Chromium Washing Process

Chromium washing plant processes refer to a series of industrial processes for washing, sorting, and purifying chromium ore. The aim is to remove impurities, improve the grade of chromium concentrate, and provide qualified raw materials for subsequent metallurgical or chemical applications. This process needs to be customized according to the ore type (e.g., laterite type, rock type), particle size distribution, mud content, and characteristics of associated minerals. It typically uses gravity separation as the primary method, supplemented by magnetic separation, and combines washing, screening, and dewatering to form a complete process.

I. Core Process Flow

1. Ore washing and desliming: Key pretreatment steps

For chromite containing a large amount of clay and mud (especially lateritic chromite), washing is a prerequisite for improving the efficiency of subsequent sorting.

• A cylindrical or trough-type ore washer is used to remove muddy impurities from the ore surface through high-pressure water jet washing and mechanical agitation.
• After washing, the material enters a vibrating screen for classification. Fine particles (typically <1.5mm) pass through the screen and proceed to gravity separation, while coarse particles on the screen can be directly discarded or further crushed.
• This process can achieve a washing efficiency of over 85%, significantly improving separation performance.

2. Crushing and grinding: Achieving the liberation of mineral monomers.

• Two-stage crushing: A jaw crusher is used to crush the raw ore to below 30mm to ensure uniform particle size before entering the grinding stage.
• Rod mill grinding: Because chromite has a relatively coarse particle size, the rod mill can effectively achieve individual particle liberation and produce a uniform and adjustable product particle size.
• After grinding, the fineness of the slurry is controlled by classification equipment (such as hydrocyclones) to avoid over-grinding and mud formation.

3. Re-selection method: the mainstream sorting method

Taking advantage of the high density of chromite (4.3–4.6), it can be separated from gangue minerals in a gravitational field.

• Spiral sluice roughing: processes -1.5mm ore slurry, controlling the concentration at 30%–35%, enriching high-density chromite particles under centrifugal force and gravity, increasing the grade from 28% to 55% of the original ore;
• Shaking table cleaning: performs secondary separation of rough and concentrate, obtaining chromite concentrate with a grade of over 63% by adjusting the stroke, frequency, and slope;
• Common equipment also includes jigs and centrifugal concentrators, suitable for different particle size ranges.

4. Magnetic separation purification: Further removal of magnetic impurities.

To obtain high-purity chromium concentrate, a magnetic separation process is often added after gravity separation.

• First, magnetite is separated using weak magnetic separation.
• Then, a three-roll high-intensity magnetic separator is used to separate weakly magnetic impurities such as ilmenite, ultimately increasing the chromium concentrate grade to over 70%.
• In one case, the wet high-intensity magnetic separation process yielded a chromium oxide concentrate grade of 47.61% with a recovery rate of 96.26%.

5. Dehydration and Packaging: Finished Product Preparation

• The selected concentrate is concentrated using a thickener, filtered using a filter press, and dried with hot air if necessary.
• The finished product's moisture content is controlled below 10% for easy storage and transportation.

II. Equipment Selection Recommendations

• ‌Ore washing equipment: cylindrical ore washer, vibrating screen, hydraulic classifier
• Crushing equipment: jaw crusher (coarse crushing), cone crusher (medium and fine crushing)
• Grinding equipment: rod mill (suitable for coarse particle liberation) or ball mill (fine particle size)
• Gravity separation equipment: spiral chute, jig, shaking table
• Magnetic separation equipment: wet high-intensity magnetic separator, three-roll magnetic separator