How to remove Fe in high purity alumina
Fe impurities mostly exist in the main products in the form of divalent or trivalent oxide. Various researchers have studied the removal of Fe impurities in different substances, such as bauxite, aluminate - alkaline solution, etc.
Bauxite is formed in tropical or subtropical climate, widely exists in basalt, limestone and other rocks and schist, and common impurities include ferrite, goethite, quartz, silicalite, corundum, titanium dioxide, etc. High quality bauxite Al ₂ O minimum ₃ content is 40%, the SiO ₂ content up to 15%; The low quality bauxite impurities are mainly quartz, ferric oxide and calcium oxide. A. Aziz, etc in the sulfuric acid leaching method is adopted in the process of alumina in the bauxite, choose A purity of 68% ethanol (C ₂ H5 - OH) almost completely removed the Fe impurities, but ethanol is expensive, in order to make the process more economic, can through the condensate recovery method for secondary use of ethanol.
Remove aluminate. The most common purification method for Fe impurities in alkaline solution is to add sodium sulfite to calcium oxide for treatment. Previously, some people have used ammonia-methyl extraction system instead of derivatives of phenol to extract Fe impurities. The extraction agent 2-hydroxy-5-alkyl (C8-C9) benzyl diethanolamine was used to successfully extract Fe impurities from aluminate - alkaline solution, and the technology has been tested in actual alumina production plants.
Because the alumina prepared by aluminum ammonium sulfate with higher Fe content is of low purity, it cannot meet the requirements of high-purity products and has great restrictions on its application, so the Fe in the raw material must be removed. The methods commonly used at present include precipitation, organic primary amine extraction and recrystallization. Precipitation can by adding additives MnO ₂, KMnO4, K ₃ [Fe (CN) 6] or K4Fe (CN) 6 · 3 h ₂ O, it has the advantage of low cost, easy to operate; The disadvantage is the large amount of aluminum ion loss, adding additives in the process to introduce new impurities. The organic primary amine extraction method is difficult to operate, the amount of extractant is large and the cost is high, and the reverse extraction is complex, so it is difficult to be applied in industry.
Recrystallization method has simple equipment, easy operation and low cost. Lu Jiangang used this method to obtain aluminum ammonium sulfate in accordance with national quality standards. Liu Ping improved the purification of the method as follows: In order to improve the filtration effect, the filter medium press cloth was changed into polymer PE microporous tube; In order to take out the crystal more conveniently, the rectangular groove was changed into a semicircular groove with a handle; Additives were added to facilitate the separation of impurities.
