Effect Of B₂O₃ On The Metallurgical Properties Of Nickel Flash Smelting Slag

The flash furnace smelting is the main way of nickel smelting,whose raw material is mainly nickel sulphide ore,and the products are nickel slag and nickel matte.As high-grade nickel sulphide ores with high nickel content and low impurity content are consumed year by year,poor quality nickel ores with high magnesium content gradually become the main raw material in the nickel smelting process.The high magnesium content leads to changes in the melting point and viscosity of the slag,causing the nickel flash furnace smelting process to deviate from the normal optimum control point.In practice the process is mainly maintained in line by significantly increasing the smelting temperature,but this strategy leads to an increase in energy consumption and raises the production costs of the company.In this study,the addition of B₂O₃ to improve the viscous flow characteristics of the slag in the nickel flash furnace melting process was proposed,and the variation of the viscous flow characteristics of the Ca O-Si O₂-Fe O-Mg O-Al₂O₃-B₂O₃ slag system was investigated.The optimum melting conditions were determined to provide a theoretical basis for the addition of B₂O₃ to improve the viscous flow characteristics of the slag and to achieve the purpose of lowering the smelting temperature and reducing smelting energy consumption.The main research results obtained are as follows.(1)The main phases during the melting process of nickel flash furnaces containing boron are the iron-containing olivine phase(Fe₂Si O₄),(Fe,Mg)₂Si O₄)and the magnesium-containing pyroxene phase(Mg₂Si₂O₆),which also contains some co-oxides(Mg_xFe_xO).As the B₂O₃ content increases,(Fe,Mg)₂Si O₄ and Mg₂Si₂O₆ in the slag gradually evolve into Mg₂B₂O₃ and the liquid phase line temperature of the slag gradually decreases.When the B₂O₃ content in the slag is 4 wt%,the liquid phase line temperature decreases to the range of 1150?1200°C.(2)The viscosity and meltability temperature of the slag decrease with increasing B₂O₃ content;the effect on viscosity diminishes when the B₂O₃ addition to the slag is greater than 3 wt%;the viscous flow activation energy of the slag decreases from157.90 k J/mol to 141.84 k J/mol when the B₂O₃ content increases from 0 wt%to 4 wt%;B₂O₃ brings about a simple trihedral structure,forming more non-bridging oxygen(NBO)and asymmetric Si-O-B structural units,and combines with Mg-containing oxides in the slag to form a low melting point material,resulting in a lower slag viscosity;the modified Urbain model was used to estimate the slag viscosity studied in this paper and the predictions were good,with an average deviation of about 15.8%for the modified model.(3)The process parameters of the slag matte separation process were optimized and predicted using single factor experiments and the response surface method,and the influence of four factors on the nickel content of the slag was obtained:settling temperature>Mg O content>Fe/Si O₂>B₂O₃content.B₂O₃ content of 2.4wt%,the model predicts a low nickel content of 0.55 wt%in the slag under these conditions.