Effect of factors on the extraction of boron from slags
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I.
INTRODUCTION
A complex ore (ludwigite) containing 30 to 35 pct Fe, 6 to 12 pct B203, 20 to 25 pct MgO, 12 to 15 pct SiO2, 1 to 2 pct A1203, and 0.4 to 1 pct CaO is a very important source of boron and iron. The key to exploiting and using the ore lies in the separation of boron and iron as well as extracting boron efficiently. Several mineral processing and metallurgical processes ll-SJ have been proposed for treating the ore, such as magnetic separation, magnetic separation combined with flotation, selective reduction and magnetic separation, melting reduction, and hydrometallurgy. However, because of complex mineralogy and very fine mineral dissemination of the ore, the application of these processes to separate and extract boron from the ore may result in poor recovery of boron and high cost. For example, the recovery of boron was 44 to 64 pct and fine grind was required to produce adequate liberation with magnetic separation. The disadvantage of the hydrometallurgical method is that excessive hydrochloric acid consumption causes high cost and environmental pollution. However, when the ore was carefully treated by a high-temperature chemical process, all of the magnesia and 90 pct of the boron were concentrated in the molten slag and separated from liquid pig iron. 16,7,8]The slags become the raw material for extracting boron instead of a waste product. The urgent need is to extract boron from the slags efficiently. The concentration of B203 in the molten slag could be about 14 to 20 pct B203, but the efficiency of extraction of boron (EEB) from the slag was lower than 50 pct under natural cooling conditions, so it is very essential to study the factors that affect the EEB. The present work is aimed at estimating the factors influencing the EEB, and optimizing the extractive process. Additionally, it may provide a useful method for extracting valuable components from slags containing vanadium or rare earth.
In this article, the effects of slag composition, heat treatment, and additive agent on the EEB have been investigated.
II.
EXPERIMENTAL
A. Slag Preparation The chemical compositions of the slags selected for the present work were from the MgO-B203, CaO-B203, and MgO-BzO3-SiOz systems, as listed in Table I and shown in Figure 1. To samples 1 and 17 were added 1 wt pct TiOz, 3 wt pct TiOz, and 1 wt pct MOx, 3 wt pct MOx, respectively (Figure 11). Magnesia, silica, boron oxide, calcium oxide, alumina, titania, and iron oxide were chemical reagents with analytical purity. The slag samples were prepared in 100-g batches using the oxide powders as raw materials. Homogeneous mixtures in a graphite crucible were quickly melted in an induction furnace at 1500 ~ and then quenched in air to room temperature.
B. Heat Treatment of the Slags The composition of the slag for heat treatment was 49.4 wt pct MgO, 20.0 wt pct B 2 0 3 , 25.0 wt pct SiO2, 2.0 wt pct A1203, and 1.8 wt pct CaO. The slags were prepared in 100-g batches using the oxide powders as raw materials, the mixtures were placed in graphite crucibles
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