氧化铝生产高压溶出及蒸发工序结疤物质的矿物学特征及形成机理

采用X射线衍射(XRD)、扫描电镜背散射电子成像(BSE)技术和电子能谱分析技术(EDS)对拜耳法生产氧化铝过程中高压溶出和蒸发工序结疤物质矿物特征、沉积结构及形成机理进行系统研究。结果表明:结疤物质形成可划分为早期沉积作用和晚期沉积作用。高压溶出工序结疤物质是以粗结晶赤铁矿、钙钛矿、针铁矿为主的化学结晶,这些粗结晶在高压溶出阶段分别垂直各自管壁生长,在管壁上形成密集粗大晶簇,之后残留粗结晶与溶液通过再结晶形成结疤填隙物,主要为细粒铝针铁矿、钠硅渣、氢氧化镁、钙镁硅渣、水化石榴石和橄榄石等组分,是以早期沉积作用为主。蒸发工序结疤物质因晚期沉积作用而形成,早期大量易结晶杂质组分结晶析出后,残余组分发生物理沉积,沉积初始形成结构松散、具有流动性的微细粒或隐晶质碳酸钠和钠硅渣基体,之后再析出钛酸钙铁、铁石榴子石、碳酸钠等晶体,沉积物最终固化形成结疤。

Mineralogical Characteristics and Formation Mechanism of Scab Materials in High-Pressure Dissolution and Evaporation Process of Alumina Productions

Mineral characteristics, sedimentary structures and formation mechanism of scabs produced in high-pressure digestion and evaporation process were analyzed by X-ray diffraction(XRD), Backscatter electron(BSE) image and electronic energy spectrometer(EDS). The results show that scab formation could be divided into early and later sedimentation respectively. The scabs generated in high-pressure dissolution are chemical crystallization including coarse crystalline hematite, perovskite and goethite, which grew toward center along tubes walls and formed a large number of dense and coarse clusters growing as perpendicular to the wall. Then the solution captured between crystals recrystallized to form fine alumogoethite, sodium-silicon residue, magnesium hydroxide, calcium magnesium silica slag, hydrated garnet and peridot, and existed in form of intergranular interstitial material. Therefore, early deposition is the main scab process in high pressure dissolution process. Formation of scabs in evaporation process is physical deposition that occurs when a large number of crystallizable impurities are reduced. Firstly, loose and fluidity fine particles or aphanitic sodium carbonate and sodium-silicon residue substrates are formed by deposition, and then calcium iron titanate, iron garnet, sodium carbonate and other crystals are precipitated and form scab. Evaporation process is dominated by late deposition.