Elimination of boron species via solvent extraction with 2,2,4-trimethyl-1,3-pentandiaol was engaged in a flow-type device into which the aqueous solution dissolving diatomaceous earth, a -candidate of the resource for high-purity silicon material. The flow-type device has a 2-stage channel with 1.0 mm width, 0.10 mm depth, and 25 mm length each, and the specific interfacial area is comparable to a typical microchannel device. Residual boron content in the aqueous solution decreased to less than 0.1 ppm after the solvent extraction under the restriction of short contact duration shorter than 100 ms. In addition, the analysis with density functional theory indicated that the number of neighbor carbon on the central carbon is one of the keys for improvement of reactivity of extractant. Hence, it is suggested that the flow-type microchannel device with solvent extraction with alkyldiol extractant can be utilized as an attractive approach toward the production of high-purity silica as a source for solar-grade silicon.