Iron Ore Processing Routes Compared

Iron ore processing isn't one flowsheet. It's a decision tree that starts with mineralogy. Magnetite and hematite respond to different unit operations, and picking the wrong route adds capex and opex without improving concentrate quality. You'll see this fork immediately when you compare low-intensity magnetic separation for magnetite against gravity or high-intensity magnetic separation for hematite.

Magnetite is a ferrimagnetic iron oxide (Fe₃O₄) that can be recovered with low-intensity magnetic fields. Hematite is a weakly paramagnetic iron oxide (Fe₂O₃) that needs high-intensity magnetic separation, gravity concentration or reverse flotation. This single difference dictates the entire plant layout. The global iron ore market prices most ores against a 62% Fe fines benchmark, CIF Tianjin, according to the USGS Iron Ore Statistics. For magnetite, in-situ grades are often low, so you'll grind fine and upgrade to a concentrate above 65% Fe.

Xinhai's project records show a 3,500 t/d iron ore plant in Mongolia produced a primary concentrate at ≥65% Fe with a mass yield of about 31%, plus a secondary concentrate at 50–60% Fe. That's a typical magnetite outcome: high grade, moderate yield, and a lot of tailings to manage.

Magnetite responds to low-intensity magnetic separation (LIMS). The process is straightforward: after grinding, pulp passes over a drum separator with a permanent magnet; magnetite sticks, gangue flows to tailings. But liberation is rarely complete in one pass. So the flowsheet loops: roughing LIMS, regrind the rougher concentrate, then cleaning LIMS. This staged approach reduces silica and raises Fe grade without overgrinding. The Mongolia plant mentioned earlier used this logic to reach ≥65% Fe.

You'll often see three or four stages of magnetic separation in a magnetite concentrator. The equipment is simple, but the piping and pumping between stages add cost. That's why beneficiation plant cost estimates always separate grinding energy from magnetic separation capital.

When magnetic and gravity methods can't get silica low enough, reverse flotation steps in. Reverse flotation means you float the gangue, not the iron. The sequence: condition the pulp with a depressant to hold iron oxides down, add a collector for quartz, then remove the froth. The underflow is your iron concentrate. This is common for hematite and for fine magnetite concentrates that need silica low enough to meet pellet plant specs.

Xinhai's pilot plant runs about 200 testwork campaigns a year across more than 70 ore types, according to the company's published figures. That testwork defines collector dosages and pH before you commit to a full-scale circuit. If you need flowsheet alternatives, the mineral processing flowsheet article explains how trade-off studies work.

Mass yield is the tonnage of concentrate divided by the tonnage of feed, expressed as a percentage. In the Mongolia magnetite example, the primary concentrate at ≥65% Fe represented a mass yield of about 31%, meaning roughly 69% of the feed mass became tailings. This ratio drives the sizing of tailings thickeners and pumps. At a 50,000 t/d plant, a 31% mass yield produces about 15,500 t/d of concentrate and 34,500 t/d of tailings. That tailings flow must be thickened; the 100 m diameter thickener mentioned earlier is a scale that matches flows of this magnitude. Water recovery is equally important: process water carries solids through grinding, magnetic separation and reverse flotation, and must be reclaimed from thickener overflow and tailings storage. A closed water balance reduces raw water intake and tailings dam risk, as discussed under tailings storage facility design. For pellet feed, moisture is a specification rather than a nuisance variable, because pelletising requires a narrow moisture window. Filtration therefore becomes part of the mass balance. These arithmetic relationships—mass yield, tailings tonnage and water recovery—are the quotable numbers that turn a flowsheet into a buildable plant. Without this closed loop, a high-grade concentrator can still fail on water permit limits or tailings handling capacity. The mass balance is completed before detailed equipment sizing, because every pump, pipe and thickener is sized from these flows.