Evolution of ferronickel particles during the reduction of low-grade saprolitic laterite nickel ore by coal in the temperature range of 900-1250°C with the addition of CaO-CaF2-H3BO3

The method of producing ferronickel at low temperature (1250-1400 degrees C) has been applied since the 1950s at Nippon Yakin Kogyo, Oheyama Works, Japan. Limestone was used as an additive to adjust the slag composition for lowering the slag melting point. The ferronickel product was recovered by means of a magnetic separator from semi-molten slag and metal after water quenching. To increase the efficiency of magnetic separation, a large particle size of ferronickel is desired. Therefore, in this study, the influences of CaO, CaF2, and H3BO3 additives on the evolution of ferronickel particle at <= 1250 degrees C were investigated. The experiments were conducted at 900-1250 degrees C with the addition of CaO, CaF2, and H3BO3. The reduction processes were carried out in a horizontal tube furnace for 2 h under argon atmosphere. At 1250 degrees C, with the CaO addition of 10wt% of the ore weight, ferronickel particles with size of 20 mu m were obtained. The ferronickel particle size increased to 165 mu m by adding 10wt% CaO and 10wt% CaF2. The addition of boric acid further increased the ferronickel particle size to 376 mu m, as shown by the experiments with the addition of 10wt% CaO, 10wt% CaF2, and 10wt% H3BO3.

Automated summary

The method of producing ferronickel at low temperature by Nippon Yakin Kogyo, Japan since the 1950s uses limestone as an additive to lower slag melting point. Experiments showed that the addition of CaO, CaF2, and H3BO3 additives can significantly increase the size of ferronickel particles below 1250 degrees Celsius, with the largest particle size achieved by the addition of all three additives.