The test ore samples were collected from the tailings of the Nanyangtian tungsten ore in Malipo South, with a fluorite content of 21.76%. The gangue minerals are mainly calcite, quartz, and silicate minerals, classified as difficult-to-select ores. Since the tailings are from the separation of white tungsten, the sample contains a large amount of chemicals, including a significant amount of water glass and paraffin wax soap as flotation reagents. The pH value of the sample is alkaline. Considering the pH environment for fluorite flotation and the study of its flotation properties, the sample was not detoxified and was directly slurry mixed and treated with chemicals for separation. The target mineral in the sample is fluorite, which has fine grain size and poor floatability. The focus of the test was to study the type, dosage of gangue mineral activators, dosage of inhibitor water glass, and type and dosage of collector.
1. Sampled Ore Characteristics
The samples were naturally dried, mixed evenly, and split before being bagged for testing. Multi-element analysis was conducted on the samples, results are shown in Table 1.
The analysis results in Table 1 indicate that the valuable mineral in the sample is fluorite, with a content of 21.76%. The other mineral elements have low concentrations and are not considered for recovery.
2. Flotation Agent for Fluorspar
Common reagents used in fluorite flotation include water glass, sodium carbonate, and oleic acid. Sodium carbonate is generally used as an adjuster, water glass as an inhibitor, and oleic acid or sodium oleate as a collector. There are many collectors for fluorite flotation, in addition to oleic acid and 731, including amines, alkyl sulfonates, sodium oleamide sulfonate, and other sulfonates, all of which can be used as collectors for fluorite flotation.
According to the different properties of gangue, inhibitors such as water glass and lignosulfonate can be used to suppress gangue minerals. Controlling the amount of water glass and adjusting the pH value are crucial factors in obtaining higher-grade tungsten and fluorite. In this test, the modulus of the water glass is 2.4, within the modulus range. The order of suppression strength of water glass on nonsulfide minerals is: quartz > calcite > fluorite > tungsten ore [4]. For the separation of fluorite and calcite, oil acid is generally used as a collector to float out fluorite first. When floating fluorite with oil acid, a small amount of aluminum salt is added to activate fluorite, and dextrin is added to suppress calcite [5]. For more complex fluorite deposits containing some calcite and dolomite, lignosulfonate is more effective in suppressing these gangue minerals. For the separation of fluorite from quartz, fatty acids or mixed fatty acids are used as collectors to float fluorite [6], while water glass acts as the inhibitor for quartz, and sodium carbonate adjusts the pulp pH to 8-9 [7]. During the testing process, it is important to control the appropriate amount of water glass, as both too little and too much fail to achieve the desired effect. A small amount activates fluorite but insufficiently suppresses quartz, while an excess inhibits fluorite. To reduce the amount of water glass added while still achieving the required suppression strength on quartz gangue, it is common to add some multivalent metal ions (such as Al+, Fe3+) and alum, aluminum sulfate, etc. Additionally, the addition of Cr3+ and Zn2+ ions is also effective, but these ions have inhibitory effects not only on quartz but also on calcite [8].
Conditioned Dosage Volume Test
3.1 Trial of activator types and dosages
The test sample is the tailings from the flotation of tungsten, during which a large amount of inhibitor water glass was used to suppress the gangue minerals. Consequently, the fluorite was also suppressed, leading to a decrease in its floatability. The industry has high grade requirements for fluorite, necessitating the addition of an activator to the ore sample to obtain the desired grade of fluorite concentrate.
3.1.1 Activator Type Test
This trial considers the use of NaF, FeCl3, and CuSO4 as adjusting agents. The experimental process is illustrated in Figure 1.
The data from Table 2 reveals that among the three activators used in equal amounts, NaF performed the best in the trial, with a high grade of 43.26% and a high recovery rate of 82.37%. Therefore, subsequent tests will adjust the dosage of NaF as an additive.
3.1.2 Experiment with Sodium Fluoride Activator Dosage
The process remains as shown in Figure 1, with all other conditions unchanged, only varying the amount of NaF for the relevant tests. The results are as shown in Table 3.
The data from Table 3 reveals that as the dosage of NaF increases, the grade of CaF2 initially rises before decreasing, while its yield tends to increase with the increase in reagent dosage. Considering all factors, a dosage of 1500g/t for NaF appears to be most suitable.
3.2 Test on the dosage of inhibitor water glass
Water glass is a conventional inhibitor in fluorspar mining, and it is also used in the chemicals employed by the mine for tungsten selection. Therefore, an experiment on the dosage of water glass was conducted. The experimental procedure is illustrated in Figure 1, with all other conditions remaining unchanged, only varying the dosage of water glass for the relevant tests. The results are as shown in Table 4.
Based on the data from Table 4, it can be observed that as the dosage of the chemical increases, the concentrate yield decreases, the grade increase of the concentrate is relatively small, but the recovery rate decrease is slightly greater. Considering these factors, a dosage of 500g/t of water glass is deemed appropriate.
3.3 Capturing Agent Types and Dosage Test
3.3.1 Test of Absorbent Types
Fluorspar minerals commonly use fatty acid-based reagents as collectors [9], with oleic acid and its modified products being the most frequently used reagents in industrial flotation. Paraffin wax naphthenate 731 is also a common collector. Therefore, this experiment used sodium oleate and paraffin wax naphthenate 731 as collectors for the flotation of ore samples [10]. The experimental process is shown in Figure 1, and the results are presented in Table 5.
The data from the table above indicates that using sodium oleate as the collector, the grade and recovery rate of the test concentrate are both higher compared to using 731. A dosage test of sodium oleate will be conducted subsequently.
3.3.2 Sodium oleate usage test
The process remains as shown in Figure 1, with a NaF dosage of 1500g/t and a water glass dosage of 500g/t. All other conditions remain unchanged; only the sodium laurate dosage was altered for the relevant tests. The test results indicate that with an increase in the dosage of the reagents, the yield, grade, and recovery rate of the refined product will slightly increase. However, based on the test phenomena, an increased dosage of the reagents results in more foam during the test process, leading to overflow and difficulty in control. Considering all factors, a dosage of 2000g/t seems to be most appropriate.
4. Conclusion
(1) The optimal reagent for preliminary selection of the sample is NaF as an activator, water glass as an inhibitor, and sodium oleate as a collector. The dosages are 1500g/t, 500g/t, and 2000g/t, respectively. Compared to using CuSO4 as an activator, water glass as an inhibitor, and sodium oleate as a collector; or NaF as an activator, water glass as an inhibitor, and 731 as a collector, the performance is superior.