More than 40 m length of drill cores were collected from four boreholes drilled by Geological Survey of Finland (GTK) and Outokumpu Oy in high-grade metamorphic rocks of Rautalampi and Käypysuo, Central Finland. The hosted rocks of the graphite mineralization were mica–quartz schist and biotite gneiss. The graphite-bearing rocks and final concentrated graphite powder were studied with petrographic microscope, scanning electron microscope (SEM-EDS), Raman spectroscopy, and X-ray analysis (XRD and XRF). A majority of the studied graphite had a distinctly flakey (0.2–1 mm in length) or platy morphology with a well-ordered crystal lattice. Beneficiation studies were performed to produce high-purity graphite concentrate, where rod milling and froth flotation produced a final concentrate of 90% fixed carbon with recoveries between 67% and 83%. Particle size reduction was tested by a ball and an attritor mill. Graphite purification by alkaline roasting process with 35% NaOH at 250 °C and leached by 10% H₂SO₄ solution at room temperature could reach the graphite purity level of 99.4%. Our analysis suggested that purifying by multistage flotation processes, followed by alkaline roasting and acid leaching, is a considerable example to obtain high-grade graphite required for lithium-ion battery production.

中文翻译：

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芬兰中部变质片岩带中的高级鳞片状石墨矿床—锂离子电池应用石墨的矿物学和选矿

在芬兰中部的Rautalampi和Käypysuo的高级变质岩中，从芬兰地质调查局（GTK）和Outokumpu Oy钻的四个钻孔中收集了40 m以上的岩心。石墨矿化的主要岩石是云母-石英片岩和黑云母片麻岩。用岩石显微镜，扫描电子显微镜（SEM-EDS），拉曼光谱和X射线分析（XRD和XRF）研究了含石墨的岩石和最终的浓缩石墨粉。大部分研究过的石墨具有明显的火星状（长0.2–1 mm）或板状形态，晶格排列良好。进行了选矿研究以生产高纯度石墨精矿，其中棒磨和泡沫浮选生产的最终精矿含90％的固定碳，回收率在67％至83％之间。通过球磨机和磨碎机测试粒度减小。在250°C下通过35％NaOH的碱性焙烧工艺提纯石墨，并用10％H浸出室温下的₂ SO ₄溶液可达到99.4％的石墨纯度。我们的分析表明，通过多步浮选工艺进行纯化，然后进行碱焙烧和酸浸，是获得锂离子电池生产所需的高级石墨的重要例子。