Kinetics of the direct synthesis of molycarbide by reduction-carburization of molybdenite in the presence of lime

Abstract

Kinetic studies were conducted on the carbon monoxide reduction of molybdenite in the presence of lime. Contrary to the expectation that the MoS 2 (s) ϩ CaO (s) ϩ CO (g) reaction will result in metal formation, molycarbide was found to form and no Mo was detected in the product. This is explained on the basis of thermochemical considerations, which indicate that the Mo 2 C formation is more feasible by eight orders of magnitude. The effects of quantity of lime in the charge, CO flow rate, temperature (1123 to 1298 K), and time of reduction have been studied. Kinetic analysis reveals that the results on the MoS 2 (s) conversion to Mo 2 C (s) fit into a modified parabolic rate law. Based on the thermochemical calculations and experimental findings, the probable reaction scheme has been identified. Molycarbide appears to form by a three-successive solid-gas reaction path consisting of (1) metal formation by the MoS 2 (s) ϩ CO (g) reaction followed by (2) in-situ carburization of Mo metal by CO (g), and finally (3) the scavenging of the COS (g) by lime, resulting in CaS (s). The latter two reactions drive the overall reaction forward. Further, out of these three consecutive reactions, progress of the overall MoS 2 ϩ CaO ϩ CO reaction seems to be governed by the intrinsic kinetics of the first one. Calcium molybdate, which forms as a transitory phase, plays a significant role by modifying the linear kinetics of the MoS 2 (s) ϩ CO (g) to one of parabolic nature.

Growth of Molybdenum Carbide–Graphene Hybrids from Molybdenum Disulfide Atomic Layer Template

“…Thus C 2 H 4 is the primary reactant that decomposes to form active carbon species to dissociate Mo-S bonds at elevated temperature. The resulted Mo is supposed to act as a catalyst for graphene growth from the initial nuclei while it also reacts with the active carbon species to form the carbide owing to the strong affinity between Mo and C. [20,21] The similar observations on the carbide formation have been reported during graphene or carbon nanotube growth on transition metal catalysts, [22,23] but it is the first time to straight forwardly observe this phenomenon with the substrate of atomic layered material of MoS 2 . To get a better picture of possible reactions, we calculated the Gibbs free energy of possible reactions as shown in Figure 3.…”

Sulfur-Emission-Free Process of Molybdenum Carbide Synthesis by Lime-Enhanced Molybdenum Disulfide Reduction with Methane

“…Many researchers have investigated the thermodynamics and kinetics of molybdenite processing by such an environmental friendly approach, using different reducing agents, i.e., hydrogen, 2,3 carbon, 4 and carbon monoxide. 5 The reduction path and mechanism have been considered as well. According to Prasad et al, 5 Mo 2 C appears to be formed from carbon monoxide reduction of MoS 2 + CaO by a threesuccessive solidÀgas reaction path.…”

“…5 The reduction path and mechanism have been considered as well. According to Prasad et al, 5 Mo 2 C appears to be formed from carbon monoxide reduction of MoS 2 + CaO by a threesuccessive solidÀgas reaction path.…”

“…It is the direct reduction of sulfides in the presence of lime as a powerful sulfur acceptor. Many researchers have investigated the thermodynamics and kinetics of molybdenite processing by such an environmental friendly approach, using different reducing agents, i.e., hydrogen, , carbon, and carbon monoxide . The reduction path and mechanism have been considered as well.…”

Molybdenite alkali fusion and leaching: reactions and mechanism

“…It has been found that molybdenite leaches slowly in dilute (1-4 M) nitric acid at room temperature [3] and the leaching of MoS 2 by sulfuric acid is a very slow process [4]. Beyond these studies, other pyrometallurgical processes such as chlorination [5], salt roasting [6], lime roasting [7] and carbothermal reduction of molybdenite in the presence of lime [8] were investigated. Presently, increasing the dissolution rate of molybdenite is a key problem for this mineral.…”