Shandong Gold Ridge iron ore beneficiation plant (referred Jinling Iron ore dressing plant) was founded in 1967, the transformation of the production process several times in 2001, has formed a production capacity of grinding more than 1 million t of. Iron in contact with a high temperature hydrothermal Jinling account skarn metal deposits, mainly metallic minerals magnetite, pyrite (containing cobalt), copper ore and yellow pyrrhotite; major gangue minerals pyroxene, Chlorite, phlogopite , vermiculite and a small amount of calcite . The ore structure is dominated by massive vermiculite, followed by disseminated, and the ore structure is mainly semi-self-shaped - he is shaped into a mosaic structure, in which a small amount of fine-grained gangue minerals are distributed, and the mosaic size is generally 0.035-0.1mm. . Before 2001, the process of Jinling Iron Ore Concentrator was: the crushing and screening process was two sections and one closed circuit, and the pre-screening was carried out before the fine crushing. The sieved objects were pre-selected and discarded by magnetic pulleys. After crushing, the inspection and screening were carried out. After the material is pre-selected by the magnetic pulley, it returns to the fine crush to form a closed circuit; after the grinding process is a closed-circuit grinding, the staged overflow firstly floats after flotation, recovers copper and cobalt, and the mixed flotation tailings recovers iron through three-stage magnetic separation. .
1 Proposed problem There is a pre-selected throwing operation before grinding. That is, the pre-screened 14-200mm ore is pre-selected with CTDG1010N permanent magnet magnetic pulley before fine crushing, and the waste rock yield is about 18%. However, the ore of 0 to 14 mm after pre-screening has not been pre-selected, and at the same time, some of the waste rock is disintegrated after fine crushing.
The traditional dry magnetic separation and throwing waste is mainly used to select large and coarse-grained strong magnetic ore, and the sorting effect on fine-grained strong magnetic ore is not ideal. Wet pre-selection of fine ore is a new and highly operational technology developed in recent years. It is mainly used to treat fine-grained ferromagnetic ore of 0-20 mm. After application, the ore dressing cost can be greatly reduced and the grinding efficiency can be improved.
The problem facing the existing process is whether the wet pre-selection technology can be used to further eliminate the waste rock in the 0~14mm grain size that cannot be removed before grinding, so that some final tailings can be discarded ahead of time, the ore grade can be improved, and the grinding can be reduced. Energy consumption.
2 Feasibility Study In order to explore the feasibility of pre-selection of fine ore, the Jinling Iron Ore Concentrator carried out a pre-selection test of powder ore in April 2002.
2.1 Powder ore wet pre-selection laboratory test 2.1.1 Test plan Take 25kg sample from the ball mill feeding belt, and divide the sample into +8mm, -8+4mm, -4+2mm, -2mm four pieces by wet sieving method. Grade, +2mm or more granular grades are selected by magnetic block, and -2mm grain size is selected by wet magnetic separator to analyze the metal content of each product to explore a suitable pre-selection scheme.
2.1.2 Test indicators The test indicators are shown in Table 1. [next]

Analysis Table 1 shows that the grades of magnetic separation tailings above +2mm are lower or close to the total tailings grade of the existing process, the metal distribution rate is very low, and can be thrown as qualified tailings, and the grain size of -2mm or less The grades of copper, sulfur and cobalt in the tailings are significantly higher than those in the concentrate, indicating that the grade must be recycled.
2.1.3 Discussion on pre-selection scheme The ore tailings of +2mm or more are used as the total tailings, the whole grade concentrate of +2mm and the whole grade of -2mm grades are used as the total concentrate. The index analysis is shown in Table 2. [next]

Table 2 shows that the pre-wet selection effect is better for the grades above +2 mm. The pre-selected tailings iron grade is only 4.38%, the copper grade is 0038%, and the cobalt grade is 0.0103%, which are lower than or close to the wet-selected tailings grade, which can be completely discarded as qualified tailings, and the throwing rate reaches 8.22%. Pre-selected concentrates of iron, sulfur, copper and cobalt grades have been improved to varying degrees.
2.2 Powder ore wet pre-selection semi-industrial test The sample used in the semi-industrial test is taken from the belt before the ball mill feeding, with a total weight of 1t, and the sample is representative. The test process is shown in Figure 1, and the semi-industrial test indicators are shown in Table 3. [next]

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3 Practical application
The existing process uses MQGφ2700×2100 lattice ball mill and 2FLG-φ1500 double spiral classifier to form a closed circuit. There are four series. According to the laboratory test and semi-industrial test results, the following scheme is determined: one CTS is added before each billiard mill before grinding. -1050×1000 magnetic separator for wet pre-selection of powder ore, pre-selected concentrate directly into the ball mill, pre-selected tailings flow to DS2P-1224 vibrating screen (screen 2mm) for screening, sieved 2~14mm grain grade as qualified waste rock After throwing off, pre-selected tailings of 0~2mm size are returned to the 2FLG-φ1500 double helix classifier.
The wet pre-selection project was completed and installed in September-October 2002. It has been operating normally since November 2002. The wet pre-selection process was examined on March 11, 2003 and the results are as follows:
(1) The iron ore grade iron is 43.82%, the copper is 0.116%, the cobalt is 0.0154%, the graded overflow ore grade iron is 47.12%, the copper is 0123%, the cobalt is 0.0160%, and the overflow ore grade is powder. The grade of the mine has increased by 3.3 percentage points.
(2) The waste stone grade is 6.06%, the copper is 0.040%, and the cobalt is 0.0080%. It is a qualified tailings and meets the requirements of throwing waste. The waste yield is 8.04%.
(3) The ball mill processing capacity reaches 40t/h (calculated from entering the wet pre-selection operation), which is 5t/h higher than before the wet pre-selection operation.
 (4) Process inspection indicators are basically consistent with the original design indicators.
4 Conclusion 
The application of the wet pre-selection technology of the fine ore mine has abandoned the waste rock which is difficult to grind and choose, has improved the beneficiation production capacity, optimized the grinding operation conditions, and reduced the tailings treatment and storage costs. The existing process has more than 1 million tons of ore per year, and more than 80,000 tons of waste rock can be thrown every year by wet pre-selection. Calculated according to the grinding fee of 10.94 yuan per ton of ore, the annual grinding cost can be saved by 900,000 yuan, and the operating expenses of 200,000 yuan can be deducted. The annual economic benefit can reach 700,000 yuan.

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