Decrease of Material Burden in a Novel Alkali-Saving Reduction Treatment Process of Nickel Slag Based on NaOH Roasting

Conventional reduction treatment methods for nickel slag show drawbacks such as high energy cost, heavy material burden or secondary pollution. Thus, a novel environmentally friendly reduction treatment method for high-silicon wastes, especially nickel slag, is proposed in this paper. The main characteristic is to lower the alkali–ore ratio (mass ratio of NaOH to ore) through introducing a high-speed premixing procedure before roasting. Optimal process parameters have been found experimentally, i.e., a roasting temperature of 823 K, alkali–ore ratio of 1.6:1, and roasting time of 30 min. The desilication ratio reached to 91.3 wt.%. Compared with previous NaOH roasting processes with stirring, the NaOH consumption is down by 60%, which greatly reduces the material burden. Through carbonation decomposition of the Na2SiO3 solution generated in the NaOH roasting, amorphous silica is recycled as the final product. The proposed method is expected to be a promising method for industrial reduction treatment of nickel slag.