Mechanistic and Kinetic Analysis of Na(2)SO(4)-Modified Laterite Decomposition by Thermogravimetry Coupled with Mass Spectrometry

Nickel laterites cannot be effectively used in physical methods because of their poor crystallinity and fine grain size. Na(2)SO(4) is the most efficient additive for grade enrichment and Ni recovery. However, how Na(2)SO(4) affects the selective reduction of laterite ores has not been clearly investigated. This study investigated the decomposition of laterite with and without the addition of Na(2)SO(4) in an argon atmosphere using thermogravimetry coupled with mass spectrometry (TG-MS). Approximately 25 mg of samples with 20 wt% Na(2)SO(4) was pyrolyzed under a 100 ml/min Ar flow at a heating rate of 10°C/min from room temperature to 1300°C. The kinetic study was based on derivative thermogravimetric (DTG) curves. The evolution of the pyrolysis gas composition was detected by mass spectrometry, and the decomposition products were analyzed by X-ray diffraction (XRD). The decomposition behavior of laterite with the addition of Na(2)SO(4) was similar to that of pure laterite below 800°C during the first three stages. However, in the fourth stage, the dolomite decomposed at 897°C, which is approximately 200°C lower than the decomposition of pure laterite. In the last stage, the laterite decomposed and emitted SO(2) in the presence of Na(2)SO(4) with an activation energy of 91.37 kJ/mol. The decomposition of laterite with and without the addition of Na(2)SO(4) can be described by one first-order reaction. Moreover, the use of Na(2)SO(4) as the modification agent can reduce the activation energy of laterite decomposition; thus, the reaction rate can be accelerated, and the reaction temperature can be markedly reduced.