Beneficiation of nickeliferous laterite by reduction roasting in the presence of sodium sulfate

In this paper, the reduction roasting of laterite ore in the absence or presence of sodium sulfate was carried out for nickel beneficiation by wet magnetic separation. Sodium sulfate is found to be capable of enhancing the reduction of laterite ore through liberating iron and nickel from Ni/Fe substituted-lizardite, as well as increasing the size of ferronickel particles considerably. When the laterite pellets were reduced at 1100 °C for 60 min, the average particle size of ferronickel grains was approximately 50 μm in the presence of sodium sulfate, which far exceeded the size of 5–10 μm in the absence of sodium sulfate. Compared with those reduced without sodium sulfate, the Ni grade of ferronickel concentrate increased from 2.33% to 9.48%, and the magnetic separation recovery of Ni increased from 56.97% to 83.01% with the addition of 20 wt.% sodium sulfate. Experimental evidence showed that troilite (FeS) serves as an activating agent to accelerate melt phase formation via a low melting point (985 °C) Fe–FeS eutectic. This markedly facilitated the aggregation of ferronickel particles during reduction, along with the selective enrichment of Ni by suppressing the complete metallization of Fe.

Reducing laterite ore in the presence of sodium sulfate, both grade and recovery of Ni in the ferronickel magnetic concentrate increase significantly. The decreasing Fe/Ni ratio in the obtained ferronickel indicates that a greater selective enrichment of Ni than Fe can be achieved with the increase of sodium sulfate dosage.Figure optionsDownload as PowerPoint slideHighlights
► Ni beneficiation of laterite ore by using direct reduction process is proposed.
► Sodium sulfate is capable of intensifying the reduction roasting of laterite.
► Average particle size of ferronickel grows up to 50 μm when reduced with Na2SO4.
► Selective enrichment of Ni can be realized by suppressing the metallization of Fe.
► New-born troilite (FeS) facilitates the aggregation of ferronickel particles.