6CO 2

C6H10O5 show that cellulose of sawdust contain α-D-glucose units. Acid treat- ment release glucose that acts as reducing agent [12] .

3.3. Effect of Mesh Size

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.

Figure 4 shows an increase in Mn content and decrease of silica and iron when the particle size (particle diameter) of the ore was decreased. EDS results revealed beneficiation of Mn from 24.05 wt% to 73.28 wt% at particle size of 300 mesh. Table 3 shows variation in elemental composition of Mn, Si and Fe at 100,

Figure 4. Variation of element concentration with mesh size.

Table 3. Elemental concentration at 100, 200 and 300 mesh size of leached Mn ore.

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 [6] [8] .

3.4. Effect of Sawdust Amount

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 [13] .

Table 4 gives variation in elemental composition of Mn, Si and Fe for 3, 4 and 5 g sawdust. Figure 5 shows an increase in Mn content accompanied by decrease

Table 4. Elemental concentration of leached Mn-ore for 3 g, 4 g and 5 g of sawdust.

Figure 5. Efficiency of manganese ore leaching at varying amount of sawdust.

in both the Si and Fe concentrations by increasing the sawdust amount.

3.5. Effect of Temperature on Manganese Ore Leaching

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.

Table 5 shows the observed variation in the elemental composition of Mn, Si and Fe for manganese ore treated at 60˚C, 90˚C and 120˚C. Figure 6 shows variation in the elemental composition with temperature. The graph indicated that manganese concentration was lower at low temperature and increased with an increase in the leaching temperature; similarly the concentration of silicon and iron decreased with increasing temperature.

3.6. Influence of Time on Leaching of Manganese Ore

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.

Table 5. Elemental concentration of leached Mn-ore sample at 60˚C, 90˚C and 120˚C temperature.

Figure 6. Effect of temperature on elemental concentration of the samples.

Table 6. The elemental concentration of Mn ore sample leached at 1 h, 2 h and 3 h.

Table 6 gives the quantitative variation in the elemental concentration of Mn, Si and Fe. Figure 7 shows the graph for variation in elemental concentration of the leached samples with change in leaching time. It was observed that by increasing time duration from 1 - 3 h the recovery increased from 66 to 83 wt%, consistent with the previous study.

3.7. Effect of Manganese Ore Amount

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.

Figure 7. Effect of leaching time on the elemental concentration of Mn-ore.

Table 7. The elemental concentration of 10 g, 15 g and 20 g Mn ore sample.

Figure 8. Effect of ore amount on the elemental concentration of leached Mn-ore samples.

Table 7 gives the elemental and oxide compositions of Mn, Si and Fe for 10, 15 and 20 g of Mn ore.

Figure 8 shows the observed variation in the elemental concentration of Mn, Si and Fe. These experiments demonstrated that by increasing the manganese ore amount the concentration of manganese decreased which may be due to insufficient amount of acid or the reducing sugar generated from the smaller amount of sawdust in comparison to the ore amount.

3.8. Effect of H2SO4 Concentration

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.

Table 8 gives elemental concentration and oxide compositions of Mn, Si and Fe measured by EDS for manganese ore treated with 5 mL, 10 mL and 15 mL H2SO4. Figure 9 shows the observed variation in elemental composition with acid concentration. EDS analysis showed that the leaching efficiency increased with an increase in the amount of acid used because the sawdust released glucose more rapidly than at relatively less acid.

4. Conclusions

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-

Table 8. Elemental concentration of Mn ore leached with 5 mL, 10 mL and 15 mL H2SO4.

Figure 9. Effect of the amount of acid on the elemental concentration in the leached samples.

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.

Acknowledgements

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.

Cite this paper
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. doi: 10.4236/jmmce.2018.61006.
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