• Resources Recycling
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• v.30 no.1
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• pp.60-65
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• 2021

The recycling of titanium turning scraps requires the removal of cutting oil and other contaminants remaining on the surface. In this study, an experiment was conducted in which titanium scraps were cleaned by a combination of ultrasonic immersion-steam cleaning and subsequent drying at high temperature. To determine the removal mechanism of cutting oil, the contact angle between titanium surface and cutting oil was measured. The result confirmed the optimum condition of the immersion solution of the titanium turning scraps. In the case of immersion cleaning of Na4P2O7 aqueous solution, the degree of carbon removed in the cutting oil was the highest at 50℃, and it was confirmed that the carbon content obtained from the combination of steam cleaning and ultrasonic immersion-steam cleaning was lower than that from steam cleaning after ultrasonic immersion. The oxidation and decomposition behaviors of cutting oil were investigated using Thermogravimetric analysis (TGA) and the result was applied in the high temperature drying process. From the results of the high temperature drying tests, it was concluded that 200℃ is the optimal drying temperature.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.1-9
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• 2020

Magnesium silicate minerals such as serpentine [Mg₃Si₂O₅(OH)₄] have a high potential for the sequestration of CO₂; thus, their reactivity toward dissolution under CO₂-free and CO₂-containing conditions in acidic solvents is a critical process with respect to their carbonation reactions. To examine the carbonation efficiency and dissolution mechanism of serpentine, hydrothermal treatment was performed to the starting material via a modified direct aqueous carbonation process at 100 and 150℃. The serpentine dissolution experiments were conducted in H₂SO₄ solution with concentration range of 0.3-1 M and at a CO₂ partial pressure of 3 MPa. The initial pH of the solution was adjusted to 13 for the carbonation process. Under CO₂-free and CO₂-containing conditions, the carbonation efficiency increased in proportion to the concentration of H₂SO₄ and the reaction temperature. The leaching rate under CO₂-containing conditions was higher than that under CO₂-free conditions. This suggests that shows the presence of CO₂ affects the carbonation reaction. The leaching and carbonation efficiencies at 150℃ in 1 M H₂SO₄ solution under CO₂-containing conditions were 85 and 84%, respectively. The dissolution rate of Mg was higher than that of Si, such that the Mg : Si ratio of the reacted serpentine decreased from the inner part (approximately 1.5) to the outer part (less than 0.1). The resultant silica-rich layer of the reaction product ultimately changed through the Mg-depleted skeletal phase and the pseudo-serpentine phase to the amorphous silica phase. A passivating silica layer was not observed on the outer surface of the reacted serpentine.