Magnetic Separation Rejection Test for Medium-Scale Iron Ore Mining

Dec 31st,2025 117 Views

To develop and utilize a medium-sized iron ore deposit, optimization experiments were conducted on the wet and dry magnetic separation discard process for raw ore (-12 mm) based on an analysis of the ore’s properties. By comparing key parameters of dry (electromagnetic) and wet (permanent magnet) magnetic separation processes at the -12 mm particle size—including drum surface linear velocity (1.20–1.70 m/s), magnetic field strength (101.06–143.24 kA/m), and bottom tank flushing water volume (0–2800 L/h), wet magnetic separation demonstrated significant advantages in tailing rejection rate (26.99–31.75%) and magnetite loss rate (<1.43%). Experimental data indicate this process reduces ball mill feed by nearly one-third while elevating mill feed grade to 44.54%, providing reliable technical support for implementing “multiple early discard” energy-saving strategies in similar mines.

1. Ore Properties

The chemical composition analysis results of the iron ore are shown in Table 1, the iron phase analysis results in Table 2, the sulfur phase analysis results in Table 3, and the mineral composition analysis in Table 4.

Table 1. Results of Multi-element Chemical Analysis of The Ore (%)
Ingredients	TFe	S	P	SiQ₂	Al₂Q₃	Na₂O	V	K₂O	Au	Ag
Content	34.01	1.01	0.55	18.83	4.47	0.14	0.049	0.80	0.07	2.7
Ingredients	CaO	MgO	MnO	Cu	Zn	Cr	TiO₂	Co	Burning Loss
Content	12.98	2.75	0.34	0.06	0.12	0.003	0.63	0.012	8.7

Note: The units for Au and Ag content are g/t.

Table 2: Ore Iron Phase Analysis Results (%)
Iron Phase	Iron Content	Distribution
Magnetite	29.13	85.65
Hematite, Limonite	2.47	7.26
Pyrite	0.28	0.83
Ferric Carbonate	0.31	0.91
Ferric Silicate	1.72	5.06
Magnetite-Pyrite	0.10	0.29
Total Iron	34.01	100.00

Table 3: Sulfur Phase Analysis Results of Ore (%)
Sulfur Phase	Sulfur Content	Distribution
Ferrous Sulfide	0.860	85.15
Sulfate	0.096	9.50
Native Sulfur	0.010	0.99
Other	0.044	4.36
Total Sulfur	1.01	100.00

Table 4: Analysis Results of Ore Mineral Composition(%)
Mineral	Magnetite	Limonite	Pyrite	Quartz	Chalcopyrite (Copper-Iron Ore)
Content	42.68	0.58	1.61	11.76	Trace Elements
Mineral	Carbonate	Chlorite	Biotite	Clay	Hematite (including pseudomorphs)
Content	14.91	7.92	7.75	4.82	3.12
Mineral	Sulfide	Pyroxene	Apatite	Feldspar	Magnetite
Content	0.01	0.25	3.42	0.11	0.22

From Tables 1 to 4, it can be seen that the iron grade of the ore is 34.01%, and the sulfur content is 1.01%. The ore exhibits a quaternary basicity of R=0.675, classifying it as a semi-autogenous iron ore. Iron primarily exists as magnetite, accounting for 85.65% of the distribution. Sulfur predominantly occurs as iron sulfide, representing 85.15% of the distribution, followed by sulfates, with other sulfides present in lower quantities. The gangue minerals are primarily carbonate minerals, calcite, and oxide quartz, with respective contents of 14.91% and 11.76%. Secondary gangue minerals include silicate minerals such as chlorite and biotite, as well as phosphate minerals apatite.

2. Magnetic Separation Rejection Test

-12 mm Dry Magnetic Separation Rejection Test

Crush the raw ore to -12 mm size and conduct a dry magnetic separation rejection test using a ϕ500 mm × 550 mm electromagnetic dry magnetic separator.

Drum Surface Linear Velocity Test

With the dry magnetic separator baffle distance fixed at 120 mm and magnetic field strength at 143.24 kA/m, a drum surface linear velocity test was conducted. Results are shown in Table 5. A drum surface linear velocity of 1.70 m/s was selected.

Table 5: Test Results for Cylinder Surface Linear Velocity
Linear Velocity(m/s)	Product	Yield(%)	Total Iron Grade(%)	Magnetic Iron Content(%)	Total Iron Recovery Rate(%)	Magnetic Iron Recovery Rate(%)
1.70	Pre-selected Concentrate	88.63	37.50	33.60	97.91	99.60
	Waste Rock	11.37	6.28	1.14	2.09	0.40
	Raw Ore	100.00	33.95	29.91	100.00	100.00
1.57	Pre-selected Concentrate	89.71	37.30	33.30	98.21	99.73
	Waste Rock	10.29	5.94	0.78	1.79	0.27
	Raw Ore	100.00	34.07	29.95	100.00	100.00
1.20	Pre-selected Concentrate	93.35	36.20	32.28	98.92	99.80
	Waste Rock	6.65	5.61	0.87	1.08	0.20
	Raw Ore	100.00	34.16	30.19	100.00	100.00

1.2 Magnetic Field Strength Test

With the dry magnetic separator baffle distance fixed at 120 mm and drum surface linear velocity at 1.70 m/s, a magnetic field strength test was conducted. Results are shown in Table 6. A magnetic field strength of 143.24 kA/m was selected.

Table 6: Magnetic Field Strength Test Results
Magnetic Field Strength(kA/m)	Product	Yield(%)	Total Iron Grade(%)	Magnetic Iron Content(%)	Total Iron Recovery Rate(%)	Magnetic Iron Recovery Rate(%)
143.24	Pre-selected Concentrate	88.63	37.50	33.60	97.91	99.60
	Waste Rock	11.37	6.28	1.14	2.09	0.40
	Raw Ore	100.00	33.95	29.91	100.00	100.00
127.32	Pre-selected Concentrate	87.74	38.11	33.99	97.78	99.66
	Waste Rock	12.26	6.20	0.81	2.22	0.34
	Raw Ore	100.00	34.20	29.92	100.00	100.00
101.06	Pre-selected Concentrate	84.98	39.31	34.91	97.07	99.23
	Waste Rock	15.02	6.74	1.53	2.93	0.77
	Raw Ore	100.00	34.42	29.90	100.00	100.00

With the drum surface linear velocity fixed at 1.70 m/s and magnetic field strength at 143.24 kA/m, a baffle distance test was conducted on the dry magnetic separator. As the baffle distance decreased, the waste rock yield increased, the iron grade of the concentrate rose, and the recovery rate decreased. After careful consideration, the baffle distance was determined to be 70 mm.

-12 mm Wet Magnetic Separation Reject Test

Crush the raw ore to -12 mm and conduct coarse-grain wet magnetic separation discard tests using a ϕ500 mm × 300 mm permanent magnet drum magnetic separator. The magnetic field strength is 318.47 kA/m. Test results for different bottom tank flushing water volumes are shown in Table 7. The selected bottom tank flushing water volume is 800 L/h.

Table 7: Test Results for Bottom Tank Flushing Water Volume
Bottom Tank Flushing Water Volume(L/h)	Product	Yield(%)	Total Iron Grade(%)	Magnetic Iron Content(%)	Total Iron Recovery Rate(%)	Magnetic Iron Recovery Rate(%)
0	Pre-selected Concentrate	73.01	44.02	40.90	94.25	98.94
	Waste Rock	26.99	7.25	1.20	5.75	1.06
	Raw Ore	100.00	34.10	30.18	100.00	100.00
800	Pre-selected Concentrate	71.80	44.54	41.55	93.92	98.77
	Waste Rock	28.20	7.35	1.30	6.08	1.23
	Raw Ore	100.00	34.05	30.20	100.00	100.00
1700	Pre-selected Concentrate	69.20	46.15	42.73	93.26	98.57
	Waste Rock	28.20	7.35	1.30	6.08	1.23
	Raw Ore	100.00	34.25	30.00	100.00	100.00
2800	Pre-selected Concentrate	68.25	46.75	43.84	93.22	98.71
	Waste Rock	31.75	7.31	1.23	6.78	1.29
	Raw Ore	100.00	34.23	30.31	100.00	100.00

Comparison of Waste Rejection Rates Between Coarse-Grain Wet Magnetic Separation and Dry Magnetic Separation

When the raw ore is crushed to -12 mm and subjected to dry magnetic separation, waste rock with a yield of 6.65% to 15.02% can be rejected. The iron grade of the rejected waste rock ranges from 5.61% to 6.74%, with magnetic iron loss rates consistently below 0.77%. When the raw ore is crushed to -12 mm and subjected to coarse-grain wet magnetic separation, waste rock can be discarded at a yield of 26.99% to 31.75%. The iron grade of the discarded waste rock ranges from 7.25% to 7.49%, with magnetic iron loss rates consistently below 1.43%. From the separation indicators, coarse-grain wet magnetic separation can discard more waste rock than dry magnetic separation. This waste rock does not enter the ball mill, thereby reducing the grinding feed volume and increasing the iron grade of the grinding feed, achieving the goal of energy saving and consumption reduction. Moreover, using coarse-grain wet magnetic separation for separation keeps the magnetic iron loss rate below 1.43%. Clearly, wet magnetic separation yields superior separation performance compared to dry magnetic separation. Therefore, coarse-grain wet magnetic separation is adopted.

This study shows that applying -12 mm coarse wet magnetic separation rejection (magnetic field strength: 318.47 kA/m, flushing water volume: 800 L/h) to semi-autogenous iron ore with 85.65% magnetite content achieves 21.53–25.1% higher tailings rejection compared to conventional dry magnetic separation, while maintaining a magnetite loss rate strictly below 1.43%.

As a leading manufacturer of mineral processing equipment, JXSC provides not only high-performance separation machines but also comprehensive ore beneficiation test services to help mines optimize their recovery rates and reduce energy consumption. Our wet magnetic separators are designed to maximize productivity while minimizing valuable mineral loss, making them ideal for iron ore, tungsten, tin, and other magnetic material processing.

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