Regular Article

Recycling of chromium sludge to promote aggregation and growth of metal during self-reduction of nickel laterite ore

¹ The State Key Laboratory of Refractory Materials and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China
² Centre for Pyrometallurgy, Department of Materials Science & Metallurgical Engineering, University of Pretoria, Pretoria 0002, South Africa
³ Key Laboratory of Iron and Steel Metallurgy and Resource Utilization, Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China
⁴ School of Mechanical Engineering, Yancheng Institute of Technology, Yancheng 224051, China

^* e-mail: songs@wust.edu.cn
^** e-mail: xuezhengliang@wust.edu.cn

Received: 13 December 2021
Accepted: 6 January 2022

Abstract

Addition of stainless steel pickling sludge, which contains hazardous hexavalent chromium, to low-grade nickel laterite ore has the potential to eliminate the hexavalent chromium and promote the aggregation and growth of iron-nickel particles during reduction with anthracite. The effect of chromium sludge on the aggregation and growth of metal particles during a self-reduction process of nickel laterite ore has been studied. The detoxification effect of hexavalent chromium in the sludge was evaluated using the standard TRGS 613 leaching test. Results showed that with increasing chromium sludge addition, the size of metal particles increased. With the addition of 13.94% by mass chromium sludge the average metal particle size in the reduce ore increased from 0.42 µm to 1.38 µm while the recovery of Fe, Ni and Cr increased from 53.73%, 19.39% and 33.36% to 78.33%, 69.22% and 58.26%, respectively. It is proposed that a low melting point eutectic phase of FeS formed in the reduced products, significantly promoted the migration and aggregation of metal particles. Leaching tests indicated that the original chromium sludge released > 600 mg/kg Cr(VI) while the slag from the combined laterite and chromium sludge released less than the EPA limit of 2 mg/kg Cr(VI).