The Preparation And Crystallization Behavior Of Precursor Solution Of Aluminum Fluoride From Fluorine-containing Materials

Due to the rapid industrial growth,the contradicton between supply and demand of“fluorite”ore which regarded as the strategic mineral resource in China,has become increasingly prominent.Generated from the primary aluminum production industry,fluorine-containing materials contain rich fluorine resource and how to achieve the high-valued ultilization of the resource has been a significant subject.So,this paper,based on the resource utilization of fluorine-containing materials,proposed a novel preparation process of aluminum fluoriede through the study on the preparation of the aluminum fluoride precursor and its crystallization process.The main conclusions of this paper are as follows:（1）Under the guidance of comprehensive analysis of the phase structure and element content of the fliter residue which obtained from the disposal of fluorine-containing materials,we established the novel preparation of the aluminum fluoride precursor with the usage of fluosilicic acid solution,which not only realized impurity removal from the residue but also accomplished the function of the adjustment of F/Al molar ratio.The optimum operation parameters for preparation of the precursor are as follows:the reaction temperature was 60°C;the reaction time was 35 min;the initial F/Al molar ratio was 3.1 and the initial concentration of fluosilicic acid solution was 18%.Under the above condition,the high-grade precursor was prepared,which the yield of fluorine and silicon could reach 86.2%and 95.2%,respectively.（2）In order to prepare theβ-Al F₃with lower crystal water content,a series of crystallization of the aluminum fluoride precursor were carried out at various temperatures.Results showed that the increasing of crystal temperature could not only drastically shorten the time consumption from10 h to 90 min but also reduce the content of product from 38.90%at 90°C to 5.37%at 150°C.（3）In order to control the main particle size and the particle-size distribution,the crystallization process and induced crystallization ofβ-Al F₃were studied.And the effect of the initial concentration of aluminum fluoride precursor、the stirring intensity and the amount of seed crystals on the process were explored.Under suitable conditions of the process（150°C,191.10 g/L,200 rpm and 5%）,the main particle size of theβ-Al F₃reached 43.21μm,and the distribution showed a narrow unimodal distribution with the coefficient of variation of 8.35%.（4）The crystal transformation process fromβ-Al F₃toα-Al F₃and the performance characterization of theα-Al F₃were explored.The results showed that the main phase of product which obtained via high-temperature roasting using theβ-Al F₃,wasα-Al F₃and the purity could reach 91.65%.The fluorine and aluminum element content in the product could meet the brand AF-0 requirements of national standard GB/T 4292-2017.Viewing from the microstructure,the aluminum fluoride crystal appeared cubic crystals with particles of uniform size.And the apparent density of the product could reach 1.03-1.14 g/cm³,which was higher than the 0.70 g/cm³required by the brand AF-2 for the aluminum fluoride by wet method in the standard.