The flake graphite ore is formed by high-pressure metamorphism, which is generally greenish gray and yellowish brown or grayish white after weathering. The associated minerals are complex, mainly accompanied by feldspar, quartz, biotite, pyrite, pyrrhotite, rutile and other impurity minerals.
According to the different characteristics of the scale graphite ore deposits and ore properties, the purification methods are also different. The main purification methods of graphite ore include flotation purification, alkali acid purification, hydrofluoric acid purification, chlorination roasting purification and high-temperature purification.
The flaky graphite ore has good floatability, so the flotation can better separate the graphite from other impurity minerals. In order to effectively protect the graphite flakes and improve the yield and grade of large pieces of graphite, the process flow plant adopts the multistage regrinding and multistage reselection process of coarse concentrate, which can screen out the dissociated large flake graphite in time and avoid the scale being broken by repeated grinding.
In the flotation process, kerosene, diesel oil, heavy oil, sulfonic acid esters, sulfates, phenols, carboxylic acids, etc. are often used as collectors, and 2 # oil and 4 # oil are used as foaming agents.
The flotation purification method is mainly suitable for low-carbon flake graphite, which can effectively protect the graphite flake and improve the grade of graphite, and has low production cost and low energy consumption. However, this process has many times of cleaning, large amount of middling return, complex process, and difficult to control production.
Alkali acid purification of flake graphite ore mainly consists of alkali melting process and acid leaching process.
Alkali melting process: taking advantage of the acid and alkali resistance of graphite, sodium hydroxide and graphite are mixed in a certain proportion and then calcined at high temperature. In the molten state, some impurities (quartz, silicate, aluminosilicate, etc.) in the alkali and graphite react chemically to generate water-soluble or acid soluble salts, and then wash to remove silicon to achieve the purification of graphite.
Acid leaching process: the products after alkali melting and desilication are subject to acid leaching treatment, so that impurities (metal oxides) that do not react with alkali in the melting process and acid generation should be converted into soluble salts, and graphite is purified through water washing and other processes.
Alkali acid purification of flake graphite ore is mainly suitable for medium carbon graphite and high carbon graphite ore. The process has simple equipment, strong applicability, small one-time investment and high grade graphite can be obtained. However, this process needs to be carried out under high temperature, which consumes a lot of energy. The agent used is easy to corrode the equipment and consumes a lot of water.
Hydrofluoric acid purification of flake graphite ore is to mix graphite and hydrofluoric acid, react at a certain temperature for a period of time, generate water soluble compounds (or volatiles), then wash off impurities, dehydrate and dry to obtain purified graphite products.
In order to effectively prevent impurities (metal ions) from generating precipitation, a small amount of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid or fluorosilicic acid will be added to hydrofluoric acid.
Graphite is acid resistant, but quartz and silicate impurities in minerals can react with hydrofluoric acid, so hydrofluoric acid purification method is mainly suitable for purifying high carbon graphite ore. The process flow is simple, the purification grade of graphite ore is high, and the cost is low. However, hydrofluoric acid is volatile and highly toxic, and improper use will cause safety accidents and environmental pollution. Therefore, safety protection measures must be taken during use, and the wastewater generated must be treated in a centralized way before it can be discharged.
Chlorination roasting to purify flake graphite ore is to mix graphite and reducing agent in a certain proportion, and then calcine at high temperature in the designated equipment. Impurities (silicate, aluminum silicate, etc.) in graphite will be decomposed into SiO2, Al2O3, Fe2O3, CaO and other oxides under high temperature. These oxides will react with chlorine gas and become chlorides of meteorological or condensed images. The low boiling point of chlorides will be used to vaporize and escape through high-temperature roasting, so as to achieve graphite purification.
The chlorination roasting purification method is mainly suitable for the treatment of silicate containing graphite ores, with high purification efficiency, but the reductant chlorine is toxic, which will cause equipment corrosion and environmental pollution. It is seldom used in actual production.
The physical and chemical purification of flake graphite mainly adopts the high-temperature method. The melting point of graphite is 3773K, its melting and boiling point is higher than that of silicate, second only to diamond, and it is one of the substances with the highest melting and boiling point in nature. The high-temperature graphite purification method uses the difference between the melting and boiling points of graphite and impurities to add graphite ore into the graphite crucible. Under certain conditions, inert gas and shielding gas are introduced, and specific equipment is used for heating. When the temperature reaches 2700 ℃, impurities will vaporize and escape, so as to achieve the purpose of graphite purification. The high temperature purification method has high purification efficiency, and the purity of graphite can reach 99.99%. However, the high temperature purification of graphite ore will be affected by many factors, and the process energy consumption is high. It requires very high equipment and raw materials, and the investment is large.
The above are several methods. As for which one to choose, it is necessary to determine the mineral properties of flake graphite ore according to the beneficiation test, and select the appropriate process to provide, so as to obtain the ideal graphite concentrate.
