Siderite Magnetization Roasting-Weak Magnetic Separation Process – Solving the Difficulty of Beneficiation

 For siderite ores with complex compositions, fine particle size, and close intergrowth with gangue minerals, single beneficiation processes (such as flotation, gravity separation, or magnetic separation) often struggle to obtain high-grade iron concentrates. At this time, the magnetization roasting-weak magnetic separation process becomes the most effective solution. This process combines roasting and magnetic separation, transforming siderite into a strong magnetic mineral through roasting, thereby realizing efficient separation with conventional weak magnetic separation equipment. It is known as the "key technology" for difficult-to-beneficiate siderite and has been widely promoted and applied in industrial production.

The core of the magnetization roasting-weak magnetic separation process is the magnetization roasting step, whose principle is to heat siderite in a reducing atmosphere (using coal, coke, natural gas, or other reducing agents) to decompose the carbonate in the ore and transform siderite into magnetite (Fe₃O₄), a strong magnetic mineral. The chemical reaction equation is: 3FeCO₃ + C → Fe₃O₄ + 3CO₂↑ + CO↑. During the roasting process, two key changes occur: first, the carbon dioxide in siderite is decomposed and discharged, which increases the iron content of the ore (theoretical iron content of magnetite is 72.4%, which is much higher than that of siderite); second, the magnetic susceptibility of iron minerals is significantly enhanced—magnetite is a strong magnetic mineral, whose magnetic susceptibility is dozens of times higher than that of siderite, making it easy to be separated by weak magnetic separation. At the same time, the magnetic properties of gangue minerals (such as quartz, calcite) remain basically unchanged, which further improves the separation effect.

The magnetization roasting process is mainly divided into three types: shaft furnace roasting, rotary kiln roasting, and fluidized bed roasting. Among them, rotary kiln roasting is the most widely used in siderite beneficiation due to its stable roasting effect, large processing capacity, and strong adaptability to ore particle size. The rotary kiln is a long cylindrical equipment that rotates continuously; the ore and reducing agent are fed into the kiln from one end, and heated to 550-700℃ (the optimal roasting temperature for siderite) by a burner at the other end. Under the action of high temperature and reducing atmosphere, siderite is gradually transformed into magnetite. After roasting, the ore (called roasted ore) is cooled to the appropriate temperature and then sent to the next process.

The roasted ore is sent to a weak magnetic separator for separation. Due to the strong magnetic properties of magnetite, it is easily adsorbed by the magnetic field of the weak magnetic separator and separated from non-magnetic gangue to form high-grade iron concentrate. The weak magnetic separation equipment used is mainly a drum magnetic separator, which has the advantages of simple structure, high processing efficiency, and low energy consumption. Compared with strong magnetic separation, weak magnetic separation has lower equipment investment and operation cost, which greatly reduces the overall cost of the beneficiation process.

The magnetization roasting-weak magnetic separation process has the advantages of high iron concentrate grade, high recovery rate, and strong adaptability to difficult-to-beneficiate siderite ores. However, it also has certain limitations: the roasting process requires a large amount of energy and reducing agents, which increases the production cost; at the same time, the roasting process will generate flue gas, which needs to be treated to meet environmental protection standards. Therefore, in industrial design, it is necessary to comprehensively consider the ore properties, economic benefits, and environmental protection requirements to optimize the process parameters.