Mechanism of vanadium slag roasting with calcium oxide

doi:10.1016/j.minpro.2015.03.007

International Journal of Mineral Processing

Volume 138, 10 May 2015, Pages 20-29

https://doi.org/10.1016/j.minpro.2015.03.007 Get rights and content

Highlights

•
Fayalite is more likely to be oxidized than vanadium spinel thermodynamically.
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Oxidation of Fe^2 + contained in the augite to Fe^3 + is hindered by diopside.
•
Lowering heating rate will improve the vanadium recovery obviously.
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Oxidations of vanadium spinel and augite overlap at heating rate of 3 °C·min^− 1.
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Only oxidation of spinel occurs in 657–914 °C at heating rate of 5 °C·min^− 1.

Abstract

Thermodynamic analyses, XRD characterization and non-isothermal oxidation kinetic analyses were conducted to find the mechanism of vanadate formation when vanadium slag was roasted with calcium oxide. The effects of heating rate, added amount of CaO, holding temperature and holding time on oxidation efficiency were investigated. Thermodynamic calculations show that the fayalite is more likely to be oxidized than vanadium spinel, formation of calcium vanadates is easier than that of Mn(VO₃)₂ and Mg(VO₃)₂ and the oxidation of Fe^2 + in augite is hindered by the presence of diopside. TGA results show that lowering the heating rate can improve the oxidation efficiency of vanadium. The maximum vanadium recovery of 93.3% was achieved when the vanadium slag with a ratio of m(CaO)/m(V₂O₅) of 0.42 was roasted at 850 °C for 2.5 h. Dynamic heating experiments indicate that oxidations of vanadium spinel and augite overlap within 608–959 °C with a heating rate of 3 °C·min^− 1, while only oxidation of spinel occurs within 657–914 °C at 5 °C min^− 1. The oxidation was controlled by a 3/2 reaction and a third order reaction, with corresponding overall apparent activation energy values of 140.3 and 247.8 kJ·mol^− 1 for the heating rates of 3 °C·min^− 1 and 5 °C·min^− 1, respectively.

Introduction

Vanadium, as a very important transition metal, is widely used in various fields (Liao and Bo, 1985, Moskalyk and Alfantazi, 2003). At present, the primary vanadium resources are vanadium slag, stone coal, steel slag and spent catalyst. Vanadium slag which is a by-product of vanadium titanomagnetite accounted for more than 38% of the world's overall vanadium production in 2009 (Polyak, 2011). Processes comprising roasting, leaching, purification of aqueous solution, and precipitation steps are commonly employed in vanadium extraction from vanadium slag to produce vanadium pentoxide, of which, roasting plays a more important role in the whole process chain of vanadium.

Since problems like difficulties in sodium salt recovery, utilization of tailings, and environmental pollution, exist in the conventional roasting process with sodium salts (i.e. Na₂CO₃, NaCl and Na₂SO₄), this process is not favored; hence, it is essential to develop some new processes for the clean production of vanadium oxide. Sub-molten salt (Liu et al., 2013), carbonate salt (Li et al., 2011) and compound salt roasting for vanadium extraction can decrease the amount of poisonous gas discharge; however, they cannot eliminate the hazard of sodium or potassium in the tailings and waste water. Calcium salt roasting was firstly proposed by the Russia Tula factory in 1970s and it was not applied commercially due to lower recovery of vanadium compared with sodium salt roasting (Liao and Bo, 1985). However, it does have benefits of lower cost of additive, no emission of pollutional gas, and no sodium or potassium contained in tailings and waste water, so this process is of increasing interest.

Vanadium slag roasting with calcium oxide is an oxidation process. Vanadium embedded in the slag presents as V^3 +, and with roasting, V^3 + is oxidized to V^4 + and V^5 + and converted to vanadate which can be dissolved in a subsequent leaching step. Many investigations (Cao, 2012, Li et al., 2012, Li, 2011) have focused on the effects of roasting parameters, including the ratio of m(V₂O₅)/m(CaO), roasting temperature and roasting time, on the vanadium recovery. Van Vuuren and Stander (1995) studied the oxidation kinetics of synthetic FeV₂O₄ over the temperature range of 200–580 °C and the oxidation of synthetic FeV₂O₄ in a sodium carbonate mixture (Van Vuuren and Stander, 2001). Voglauer et al. (2004) investigated the reaction kinetics of vanadium roasting process in steel slag. In this paper, the thermodynamics of a converter vanadium slag roasting process with calcium oxide was analyzed. Effects of heating rate, added amount of CaO, holding temperature and holding time on oxidation and recovery of vanadium, and experimentally the relationships between the heating rate and the optimum holding temperature were studied. The roasted samples prepared under different roasting conditions were characterized by X-ray diffraction (XRD). The oxidation kinetic equations and apparent activation energy values for a vanadium slag roasting process in the presence of calcium oxide were obtained using differential scanning calorimetry and thermal gravimetric (DSC–TG) methods.

Section snippets

Materials

The chemicals used in this study (CaO, H₂SO₄, (NH₄)₂Fe(SO₄)₂·6H₂O, C₁₃H₁₁NO₂, H₂NCONH₂, NaNO₂ and KMnO₄) were all of analytical grade (Sinopharm Chemical Reagent Co., Ltd, purity > 98%). CaO was used as the additive for vanadium slag roasting and was dried in an oven at 120 °C for 24 h before use. The other chemicals were used to determine vanadium content in the slag with ammonium ferrous sulfate titration method. Water used in experiments was deionized one time. Vanadium slag was supplied by

Thermodynamic analysis for roasting process

Vanadium spinel surrounded by matrix phases—fayalite and augite, is the main vanadium-bearing phase in converter vanadium slag. In order to obtain a high oxidation efficiency of vanadium, the structure of the binding phases should be destroyed firstly to liberate the vanadium spinel and then it is easier for oxygen to contact with vanadium spinel directly. The trivalent vanadium is oxidized into pentavalent vanadium and then converted to dilute acid soluble vanadate.

Reactions possibly occurring

Effects of heating rate and holding temperature

It was found previously that the cooling rate of roasted slag had little effect on vanadium recovery (Cao, 2012). This paper presents the effect of heating rate on vanadium recovery and the relationships between heating rates and the obtained optimum roasting temperatures under the conditions where 6% CaO was added (assuming the vanadium slag weight as 100%), particle size was within 48–75 μm and holding time was 2 h. The results are shown in Fig. 7.

Reducing the heating rate from 4 to 2 °C per

Evaluation of the results

Using calcium roasting process to extract vanadium from converter slag was proposed in the 1970s, however, an understanding of the roasting mechanism of converter slag with CaO is still not clear and needs to be developed.

In this paper, from the thermodynamic analyses, it is found that metal iron and fayalite should be oxidized thermodynamically more easily than vanadium spinel. Some Mn^2 + in the slag can be oxidized to Mn₂O₃, while other Mn^2 + can react with V₂O₅ to form Mn(VO₃)₂ at temperatures

Conclusions

(1)
The roasting process of vanadium slag with lime was investigated. Thermodynamic analysis predicts that oxidation of fayalite is more favorable than that of vanadium spinel; formation of calcium vanadates is energetically easier than that of manganese vanadate (MnV₂O₆) and magnesium vanadate (MgV₂O₆); oxidation of Fe^2 + to Fe^3 + in augite is hindered by the chemically stable diopside. Oxidation of fayalite, spinel and augite and formation of vanadates are all exothermic reactions.
(2)
Lowering heating

Acknowledgments

This project (FMRU2007K10) was supported by the Open Research Fund of Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology.

References (17)

I. Barin
Thermochemical Data of Pure Substances
(1995)
P. Cao
Research on vanadium slag roasting with calcium salt
Iron Steel Vanadium Titan.
(2012)
H.S. Chen
Study on extracting vanadium pentoxide from roasted vanadium slag with lime
Iron Steel Vanadium Titan.
(1995)
A.W. Coats et al.
Kinetic parameters from thermogravimetric data
Nature
(1964)
D.S. He et al.
An environmentally-friendly technology of vanadium extraction from stone coal
Miner. Eng.
(2007)
M. Kowalski et al.
Slag Atlas
(1995)
X.S. Li
Mechanism Research on Oxidation Roasting and Leaching Process of High Calcium Low-Grade Vanadium Slag
(2011)
X.S. Li et al.
Oxidation process of low-grade vanadium slag in presence of Na₂CO₃
Transit. Nonferrous Met. Soc. China
(2011)

There are more references available in the full text version of this article.

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View full text

Mechanism of vanadium slag roasting with calcium oxide

Highlights

Abstract

Introduction

Section snippets

Materials

Thermodynamic analysis for roasting process

Effects of heating rate and holding temperature

Evaluation of the results

Conclusions

Acknowledgments

Thermochemical Data of Pure Substances

Research on vanadium slag roasting with calcium salt

Iron Steel Vanadium Titan.

Study on extracting vanadium pentoxide from roasted vanadium slag with lime

Iron Steel Vanadium Titan.

Kinetic parameters from thermogravimetric data

Nature

An environmentally-friendly technology of vanadium extraction from stone coal

Miner. Eng.

Slag Atlas

Mechanism Research on Oxidation Roasting and Leaching Process of High Calcium Low-Grade Vanadium Slag

Oxidation process of low-grade vanadium slag in presence of Na2CO3

Transit. Nonferrous Met. Soc. China

Oxidation process of low-grade vanadium slag in presence of Na₂CO₃