Mechanistic and Kinetic Analysis of Na2SO4-Modified Laterite Decomposition by Thermogravimetry Coupled with Mass Spectrometry

Abstract

Nickel laterites cannot be effectively used in physical methods because of their poor crystallinity and fine grain size. Na2SO4 is the most efficient additive for grade enrichment and Ni recovery. However, how Na2SO4 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 Na2SO4 in an argon atmosphere using thermogravimetry coupled with mass spectrometry (TG-MS). Approximately 25 mg of samples with 20 wt% Na2SO4 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 Na2SO4 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 SO2 in the presence of Na2SO4 with an activation energy of 91.37 kJ/mol. The decomposition of laterite with and without the addition of Na2SO4 can be described by one first-order reaction. Moreover, the use of Na2SO4 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.

Assessment of Residual Solvent and Drug in PLGA Microspheres by Derivative Thermogravimetry

“…DTG makes it possible to obtain parameters related to a thermal event, such as its onset and end temperatures (To and Te), as well as the temperature at which the rate of mass change is highest (Tp). DTG has been used for thermal decomposition studies of various materials such as carbon spheres, polyaniline-cellulose nanofiber, laterite, and amyrenone [16][17][18][19]. DTG was also used to analyze the composition ratio of a polymer composite.…”

Mechanism of Calcium Sulphate on the Aggregation and Growth of Ferronickel Particles in the Self-Reduction of Saprolitic Nickel Laterite Ore

“…Calcium oxide reacted with silicate to form pigeonite, troilite generated by the reaction of S 2 with iron oxides or iron [25,34]. As a similar mechanism, pigeonite was found in the reduced sample in the presence of calcium oxide and troilite appeared in the reduced sample with an additive of sulphur.…”

“…The corresponding EDS results of the mineral composition are listed in Tables 2-4. calcium oxide and sulphur in a reducing atmosphere [35]. 2CaSO4+6CO=2CaO+S2+6CO2 (19) Calcium oxide reacted with silicate to form pigeonite, troilite generated by the reaction of S2 with iron oxides or iron [25,34]. As a similar mechanism, pigeonite was found in the reduced sample in the presence of calcium oxide and troilite appeared in the reduced sample with an additive of sulphur.…”

“…Additives contribute to the aggregation and growth of ferronickel particles [20][21][22][23][24][25][26][27][28][29][30][31]. Sulphur promotes the aggregation and growth of ferronickel particles by reducing the surface tension of ferronickel particles, and the formation of an Fe-FeS eutectic facilitates the aggregation of ferronickel particles during reduction, the mechanism of sulphates on the aggregation and growth of ferronickel particles is consistent of sulphur [20,[22][23][24][25][26][27][32][33][34][35]. Saprolitic ore has a high content of silica, while alkali oxides contribute to liquid phase by reacting with silica, which is conducive to mass transfer [19].…”

Influence of Calcium Chloride Addition on Coal-Based Reduction Roasting of Low-Nickel Garnierite Ore

“…The limited amount of hydrogen chloride further leads to suppressed production and reduction of metal chlorides. Moreover, the reduction of NiO is occurs prior to that of maghemite at low temperatures, therefore, a small amount of maghemite is reduced to the metallic state, which results in a low recovery and high grade of nickel 23,24) . A further increase in the reducing temperature to 1300 C contributes to a decrease of the nickel content to 4.01% and a slight drop in the nickel recovery.…”