• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.31-38
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• 2003

It has been recently reported that the presence of sulphate causes abnormal volume changes in lime-stabilized soils. Volume changes in lime-stabilized soils can take place due to sulphate compounds such as ettringite. Sulphate compounds caused a variety of serious geotechnical hazards such as swelling pressure and damages to light structures and pavements. This paper discusses the influence of sulphate on the soil specimens treated with quicklime and chemical additives. The physical and mechanical characteristics were studied by means of laboratory tests. The results showed that the presence of sulphate treated soil reduced the shear strength of the lime treated soils and increased the swelling properties. SEM and XRD results indicated that the presence of sulphate producted needle-like crystals such as ettringite. Moreover, the role of needle-like crystals in specimen was probably related to the swelling properties.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.611-617
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• 2009

This paper reports an experimental study on the damage mechanism and resistance of Type I portland cement mortar and paste samples exposed to 5% sodium sulfate solution with different solution temperatures; namely, $4^{\circ}C$, $10^{\circ}C$ and $20^{\circ}C$. The resistance of mortar samples was evaluated using expansion, compressive strength and flexural strength measurements. Some microstructural observations such as x-ray diffraction, differential scanning calorimetry and scanning electron microscopy were also introduced to elucidate reactants formed by sulfate attack, especially in a low temperature condition. From the results, it was found that the degree of damage in the mortar samples was significantly associated with the temperature of sulfate solution. Low temperature of the sulfate solution led to the formation of thaumasite in mortar and paste samples, and subsequently a poor resistance to sulfate attack. Thus, it is noted that when concrete structures are exposed to sulfate media in the condition of a cold region or whether, special care should be taken.

• Journal of Environmental Impact Assessment
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• v.32 no.2
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• pp.123-133
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• 2023

Wastewater generated in the secondary battery production process contains lithium and high-concentration sulfate. Recently, as demand as demand for high-Ni precursors with high-energy density has surged, nickel emission is also a concern. Lithium and sulfate are not included in the current water pollutant discharge standard, so if they are not properly processed and discharged, the negative effect on future environment may be great. Therefore, in this study, the ecotoxicity of lithium, nickel, and sulfate, which are potential contaminants that can be discharged from the secondary battery production process, was evaluated using water flea (Daphnia magna) and luminescent bacteria (Aliivibrio fischeri). As a result of the ecotoxicity test, 24-hour and 48-hour D. magna EC₅₀ values of lithium were 18.2mg/L and 14.5mg/L, nickel EC50 values were 7.2mg/L and 5.4mg/L, and sulfate EC₅₀ values were 4,605.5mg/L and 4,345.0mg/L, respectively. In the case of D. magna, it was found that there was a difference in ecotoxicity according to the contaminants and exposure time (24 hours, 48 hours). Comparing the EC₅₀ of D. magna for lithium, nickel, and sulfate, the EC₅₀ of nickel at 24h and 48h was 39.6-37.2% compared to lithium and 0.1-0.2% compared to sulfate, which was the most toxic among the three substances. The difference appeared to be at a similarlevelregardless of the exposure time. The EC₅₀ of sulfate was 253.0-299.7% and 639.5-804.6%, respectively, compared to lithium and nickel, showing the least toxicity among the three substances. The 30-minute EC₅₀ values of luminescent bacteria forlithium, nickel, and sulfate were 2,755.8mg/L, 7.4mg/L, and 66,047.3mg/L,respectively. Unlike nickel, it was confirmed that there was a difference in sensitivity between D. magna and A. fischeri bacteria to lithium and sulfate. Studies on the mixture toxicity of these substances are needed.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.443-450
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• 2015

This paper presents an investigation of the mechanical and microstructural properties of Class F fly ash based geopolymer containing sodium sulfate as an additive. Sodium sulfate was used as an chemical additive at the dosage levels of 0, 2, 4, and 6wt% of fly ash. Sodium hydroxide and sodium silicate solutions were used to activate fly ash. The compressive strengths of geopolymer pastes were measured at the age of 28 days. The microstructures of the geopolymer pastes were examined using XRD, MIP and SEM tests. The additions of 2wt% and 4wt% sodium sulfate produced geopolymers with high strength, while increasing the dosage of levels to 6% resulted in almost no changes in strength, comparing with the control geopolymer. The optimum increase in strength was obtained with the addition of 4wt% sodium sulfate. As the amount of sodium sulfate is increased, no additional crystalline phase was detected and no change of amorphous phase indicated despite the change in the strength development. The increase in the strength was due to the change of pore size distribution in samples. As addition of sodium sulfate altered the morphologies of reactive productions and Si/Al ratios of the reaction products, the strengths were thus affected. It was found that the strengths of geopolymer were larger for lower Si/Al ratios of reaction products formed in samples. The optimal amount of sodium sulfate in the fly ash based geopolymer helps to improve mechanical properties of the geopolymer, on the other hand, the high percentage of sodium sulfate could exist as an impurity in the geopolymer and hinder the geopolymer reaction.

• Journal of the Korean Magnetics Society
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• v.21 no.5
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• pp.157-162
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• 2011

The effect of ferrous/ferric molar ratio and precipitants on the formation of nano size magnetite particle was investigated by coprecipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide and ammonium hydroxide was used as a precipitant. Single phase magnetite was synthesized with all of experiment conditions (ferrous/ferric molar ratios and precipitants). Particle size was smaller, and particle size distribution was narrower when NaOH was used than $NH_4OH$ was used. The crystallinity and particle size was increased and narrower particle size distribution with increasing molar ratio ferrous/ferric sulfate with the same precipitant. Super paramagnetism could be obtained at all of experiment conditions. The highest saturation magnetization (72 emu/g) was obtained when the ferrous/ferric molar ratio was 2.5 and precipitant was used $NH_4OH$.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.766-769
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• 2010

본 논문은 콘크리트 구조물 중 원전구조물에서 열화요인에 따른 미세구조적 변화에 대해서 평가하였다. 이는 원전구조물의 경우 열화현상이 발생하게 되면 일반 구조물에 비해 심각한 영향을 초래하기 때문에 기존의 열화 평가 방법에 의존하기 보다는 미세구조적 관점에서 콘크리트의 열화를 재평가해야 한다. 그에 일환으로 열화 요인 중 동결 융해와 황산염에 대한 미세구조 평가를 실시하였다. 동결융해의 경우, 미세구조적 관점에서의 미세공극의 양이 증가하는 것을 확인하였으나 그 증가 폭이 크지 않음을 알 수 있었으며, 물리적 실험에서도 그 변화가 매우 작음을 확인할 수 있다. 그리고 황산염에서는 초지 침지 구간에서는 플라이 애쉬를 사용한 원전 콘크리트 배합이 콘크리트에 더 유리하게 작용함을 알 수 있다.

• Applied Chemistry for Engineering
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• v.2 no.4
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• pp.372-384
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• 1991

The sulfation of the domestic titaniferous magnetite ore with ammonium sulfate was investigated to find a cyclic process for the production of synthetic rutile and high purity iron oxide and to test the feasibility of ammonium sulfate being an alternative sulfation agent. The proper sulfation conditions were determined to be a temperature of $425^{\circ}C$, 2.5 hours of reaction time, the weight ratio of ammonium sulfate to titaniferous magnetite : 11, and particle size or titaniferous magnetite : -250 mesh. 90.4 % of $TiO_2$ and 85.3 % of iron were extracted from the titaniferous magnetite sulfated under these conditions by the water leaching. From the leachate $TiO_2$ of 93.8 % purity as a mixture of rutile and anatase and ${\alpha}-Fe_2O_3$ of 97.6 % purity were obtained.

• Journal of the Korean Geotechnical Society
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• v.39 no.8
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• pp.7-16
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• 2023

This study aimed to evaluate the sulfate removal capacity of the enzyme-induced carbonate precipitation (EICP) technique through the chemical precipitation of sulfate with calcium ions. The optimal EICP recipe was obtained to retain the excess calcium cations in the solution for the generation of a sufficient amount of calcium carbonate (CaCO₃) mineral. The effect of gypsum precipitation on the EICP-treated sand specimen was investigated by measuring the shear wave velocity and by visual inspection via scanning electron microscopy. The EICP solution using soybean crude urease, as an alternative to laboratory-grade purified urease, exhibited a lower sulfate removal efficiency at a similar CaCO₃ production rate compared with the optimal EICP recipe because of soybean impurities.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.4
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• pp.218-224
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• 2003

Magnesium hydroxide, which recently registered as a Mg fertilizer, is greatly different from magnesium sulfate in its solubility and effect on soil pH. In this study, the effects of magnesium hydroxide and magnesium sulfate on growth of chinese cabbage were compared at the application rate of $300kg\;MgO\;ha^{-1}$ in a Gyeongsan clay loam soil. Although magnesium hydroxide was effective in increasing number of leaf and fresh weight, overall effects of magnesium hydroxide and magnesium sulfate on the growth of chinese cabbage were not significantly different ($p{\leq}0.05$). Comparing the two magnesium fertilizer treatments, magnesium content of chinese cabbage was relatively higher in the magnesium sulfate treatment in the early stage of growth, but it was higher in the magnesium hydroxide treatment at harvest. Contents of Ca, P, and K in chinese cabbage were relatively higher in the magnesium hydroxide treatment than those in magnesium sulfate treatment. But, the differences in nutrient uptakes by chinese cabbage between the treatments were not significant ($p{\leq}0.05$). Therefore, magnesium hydroxide is expected to be used with nearly the same effects on crops as magnesium sulfate at the same application rate of Mg. Soil pH in the treatment of magnesium sulfate was lower than that of control treatment, but magnesium hydroxide could increase pH. Magnesium hydroxide can be used preferentially in acid and/or sandy soils, where magnesium sulfate can induce further soil acidification and leaching loss of Mg is often a severe problem.

• Journal of the Korean Chemical Society
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• v.45 no.6
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• pp.546-548
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• 2001

Neat chlorosulfonic acid reacts with silica gel to give silica sulfuric acid in which sulfuric acid is immobilized on the surface of silica gel via covalent bond. A combination of silica sulfuric acid and wet SiO$_2$ was used as an effective deacetalizating agent for the conversion of acetals to their corresponding carbonyl derivatives by using microwave irradiation under solvent free conditions.