首页|Thermal properties and pyrolysis kinetics of phosphate-rock acid-insoluble residues
Thermal properties and pyrolysis kinetics of phosphate-rock acid-insoluble residues
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NETL
NSTL
Elsevier
In the phosphorous-sulphur two-step process for the clean production of phosphoric acid, a phosphate-rock acid-insoluble residue (PAIR) is a solid filter residue obtained via the phosphoric acid acidolysis of phosphate rock (PR). PAIR combined with other raw materials can be used to prepare cement, ceramics and glasses, opening a potential avenue for large-scale PAIR utilisation. However, the preparation of such materials requires high-temperatures calcination. Understanding the high-temperature thermal properties of PAIR can enable its more targeted comprehensive utilisation or disposal. In this study, the thermal properties and pyrolysis kinetics of PAIR were systematically studied using a multiple heating rate method based on thermogravimetric analysis and a kinetic model. Results showed that from room temperature to 1200 ℃, the main changes in the PAIR were the complete removal of fluorine and sulphur, partial removal of phosphorus and conversion of quartz to cristobalite. Moreover, during these processes, H_2O(g), NH_3, N_2, CO_2, SO_2, P_2O_5(g), CO, CF_3~+ and organic gases were volatilised. Herein, the pyrolysis kinetics of PAIR is divided into five stages. Stage 1 (conversion rate a: 0.05-0.2) conforms to the random nucleation and growth as well as the Avrami-Erofeev (n = 2/3) mechanism; the corresponding mechanism function is F(α) = [-Ln(l - α)]~(2/3). Stage 2 (α: 0.2-0.4) conforms to the first-order chemical reaction mechanism; the corresponding mechanism function is F(α) = -Ln(l - α). Stage 3 (α: 0.4-0.6) conforms to the phase boundary-controlled reaction and one-dimensional movement mechanism; the corresponding mechanism function is F(α) = α. Stage 4 (α: 0.6-0.8) conforms to the three-dimensional diffusion process (Jander model); the corresponding mechanism function is F(α) = [1 - (1 - α)~(1/3)]~2. Stage 5 (α: 0.6-0.95) conforms to the one-dimensional diffusion process; the corresponding mechanism function is F(α) = α~2.
NETL
NSTL
Elsevier
