ALTERNATIVE BINDERS TO BENTONITE FOR IRON ORE PELLETIZING : PART II : EFFECTS ON METALLURGICAL AND CHEMICAL PROPERTIES

Osman Sivrikaya,A I Arol

doi:10.15628/holos.2014.1759

Abstract

This study was started to find alternative binders to bentonite and to recover the low preheated and fired pellet mechanical strengths of organic binders-bonded pellets. Bentonite is considered as a chemical impurity for pellet chemistry due to acid constituents (SiO2 and Al2O3). Especially addition of silica-alumina bearing binders is detrimental for iron ore concentrate with high acidic content. Organic binders are the most studied binders since they are free in silica. Although they yield pellets with good wet strength; they have found limited application in industry since they fail to give sufficient physical and mechanical strength to preheated and fired pellets. It is investigated that how insufficient preheated and fired pellet strengths can be improved when organic binders are used as binder. The addition of a slag bonding/strength increasing constituent (free in acidic contents) into pellet feed to provide pellet strength with the use of organic binders was proposed. Addition of boron compounds such as colemanite, tincal, borax pentahydrate, boric acid together with organic binders such as CMC, starch, dextrin and some organic based binders, into magnetite and hematite pellet mixture was tested. After determining the addition of boron compounds is beneficial to recover the low pellet physical and mechanical qualities in the first part of this study, in this second part, metallurgical and chemical properties (reducibility - swelling index – microstructure – mineralogy - chemical content) of pellets produced with combined binders (an organic binder plus a boron compound) were presented. The metallurgical and chemical tests results showed that good quality product pellets can be produced with combined binders when compared with the bentonite-bonded pellets. Hence, the suggested combined binders can be used as binder in place of bentonite in iron ore pelletizing without compromising the pellet chemistry.

Highlights

Bentonite is the most widely used binder in iron ore pelletizing
Metallurgical and chemical properties of thermally treated pellets of pellets produced with combined binders were determined and presented
In the first part of the study, the addition of boron compounds into pellet mixture was found to improve the lower preheated and fired pellet physical strength encountered with use of organic binders

Summary

Introduction

The use of bentonite is favorable in terms of physical, mechanical and metallurgical pellet qualities, because of its acid constituents (SiO2 and Al2O3) it is considered as an chemical impurity especially for concentrate with high SiO2 content. These acid oxides are known for their adverse effects on the iron-steel making economy. Since the purpose of iron ore processing is to remove silicate minerals from the ore, adding silicates back in the form of binder is counterproductive This has prompted long-term interest in developing or discovering binders that contain no silica. Because of good binding properties without contaminating the product pellets, organic binders have attracted attention among researchers. (Eisele and Kawatra, 2003, Sivrikaya, 2011)

Methods

Results

Conclusion