THE DIGESTION OPERATION IN THE ALKALI ALUMINAT SOLUTIONS OF ALUMINUM HYDROXIDES IN THE BOEHMITIC BAUXITES

Abstract

At present more than 90 per cent of the world's alumina is produced by the Bayer process, a simple technology providing high purity final product. A part from some exceptional local conditions, bauxite is processed almost solely by this technology. As a benefication process, alumina production releases the aluminum oxide content of bauxite from other accompanying oxides thus providing alumina suitable for electrolysis in a cryolite melt. The basic theory of the Bayer process was elaborated by K.J. Bayer and described in his patents in 1887 and 1892. The first patent refers to the aid of seed crystals of aluminum hydroxide or of carbonic acid, that is, to the precipitation and carbonation processes. The second patent formulates the concept that the aluminum oxide content of bauxites can be dissolved in sodium hydroxide solutions, with the formulation of sodium aluminate, a process called digestion nowadays. The most important operations of the Bayer technology are bauxite preparation, crushing, grinding, digestion, red mud separation, thickening, washing, filtration, precipitation, calcination and evaporation. In spite of its great significance as regards the complete Bayer technology, the structure of sodium aluminate solutions has not been cleared up definitely yet. Boehmite is the most important aluminum mineral of karstic bauxites. Some experimental results showing the various effects on aluminum hydroxides by alkali process from boehmitic bauxites and the factors gowerning the digestion operation of aluminate solutions were investigated.

Keywords

• Boehmitic, Bauxite, Alkali, Sodium oxide, Aluminum hydroxide

BÖHMİTİK BOKSİTİN YAPISINDA BULUNAN ALUMİNYUM HİDROKSİTİN ALKALİ ÇÖZELTİLERİNDEKİ ÇÖZÜNÜRLÜĞÜ

Öz

Bugün dünya alümina üretiminin % 90'ından fazlası Bayer prosesi ile yapılmaktadır. Basit bir proses oluşu, yüksek saflıkta ürün vermesi, bu prosesin uygulanmasının en önemli sebeplerindendir. Bayer prosesinin esası, boksit mineralindeki aluminyum oksitin sodyum hidroksit çözeltisi ile muamelesi sonucu çözünürleştirilmesine dayanır. Sodyum aluminat çözeltilerinin yapısı çok kompleks olup henüz tam aydınlatılmamıştır. Burada böhmitik boksitin yapısında bulunan aluminyum hidroksitin alkali alüminat çözeltisindeki çözünürlüğü incelenmiştir.

Anahtar Kelimeler

• Böhmitik, Boksit, Alkali, Sodyum oksit, Aluminyum hidroksit