The purpose of this paper is to develop high efficient lithium adsorbent of magnesium oxide by mechanochemical treatment. Especially, the simple ball mill handling intends not to crush the primary particle of magnesium oxide powder, but to stimulate the mechanochemical interaction among primary particles of magnesium oxide powder. And, the result of it, the stimulated magnesium oxide powder gains the mechanochemical effect on the particle surfaces and plays a role of high efficiency adsorbent of lithium. From view of this point, the mechanochemical effect caused by ball mill handling is systematically and experimentally discussed. And the following interesting results are obtained. 1) The particle size of primary particle of magnesium oxide powder is not crushed and keeps almost constant within the experimental region 0 to 48 h by ball mill handling. This experimental knowledge coincides with the surface observations by SEM. 2) The optimum ball mill handling hours is pointed out to exist at 36h, at which shows the maximum lithium adsorption by magnesium oxide. 3) The maximum lithium adsorption quantity mentioned above is pointed out to about 5 times of value in comparison with 0 h handling. 4) These above results from 1) to 3) indicate high efficient lithium adsorbent of magnesium oxide can be prepared by ball mill handling, presented in this paper.
For recovering CaO from spent gypsum at relatively low temperatures, decomposition behavior of CaSO4 was studied by using a thermogravimetric analyzer in CO-CO2-N2 and H2-C2-N2 atmosphere in a temperature range of 1123-1273K. The conversions of CaSO4 to CaO and CaS byproduct were determined by the weight change of the decomposition of CaSO4 and the oxidation of CaS to CaSO4, respectively. It was found that the conversion of CaSO4 to CaO increased with an increase in temperature in both CO-N2 and H2-N2 atmosphere. On the other hand, the formation of CaS byproduct increased with the increase in CO and H2 concentrations, whereas the yield of CaO was decreased. It was possible to suppress the formation of CaS by adding high concentration CO2 to CO-O2-N2 and H2-CO2-N2 gas atmosphere. The conversion, greater than 90% of CaSO4 to CaO was obtained in a mixed gas of CO : 2%, CO2 : 30%, N2 : 68% at 1273K. The formation of CaS byproduct was not detectable in this condition.
SO2 absorption characteristic of CaO regenerated by CO and H2 reductive gas from gypsum (CaSO4) was studied. The reaction cycle of SO2 absorption and CaO regeneration from produced CaSO4 was conducted in a gas-flow type tubular reactor. The SO2 absorption of CaO was carried out in a mixed gas of 0.35 vol% SO2, 5 vol% O2 and balance N2 at 1123 K. Then, CaSO4 produced after SO2 absorption was regenerated to CaO in a reductive gas mixture of 2 vol% CO, 30 vol% CO2 and balance N2 at 1273 K. It was found that CaO regenerated from CaSO4 by CO and H2 in a TG apparatus had almost the same pore volume, although the pore size of CaO regenerated by H2 is larger than that of CaO regenerated by CO. There was no large difference between the CaO regenerated by CO and H2, in terms of SO2 absorption rate and SO2 absorption capacity. It was also found that CaO regenerated from CaSO4 had a higher SO2 absorption performance than CaO calcined from CaCO3, due to a larger pore volume as well as a larger pore diameter of the regenerated CaO.
Properties of aluminous cement mortar containing the waste glass powder were examined, and following conclusions were obtained; By adding the waste glass powder to the aluminous cement mortar, the flow value became smaller and the air volume in the mortar increased significantly. As for the reduction in the flow value due to adding the waste glass powder, an air entrainment was considered to be a major factor. It was proved that the waste glass powder was contaminated by some compound alike surfactant. The air entrainment of the waste glass powder was supposed to have resulted from the quasi-compound of surfactant. When the waste glass powder was added to the aluminous cement mortar, its compressive strength got small. That is due to the air entrainment property of the waste glass powder. When the entrained air was controlled using antiforming agent, the compressive strength got high. The waste glass powder suppresses the conversion of the aluminous cement, and the consequent reduction in the strength, as well. Those effects were remarkable according as the substitution ratio is high and the powder fineness is high. That is due to the stratlingite formation by the reaction between the waste glass powder and the aluminous cement hydrate.
This paper was made to investigate about preparation of large-sized gypsum dihydrate from waste gypsum board under coexisting ammonium chloride. The gypsum hemihydrate was obtained by aging waste gypsum dihydrate for 2 hours in 2.8 mol·dm-3 ammonium chloride solution at 102°C.The dehydration rate from the dihydrate to gypsum hemihydrate was promoted by addition of fine gypsum hemihydrate seed crystal over 5 mass%. The large-sized gypsum dihydrate was formed by cooling the suspension including needle-like gypsum hemihydrate to 60°C. However, synthetic conditions such as cooling rate, amount of gypsum dihydrate seed crystal and citric acid monohydrate in the hydration process of gypsum hemihydrate, affected the crystal shape of large-sized gypsum dihydrate. Finally, the blocky dihydrate with length of about 55μm and thickness of 17μm was formed.