3 methods to recover limonite

Common iron ores include magnetite, hematite, limonite, and siderite. Among these, limonite stands as a typical difficult-to-process iron ore, characterised by its tendency to become muddy and poor separation indices. Nevertheless, its abundant reserves make it a valuable resource for addressing iron ore scarcity. Common limonite beneficiation methods primarily comprise single-stage separation processes and combined separation processes.

The single-stage beneficiation process for limonite primarily encompasses gravity separation, magnetic separation, and flotation (both positive and reverse flotation).

01 Gravity Separation of Limonite

Gravity separation employs gravitational forces for classification. As the primary beneficiation method for limonite, it is predominantly used to process coarse-grained, disseminated ore. To further enhance concentrate grades, most limonite processing plants employ a washing-gravity separation sequence. This involves preliminary washing using equipment such as drum screen washers, trough washers, and scrubbers, followed by gravity separation using heavy media and jigs. This sequence is predominantly applied for separating limonite and pseudomorphous hematite. The advantages of this beneficiation method lie in the simplicity, low cost, and reduced power consumption of gravity separation equipment. Its disadvantages include low recovery rates and high tailings grades, which hinder comprehensive resource recovery.

02 Magnetic Separation of Limonite

Given the iron content within limonite, these ores exhibit magnetic properties. Variations in iron concentration within the ore result in differing magnetic characteristics, enabling separation through magnetic differentiation. Strong magnetic separation is commonly employed for limonite processing; however, this method demonstrates poor recovery efficiency for fine-grained fractions (-20μm iron minerals).

03 Limonite Flotation Method

Single flotation demonstrates superior recovery for fine-grained iron minerals. However, limonite's tendency to become muddy severely impedes flotation efficiency. Consequently, pre-treatment involving desliming or enhanced dispersion of mineral slime is crucial.

Due to their fine size, mineral mud particles struggle to adhere to bubble surfaces to form distinct mineralised froth layers for flotation, instead readily attaching to coarse grain surfaces. When coarse goethite grains become coated with gangue mud, their selectivity and floatability significantly diminish. Mineral mud possesses a large specific surface area and surface energy (activity). Firstly, it adsorbs substantial flotation reagents, resulting in a pulp with excessive oil and reagents, high viscosity, and reduced selectivity and floatability of easily floatable minerals. Secondly, it exhibits strong hydration capacity; once adhered to bubbles, the hydration film on the bubble surface becomes difficult to remove. This poses severe challenges for concentrate thickening and filtration, leading to reduced recovery rates.

The unique structural characteristics of limonite ore render it prone to over-grinding and pulverisation during crushing and grinding, resulting in mud formation that impedes separation and recovery. Furthermore, its gangue mineral composition exhibits significant variability. Given these distinctive properties, mineral processing tests should be conducted to determine the predominant iron minerals and gangue mineral types within the limonite ore. This information should then inform the development of an appropriate mineral processing method tailored to limonite ore.