Abstract: Ulexite，a sodium-calcium borate hydrate（Na2O·2CaO·5B2O3·16H2O） from Bolivia，was used as raw material in the preparation of boric acid with nitric acid.With washing ulexite and leaching ulexite concentrate，the Cl- removal and B2O3 extraction processes of ulexite were investigated，respectively.Results indicated that in the washing process of ulexite，Cl- removal rate reached up to 92.17% with liquid volume to solid mass ratio of 6 mol/L and washing time of 20~30 min，and under the conditions of nitric acid consumption being 90% of theoretical addition，liquid-to-solid mass ratio of 5∶1，reaction temperature of 60 ℃，and reaction time of 40~60 min，the B2O3 extraction rate of ulexite concentrate could achieve more than 98% in the decomposition process.Mother liquor was obtained by boric acid filtration，with the recycle of mother liquor continued， both calcium nitrate and sodium nitrate in mother liquor were accumulated，but boric acid concentration was generally remained a fixed value，thus the proper cycles were dedicated to boric acid recovery and increasing concentrations of nitrate in mother liquor.The Ca，Na-containing nitrate solution after recycle could be used to produce calcium carbonate or sodium nitrate as by-products.

Key words: ulexite, nitric acid, boric acid, washing