Chemical Analysis of Hematite Ore Collected from Pokhari, Nawalparasi, Nepal

Iron is the principal raw material for steel industries and Hematite is a principal ore of iron. Quantitative and qualitative estimation of iron in its ores is a crucial factor before its extraction. In this work, quantitative chemical analysis of iron was carried out from the collected seventy-two hematite samples from Pokhari, Nawalparasi. Sampling of the hematite ore was performed by channel sampling method. Chemical analysis was carried out by gravimetric, titrimetric, UV-Vis spectrophotometric and atomic absorption spectroscopic methods. The findings of different parameters in percentage areas follows: loss on ignition (1.76 ± 0.17), silica (47.06 ± 4.01), and iron (36.75 ± 2.50) by titrimetric analysis. Based on the chemical analysis, the Fe content in the collected hematite sample is in intermediate range. Thus, for the profitable iron extraction, other factors such as coverage of ores, extraction costs, and market value should be considered.


Introduction
Determination of iron content in rocks and minerals is an important aspect in metallurgical, geochemical, and petrochemical investigations [1]. Iron is the least expensive and most widely used metal which is extensively used for the infrastructure development works, heavy machinery tools, agricultural tools, and household utensils. Hematite and magnetite are commonly exploited iron-bearing ores among the various minerals of iron like hematite (α-Fe 2 O 3 or α-polymorph of ferric oxide), maghemite (c-Fe 2 O 3 ), magnetite (Fe 3 O 4 ), limonite (FeO (OH). nH 2 O or hydrated ferric oxide hydroxide), goethite (α-polymorph of limonite), siderite (FeCO 3 ), and pyrite (FeS 2 ) [2,3]. Except hematite, other ores are less stable in ambient conditions, and also, contain less amount of iron. e presence of impurities lowers the percentage of iron in the ore. e quality of iron ore is evaluated based on the iron content. More specifically, the ores having iron content above 65% are regarded as highgrade; iron content in the range of 62-64% is medium (average) grade, and iron content below 58% is considered as low-grade ores [4,5]. Generally, hematite ores containing less than 30% iron are not preferable for extraction from economic point of view until and unless it is not ruled out by some other relevant factors such as superficial location of ores, cheap economy of extraction, and surface located ores. However, dawn of newer technology can support the extraction of ores under minimum cost contrary to the conventional methods of extraction.
It is reported that iron (III) oxide has four polymorphs, namely, alpha, beta, gamma, and zeta-iron oxides with molecular representation, α-Fe 2 O 3 (hematite), β-Fe 2 O 3 , Υ-Fe 2 O 3 (maghemite), є-Fe 2 O 3, respectively. Out of them, α-Fe 2 O 3 is antiferromagnetic while the remaining all are ferromagnetic [6,7]. Magnetite (Fe 3 O 4 ) is also ferromagnetic substance. Hematite (Fe 2 O 3 ) is a reddish-brown, heavy, and relatively hard oxide mineral of iron. It is harder and more brittle than pure iron. Fe 2 O 3 possesses a corundum structure specifically trigonal hexagonal scalenohedral, holohedral, and rhombohedral crystal structure, and it is highly stable in ambient conditions [8]. Iron is a major component of hematite ore and forms a principal constituent of steel. e world's iron ore production increased from 274 million tons (in 1950 AD) to 1554 million tons (in 2005 AD) [9]. By the end of the twentieth century, iron consumption for steel manufacture only was standing 850 million tons. It is estimated that the world resource of crude iron ores is approximately 800 billion tones containing more than 230 billion tons of iron [10]. e known resources of iron ores could run out within the next 64 years as the demand for iron is increasing 10% per year. Most of the known deposits contain low-grade ores with iron contents less than 30% [11]. In this context, it is very urgent to search the mines of iron ore, their distribution, deposits, financial, economic, and chemical tests to extract iron from it.
In the case of Nepal, though iron ores were mined and smelted sporadically even before 1951 (2007 BS), no significant progress has been made hitherto [12]. Preliminary studies show some iron deposits in Nepal. ough the occurrences of iron ores are known in many places but only four occurrences in notable quantity are reported. ey are Phulchoki iron deposit in Lalitpur district. ose iron deposit in Ramechhap district, Labdi iron deposit in Tanahu district, and Dhaubadi iron deposit in the East Nawalparasi district. e estimated total ore content in these four places is 124.1 million tons [13,14]. By now, Dhaubadi iron deposit is quantitatively the largest mine of iron reported in Nepal.
Dhaubadi area of Nawalparasi district shows 25-100-m thick hematite mineralized bed with a strike length of about 10 km from Pokhari to Dhaubadi at 3-5-km width in preliminary and follow-up exploration [15]. To establish the project for the extraction of iron from Dhaubadi iron deposits, geographical, deposition estimation, economic, and financial estimation have been carried out. It is reported that the return of investment (ROI) is 34% and hence it is an economical and beneficial project for the extraction of a large amount of iron ore from the Pokhari area [16]. e iron ores of Dhauwadi are expected to be extracted more economically due to its superficial location compared to the other known iron reserves. is new reserve is important due to its relatively high deposit of iron ore in addition of being rural area and low population density which supports for the relatively lower cost of investment. e chemical compositional analysis is also a crucial step to establish an extraction project. Based on the percentage of iron content, financial and economical investment can be estimated. In this context, from the chemist view point, it is utmost necessary to determine the iron content precisely. For this purpose, various chemical techniques and procedures can be adopted. Commonly used methods for the determination of iron content are X-ray fluorescence spectroscopy, atomic absorption spectroscopy, or plasma atomic emission spectrometry [1]. For high iron content sample, titrimetric analysis can be a good method for quantitative analysis. Besides this, other precise methods of quantitative analysis such as determination of concentration of iron by UV-visible spectrophotometric method and atomic absorption spectroscopy method can be adopted. e quantitative analysis of iron can be studied under different parameters like finding the loss on ignition (LOI), sulphur content, acid insoluble matter, and percentage iron content. Based on the findings, the appropriate methods of extraction can be recommended. For instance, iron ores pellets are essential input materials in the manufacture of steel which can be reduced by reducing gas (a mixture of hydrogen and nitrogen gas) [17]. In the work of Jonathan et al., iron was separated from zinc mine tailings via wet magnetic separation followed by carbothermal reduction of self-reducing briquettes [18]. Jorge et al. developed a self-reducing briquettes using biomass source such as charcoal, palm oil charcoal, eucalyptus bark charcoal, and basic oxygen furnace dust [19]. All in all, before embarking the extraction process, it is the parts and parcel to assess the ores chemically.
In this work, it is hypothesized that the presence of some volatile impurities, moisture and acid insoluble impurities in hematite ore, largely affects on the determination of percentage of iron. erefore, this study aims to find the percentage of extractable iron from the ore besides finding loss on ignition (LOI), sulphur content, and acid insoluble matter in the sample. Furthermore, qualitative and quantitative estimation of iron from the hematite ore is also carried out by UV-Vis analysis and AAS method. Total iron content is determined by titrimetric method as per the protocol of IS: 1493 (part 1): 1981 method [20]. A comparative data of iron content in the hematite ore has been presented in this work. Ltd. All reagents were of analytical grades and were used without any further purification. Hematite ores collected from Pokhari, Nawalparasi were used for analysis.

Sample
Collection. Seventy-two hematite samples were collected from the Pokhari area of the east Nawalparasi district by channel sampling method. All samples were collected from 8 different channels, each channel containing nine samples. Channels were drilled 750 m apart. e topogeological map of the sample collection site is given in Figure 1. . About 20 gram of each sample was dried in an oven at a temperature of about 100°C for an hour and allowed to cool down inside a desiccator. A known weight (1 g) of each sample was taken in a crucible and allowed to heat at a temperature of 1000°C for one hour in an electric muffle furnace (NABERTHERM, LE6/11/R7, Germany) at a rate of 10°C/min to expel all volatile impurities and to oxidize all iron content into iron oxide. en the sample in crucible was cooled in controlled condition. en, weight of each sample was measured using 4-digit balance and weight difference before and after ignition was calculated [22,23].

Gravimetric Determination of Sulphur Content.
e iron ore is likely to be associated with sulphide (Iron pyrite, chalcopyrite and others) and sulphate ores for which sulphur estimation is inevitable [24]. In this work, sulphur content was determined gravimetrically. All the sulphur (sulphate sulphur) was targeted to convert into barium sulphate. Any sulphide ions can be precipitated by treating with barium chloride but this work was limited for the estimation of sulphate sulphur [25]. For the determination of sulphur in the sample, 0.5 g of dry ore sample was taken into a 500 mL beaker, 70 mL of acid mixture (60 mL HCl and 10 mL HNO 3 ) was added, and then heated at 110°C to evaporate till dryness followed by cooling. en, 30 mL of dil. HCl was added in it, warmed, 25 mL of water was added on it, and then boiled for 5 minutes. e solution was filtered through Whatman no. 40, and the filtrate was collected into a beaker and evaporated to 25 mL and cooled. 3 mL (1 : 1) HCl and 50 mL water were added in it and then heated. en, 10 mL of 10% BaCl 2 solution was added on hot solution slowly and the solution was heated to the boiling for 5 minutes. e white precipitate of barium sulphate was filtered off through Whatman no. 42 and washed to make it free from impurities. e precipitate was dried and ignited into an electric muffle furnace at 500°C for 30 minutes then 800°C for another 30 minutes until a constant mass was obtained, and the amount of sulphur was calculated.
where m 1 is the mass in grams of platinum crucible and BaSO 4 , m 2 is the mass in grams of platinum crucible only, and m 3 is the mass of sample taken.  further heated for half an hour. e samples were leached with 10 mL of conc. HCl and then added 20 mL of water. e solution was filtered through Whatman no. 40 filter paper. e filtrate was collected into a volumetric flask and the volume was made 500 mL. e acid-insoluble residue was heated into a muffle furnace for an hour at a temperature of 1000°C, and then the percentage of acid insoluble matter or silica was calculated [22].

Titrimetric Determination of Iron Content.
In this experiment, the total iron content was measured by the titrimetric method. Total iron content in the sample was determined as per the protocol of IS: 1493 (part 1): 1981 method. For this, 20 mL of aliquot was titrated against 0.1-N potassium dichromate solution using diphenylamine sulphonate as an indicator in the presence of stannous chloride, mercuric chloride, a mixture of H 2 SO 4 -H 3 PO 4 reagents. Here, sulphuric acid-phosphoric acid combination was used for leaching. In a similar work, AMilton et al. also used sulphuric acid-phosphoric acid for leaching [26]. Total iron present in a given ore is calculated by the following formula [23]: Here, V is the volume of aliquot in mL and N is the normality of solution.

UV-Vis Spectrophotometric Determination of Iron
Content. It is reported that the iron content in the ore from Europe and Brazil measured by the titrimetric method was highly correlated with spectrophotometric measurement [27]. e amount of iron content present in the ores was measured by UV-Vis spectrophotometric method. For this purpose, 100-ppm standard reference solution was prepared by dissolving ammonium iron (III) sulphate dodecahydrate in deionized water.

Method
Validation. Different concentrations of iron (III) solution (80, 40, 20, 10, 2.5, 1, 0.50, 0.25 ppm) were prepared by serial dilution of 100-ppm solution [23]. For color development, 1 mL of 0.1 M KSCN solution was added into 9 mL of each diluted solution. e double beam UV-Vis spectrophotometer (Labtronics, Model LT-2802) was used for the measurement of absorbance of the solution [28]. e method validation is useful to determine the limit of detection (LOD � SD of blank solution × 2), limit of quantification (LOQ � SD of blank solution × 10), linearity range, and measurement of uncertainty (MU). e measurement of uncertainty was evaluated from the relation, MU � SD of any measured solution × 2.

λ max Determination.
e wavelength for maximum absorption was determined by taking 2.5-ppm standard solution.

Preparation of Calibration Curve.
e calibration curve was plotted by taking a series of standard ferric thiocyanate (0.5, 1, 5, 10 ppm) solution.
is calibration curve was used to determine the concentration of iron in the analyte solution.

Determination of Iron Content by AAS Method.
e quantitative estimation of iron in the hematite ores collected from Pokhari, Nawalparasi District was carried out by Atomic Absorption Spectroscopy (AAS) method (SHI-MADZU, Model AA-7000, Japan). In this method, 1 g of powder sample was taken and 10 mL of 1 : 1 HNO 3 was added and refluxed for 10 minutes, followed by the addition of 5 mL concentrated HNO 3 and refluxed till the total volume was reduced to 5 mL. In the reduced volume, 2 mL of water was added followed by the addition of 3% of H 2 O 2 until the bubbling subsides. e solution was further refluxed to reduce volume up to 5 mL. en, 10 mL of concentrated HCl was added and refluxed for 15 minutes. e whole sample was filtered through Whatmann no. 42. e filtrate was taken and diluted to 100 mL in a volumetric flask [29]. is was taken as an analyte sample.

Method Validation.
For the method validation of iron estimation, different concentrations (from 0.25 to 100 ppm) of iron (III) were prepared and the blank solutions were taken. en their absorbance was measured in AAS.

Preparation of Calibration
Curve. Standard Fe (III) solutions of 0.5, 1, 5, 10 ppm concentrations were taken and their absorbance was measured to prepare a calibration curve.

Loss on Ignition.
Loss on ignition (LOI) is particularly performed at high temperature (in the range of 1000°C) for minerals. It represents organic as well as inorganic carbons, water, and volatile impurities which are chemically bound in the minerals. Strong heating (ignition) of an analyte at a specified temperature expels the volatile substances, organic and inorganic carbons. Metallic ores consist of moisture, water of crystallization, and other associated volatile impurities. e total volatile impurities contain carbonate, moisture, water of crystallization, sulphur dioxide, etc.

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Moreover, the LOI in hematite ore gives the rough proportion of the carbonate content, but not enough to claim actual content. e data obtained for each channel samples are presented in Table 1. Here, the value of LOI in the measured sample is in the range of 0.75 to 3.75% with mean ± SD value of 1.76 ± 0.17 as presented in Figure 2, indicating good level of precision in the result. is value is less in comparison to those obtained in the analysis of bauxite residue (14.5% and 14.8%, respectively, at 900°C and 1100°C) from a press filter system in the work of AMilton et al. [30]. erefore, it can be said that the loss on ignition is relatively less in the hematite ores.
e loss on ignition of the material reflects the actual materials lost during smelting or refining in a furnace. e weight loss could be attributed to the loss of volatile impurities, hydrates and labile hydroxyl compounds, and carbon dioxide from carbonates.

Gravimetric Determination of Sulphur Content.
To find the amount of sulphur content in the hematite ore as an impurity, experiments were carried out but sulphur was not found in measurable quantity.

Determination of Acid Insoluble Matter (AIM).
Silicon dioxide is a principal earthy material associated with iron ores. erefore, a lower percentage of silicon dioxide reflects a higher percentage of iron. In this work, the acid insoluble matter was estimated based on the gravimetric estimation. e percentage of AIM in every sample is found   in between 37 and 54% in the ore as represented in Table 2 and Figure 3. e majority of the acid insoluble material is considered to be silica, an earthy material. is value is a bit higher than a theoretical value. In the similar work on the magnetite-hematite ore of Mikhailovskoye, Nikolaeva reported the average content of silica in the range of 39.0-41.80% [31]. e hematite ores with minimum silica content are easy to remove the silica and the ores are considered to be profitable for the extraction of iron from the economic point of view. Nitric acid reacts with metal and hence oxidizes it. Even though the amount of acid insoluble material is a bit high, the hematite ore of the selected area is still not bad to establish the iron extraction industry.

Titrimetric Determination of Iron Content.
Iron is the major constituent of hematite ore. e collected samples of hematite ores from all channels were analyzed in the lab by titrimetric method. In this method, sulphuric-phosphoric acid combination is used for leaching, especially alumina [30]. In this work, experimental finding shows that Fe ranges from 34.06 to 42.53%. ese values are expressed in Table 3 and in Figure 4. e mean value is 36.75 ± 2.50 in terms of iron percentage. In the similar work, the iron content in magnetite-hematite ore of Mikhailovskoye as reported by Nikolaeva was also found in the range of 38.3-40.1% for which they regarded as "low-Fe grade". In the work of Jonathan et al. the concentrated materials showed 40.4% of iron where hematite ore was concentrated by flotation process [32]. Our findings of iron content in hematite ore are around the same value as reported by Nikolaeva [31]. eoretical value of iron in ultra-pure hematite ore is 70% and the ore containing less than 30% iron is not preferable for extraction until and unless the extraction is supported by low cost of extraction and market price of iron. However, the value obtained in this work falls in the lowgrade range and prospects to establish an extraction  industry. Here, it is to be emphasized that, not only the percentage iron content but also the total amount of deposition of ore determines the fate of iron extraction industry. Iron estimation of hematite ore by titration method, LOI, and SiO 2 content in the samples assigned from A to H is tabulated in Table 4.

UV Spectrophotometric Determination of Iron Content.
Iron solution only does not exhibit any peak in spectrophotometric determination. erefore, iron (III) was made complex with potassium thiocyanate to develop potassium hexathiocyanatoferrate (III) which can exhibit a color by interacting with photon of UV-Vis energy range. e chemical reaction takes place as follows: Method validation was carried out by taking a series of solution having concentrations of 80, 40, 20, 10, 2.5, 1, 0.50, 0.25 ppm as in Figure 5(a). From the measurement of UVvisible spectrophotometer, it was found that the limit of detection (LOD) was found to be 0.25 ppm. e limit of quantification (LOQ) was found to be 2.5 ppm, and the   Figure 5(b). is wavelength was taken as λ max . e calibration curve with R 2 � 0.998 was established by taking standard ferric thiocyanate solution as in Figure 5(c). is calibration curve was used to determine the concentration of iron in the analyte solution through which % of the iron in the hematite ore sample was calculated. e amount of iron was determined as in Figure 5(d). e iron content values of different samples of hematite ore determined by UV spectroscopic method are given in Table 5.

Determination of Iron Content by AAS Method.
In the determination of iron by AAS method, the uses of nitric acid react with metal and hence oxidizing it. In some cases, high silica content could be the problem in leaching step as it may cause silica gel formation. e silica gel formation can be avoided using hydrogen peroxide [30]. e standard deviation obtained by measuring the absorbance of the blank solution, limits of detection (LOD), and limits of quantification (LOQ) were calculated and found to be 0.003616 and 0.012054, respectively. Similarly, the linearity range was calculated and found from 0.25 to 20 ppm with R 2 � 0.998. Measurement uncertainty (MU) was determined by taking the reference of 2-ppm solution and found to be ±0.011. Method validation is further expressed in the following diagram 6(a). Standard Fe (III) solutions of 0.5, 1, 5, 10 ppm concentrations were taken and their absorbance was measured to prepare a calibration curve. e calibration curve obtained for this purpose was given in Figure 6(b) with an R 2 value of 0.998.
After the preparation of the calibration curve, the amount of iron present in the analyte sample was measured.
e percentage of iron content present in the samples was found similar to the titrimetric method. ese are shown in Figure 6(c). Iron content values of different samples of hematite ore determined by AAS measurement method are shown in Table 6.

A Comparative Study.
A comparative study shows that total eight samples, one from each channel were measured by the AAS method and compared with the UV-Visible Spectroscopic method and titrimetric method. e results obtained by all three methods are presented in Figure 7 and Table 7.
ough each method has its own pros and cons, AAS method is highly preferable and more accurate in comparison to others. It is because the data obtained by this method are highly précised. Taking example of channel D, the mean values for iron content measured by AAS, UV, and titration methods are 39.87, 35.28, and 42.53, respectively. Here, the value obtained by titration method is higher than that of AAS method. e reason behind it may be precise and careful visual and volumetric errors in titrimetric analysis. Such errors are not present in the instrumental methods so that they give more accurate results. But, the value obtained by UV measurement is lower than among. is could be more accurate but as we found that UV-Vis has high MU value, this may less precise value in comparison. e value obtained by AAS method is intermediate with high precision and could be more accurate. Also AAS has lower MU and less relative standard deviation in the results obtained by this method. All in all, results obtained from these three methods are comparable.

Conclusion
Total iron content and other parameters are measured by the titrimetric method using a standard protocol. e determined values show that the total iron content in the sample  is more than 36% representing the intermediate content. All in all, the adopted methods of test, i.e., AAS, UV-vis, and titration give the near value of iron content. e result showed a low-iron grade ore. Establishment of industry is influenced by some other factors such as processing cost, labor costs, and market prices. Considering several other factors determining the fate of running an iron industry, operation of iron industry could be feasible in case of high reservation of iron on relatively shallow mining state. As the extension of ore is about 10 km in length, 3-5 km in width, and 100 m deep with the expectation of about 100 million tons of reserved iron, the iron extraction industry could be profitable.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Additional Points
Highlights. Seventy-two samples of hematite ores were collected from Nawalparasi. LOI, sulphur content, and acid insoluble contents in the samples were studied. Titrimetric, UV analysis, and AAS methods were applied for the analysis of Fe. Collected samples have intermediate Fe content.

Conflicts of Interest
e authors declare that they have no conflicts of interest.