
þ CO
2
DG
o
¼170:71 0:004T ; kJ =mol ð25 1100
CÞ
(5)
Mn
3
O
4
þ C ¼ 3MnO þ CO
DG
o
¼ 110:96 0:21T ; kJ =mol ð25 1244
CÞ
DG
o
¼ 84:35 0:20T ; kJ =mol ð1244 1700
CÞ
(6)
* Corresponding author.
E-mail address: earanci@firat.edu.tr (E. Arancı
€
Oztürk).
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
https://doi.org/10.1016/j.molstruc.2019.126875
0022-2860/© 2019 Elsevier B.V. All rights reserved.
Journal of Molecular Structure 1198 (2019) 126875