The coal is cleaned by screening and hand picking, or partly heavy medium separation in most of the coal mines of Korea. Generally, coal ore of + 65 mm size is treated by hand picking and the less size range is treated by screening or heavy medium separation. However, the low grade small lump coal ores of - 65 mm + 25 mm are left in large quantities owing to uneconomic cleaning cost. Therefore, in the present study "Leap-bourd picker" was newly designed and applied as a method of dry type coal cleaning for simple to upgrade low-grade lump coal. The coal samples used in this study are dump coal and coal middling obtained from the Gyung-dong coal mine. "Leap-bound picker" consists of feeding chute, rotating elastic drum and divider of cleaning products. It was also manufactured so that the revolution speed of rotating elastic drum, appropriate length and slop angle of feeding chute, and the drop length between chute tip and top of the elastic drum could be controlled well. The principle of coal cleaning by the "Leap-bound picker" is based on the differences of physical properties between coal and gangue minerals such as shape, specific gravity, friction force and elasticity when the small lump coals are dropped from the chute to the upper surface of rotating elastic drum. From the results of coal cleaning experiment, clean coal of 3600 kcal/kg was obtained from dump coal of 3000 kcal/kg with the recovery of 91% and in addition, coal middling of 3800 kcal/kg was cleaned to 4600 kcal/kg with the recovery of 94% using the Leap-bound picker.

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Removal of selenate ion (SeO₄^2-) by chemical reduction using Fe₃O₄ powder is investigated. Selenate is reduced to elemental selenium which is precipitated on the surface of the Fe₃O₄ powder. Both selenite ion (SeO₃^2-) and hydrogen selenide (H₂Se) are not detected during the experiments. Ferrous and ferric ions which are accumulated during the reaction are not effected on the reduction of the selenate. The reduction rate increases with decreasing in pH and increasing temperature. Selenium (IV) concentration in the solution containing approximately 10 g·m-³ is decreased less than 0.3 g·m-³ at 343 K.

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In order to increase the capacity and to obtain higher accuracy of separation the main Baum jig in Ikeshima colliery has been improved into a VARI-WAVE jig, which has been developed to create a desired wave pattern of pulsation. The existing rotary valve of mechanical type on each cell was replaced by an exhaust valve and two inlet valves to admit high and low pressure air. Each valve is driven by an air cylinder and an electromagnetic valve which is periodically operated by a controller. A set of new blower and air duct have been installed for a high pressure air supply while the existing system has been utilized for a low pressure air supply. The existing refuse ejector of gate type has been replaced by that of star wheel type whose speed is controlled automatically. One of the most distinct advantages offered by the improvement is an easy and prompt control of the pulsation. The wave height, the wave pattern and the period of pulsation became very easy to change and adjust. It has been found that the wave pattern of pulsation has a noticeable effect on the mobility and the separation of the particles. After the improvement the jig is operating successfully. The float-and-sink analysis of the product of the first bucket elevator shows that it can be expected to recover about 10, 000 tons of steam coal a year.

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