漳州风化残积型高岭土矿床的矿物学特征

Mineralogical Features of Weathered Residual Kaolin Deposit in Zhangzhou Area, China

本文运用化学成分分析、X射线衍射、红外光谱、热重-热流和扫描电镜等方法对福建漳州地区某风化残积型高岭土矿床中的矿物组成和微观形貌进行了系统研究。结果表明:虽然该区风化残积型高岭土的矿物组成简单,主要为高岭石和石英,次为钾长石,但石英含量相对较高导致样品的化学成分呈现高硅低铝的特征,n(Si O_2)/n(Al_2O_3)在4左右。样品的w(K_2O)波动范围较大,w(Na_2O)、w(Mg O)和w(Ca O)低,而有害组分Fe、Ti含量相对较高。该风化残积型高岭土矿床风化不完全,高岭石结晶度较差,其X射线衍射峰峰形弥散,对称程度差。在扫描电镜下高岭石的六方片状晶形难以辨认,其形状不规则,呈片状、鳞片状集合体和团块状。此外,样品的热稳定性相对较差,其脱羟基温度≤500℃,进而说明该地区风化残积型高岭土结晶度较低。

Mineral composition and micromorphology of minerals in the weathered residual kaolin deposit from Zhangzhou Area, China were studied using chemical composition analysis, X-ray diffraction（XRD）, Infrared spectroscopy（IR）, thermogravimetry-differential scanning calorimetry（TGA-DSC） and scanning electron Microscope（SEM）. Although the mineral composition only consists of kaolinite, quartz and minor potassium feldspar, the quartz content is relatively high. As a result, chemical composition of the sample presents the feature of high silicon and low aluminum, and the molar ration of Si O_2/Al_2O_3 is approximately 4. The sample has a low content of K, Ca, and Mg, but high contents of Fe and Ti, while the content of K varies in a wide range. The kaolin deposit is not fully weathered and the kaolinite presents a poor crystallinity, which can be evidenced by the dispersive and asymmetric XRD reflections of the sample. The SEM images for the samples do not show regular hexagonal plate which is a symbol of well-ordered kaolinite, but irregular and crumby morphology. Additionally, the samples show a low thermal stability with dehydroxylation below 500 ℃, further demonstrating the poor crystallinity of the kaolinite.