Biological Enrichment of Chromite ore on Alkaline Roasting using Seidlitzia Rosmarinus Ash

Introduction

Chromium and its byproducts have broad applications as stainless steel production, chromic acid plating, corrosion control and etc.^1-3 chromium is present in many minerals, occasionally combined with iron oxides and other transition metal oxides such as manganese, titanium, vanadium, niobium and etc. ⁴

Chromite ore  belongs to the  spinel group with the general chemical formula of XY₂O₄ which  X and Y  represent  divalent and trivalent metal ions .the natural mineral is usually represented by the general formula (Fe²⁺ ,Mg )(Cr, Al ,Fe³⁺)₂O₄ with sometimes small quantities of  Magnesium , Titanium  and Vanadium ⁵.

Production of sodium chromate from chromite ore is requisite reaction for producing other products ⁶. sodium chromate was manufactured by leaching of chromite ore using sodium hydroxide and sodium carbonate at temperatures 1000°C in an atmosphere of oxygen ^7,8. A process such as soda- ash roasting ⁹, acid leaching ¹⁰, alkaline leaching ^11,12,  alkaline roasting using sodium hydroxide, potassium hydroxide and water leaching ¹³, have been developed for the processing of chromite ore in order to produce sodium chromate.

The conventional  methods such as Pyro metallurgy or Hydrometallurgy, are not economic and ecofriendly. therefore   Bioleaching of minerals is a suitable way for solves these problems. recently Bioleaching of ores using microorganisms was reported ¹⁴.

In this study, leaves and branches of S. Rosmarinus in oxidizing atmosphere was used as environmentally friendly and economical source for alkaline roasting of chromite and resulting solid cake was dissolved in distilled water to remove insoluble Iron (III) oxide and magnesium oxide from  soluble chromates.

Experimental Methodology

The Concentrated chromite was obtained from a sabzan mine of faran, Kerman, Iran. The composition of concentrate sample used is given in table1. Concentrate was sieved into 200 mesh. S. Rosmarinus Leaves was collected from desert of bajestan, Khorasan, Iran.

The S. Rosmarinus leaves were cleaned with double distilled water, shade-dried and ground to powder and stored for further study.

3.3 g of chromite ore and 6.6 g of grinding plant was wearing up and uniformed. The mixture was transferred to crucible and putting up in 1100°C for 2h. Roasting mixture Chromite was cold and wear up in pounder and then mixed with water in 50 ml flask with fixed temperature 60°C in presence magnetic stirrer.

The UV–vis spectrum was recorded on a double beam spectrophotometer (Shimadzu, model UV-2550) from 200 to 500 nm. The solution was filtered, concentrated and dried in an oven for further analysis. Element Analysis of solid sample was confirmed by ED 2000 belong Oxford company of England X-ray Fluorescence (XRF) Spectrometer. for evaluation of the mineral structure of sodium chromate, X-ray powder diffraction using Cu-Kα radiation over an angle (2θ) range of 5 to 90°. With step: 0.04 with the support of X’ Pert software was used.

Results and Discussion

Characterization of chromite ore

The original mineral phase in chromite is FeCr₂O₄ .also  existence of trace of titanium. nickel and manganese has been proven ¹⁵.

The elemental analysis results of chromium have shown in table 1. this result shows that the most percentage of elements respectively belong to chromium, silicon, iron and magnesium.

Table 1: Chemical composition of chromite was determinate by XRF

Compound	Cr2O3	SiO2	Fe2O3	MgO	Al2O3	SO3	P2O5	MnO	CaO	TiO2	NiO
Percentage	44.94	20.47	18.89	10.06	2.91	0.56	0.55	0.45	0.22	0.16	0.16

 

Characterization of S. Rosmarinus ash

Chemical compositions of roasted plant in 1100°C determinate by XRF and were shown in table 2. this result shows the existence of elements such as sodium, potassium, calcium, magnesium and Strontium that confirmed alkaline assistance role of S. Rosmarinus ash.

Table 2: Chemical composition of S. Rosmarinus was determined by XRF

Compound	CaO	SiO2	K2O	Na2O	MgO	SO3	Cl	Fe2O3	Al2O3	SrO	TiO2	MnO	other
Percentage	31.63	18.05	11.32	8.49	7.67	7.23	4.6	4.97	3.34	0.71	0.54	0.54	0.48

 

Roasting of Chromite using S. Rosmarinus ash and leaching with water

The comparison, chemical composition of chromium, S. Rosmarinus and soluble chromates in table 1,2 and 3, show a large percentage of chromium has been belonging to SiO₂, that destroyed during the process. deletion of Fe₂O₃ and decreasing in the percentage of magnesium show formation of insoluble compound as Fe₂O₃ and MgO.  Low change in the percentage of potassium and sodium, and increase in the percentage of chromium, confirm the formation of soluble chromates as Na₂CrO₄ and K₂CrO₄.

Table 3: Chemical composition of soluble chromates produced by roasting using S. Rosmarinus and leaching with water

Compound	Cr2O3	SO3	Na2 O	K2O	Cl	MgO	Al2O3	CaO	SiO2	MnO	Sb2O3
Percentage	65.07	13.66	7.52	6.18	2.83	1.87	1.26	0.42	0.38	0.23	0.18

 

The Comparison chemical composition of S. Rosmarinus ash and soluble chromates in table 2 and 3 show decrease in the percentage of elements as calcium, strontium and magnesium, that Proves formation of insoluble chromates include CaCrO₄, MgCrO4 and SrCrO₄. This changes justified by equation 1 to 7.

Meanwhile roasting of chromite, probable reaction was accrued that  equation 1to 7 shows this process.

(M is Representative of alkali metals)

Equation 3-6 show possibility reaction of some of impurities as SiO₂, FeAl₂O₄ and MgFe₂O₄ with MOH, but ∆G in equation 1 and 2 is more negative therefore the formation of Chromates is more likely ¹⁶.

Analysis of UV-Vis Spectroscopy

The UV–vis pattern of Na₂CrO₄ in Fig1 showed bands in 270 and 370nm mainly attributed to ligand -to -metal charge transfer (LMCT) band [17].

Figure 1: UV-Vis spectrum sodium chromate Click here to View figure

 

XRD Studies

Fig 3 shows XRD Pattern of sodium chromate. Intense Peaks at the various angular position which indexed to JCPDS 22-1365 was attributed to Na₂CrO₄ with orthorhombic structure and network Parameters a=7. 1462 b=9.2635, c=5.864, existence a few impurities Na_0.2K_0.8CrO₄ with monoclinic structure and network Parameters a=9. 939, b=5. 625, c=7. 163 were confirmed ¹⁸.

Figure 2: XRD spectrum of Na2CrO4 Click here to View figure

 

Conclusion

In summary, the conversion of chromite ore to soluble chromates was achieved in two steps, alkali roasting by S. Rosmarinus ash and water leaching. XRF studies showed increases in the percentage of chromium from 44.94 to 65.07. Therefore S. Rosmarinus ash could act as Leach suppliers. UV-vis studies showed three picks due to charge transfers that confirmed formation of sodium chromate. The results obtained from XRD studies showed indicator picks due to orthorhombic structure of Na₂CrO₄.

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This work is licensed under a Creative Commons Attribution 4.0 International License.