原始高岭土的沉积物,位于西安达卢西亚(西班牙),在这项工作中使用一个代表性的样本进行了研究。表征方法为X射线衍射(XRD),X射线荧光(XRF),通过筛分和沉降进行粒度分析,和热分析。测定了陶瓷性能。来自Burela(Lugo,西班牙),在陶瓷工业中的应用,在某些确定中用于比较目的。高岭土矿床是由富含长石的岩石蚀变产生的。这种原始高岭土在当地的陶瓷和耐火材料生产中用作添加剂。然而,以前没有关于其特性和烧制性能的研究。因此,这项调查的意义是对这个问题进行科学研究,并评估应用的可能性。用水洗涤粗高岭土以进行岩石的选矿,以增加所得材料的高岭石含量。结果表明,通过XRD测定,原料的高岭石含量为20wt%,显示约23重量%的颗粒低于63微米。低于63μm的部分的高岭石含量为50重量%。因此,通过湿法分离提高了该原料高岭土的高岭石含量。然而,高岭土被认为是废高岭土,有了微斜线,通过XRD鉴定白云母和石英。通过热膨胀法(TD)进行热分析,差热分析(DTA)和热重分析(TG)允许观察高岭石热分解,石英相变和烧结效应。这种生高岭土的压制样品,通过水洗获得的低于63µm的馏分和使用锤磨机研磨的原始高岭土在1000-1500°C范围内的几个温度下烧制2h。确定并比较了所有这些样品的陶瓷性能。结果表明,通过烧结这些样品,在低于63µm的分数中,最大值为~9%。总的来说,在1300°C烧制后,烧制样品的吸水率从1050°C时的〜18-20%下降到几乎为零,其次是实验值的增加。在1350°C下烧制2小时后,开口孔隙率几乎为零,并且堆积密度达到最大值2.40g/cm3,如在研磨的原始高岭土样品中观察到的。烧结样品的XRD检查表明,它们由莫来石组成,从高岭石热分解,还有石英,存在于原始样本中,作为除玻璃相外的主要结晶相。通过在1300-1350°C下烧制2小时获得完全致密或玻璃化的材料。在本研究的第二步中,研究了通过将氧化铝(α-氧化铝)掺入该高岭土样品来增加莫来石的量的先前研究的有希望的应用。烧制混合物,使用该高岭土和α-氧化铝在湿法加工条件下制备,通过在高于1500°C的温度下反应烧结2h,使莫来石的相对比例增加。因此,莫来石耐火材料可以用这种高岭土制备。先前的尺寸分离有利于高氧化铝耐火材料的这种处理,这增加了高岭石的含量,或更好的研磨处理的原料高岭土。
A deposit of raw kaolin, located in West Andalusia (Spain), was studied in this work using a representative sample. The methods of characterization were X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size analysis by sieving and sedimentation, and thermal analysis. The ceramic properties were determined. A sample of commercial kaolin from Burela (Lugo, Spain), with applications in the ceramic industry, was used in some determinations for comparison purposes. The kaolin deposit has been produced by alteration of feldspar-rich rocks. This raw kaolin was applied as an additive in local manufactures of ceramics and refractories. However, there is not previous studies concerning its characteristics and firing properties. Thus, the meaning of this investigation was to conduct a scientific
study on this subject and to evaluate the possibilities of application. The raw kaolin was washed for the beneficiation of the rock using water to increase the kaolinite content of the resultant material. The results indicated that the kaolinite content of the raw material was 20 wt % as determined by XRD, showing ~23 wt % of particles lower than 63 µm. The kaolinite content of the fraction lower than 63 µm was 50 wt %. Thus, an improvement of the kaolinite content of this raw kaolin was produced by wet separation. However, the kaolin was considered as a waste kaolin, with microcline, muscovite and quartz identified by XRD. Thermal analyses by Thermo-Dilatometry (TD), Differential Thermal Analysis (DTA) and Thermo-Gravimetry (TG) allowed observe kaolinite thermal decomposition, quartz phase transition and sintering effects. Pressed samples of this raw kaolin, the fraction lower than 63 µm obtained by water
washing and the raw kaolin ground using a hammer mill were fired at several temperatures in the range 1000-1500 °C for 2 h. The ceramic properties of all these samples were determined and compared. The results showed the progressive linear firing shrinkage by sintering in these samples, with a maximum value of ~9% in the fraction lower than 63 µm. In general, water absorption capacity of the fired samples showed a decrease from ~18-20% at 1050 °C up to almost zero after firing at 1300 °C, followed by an increase of the experimental values. The open porosity was almost zero after firing at 1350 °C for 2 h and the bulk density reached a maximum value of 2.40 g/cm3 as observed in the ground raw kaolin sample. The XRD examination of fired samples indicated that they are composed by mullite, from kaolinite thermal decomposition, and quartz, present in the raw sample, as main crystalline phases besides a vitreous phase. Fully-densified or vitrified materials were obtained by firing at 1300-1350 °C for 2 h. In a second step of this research, it was examined the promising application of the previous
study to increase the amount of mullite by incorporation of alumina (α-alumina) to this kaolin sample. Firing of mixtures, prepared using this kaolin and α-alumina under wet processing conditions, produced the increase of mullite in relative proportion by reaction sintering at temperatures higher than 1500 °C for 2 h. Consequently, a mullite refractory can be prepared using this kaolin. This processing of high-alumina refractories is favoured by a previous size separation, which increases the kaolinite content, or better a grinding treatment of the raw kaolin.