Process for the preparation of pure aluminium oxide

摘要

The invention relates to a process for the preparation of pure aluminium oxide by digesting clays or alumina-containing minerals with hydrochloric acid. The aim of the invention is to remove all the acid-soluble alkali metals and alkaline earth metals, coming forward with the clay, together with the crystallisation mother liquor. The invention is based on the object of processing the dust contained in the decomposition gases to give a solution which is as rich in AlCl3 as possible and as low in HCl as possible, or to give solid AlCl3.6H2O. According to the invention, the object is achieved when the fine-granular dust from the exit gases of the thermal decomposition of the crystallised product is converted by washing with suitable AlCl3 solutions into an AlCl3-rich, HCl-poor solution or solid AlCl3.6H2O, the resulting quantity of solution or crystals being removed from the washing solution circulation and the quantity of HCl required to be discharged and a part of the required water being condensed out of the decomposition gas by suitable temperature control.