This study was examed about leaching behavior in order to separate plasticizer selectively before dechlorination from flexible PVC material in alkali solutions at . The dechlorination of that was not almost occurred below . But the yield of elution of plasticizer was 100% above 5M NaOH. Therefore, by controlling alkali concentration and reaction temperature, it is possible to extract the plasticizer selectively without taking dechlorination.

A sulfuric acid leaching of as cathodic active materials of lithium ion secondary batteries was investigated in terms of reaction variables. In the absence of a reducing agent, the extraction of cobalt was less than 40% in 2 M sulfuric acid at instead of that of lithium could be almost 100% in the same conditions. To improve the Co extraction, hydrogen peroxide was used as a reducing agent in the range 2~20 vol%. When over 10vo1% hydrogen peroxide was added, the extractions of both metals were improved to about 95%. It seems to be due to the reduction of Co(III) to Co(II) that can be readily dissolved. The extractions of Co and Li were increased with increasing concentration and temperature, and amount of hydrogen peroxide and with decreasing of pulp density. The optimum leaching conditions were determined at concentration, operating temperature, 100 g/L. initial pulp density, 20 vol% addition and 30 min.

Shape-controlled copper oxides have been recovered from copper-containing waste etchant by neutralization with alkalihydroxide. Large amount of copper-containing waste etchant is generated from Printed Circuit Board industry. In an environmental and economic point of view, retrieve of the valuable natural resource from the waste is important. In recycling process of copper oxide from the waste etchant, reaction temperature controls shapes and sizes of the products. Copper oxide recovered below reaction temperature was of a needle shape, while copper oxide comes in a platy shape above . Physical properties of samples have been characterized using SEM, XRD, TGA and Atomic absorption spectroscopy.

A study on the recovery of yttrium was conducted using the phosphor sludges generated in the recycling process of obsolete CRTs. Yttrium was leached by HCl and . The leaching efficiency of yttrium was extensively investigated in terms of acid concentration, leaching temperature and time, and pulp density. Yttrium and lead was recovered from leaching solutions also by precipitation method. The leaching behavior of yttrium was similar in both acids. The leaching efficiency of yttrium for both acids increased with time at the conditions of 3.0M, , and 280 g/L of pulp density. After 40 minutes, it was saturated to 93% and 90% for HCl and HNOrespectively. Yttrium was recovered from leaching acid solution by the addition of while lead was removed as by .

Fly ash powders were refined and separated into fine and coarse size by multi-air classification, and each particle was used for synthesizing mullite and zeolite. Mullite was prepared by sintering the mixture of fine fly ash with mean size of 6.5 m and powder at above . Zeolite was synthesized through hydrothermal reaction with coarse fly ash mean size of m in 3.5 M NaOH solution at . The whole range of particle size can be recycled through size classification into fine and coarse fractions, which are used for syntheses of inorganic materials.

A study was conducted in order to remove Poly vinyl chloride (PVC) from granular plastic mixture by using Air Table. The motion of plastic particle on Air Table was investigated, and separation test on the plastic mixture with the mixing ratio of PVC 10% and PE 90% was conducted. At the optimum condition obtained from this study, that is frequency of 9.2Hz, air velocity of 1.05 m/sec, End-slope of , Side-slope of , Feeding speed of 450 g/min, etc., we could separate the PE-PVC mixture to PE (99.96% grade and 98.9% yield) and PVC (88.7% grade and 99.6% yield).

This study was conducted to obtain granular crystalline gypsum that can be used as raw material for Plaster boards or cements from waste Plaster board. Gypsum could be Preferentially disintegrated to gypsum needle in or less size by hydration after the dehydration of crushed waste Plaster board. The finer the gypsum needle, it is easier to remove coarse impurities and to recover the gypsum needle. The optimum conditions for obtain the finer gypsum size were dehydration rate of 75~85%, solid concentration at hydration of 10~15%, agitation speed of 250~400 rpm, crushing size before dehydration of 2 cm or less. Gypsum of 98.21% grade was recovered with 99.0% yield as the undersize of 325 mesh wet screening followed by the dehydration-hydration process performed at the conditions of dehydration rate of 80%, solid concentration at hydration of 15%, agitation speed of 300 rpm, crushing size before dehydration of 2 cm or less. After the recrystallization of recovered gypsum, Plate-like gypsum of size with 99.49% grade was obtained as the oversize of 270 mesh in a wet screening.