The depletion of natural resources is rapidly deteriorating the grade of primary resources, resulting in previously unexpected problems in the existing recovery processes for high-grade resources. In addition, remarkable efforts have been made to recover valuable metals and materials from various se...
The depletion of natural resources is rapidly deteriorating the grade of primary resources, resulting in previously unexpected problems in the existing recovery processes for high-grade resources. In addition, remarkable efforts have been made to recover valuable metals and materials from various secondary resources. In this regard, kinetic studies offer basic knowledge for sustainable development and process design based on the effects of variables and kinetic parameters, facilitating the recovery of valuable metals and materials from intractable primary and worthless secondary resources. Therefore, this thesis investigated the kinetics of the solid–gas reaction for recovering valuable metals and materials, especially copper and titanium, from primary and secondary resources. The five case studies examined are as follows: 1) oxidation of copper and gold concentrate, 2) hydrogen reduction of primary ilmenite concentrate, 3) reduction of preoxidized ilmenite concentrate, 4) reduction of ilmenite mud waste by hydrogen, and 5) reduction of brass waste by hydrogen. Overall, kinetic reactions were affected by various variables, particularly the morphology of the raw material. The reaction rate increased with temperature and the concentration of the reducing gas.
In case study (1), the oxidation of a copper and gold concentrate was investigated to clarify the effect of adding the gold concentrate at 1173−1373 K. The oxidation reaction proceeded in two steps: 1) direct oxidation and 2) thermal decomposition and successive oxidation. The nucleation and growth model controlled the overall reaction. For the first and second steps, the calculated activation energies under an air atmosphere were 15−25 and 32−70 kJ/mol, respectively, and 19−28 and 25−58 kJ/mol, respectively, under an oxygen-enriched atmosphere.
In case study (2), primary ilmenite concentrate was reduced by hydrogen to investigate the reduction kinetics from 1273 to 1473 K. The reduction reaction was controlled by a chemical reaction at the interface, and the calculated activation energy was 42 kJ/mol. Meanwhile, pre-reducing ilmenite decreased energy consumption and emission by half compared to using raw concentrate in the smelting process.
In case study (3), the reduction of preoxidized ilmenite concentrate at 1173−1373 K was investigated to determine the temperature effect. The decrease in reduction rate was associated with pseudobrookite formation, which was generated at an oxidation temperature above 1173 K. The oxidization of ilmenite at 873 and 1273 K was controlled by the nucleation and growth and chemical reaction models, respectively. The corresponding activation energies calculated for these models were 55.73 and 117.41 kJ/mol, while those calculated for the isoconversion method were 44.31 and 101.55 kJ/mol, respectively. Adding the preoxidation process had advantages in terms of energy consumption and emission during the smelting process.
In case study (4), the hydrogen reduction of ilmenite mud waste was studied from 1173 to 1273 K. The ilmenite mud waste was first oxidized owing to its sulfur component, and then it was reduced in two steps. In the second step, the reduction of preoxidized ilmenite mud was controlled by the nucleation and growth model. The reaction order of ≈1 was obtained from the general Avrami–Erofeev equation. The kinetic parameters, that is, the pre-exponential factor A and activation energy Ea, were determined to be 1527 min–1 and 118.28 kJ/mol, respectively.
In case study (5), the hydrogen reduction of brass waste was carried out between 1073 and 1273 K. The kinetic reaction occurred in two steps: 1) chemical reaction at the interface and 2) Zn vaporization via the power law. The reaction order of the hydrogen partial pressure was 0.63, and the activation energies for the chemical reaction and power law models were 114.9 and 120.0 kJ/mol, respectively.
The depletion of natural resources is rapidly deteriorating the grade of primary resources, resulting in previously unexpected problems in the existing recovery processes for high-grade resources. In addition, remarkable efforts have been made to recover valuable metals and materials from various secondary resources. In this regard, kinetic studies offer basic knowledge for sustainable development and process design based on the effects of variables and kinetic parameters, facilitating the recovery of valuable metals and materials from intractable primary and worthless secondary resources. Therefore, this thesis investigated the kinetics of the solid–gas reaction for recovering valuable metals and materials, especially copper and titanium, from primary and secondary resources. The five case studies examined are as follows: 1) oxidation of copper and gold concentrate, 2) hydrogen reduction of primary ilmenite concentrate, 3) reduction of preoxidized ilmenite concentrate, 4) reduction of ilmenite mud waste by hydrogen, and 5) reduction of brass waste by hydrogen. Overall, kinetic reactions were affected by various variables, particularly the morphology of the raw material. The reaction rate increased with temperature and the concentration of the reducing gas.
In case study (1), the oxidation of a copper and gold concentrate was investigated to clarify the effect of adding the gold concentrate at 1173−1373 K. The oxidation reaction proceeded in two steps: 1) direct oxidation and 2) thermal decomposition and successive oxidation. The nucleation and growth model controlled the overall reaction. For the first and second steps, the calculated activation energies under an air atmosphere were 15−25 and 32−70 kJ/mol, respectively, and 19−28 and 25−58 kJ/mol, respectively, under an oxygen-enriched atmosphere.
In case study (2), primary ilmenite concentrate was reduced by hydrogen to investigate the reduction kinetics from 1273 to 1473 K. The reduction reaction was controlled by a chemical reaction at the interface, and the calculated activation energy was 42 kJ/mol. Meanwhile, pre-reducing ilmenite decreased energy consumption and emission by half compared to using raw concentrate in the smelting process.
In case study (3), the reduction of preoxidized ilmenite concentrate at 1173−1373 K was investigated to determine the temperature effect. The decrease in reduction rate was associated with pseudobrookite formation, which was generated at an oxidation temperature above 1173 K. The oxidization of ilmenite at 873 and 1273 K was controlled by the nucleation and growth and chemical reaction models, respectively. The corresponding activation energies calculated for these models were 55.73 and 117.41 kJ/mol, while those calculated for the isoconversion method were 44.31 and 101.55 kJ/mol, respectively. Adding the preoxidation process had advantages in terms of energy consumption and emission during the smelting process.
In case study (4), the hydrogen reduction of ilmenite mud waste was studied from 1173 to 1273 K. The ilmenite mud waste was first oxidized owing to its sulfur component, and then it was reduced in two steps. In the second step, the reduction of preoxidized ilmenite mud was controlled by the nucleation and growth model. The reaction order of ≈1 was obtained from the general Avrami–Erofeev equation. The kinetic parameters, that is, the pre-exponential factor A and activation energy Ea, were determined to be 1527 min–1 and 118.28 kJ/mol, respectively.
In case study (5), the hydrogen reduction of brass waste was carried out between 1073 and 1273 K. The kinetic reaction occurred in two steps: 1) chemical reaction at the interface and 2) Zn vaporization via the power law. The reaction order of the hydrogen partial pressure was 0.63, and the activation energies for the chemical reaction and power law models were 114.9 and 120.0 kJ/mol, respectively.
주제어
#Primary resources Secondary resources Solid?gas reaction Kinetics Reaction models Activation energy
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