Natural graphite, as its name implies, is naturally formed graphite in nature. It generally occurs in graphite schist, graphite gneiss, graphite containing schist and metamorphic shale. Graphite belongs to the complex hexagonal biconical crystal type, which is in the form of hexagonal plate crystal. The common single form includes parallel double sides, hexagonal biconical and hexagonal column, but the intact crystal form is rare, generally in the form of flake or plate, and the aggregate is in the form of dense block, earth or spherical.
The natural graphite minerals are iron black and steel gray, and the stripes are bright black; Metallic luster, cryptocrystalline aggregate is dull and opaque; The hardness is anisotropic, the vertical cleavage plane is 3-5, and the parallel cleavage plane is 1-2; It is soft, with a density of 2.09-2.23g/, with a feeling of greasiness and easy to pollute the fingers. Natural graphite is rarely pure and often contains impurities, including SiO2, A12O3, FeO, Cao, P2O5, Cuo, etc.
According to different crystal forms, natural graphite is divided into crystalline graphite, cryptocrystalline graphite and dense crystalline graphite.
Crystalline graphite generally refers to flake graphite, which is the most widely distributed graphite ore in the world and has the largest proven reserves. Its original ore grade is low, generally 3-15%, so it needs to be beneficiated after being opened. Beneficiation methods include high temperature method, flotation method and alkali acid method. Most domestic flotation methods are adopted, and the recovery rate is generally only 40% – 50%.
Aphanitic graphite is also called microcrystalline graphite and earthy graphite. Its crystal is small and often embedded in clay, so it is difficult to separate. Generally, the grade of raw ore is 60-80%, so the enterprises mostly sell graphite powder directly after grinding and processing.
There are two kinds of natural graphite ores in China, one is flaky graphite ore and the other is earthy graphite ore. The scale graphite ore is concentrated in Heilongjiang, Shandong, Inner Mongolia and Henan. The large output is Heilongjiang Liumao graphite ore, Shandong nanshau graphite ore and Inner Mongolia Xinghe graphite ore. The earthy graphite ore is mainly in Hunan Province, which is the Lutang graphite ore in Hunan Province.
Heilongjiang Liumao graphite mine. The mine produces flake graphite. The size of raw ore is – 550mm, the size of incoming grinding is – 20mm, the selected size is – 100 mesh, accounting for 70%, and the grade of raw ore is 14% ~ 16%. After flotation, the graphite coarse concentrate is reground for 5 times, cleaned for 6 times, and the medium ore is returned to the rough grinding circuit. The concentrate grade is 93% ~ 95%, the tailings grade is 3% ~ 4%, and the beneficiation recovery rate is about 75%.
Shandong Nanshu graphite mine. The mine is located in Laixi County, Shandong Province and produces flake graphite. The processing capacity of raw ore in the concentrator is about 350000 T / A, the particle size of raw ore is – 450mm, the grinding particle size is – 15mm, and the selected particle size is – 0.15mm, accounting for 60% ~ 65%. The raw ore grade is 4.39% ~ 4.45%, the concentrate grade is 88% ~ 89%, the recovery rate is about 80%, and the tailings grade is 0.6% ~ 0.8%. The flotation concentrate is purified by alkali acid method. The final graphite concentrate grade reaches 98% ~ 99%, and the operation recovery rate reaches 88%.
Xinghe graphite mine, Inner Mongolia. The annual processing capacity of the two concentrators is about 300000 t, and the graphite output is about 7000 t. The raw ore particle size is – 350mm, the grinding particle size is – 10mm, and the selected particle size is – 0.15mm, accounting for 38%. The raw ore grade is 3.82% ~ 4.07%, the concentrate grade is about 88%, the tailings grade is 1.34% ~ 1.68%, and the recovery rate is about 68%. The grade of flotation concentrate can reach 94% ~ 99.5% after chemical purification.
Hunan Lutang graphite mine. The mine produces cryptocrystalline graphite. The grade of raw ore is 65% ~ 68%, and the particle size is – 250mm, which is fine-grained. The processing process is relatively simple, mainly composed of manual separation, coarse crushing, screening, medium crushing, drying, grinding and grading. The raw ore processing capacity of the concentrator is about 60000t / D, and the grinding particle size is – 40mm. The grade of manual concentrate is 70% ~ 88%, the grade of manual tailings is less than 60%, and the beneficiation recovery rate is 90%.