二氧化碳沉淀法制备高纯二氧化硅的工艺研究

研究了用二氧化碳沉淀法制备高纯二氧化硅的工艺,试验内容主要分为两个工艺段,首先用工业二氧化碳与空气的混合气体从初步净化后的偏硅酸钠溶液中沉淀出偏硅酸,控制好温度、气体流量、二氧化硅浓度及pH等条件,在沉淀过程中溶液中的部分杂质不与偏硅酸一同沉淀,实现与部分Al,B,P等杂质的分离,从而获得铝、铁含量较低的偏硅酸。获得的偏硅酸用去离子水充分洗涤后,烘干脱水,分析其中的杂质含量;其次是用盐酸溶出获得的偏硅酸中的杂质,控制液固比、温度、反应时间及酸浓度,在常压下反应一定的时间、然后抽滤、分离得偏硅酸,用去离子水洗至中性后,再用一定含量的氯化铵溶液洗涤,最后用去离子水充分洗涤,获得的偏硅酸在850℃下煅烧2 h,就获得了纯度≥99.99%的二氧化硅。

Preparation of High Purity Silica by Carbon Dioxide-Precipitation Method

The technology of preparation high purity silica by carbon dioxide-precipitation was investigated.The test content mainly included two process sections.First,the silicic acid was prepared from the preliminary purification solution by carbon dioxide and air mixed gas.Some impurities in aqueous solution were not precipitated with silicic acid in the precipitation process under the controlling conditions of temperature,gas flow rate,silica concentration and PH.So the silicic acid with low content of aluminum and iron could be obtained after realizing that some impurities such as Al,B,P were separated in the precipitation process.The getting silicate was dried and dehydrated after fully washing with deionized water,then the content of impurities was analyzed.Second,the impurities in the obtained silicate were dissolved by hydrochloric acid under the controlling conditions of temperature,ratio of liquid to solid,reaction time and concentration of hydrochloric acid,the mixed solution was filtered and the silicic acid was isolated after the reaction for a certain time under normal pressure.The obtained silicate was washed by a certain content of ammonium chloride solution after being washed to neutral by deionized water.Finally,the silicic acid was washed to neutral again.The purity of the silica was not less than 99.99% after the obtained silicate was calcinated at 850 ℃ for 2 h.