Evaluation of Pyrolusite Flotation Behavior Using a ... - Springer Link

ISSN 1062-7391, Journal of Mining Science, 2014, Vol. 50, No. 5, pp. 982–993. © Pleiades Publishing, Ltd., 2014.

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MINERAL DRESSING

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Evaluation of Pyrolusite Flotation Behavior Using a Cationic Collector1 Akbar Mehdilo and Mehdi Irannajad Department of Mining and Metallurgical Eng., Amirkabir University of Technology, 424 Hafez Ave, Tehran, 15875-4413 Iran e-mal: [email protected] Received November 21, 2014

Abstract—Floatability of pyrolusite from an Iranian low grade manganese ore (13.6% MnO) containing calcite as the main gangue mineral was investigated with Armac C as a cationic collector. In the single mineral flotation experiments, the maximum recovery of pyrolusite is obtained at 82.2%, using 2000 g/t Armac C at a pH of 9, while at these conditions the flotation recovery of calcite is almost 78%. Quebracho and sodium hexa methaphosphate (SH) depress both minerals strongly at a wide range of dosages while low dosages of sodium silicate and zinc oxide depress the calcite mineral more than pyrolusite. Ca2+ ions affect the flotation recovery of pyrolusite negatively. The effective depression of calcite occurs using 1000–2000 g/t sodium silicate. However, in the ore flotation experiments, the favorable selective flotation of pyrolusite does not occur but the optimal concentrate containing 21.5% MnO with 51% recovery is obtained using 2000 g/t collector and 1000 g/t sodium silicate. A concentrate containing 37% MnO is achieved by carrying out flotation experiments on the jigging pre-concentrate under optimal conditions including pH = 9, 1000 g/t Armac C, 1000 g/t sodium silicate and 120 g/t pin oil. Keywords: Pyrolusite, manganese ore, flotation, cationic collector, depressant. DOI: 10.1134/S1062739114050184

INTRODUCTION

Manganese is used mainly in steel production, directly in pig iron manufacturing and indirectly in upgrading ore to ferroalloys. Globally, most of (90 to 95%) Mn is used in the metallurgical industry as a requisite deoxidizer and desulfurizer in steel making and as an important alloy component. Various amounts of Mn are commonly added to steel for industrial use, making low or high Mn alloys. The high grade ores (containing more than 42% Mn) are usually used in metallurgical applications. The remainder (5 to 10%) is used in the chemical industry, light industry, production of dry cell batteries, in plant fertilizers and animal feed, and also as a brick colorant [1]. The most important manganese minerals are the oxide minerals, such as pyrolusite (MnO2); hausmannite (Mn3O4) and manganite (MnO(OH)). Manganese is also found in several minerals such as pink rhodochrosite (MnCO3), rhodonite (MnSiO3), black manganite (MnO(OH)), wad and alabandite (MnS) [1–3]. The minerals such as rhodochrosite, rhodonite and hausmannite are often replaced by pyrolusite. Pyrolusite containing 63.2% Mn is the most common manganese mineral [4]. Manganese ores may accumulate in metamorphic rocks or as sedimentary deposits, frequently forming nodules on the sea floor. Manganese nodules or ferro-manganese concretions, usually containing 30–36% Mn have been found on ocean floors and can provide another source of manganese. The main sources of manganese come from the former U.S.S.R, Brazil, South Africa, Australia, Gabon and India. Russia and South Africa produce about 85% of the world’s pyrolusite resources [2, 3, 5]. Each type of a manganese deposit is a problem by itself in the matter of selection of a proper method of concentration, depending on the manganese minerals and their gangue constituents [6]. The

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gravity separation methods such as sink-float, jigging and tabling, and high-intensity magnetic separation are usually used to upgrade manganese ores. Flotation is one of the developed processes for the beneficiation of lower grade and more refractory resources especially in fine size fractions [2, 7]. The point of zero charge (PZC) of minerals plays an important role in its flotation with physisorbing but not with chemisorbing collectors [8]. Fuerstenau and Rice (1968) studied the flotation response of pyrolusite with sodium oleate, sodium dodecyl sulfonate and dodecyl ammonium chloride. Their results indicated that the flotation in the presence of dodecyl sulfonate (below pH 7.4) and dodecylamine (pH of 7.4–-11.5) is due to electrostatic interaction between pyrolusite and collectors. In the case of sodium oleate, there are two maximum flotation recoveries, one at a pH of 4 and the other at a pH of 8.5. The flotation response in the acidic pH range is due to electrostatic interaction between the positively-charged pyrolusite and anionic collector. However, the flotation peak at a pH of 8.5 is due to chemisorption of oleate on the mineral surface [3, 8–11]. In another study, two maximum flotation recoveries were also observed, one at the neutral pH and the other in the alkaline range. In the previous works which focused on flotation of pyrolusite or other manganese oxide minerals, often the anionic collectors have been investigated. Some of these collectors are sodium or potassium oleate, dodecyl sulfonate, dodecyl sulfate, 2-ethylhexyl sulfosuccinate and dodecylbenzene sulfonate [3]. In addition, in the previous works, mostly the flotation behavior of pure pyrolusite and manganese oxide minerals has been investigated but, their flotation from gangue minerals has not been considered significantly. Thus, the floatability of pyrolusite using coco alkyl amine acetate (Armac C) as a cationic collector is investigated in this work. After characterizing of the samples, the flotation of pyrolusite and calcite (as an associated gangue mineral) are studied in both micro (Hallimond tube) and laboratory (flotation cell) scales. 1. MATERIALS AND METHODS 1.1. Materials

The representative sample was collected from different trenches of Charagah manganese ore deposit located 82 km northwest of Tabriz, Iran [12, 13]. The characteristics of the ore sample used in the flotation experiments are presented in detail in section 3-1. For carrying out the single mineral flotation tests, lumps of pyrolusite and calcite were taken from the deposit. These samples were crushed and ground under 150 µm, and were prepared separately in a size fraction of -150+45 microns. The purification of minerals was performed using sieving and several stages of tabling. Finally, the single minerals with purity above 90% were eventually used in Hallimond tube experiments. The reagents used in the flotation experiments are listed in Table 1. Table 1. Reagents used in flotation experiments Chemicals

Concentration

Supplier

Role

99 97 96 99 99 99 99 99

Akzo Nobel Merck Scharlau Merck Merck Penn Chemical Merck Merck

Collector Depressant Depressant Depressant Depressant Frother pH adjuster pH adjuster

Armac C (coco alkyl amine acetate) Sodium Silicate Sodium Hexa Methaphosphate Zinc oxide Quebracho Pin oil H2SO4 NaOH

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1.2. Methods 1.2.1. Characterization

The corresponding polished and thin sections were studied for determining ore and rock-forming minerals and their textural relationships by reflected and transmitted light microscopy. The chemical composition of the samples was determined using X-ray fluorescence (XRF, Philips X Unique II). The phase composition was analyzed with a XPERT MPD diffractometer employing Cu Ka radiation. The Philips XL30 model scanning electron microscopy (SEM) equipped with WDX (Wavelength dispersive X-ray, model: 3pc) was used for evaluation of textural, structural and compositional features of minerals. 1.2.2. Flotation experiments

Single mineral flotation tests were carried out in a 300 ml micro flotation cell (Hallimond tube). For each test, 2 g of mineral samples were added into 350 ml of water under agitation with a magnetic stirrer. After the sequential addition of pH modifiers and collectors, the suspension was conditioned for 1and 3 min, respectively. Flotation time was fixed for 4 min. After the flotation tests, the concentrate and tailings were filtered, dried and weighed. The ore flotation tests were conducted on 300 grams of the sample, using a 1-liter laboratory Denver flotation cell, at 1250 rpm impeller speed with a constant flow of air (the maximum permitted by the system), and the pulp conditioning time was 5 minutes. In cationic flotation tests, the slurry with 25% solid was conditioned with collector and depressant for 5 min. Pine oil (120 g/t) was used as a frother with conditioning time of 2 min. 1.2.3. Zeta potential measurement

The zeta potential of mineral suspension was measured using a Malvern instrument (UK). The samples were ground under 15 µm. The suspension was prepared by adding 50 mg of pure pyrolusite or calcite to 100 ml of distilled water containing 10-3 Mole/liter KCl as a supporting electrolyte. The resulting suspension was conditioned for 15 min during which suspension pH was measured. The pH was adjusted using either NaOH or H2SO4 over the pH range of 3–12. Zeta potential was measured following the procedures described in the instrument manual. The reported results are the average of at least three full repeat experiments. The repeated tests showed a measurement error of±1 mV. 1.2.4. FT–IR analysis

The FT–IR spectra were obtained with NEXU670 FT-IR (Nicolet Corporation, USA) to characterize the nature of the interaction between the collector and the minerals. The mineral sample was ground to smaller than 0.015 mm before contact with the collector. In each test, the conditioning of suspension was performed similar to the flotation experiments. The suspension was then filtered, and the solids were air dried overnight at room temperature 2. RESULTS 2.1. Ore Characterization 2.1.1. Chemical and mineralogical composition

According to the X-Ray diffractography (Fig. 1a), the studied ore consists of pyrolusite as the main valuable mineral and calcite and quartz as gangue minerals. The chemical composition of the representative sample analyzed by XRF is shown in Table 2. This ore containing 13.8% MnO which implies about 17% pyrolusite (by considering 81.6% theoretical MnO for pyrolusite) is one of the low grade deposits in the world. Based on XRD and XRF analysis, almost 79% and 3-4% of the ore is formed by calcite and quartz, respectively. The chemical analysis of purified pyrolusite used in microflotation experiments is shown in Table 1. The chemical composition and XRD pattern (Fig. 1b) of the purified sample suggest that the purified sample is essentially composed of pyrolusite (almost 94%). JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014


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Fig. 1. X-ray diffraction pattern of (a) representative ore sample and (b) purified pyrolusite: Py—pyrolusite; Ca—calcite; Q—quartz; Ba—barite.

Table 2. Chemical composition of purified pyrolusite and representative ore samples Composition

MnO CaO SiO2 Al2O3 As2O3 BaO MgO CuO

SO3

Pure pyrolusite

76.6 2.62

-

-

0.58

3.18

0.31

0.33

0.59

1.47

13.19

1.13

Ore sample

13.6 44.7

3.5

0.78

0.21

0.31

0.56

-

0.28

0.65

34.57

2.78

Sample

Fe2O3 L.O.I Others

2.1.2. Microscopic studies

Based on the results obtained from transmitted-light microscopy studies, the coarse and fine grains of ore minerals are surrounded by gangue minerals including calcite and quartz. The interlocking of ore and gangue minerals is shown in Fig. 2. The study of polished sections by reflected-light microscopy showed that pyrolusite (about 12–15 vol. %) is the main ore mineral (Fig. 3). The small amount of hematite is also found in the samples. The studies by scanning electron microscopy indicated that the mineralization of pyrolusite occurs in two forms. The coarse grain pyrolusites with a size between 50 to 500 μm have simple interlocking with gangue minerals. (Fig. 4a). Another kind of pyrolusites has a complicated texture, and interlocking is even finer than 10 micron sizes (Fig. 4c). In fact, these very fine pyrolusites are disseminated within the gangue minerals. The distribution or XRay mapping of manganese (Mn) as a demonstrator of pyrolusite is shown in Figs. 4b and 4d. The small amount of barite particles is also observed in SEM studies which is evidenced by WDX analysis. Its content in the ore is negligible and could not have a considerable effect on pyrolusite flotation response.

Fig. 2. Study by transmitted light microscopy: (a) interlocking of calcite, quartz and coarse grains of ore minerals (pyrolusite); (b) fine grains mineralization surrounded by gangue minerals. JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014

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Fig. 3. Study by reflected light microscopy (Interlocking of pyrolusite and gangue minerals).

Fig. 4. BSE (Backscattered electron) images and elemental X-Ray mapping: (a) interlocking of coarse grains of pyrolusite and gangue minerals containing calcite and quartz (-180+150 μm size fraction); (b) X-Ray maps of MnKa in Fig. 4a; (c) dissemination of fine pyrolusites within the gangue minerals; (d) X-Ray maps of MnKa in Fig. 4c.

2.1.3. Liberation degree

One of the prepared 1 kg representative samples was sieved and a polished section was provided from each of eight sieve fractions. BSE (Backscattered electron) images were taken from different parts of each polished section. In all images of each section the surface area of liberated and locked pyrolusites were measured using JMicroVison software. Then the percentage of liberation degree is calculated using equation 1 for different fractions. The results as percentage of liberation degree versus size fraction are shown in Fig. 5. JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014


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Fig. 5. Liberation degree of pyrolusite, determined using JMicroVison.

Based on these results, the liberation degree of pyrolusite is determined as d80 = 180 microns. S LP (1) LD , % = × 100 , S LP + S IP where S LP and S IP are the total surface area of liberated pyrolusites and the surface area of interlocked pyrolusites in all images of each polished section, respectively. 2.2. Flotation Experiments 2.2.1. Microflotation

In these experiments, the flotation behavior of pyrolusite and calcite (as the main gangue mineral) was investigated. 2.2.1.1. Effect of pH

The flotation recoveries of pyrolusite and calcite as a function of pH using 2000 g/t Armac C are shown in Fig. 6. Pyrolusite is not floated in strong acidic solutions. The flotation recovery of pyrolusite increases with rising pH, and the maximal flotation occurs at a pH of 8-9. As pH increases, the flotation recovery of pyrolusite enhances and reaches its maximum of 82.2% at a pH of about 8. This behavior is in good agreement with results reported for the flotation of pyrolusite [3] and γmanganese dioxide [8] with dodecylammonium chloride as collector. As seen from Fig. 6, calcite is easily floated using Armac C in a wide pH range and its flotation recovery is higher than 70% at pHs between 6 and 12. Thus, the use of suitable depressant agent for calcite is necessary.

Fig. 6. Flotation recovery of pyrolusite and calcite as a function of pH (Armac C 2000 g/t). JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014

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2.2.1.2. Collector concentration

The flotation recovery of pyrolusite and calcite as a function of Armac C concentration at a pH of 9 is shown in Fig. 7. The increase of collector concentration increases the flotation recovery rapidly for both minerals. At higher dosages of collector, the flotation recovery of pyrolusite reaches above 95% but the difference between the recoveries of minerals is decreased significantly. However, the maximum difference between the flotation recoveries of pyrolusite and calcite (about 26%) is obtained using 1000 g/t Armac C but, the pyrolusite recovery is relatively low (59%) at this dosage of collector. The optimal dosage of Armac C for pyrolusite is 2000 g/t which results in flotation recovery of 82.2%. At this condition calcite flotation recovery is about 68%. 2.2.1.3. Effect of calcium ions

In the pyrolusite–calcite flotation system, the Ca2+ ions released from semi soluble calcite mineral will be the most common mineral ions. For evaluating the effect of these ions on flotation behavior of pyrolusite, some microflotation experiments were carried out in the presence of Armac C and a different dosage of CaCl2 at a pH of 9. As seen from Fig. 8, the increase of CaCl2 dosage decreases the flotation recovery of pyrolusite. This can be due to the adsorption of Ca2+ ions on the pyrolusite stern layer and the increase of its surface zeta potential which results in the reduction of physisorption interaction between the cationic collector and pyrolusite surface.

Fig. 7. Flotation recovery of pyrolusite and calcite as a function of collector concentration at a pH of 9.

Fig. 8. Flotation recovery of pyrolusite as a function of CaCl2 concentration (2000 g/t Armac C, pH 9). JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014


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2.2.1.4. Effect of depressants

For depressing the calcite mineral, some depressants including sodium silicate (SS), Quebracho, sodium hexa methaphosphate (SH) and zinc oxide (ZnO) were examined. The effect of these depressant reagents was also investigated on pyrolusite floatability. The flotation recoveries as a function of depressants dosage using 2000 g/t collector at a pH of 9 are shown in Fig. 9. As shown in Fig. 9, at lower dosages (lower than 2000 g/t), sodium silicate depresses calcite more rapidly than pyrolusite. The further increase in sodium silicate dosages depresses pyrolusite similar to calcite. Thus, a relatively suitable separation of pyrolusite from calcite can be achieved using 1000–2000 g/t of sodium silicate. The maximum difference of the flotation recoveries of two minerals occurs with 1500 g/t sodium silicate which results in a recovery of 74% and 43% for pyrolusite and calcite, respectively. Quebracho decreases the flotation recovery of both minerals more rapidly than the three other depressants. Using 1000 g/t of quebracho, the recovery of calcite and pyrolusite is obtained at 41% and 24%, respectively. The further increase in its dosage practically stops the flotation recovery of both minerals. The chemical composition and structure of quebracho is highly complex and contains varieties of polyphenols and tannic acid. From the depressing action point of view, the high molecular-weight components of quebracho play an important role. It is believed that the depressing action of quebracho is due to the fact that it displaces the collector from the mineral surfaces. In specific cases, calcite depression results from the adsorption of quebracho into the calcite by the formation of calcite complex Ca2+ ions and the OH groups of quebracho catechol/pyrogallol B ring [14]. As seen from Fig. 9c, SH depressing both minerals, depresses pyrolusite more effectively than calcite. Thus, SH is not a suitable depressant for selective flotation of pyrolusite from calcite.

Fig. 9. Flotation recovery as a function of different depressants concentration: (a) sodium silicate, (b) quebracho, (c) sodium hexa methaphosphate (SH), (d) ZnO (Armac C 2000 g/t, pH = 9). JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014

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However, lower dosages of ZnO decrease the flotation recovery of both minerals but its depressing action on calcite is more clear than pyrolusite. Fig. 9d shows that the optimal results are obtained in the presence of 50 g/t ZnO which decreases the flotation recoveries of calcite and pyrolusite from 77.9 to 52% and 82.2 to 65%, respectively. The further increase in ZnO dosage results in the similar depression behavior for calcite and pyrolusite. Since the maximum difference between the recoveries of calcite and pyrolusite is obtained with sodium silicate, therefore this reagent is better than the three other depressants for calcite depression in the pyrolusite flotation. 2.3. Zeta Potential

The relationship between the zeta potential and pH value of pyrolusite and calcite particle surface is presented in Fig. 10. It can be seen that the pH value at the IEP (iso electric point) of pyrolusite is 7.5. The IEP of calcite is about 10.4. It is expected that in the pH ranges from 7.5 to 10.4, the cationic collector is adsorbed on negatively charged pyrolusite through the physisorption mechanism but is not physisorbed on calcite with positive surface charges. The flotation results show (Fig. 6) that Armac C is adsorbed on the calcite mineral considerably which results in its significant floatability. The zeta potential measurements of pyrolusite and calcite after being treated with collector in the absence and presence of sodium silicate and zinc oxide at a pH of 9 is given in Table 3. Without any depressant the zeta potential of pyrolusite and calcite is -3.1 mV and -6.82 mV, respectively. This means that Armac C is adsorbed on the pyrolusite surface somewhat more than the calcite surface. This is in good agreement with the flotation results at a pH of 9. The negative zeta potential of both minerals in the presence of Armac C is probably due to the CH3COO- (released from collector) and OH- anions. In the presence of 1500 g/t sodium silicate and 50 g/t zinc oxide, the zeta potential of pyrolusite is higher than that of calcite. This can be attributed to more depressing action of these reagents on calcite. The differences between the zeta potential of pyrolusie and calcite in the presence of sodium silicate and zinc oxide are 10.8 mV and 5.5 mV, respectively. This is in good agreement with flotation results obtained using these depressants at a pH of 9; where the differences between the flotation recoveries of pyrolusite and calcite are 31% for sodium silicate and 16% for ZnO.

Fig. 10. Relationship between zeta potential and pH value for pyrolusite and calcite.

Table 3. Zeta potential of pyrolusite and calcite after being treated with Armac C and depressants at pH 9 Mineral

Zeta potential, mV

Condition

Pyrolusite

Calcite

Armac C

-3.10

-6.82

Armac C + 1500 g/t sodium silicate

-7.9

-18.7

Armac C + 50 g/t zinc oxide

-10.4

-15.9



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Fig. 11. FT–IR spectra of pyrolusite and calcite treated with 2000 g/t Armac C at pH 9.

2.4. FT–IR Analysis

Infrared spectra of pyrolusite and calcite after being treated with the Armac C solution at a pH of 9 are shown in Fig. 11. The peaks appeared in similar wavenumbers for both minerals and are related to the collector adsorbed on minerals surfaces. The peaks at wavenumbers from 2925 cm−1 to 2850 cm−1 are attributed to CH2 bands of the alkyl chain. The peaks at 1730 and 1794 cm−1 are related to C=O stretching while the peaks at 1428 to 1430 cm−1 are attributed to stretching vibration of the COOgroup. The observed peaks for both minerals in the region of 876 to 880 cm−1are related to the N-H band of primary amine [15]. By comparing the spectra presented in Fig. 11 with FT–IR spectra of pyrolusite [16, 17] and calcite [17, 18] minerals, there are not any new peaks in the spectra of minerals treated with the collector. This means that the collector has been physisorbed on the minerals surfaces. It seems that some anions present in the flotation system are adsorbed on the Helmholtz layer of calcite and result in its surface activation. 2.5. Ore Flotation Experiments

Based on the microflotation results, some ore flotation experiments were carried out using different concentrations of sodium silicate as depressant agent. The flotation response of pyrolusite as a function of sodium silicate dosage is shown in Fig. 12. The increase of sodium silicate concentration does not have a significant effect on MnO grade and recovery. A better concentrate containing 21.5% MnO with a recovery of about 51% is obtained using 2000 g/t collector in the presence of 1000 g/t sodium silicate. At this condition, the CaO grade and recovery are 37.6 and 32%, respectively. Some other experiments were conducted on the ore sample and jigging concentrate (containing 20.7% MnO) after grinding under 150 μm with and without sodium silicate as a depressant. The results are presented in Table 4. In the case of the ore sample, using 1000 g/t collector without any depressant, a concentrate with 21.8% MnO and 46.8% recovery is produced while the use of jigging concentrate as a flotation feed material results in a concentrate containing 34.1% MnO with 62.8% recovery. In the case of jigging concentrate, by increasing the collector concentration, a pyrolusite concentrate with 32.5% MnO is achieved. In the absence of depressant, the increase of collector dosage results in the higher calcite flotation which decreases the MnO content of pyrolusite concentrate. Thus, these results show that a decrease in collector concentration increases the MnO grade of the concentrate and improves flotation selectivity. This is in good agreement with the microflotation experiments. The lower content of MnO in the flotation concentrate can be attributed to the depressing effect of Ca2+ ions (released from calcite into the flotation pulp) on the pyrolusite mineral as shown in Fig. 8. Although at the lower dosages of sodium silicate its depressing effect on the pyrolusite flotation is less than that of calcite, the presence of Ca2+ ions promotes the depression of pyrolusite. JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014

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Fig. 12. Flotation results of ore samples as a function of sodium silicate concentration (Armac C 2000 g/t, Pin oil 120g/t, pH 9).

Table 4. Flotation results on the ore sample and jigging concentrate with and without depressant consumption Flotation feed

Depressant, g/t

Collector, g/t

Ore sample

-

1000

Jigging concentrate

-

1000

Jigging concentrate

-

2000

Jigging concentrate

1000

1000

Products Concentrate Tailing Concentrate Tailing Concentrate Tailing Concentrate Tailing

Grade, % MnO 21.8 12.2 34.1 11.9 32.5 11.7 36.9 11.2

CaO 37.5 46.8 28.8 39.7 30.3 38.6 26.1 40.7

Recovery, % MnO 46.8 53.2 62.8 37.2 54.4 45.6 61.6 38.4

CaO 28.7 71.3 29.2 70.8 36.2 63.8 26.9 73.1

In the case of jigging concentrate, the use of 1000 g/t sodium silicate in the presence of 1000 g/t collector improves MnO grade up to almost 37% without a significant decrease in its recovery. This shows that by decreasing the content of gangue minerals in the jigging concentrate, the MnO grades and recoveries are improved. 4. DISCUSSION

Pyrolusite responds to the Armac C as cationic collector at pHs of 8-9 above the PZC where pyrolusite is charged negatively. This suggests that the collector is physically adsorbed by electrostatic interaction with the negatively charged mineral surface. Contrary to expectations, the flotation experiments and FTIR analysis showed that Armac C is also physisorbed on the calcite surface. This is probably due to the activation of the calcite surface by some anions present in the flotation system. By adding ZnO (Zn2+ cations), the anions are neutralized and the calcite surface is prevented from being active, and the calcite flotation recovery consequently decreases. Although the further increase of Zn2+ ions depress the calcite mineral significantly, it increases the zeta potential and PZC of pyrolusite, and hence affects the collector adsorption on the pyrolusite surface and its flotation negatively. In the pyrolusite–calcite flotation system (ore sample flotation) calcium ions dissolved from calcite are relatively abundant which have a negative effect on pyrolusite floatability. This can be due to the increase of pyrolusite zeta potential by adsorption of Ca2+ ions on its Helmholtz layer which results in a decrease in cationic collector adsorption and pyrolusite flotation. Sodium silicate known as a suitable depressant for the calcite mineral interacts with calcium ions in the solution forming nearly insoluble calcium silicate [16] which results in calcite depression. Also, the interaction of sodium silicate with calcium ions can eliminate their negative effects on pyrolusite floatability. This occurs at low dosages of sodium silicate as observed from Fig. 12. At higher dosages of sodium silicate pyrolusite is also depressed strongly. For the studied ore, a proper way for achieving an appropriate manganese concentrate is flotation of pyrolusite from the pre-concentrate prepared by gravity separation methods. Because, by reducing the calcite mineral volume in the flotation feed the negative effect of dissolved Ca2+ ions is considerably decreased. JOURNAL OF MINING SCIENCE Vol. 50 No. 5 2014


993

CONCLUSIONS

However, pyrolusite is floated significantly using Armac C at a pH of 8-9, but calcite mineral is also floated in this pH range. Armac C is physisorbed on pyrolusite with negative surface charge while its physisorption on calcite occurs after its activation with present anions in the flotation system. The low dosage of sodium silicate and zinc oxide depresses calcite more than pyrolusite while at the high dosages they depress both minerals. Quebracho and sodium hexa methaphosphate (SH) strongly depress pyrolusite and calcite. Calcium ions negatively affect the flotation recovery of pyrolusite. The ore flotation experiments indicated that the selective flotation of pyrolusite using Armac C is very difficult. This can be due to higher content of Ca2+ ions dissolved from the semi soluble calcite mineral in the flotation pulp which results in the decrease of pyrolusite floatability. It is possible to attain a suitable concentrate by carrying out flotation under optimal conditions on gravity method pre-concentrates containing a lower amount of calcite. REFERENCES 1. Delian Fan and Peiji Yang, Introduction to and Classification of Manganese Deposits of China, Ore Geology Reviews, 1999, vol, 15, pp. 1–13. 2. Corathers L.A. and Machamer J.F., Manganese, Industrial Minerals and Rocks, Jessica Elzea Kogel, Nikhil C. Trivedi, James M. Barker and Stanley T. Krukowsk (Eds.), 2006, pp. 631-637. 3. Fuerstenau, M. C., Han, K.N., and Miller, J.D., Flotation Behavior of Chromium and Manganese Minerals, Proc. Arbiter Symposium, Advances in Mineral Processing, 1986, pp. 289–307. 4. Wensheng Zhang and Chu Yong Cheng, Manganese Metallurgy Review. Part I: Leaching of Ores/Secondary Materials and Recovery of Electrolytic/Chemical Manganese Dioxide, Hydrometallurgy, 2007, vol. 89, pp. 137–159. 5. Bochkarev, G.R., Pushkareva, G.I., and Kovalenko, K.A., Sorption Properties of Manganese Ores, J. Min. Sci., 2011, vol. 47, no. 6, pp. 837–841. 6. Abeidu A.M., The Feasibility of Activation of Manganese Minerals Flotation, Trans. JIM, 1972, vol. 14, pp. 45–49. 7. Mishra, P.P., Mohapatra, B.K., and Mahanta, K., Upgradation of Low-Grade Siliceous Manganese Ore from Bonai-Keonjhar Belt, Orissa, India, Journal of Minerals & Materials Characterization & Engineering, 2009, 8 (1), pp. 47–56. 8. Fuerstenau, D.W. and Shibata, J., On Using Electrokinetics to Interpret the Flotation and Interfacial Behavior of Manganese Dioxide, International Journal of Mineral processing, 1999, vol. 57, pp. 205–217. 9. Fuerstenau, D.W. and Pradip, T., Zeta Potentials in the Flotation of Oxide and Silicate Minerals, Advances in Colloid and Interface Science, 2005, vol. 114–115, pp. 9–26. 10. Fuerstenau, M.C. and Palmer, B.R., Anionic Flotation of Oxide and Silicates, Flotation. A.M. Gaudin Memorial Volume, Fuerstenau, M.C. (Ed.), AIME, New York, 1976, Chap. 7, pp. 148–196. 11. Natarajan, R. and Fuerstenau, D.W., Adsorption and Flotation Behavior of Manganese Dioxide in the Presence of Octyl Hydroxamate, International Journal of Mineral Processing, 1983, vol. 11, pp. 139–153. 12. Mehdilo. A., Hojjati-rad. M.R., and Irannajad, M., Process Mineralogical Studies of Charagah Manganese Ore, Proc. International Mining Congress and Exhibition, 2010, Tehran, Iran. 13. Irannajad, M., Beneficiation of Charagah Manganese Ore, Report of Research Project, 2010, Amirkabir University of Technology, Tehran, Iran. 14. Srdjan, M. Bulatovic, Handbook of Flotation Reagents Chemistry, Theory and Practice: Flotation of Sulfide Ores, Elsevier Science & Technology Books, 2007. 15. Donald L. Pavia, Gary M. Lampman, George S. Kriz, and James R. Vyvyan, Introduction to Spectroscopy, Fourth Edition, Brooks/Cole, Cengage Learning, 2009. 16. Russell M. Potter and George R. Rossman, The Tetravalent Manganese Oxides: Identification, Hydration, and Structural Relationships by Infrared Spectroscopy, Amer. Mineralogist, 1979, vol. 64, pp. 1199–1218. 17. http://minerals.gps.caltech.edu/FILES/Infrared_MIR/index.htm. 18. Hans H. Adler and Paul F. Kerr, Infrared Study of Aragonite and Calcite, Amer. Mineralogist, 1962, vol. 47, pp. 700–717.
