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When it comes to the chrome mining processes, we should start from the nature of chrome ore, which has the characteristics of oxygen and siderophile affinity. Currently, the chrome ore with industrial value is generally chromium magnesium spinel or chromium iron spinel minerals, which contain a large amount of chromium oxide (18%-62%), aluminum, nickel and other metals. The characteristics of chrome ore make the chrome mining processes rich and various.
Due to the nature of chrome, the common chrome mining processes include gravity separation process, magnetic separation process, flotation process, combined process, chemical process, etc. The industrial chrome mining processes mainly include single gravity separation process, single magnetic separation process, and gravity separation - magnetic separation process. Generally, chrome ore contains a certain amount of iron, so the combination process of gravity separation and magnetic separation is a common chrome mining process.
In terms of chrome mining equipment, the gravity separation stage usually uses the shaking table and jigging machine, while the equipment used in the magnetic separation stage often depends on the magnetism of the ore, mainly including magnetic separator, magnetic drum.
Here are some cases of chrome extraction plants:
The Philippines chrome ore mining plant contained 23.47% of chrome oxide, and a small amount of pyrite and nickel pyrite. The gangue minerals were mainly serpentine and small amounts of carbonate. In the ore dressing experiment, magnetic separation, shaking table and spiral chute were respectively used for roughing tailings discharging test. The test results showed that the shaking table and spiral chute had the better tailings discharging effect, but the rate of tailings discharging by the spiral chute was low, so the shaking table was used for the chrome mining. After expanding the test scale and testing the grinding variable, finally the chrome mining process adopted one stage shaking table for roughing, re-separation of shaking table middlings, roughing of concentrate middlings, re-separation concentrate merge. With this chrome mining process, the yields of concentrate was 57.19%, the grade of chromic oxide was 37.46%, and the recovery rate was up to 88.78%.
For the low-grade chrome ore mining plant in Yunnan, China, the content of chromium oxide was only 8.51%, the content of chromite was 16.81%, and the content of magnetite was only 0.65%. the gangue minerals mainly included serpentine, quartz. At the stage of classifying desliming test, the hydrocyclone with an output size of 6mm was used for desliming, so that the raw ore was enriched effectively and the grade of chromium oxide reached 18.52%. After the single shaking table test and single high gradient magnetic separation test, the results showed that the shaking table can obtain the better chrome mining effect, the chrome oxide grade was 40.56%, while the chrome oxide grade was only 38.93% after the high gradient magnetic separation process. Then, the grade of chromic oxide reached 45.29% by the magnetic separation – gravity separation test. Therefore, chrome ore mining plant adopted classification desliming, magnetic separation - gravity separation process.
For a China chrome ore mining plant, the content of chrome oxide was 35.28%, the content of ferrous oxide was 8.55%, so the structure was simpler, and the particles were coarser. The major gangue minerals included olivine, serpentine, chlorite, etc. Under the comparison among shaking table, shaking table - magnetic separation, strong magnetic separation process, the chrome ore mining plant obtained the better indicators by the wet magnetic separation process. Finally, take the chrome mining process was wet strong magnetic separation – roughing – scavenging technology, the concentrate grade of chromic oxide was 47.61% and the recovery rate was 96.26%.
From the above cases, we can see:
For rich chrome ores with high content of chromium oxide, a single gravity separation process or magnetic separation process can be adopted.
For the chrome ores with low content of chromium oxide, the magnetic separation process – gravity separation process can get the better indicators than the single process.
The specific chrome mining process shall be determined according to the nature of the ore itself.
In the selection of chrome mining process and equipment, we can refer to the mineral processing test indicators, consult with the qualified processing equipment manufacturers, take the appropriate process and equipment configuration, thus reducing the cost, improving the economic benefits.