硝酸分解钠硼解石制备硼酸的工艺研究

以玻利维亚钠硼解石矿为原料，采用硝酸酸解硼矿制备硼酸。考察了钠硼解石的洗矿和酸解工艺，结果表明：在洗矿工艺中，控制液固体积质量比为6 mL/g和洗矿时间为20~30 min，氯离子的脱除率达到92.17%；在酸解工艺中，控制硝酸用量为理论用量的90%、液固质量比为5、反应温度为60 ℃和反应时间为40~60 min，硼的浸出率达到98%以上。在上述工艺条件下进行硼酸母液循环研究，结果显示，随着循环次数的增加，虽然母液中的硝酸钙和硝酸钠不断积累，其质量浓度不断增加，但硼酸的质量浓度保持稳定。合适的循环次数有利于硼的回收和母液中硝酸盐浓度的提高，使母液可以用于生产硝酸钠和碳酸钙等附加值高的副产品。

Study on preparation of boric acid by leaching ulexite with nitric acid

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.