In this research work, sawdust was used as a reducing agent for sulphuric acid leaching of manganese ore from Prang Ghar, Lower Mohmand Agency, Pakistan. X-ray diffraction of the powdered sample indicated the presence of Hausmannite (Mn 3O 4), Calcium Aluminum Silicate Hydrate, Silica (SiO 2) and Hematite (Fe 2O 3). X-ray diffraction and the energy dispersive spectroscopic analysis show that the manganese ore sample was siliceous in nature. In the present study, six process parameters were investigated i.e. the particle size of the ore, leaching temperature, time duration, Mn ore amount, sulphuric acid concentration and amount of sawdust. Manganese extraction of 88.93 (wt%) was achieved for a leaching time of 60 minutes at 120 ° ;C using 5% (v/v) H 2SO 4 concentration for 10 g Mn ore and 5 g sawdust. The results demonstrate that sawdust is a low cost, renewable and non-hazardous reducing agent in comparison to other available reagents.
Manganese is an important element with a number of uses in major industrial applications i.e. production of steel, preparation of dietary additives, fertilizers, dry cells, paint production, animal feeds, textile dyes, medicines and colorants for bricks. Low-grade manganese ore can be treated either by reductive roasting or by reductive acid leaching [
Using glucose as reducing agent in dilute nitric acid medium at 90˚C for 32 h, 99% manganese has been extracted. It is concluded that high grade manganese can be obtained using nitric acid instead of sulphuric acid [
Using cane molasses as reducing agent in nitric acid medium raises manganese content from 37.5% to ~98% at optimum conditions of 2.7 M HNO3, cane molasses 20% by weight, grain size 74 μm, solid/liquid ratio 1:12 for 2 h at 95˚C [
In the present work, sawdust was used as a reducing agent in dilute sulfuric acid medium to extract manganese from ferromanganese ores. The use of sawdust for reduction of manganese dioxide is a simple, low cost and economical method in comparison to the other reductants.
Representative sample of manganese ore was collected from Prang Ghar (34˚25'N, 71˚37'3"E), Upper Mohmand Agency, Khyber Pukhtunkhwa (KP), Pakistan. Manganese ore was crushed, grinded and then passed through 149 and 74 µm sieves. Semi-quantitative EDS detected 24.05 wt% Mn, 21.15 wt% Ca, 15.24 wt% Si, 6.87 wt% Al, 29.44 wt% Fe and 3.25 wt% Mg in as-mined ore sieved at 74 µm.
The leaching experiments were performed in a 500 mL glass beaker kept on a ceramic hot plate and magnetic stirring system in a fume hood. Initially 100 mL solution 5% (v/v) H2SO4 (5 mL H2SO4 and 95 mL distal water) was mixed thoroughly with weighed amount of sawdust (3, 4 and 5 g) to release glucose into the acid. After 15 min, the weighed amount of ore powder was transferred to the pulp. The leaching experiments were carried out for different sets of parameters i.e. particle size of Mn ore, leaching temperature, leaching time, Mn ore amount, sulphuric acid concentration and amount of sawdust.
Room temperature X-rays diffraction (XRD) data were recorded using a JEOL JDX-3532 X-ray diffractometer, operating at 40 kV and 30 mA, with Cu Kα radiation (λ ~0.154 nm) at Centralized Resource Laboratory (CRL), University of Peshawar, Pakistan. The samples were scanned from 10˚ - 70˚ (2θ) with a count time/step of 1.25 s and 0.02˚ step size. Secondary electron scanning electron microscope (SEM) images of chemically etched samples were recorded using a JEOL JSM5910 SEM, operating at 30 keV. Semi-quantitative energy dispersive X-ray electron spectroscopy (EDS) data were collected using an INCA200 EDS detector (Oxford instruments, UK), connected with a JEOL-JSM5910 SEM. A PMG-3 microscope coupled with a DP-12 CCD camera, Olympus (Japan) was used for recording optical images in the present study at CRL.
The long and straight dark thick strip marked as “A” crossing two different types of regions (appearing light greenish dark region with granular morphology and the plane white region) may be due to the combination of oxides of manganese and iron that impart iron black color [
Elements/Region | Elemental concentration (wt%) | |||||
---|---|---|---|---|---|---|
Mg | Al | Si | Ca | Fe | Mn | |
Gross composition | 3.25 | 6.87 | 15.24 | 21.15 | 29.44 | 24.05 |
A | ----- | ----- | 10.16 | 9.14 | 20.30 | 60.40 |
B | ----- | 16.07 | 31.61 | 4.86 | 8.51 | 38.95 |
C | ----- | 17.35 | 30.51 | 7.47 | ----- | 44.67 |
D | ----- | ----- | 100 | ----- | ----- | ---- |
or pseudo-hexagonal grains labeled as B and dark grey silica rich plane micro- region labeled as D. The elemental compositions of these micro-regions are given in
Using XRD Cheng et al. reported the presence of pyrolusite (MnO2) as the major phase along with small amounts of MgO, silica (SiO2), hematite (Fe2O3) and Al2O3 in manganese ore from Guangxi, China [
EDS analysis | XRD analysis | |||
---|---|---|---|---|
Elements | Wt% | Mineral | Formula | PDF # |
Si | 15.24 | Quartz | SiO2 | 38 - 360 |
Mn | 24.05 | Hausmanite | Mn3O4 | 75 - 1560 |
Fe | 29.44 | Hematite | Fe2O3 | 6 - 502 |
Al | 2.87 | Calcium aluminium silicate hydrate | 20-452 | |
Ca | 22.40 |
low-grade manganese ore from Guangxi, China reported the presence of todorokite (Mn6O12∙4∙16H2O) and hematite (Fe2O3) as the major phases and the gangue minerals were quartz (SiO2) and kaolinite (Al2Si2O5(OH)4) [
Basic chemical reaction for leaching of MnO2 using sawdust C6H10O5 can be as following
12MnO 2 + C 6 H 1 0 O 5 + 12H 2 SO 4 → 12MnSO 4 + 17H 2 O + 6CO 2 ↑
C6H10O5 show that cellulose of sawdust contain α-D-glucose units. Acid treat- ment release glucose that acts as reducing agent [
Influence of particle size of ore on efficiency of leaching was studied at 100, 200 and 300 mesh sizes while keeping the other parameters constant i.e. 5 g sawdust, 10 g Mn ore, 5% (v/v) H2SO4, 90˚C and 60 minutes leaching time.
Mesh size | Elemental composition (wt%) | ||
---|---|---|---|
Mn | Si | Fe | |
100 | 37.05 | 26.03 | 36.92 |
200 | 66.11 | 4.02 | 29.87 |
300 | 73.28 | 3.36 | 23.36 |
200 and 300 mesh sizes of manganese ore. An increase in leaching efficiency with increasing mesh size has been reported by Hariparsad et al., and Tian et al [
Sulfuric acid cannot be used directly for leaching of manganese ores. However; reducing substances like sawdust can be used in acidic solution for high efficiency of manganese leaching.
For investigating the effect of sawdust, various leaching experiments were performed by changing sawdust concentration from 3.0 to 5.0 g/L while keeping other parameters fix i.e. 5 % (v/v) sulfuric acid concentration, leaching time of 60 min, manganese ore amount of 10 g, leaching temperature of 90˚C and mesh size of 200.
Since XRD analysis confirmed the presence of hematite phase in manganese ore sample. However; crystalline nature of hematite requires a highly acidic medium due to its consumption of H+ ions. Increasing the amount of sawdust at a certain temperature and acid concentration causes an increase in the leaching efficiency of Mn due to excess availability of H+ ion concentration [
Sawdust amount | Elemental composition (wt%) | ||
---|---|---|---|
Mn | Si | Fe | |
3 g | 32.82 | 10.61 | 56.57 |
4 g | 37.02 | 36.29 | 26.68 |
5 g | 66.11 | 4.02 | 29.87 |
in both the Si and Fe concentrations by increasing the sawdust amount.
The influence of leaching temperature on leaching efficiency at 60˚C, 90˚C and 120˚C was investigated while keeping the other parameters constant i.e. 5 g sawdust, 5 % (v/v) concentration of H2SO4, leaching time of 60 min, 10 g Mn-ore of 200 mesh size.
Three sets of experiments were performed in order to study the influence of time on leaching efficiency of manganese ore. The ore sample was treated for 1 h, 2 h and 3 h at constant sawdust amount 5 g, sulfuric acid concentration 5 % (v/v), leaching temperature 90˚C and 200 mesh size Mn-ore = 10 g.
Temperature | Elemental composition (wt%) | ||
---|---|---|---|
Mn | Si | Fe | |
60˚C | 43.17 | 27.63 | 19.20 |
90˚C | 66.11 | 4.02 | 29.87 |
120˚C | 88.93 | 2.12 | 8.95 |
Time | Elemental composition | ||
---|---|---|---|
Mn | Si | Fe | |
1 h | 66.11 | 4.02 | 29.87 |
2 h | 74.11 | 8.24 | 17.65 |
3 h | 83.35 | 6.61 | 10.04 |
Leaching experiments were also performed for 10 g, 15 g and 20 g 200 mesh Mn ore samples at fixed values of 5% (v/v) H2SO4, 5 g sawdust, 90˚C temperature and 1 h leaching time.
Ore amount | Elemental composition | ||
---|---|---|---|
Mn | Si | Fe | |
10 g | 66.11 | 4.02 | 29.87 |
15 g | 68.71 | 14.49 | 16.79 |
20 g | 62.44 | 11.78 | 25.78 |
The influence of the amount of acid used on the leaching efficiency was also investigated. 5 mL, 10 mL and 15 mL H2SO4 was used for 5 g sawdust, at 90˚C leaching temperature, with a leaching time of 60 min and 200 mesh size 10 g Mn ore sample.
In this study, manganese ore from Prang Ghar, Lower Mohmand agency, Pakistan was characterized using XRD, SEM, EDX and optical microscopy. Prang Ghar manganese ore is a low grade ferruginous manganese ore. The major non-
H2SO4 concentration | Elemental composition (wt%) | ||
---|---|---|---|
Mn | Si | Fe | |
5 mL | 66.11 | 4.02 | 29.87 |
10 mL | 76.21 | 16.19 | 7.61 |
15 mL | 80.77 | 8.63 | 10.60 |
oxide elements detected by EDS in this ore are Manganese, Silicon and Iron. The mineralogy of manganese ore is complex. The constituent phases of manganese ore samples identified using XRD analysis are Hausmannite (Mn3O4), Calcium Aluminum Silicate Hydrate, Silica (SiO2) and Hematite.
The chemical beneficiation of manganese ore was carried out using a commercial grade concentrated H2SO4 and sawdust as reductant. The investigated parameters included temperature; Mn ore mesh size and amount, leaching time, acid concentration and sawdust amount. The highest manganese concentration of 88.93 (wt%) was achieved at 120˚C, 200 mesh size Mn ore, 60 minutes leaching time, 5% (v/v) H2SO4 and 5 g sawdust. Mn extraction increases with an increase in temperature, ore particle size, sawdust amount, time duration and the amount of acid. The observed decrease in Mn concentration with increasing Mn ore amount may be due to insufficient amount of acid or the reducing sugar generated from the sawdust. In all the experiments, the decrease in Si and Fe has been observed with increase in all the six parameters. Considering the observed productivity of the utilized sawdust, the process is beneficial from both the economic and environmental perspective.
The authors highly appreciate and acknowledge the financial support of the Higher Education Commission, Pakistan and the US National Academy of Science under the Pak-US S&T Cooperation Program for Materials Connection Center. We also admire and thanks for the financial support of Khyber Pukhtunkhwa Government through the pilot research studies program of the Directorate of Science & Technology, KP for extension in Mineral Up-gradation Pilot Plant and Up-gradation of Materials Research Laboratory, University of Peshawar.
Ali, S., Iqbal, Y., Ahmad, K. and Afridi, B. (2018) Phase, Microstructure and Beneficiation of Manganese Ore by Acid Leaching. Journal of Minerals and Materials Characterization and Engineering, 6, 60-71. https://doi.org/10.4236/jmmce.2018.61006