Patent ID: 9238876
Filing Date: 2016-01-19
CPC Classification: C01B,C30B

Claim Text:
1. A method of washing polycrystalline silicon lumps produced by the Siemens method comprising: a step of acid cleaning in which the polycrystalline silicon lumps retained in a basket are cleaned with an acid solution in an acid clean bath; a step of transferring the basket retaining the acid cleaned polycrystalline silicon lumps to a supporting surface of a platform provided directly on the bottom plate of a water cleaning bath filled with pure water, a cross section of the supporting surface taken along the longitudinal direction of the water cleaning bath being parallel to the cross section of the bottom plate also taken along the longitudinal direction of the water cleaning bath and higher than the bottom plate of the water cleaning bath in a vertical direction; a step of overflowing pure water by supplying pure water to the cleaning bath after the step of transferring; a step of immersing the polycrystalline silicon lumps in the pure water after the step of overflowing in the water cleaning bath for at least 2 hours to remove residual of the acid solution on surfaces of the polycrystalline silicon lumps, the pure water cleaning tank provided with a pure water supply device, which is positioned to one end of the water cleaning bath in a longitudinal direction of the water cleaning bath and a pure water drainage device, which is positioned to the other end of the water cleaning bath in the longitudinal direction and to the bottom plate of the water cleaning bath; a step of measuring an electrical conductivity C of the pure water by an electrical conductivity measuring device provided in a vicinity of a feed-water inlet of the pure water supply device after the step of immersing; a step of repeating the step of immersing after replacing the pure water in the water cleaning bath with fresh pure water when the electrical conductivity is more than 2 μS/cm in the step of measuring; a step of ending the step of immersing in a case where the electrical conductivity C measured in the step of measuring is 2 μS/cm or lower, wherein, the bottom plate of the water cleaning bath is sloped down toward the water drainage device in the longitudinal direction the water cleaning bath with respect to the bottom plate, the supporting surface of the platform is sloped in a width direction of the water cleaning bath, a plurality of through-holes are provided between the lower end surface of the platform and the bottom surface of the water cleaning bath in the longitudinal direction of the water cleaning bath.