• Analytical Science and Technology
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• v.13 no.2
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• pp.158-165
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• 2000

The purity of gypsum and quantitation of impurities of flue gas gypsum will not only play an important role in deciding of the optimal condition during a trial run of FGD (flue gas desulfurization), but also can be utilized in quality control of gypsum. The purity of gypsum can be determined from combined water, sulfur trioxide and calcium concentration. We found that the thermal analysis by TGA (thermogravimetric analysis) was the most accurate and convenient method to determine the purity of gypsum. This method will be done in a hour and the results were reproducible. On the other hand, the best way of the analysis of impurities in gypsum was fusion method using $LiBO_2$ as a fusion agent. We also determined the amount of $CO_2$ gas to analyze magnesium carbonate and calcium carbonate contents. The analyses of combined water by TGA, fusion method followed by ICP-AES (inductively coupled plasmaatomic emission spectroscopy) and determination of $CO_2$ amount can lead to more accurate and convenient method for gypsum analysis.

• Resources Recycling
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• v.15 no.3 s.71
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• pp.20-29
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• 2006

This study was carried out for to recover the purified crystalline gypsum from phosphogypsum by means of using it's crystallographical Properties. The dehydration of hydrated phosphogypsum to $\alpha$-hemihydrate is completed with the 2 hours treatment of it in $99^{\circ}C$ waterrs. The purified crystalline gypsum having the maximum size of $200{\mu}m$ was obtained by 325# wet screening after recrystallization of the $\alpha$-hemihydrate gypsum at the condition of $Na_2SO_4$ 10 wt%, slurry density 20%, $pH\;5{\sim}6,\;65^{\circ}C$ and 4hr. In this process, the yield of gypsum was 93.9% and its grade was 99%.

• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.861-869
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• 1997

In order to investigate the reaction in the system of anhydrite II-blast furnace slag, the paste hydration which made up with a liquid/solid ratio of 0.45 for 1, 3, 7, 14, 28days by the addition of accelerators to 10~30wt.% slag with natural gypsum calcined for 1hour at 500/$700^{\circ}C$ was studied by combined water determination, XRD, DTA, DSC and SEM. As a result of this experiment, it was found that hydration rate was faster in the system calcined at 50$0^{\circ}C$. Therefore the anhydrite was converted to calcium sulfate dihydrate in the hydration for 1day but the slag was not almost reacted. For the gypsum calcined at $700^{\circ}C$, the hydraton rate in the system of K2SO4 addition was faster than others in the earier period, but the activated effect of the system of Al2(SO4)3 addition was regarded as the highest over 3days. As the amount of slag was increased, they dydration rate was delayed and ettringite was observed in the case of K2SO4 system. However both Al2(SO4)3 and AlK(SO4)2 systems showed calcium sulfate dhydrate only as hydrated products.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.729-735
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• 2009

In this study, it is experimentally verified a feasibility of the wasted phosphogypsum ($CaSO_4/H_2O$) that is a byproduct from the phosphoric acid process of manufacturing fertilizers can be applied as an admixture in slag cement. For the test, phosphogypsum is modified as dihydrate, hemihydrate, type III anhydrite, and type II anhydrite, and then chemical characteristics and mechanical properties of various slag cements containing above mentioned gypsum materials were analyzed. The test results show that the gypsum made at high temperature has better quality with decrease of water-soluble phosphoric acid ($S-P_2O_5$) which has an effect on the quality of cement. And type II anhydrite shows superior quality in terms of drying shrinkage and the compressive strength of cement paste with hemihydrate at 56 days is higher than other gypsum material.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.998-1001
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• 2010

Most firming agent used in Korea is cement-firming agent. Cement-firming agent absorb water for combination, and then it makes ettringite. Through this chemical process, soft ground is firmed by cement-firming agent. Although most cement-firming agent used in Korea made from CSA, it relies on imports. Therefore, the development of soft ground firming agent using new materials is required. In this study, we suggested that EAF reduction slag not used for anything in the steel industry is available for material of soft ground firming agent. If EAF reduction slag is used in soft ground firming agent, it will be possible to solve the problem with treatment of slag and improvement of soft ground.

• Journal of the Korean Ceramic Society
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• v.18 no.4
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• pp.237-246
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• 1981

The effects of impurities, included in the by-produced phosphogypsum from the dihydrate process, on the hydration of portland cement were studied. Six gypsums were adopted in this study; four different raw phosphogypsums from domestic fertilizer plants, a reprocessed phosphogypsum and a reagent grade pure gypsum. Cements with differing $SO_3$ content, were synthesized by grinding two different commercial clinkers and the above six gypsums together. The effects of the impurities were investigated by measuring the setting time, the non-evaporable water coatent, X-ray phase analysis of cement pastes and the compressive strength of cement mortar specimens. It was found that the soluble $P_2O_5$ known as one of injurious impurities on the hydration of portland cement, included in the demestic raw phosghoypsum cxneedigply by far the specified amounts of the Korean Industrial Standards (L9005), and retarded the setting time severely, thus the strength development of cement was delayed at the earlier stage of hydration.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.673-680
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• 1997

NaOH, $Na_2CO_3, CaO, Ca(OH)_2$ and $CaCO_3$ are widely used counteractives for neoutralizing the waste sulphuric acid produced during the metal surface treatment process and/or the metal refining process. To reduce the tremendous expenses for the neutralization treatment of the waste sulphuric acid, the sludge from calcination plant and the stainless refining dust in POSCO (Pohang Iron ＆ Steel co. Ltd.) was utilized. For the sludge, it will be effective to use calcined and then hydrated sludge in strong acid region (pH<2) and to use the sludge itself in weak acid region (pH>2), The gypsum, the by-product of this treatment, was tested to fit the industrial standard of gypsum, so it is expected that it will solve the lack of gypsum supply. For the stainless refining dust, the phase and the morphology of produced gypsum from waste suiphuric acid neutralization was compared with those from pure sulphuric acid. Because of high reactivity and reaction temperature, $CaSO_4$ non-hydrate was obtained in pure sulphuric acid. But $CaSO_4$ dihydrate was obtained in waste sulphuric acid. It is also judged to be a good material for a counteractive of the waste sulphuric acid.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.144-151
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• 2010

In this study, it is investigated the mechanical chemical properties of cement matrix using phosphogypsum and kaolin as a admixture for the substitutive materials to silica fume which is so expensive. For the test, phosphogypsum is modified as dihydrate, hemihydrate, type III anhydrite, and type II anhydrite, respectively and furnaced kaolin at $900^{\circ}C$ was also manufactured into meta kaolin by air cooling and water cooling method. The chemical characteristic and mechanical properties of various type of blended cements contained above mentioned gypsum and meta kaolin materials analyzed and compared with those characteristics of cement matrix with silica fume. From the test, the cement mixed meta kaolin made in water cooling has more excellent quality than other material.