Coastal sand (also referred to as coastal placer ore) is normally abundant in high‑value minerals including ilmenite, zircon, rutile and rare‑earth‑bearing monazite. Subject to long‑term natural weathering, most minerals achieve favourable liberation. For this reason, complex crushing and grinding are not required for separation. Instead, the combined process of gravity pre‑concentration ➔ magnetic separation ➔ electrostatic purification is predominantly applied.
The complete standard separation process consists of the following key stages:
1. Washing and Screening (Pretreatment)
Mined raw coastal placer ore is first fed into a trommel screen for washing and classification.
Function: High‑pressure water jets remove impurities such as clay, shell fragments and organic matter on the ore surface. Oversized gravel is screened out, leaving fine‑grained sand with uniform particle size to create favourable conditions for subsequent separation.
2. Gravity Pre‑concentration (Roughing and Cleaning)
This is the core stage for discarding large quantities of useless gangue (e.g. quartz sand). Separation is achieved based on differences in mineral specific gravity.
- Spiral concentrator (Roughing): Screened fine sand is fed into spiral concentrators. Under the combined effect of water flow and centrifugal force, high‑density heavy minerals (ilmenite, zircon, monazite, etc.) are concentrated along the inner trough, while low‑density light minerals (mainly quartz sand) are flushed away and discharged as tailings.
- Shaking table (Cleaning): Rough concentrates from spiral concentrators are further treated by shaking tables. Reciprocating vibration of the table surface and scouring cross‑flow water eliminate residual light impurities such as silica sand. Mixed heavy‑mineral concentrates dominated by titanium, zirconium and rare‑earth minerals are obtained.
3. Magnetic Separation (Separation by Magnetic Properties)
After drying, mixed heavy‑mineral concentrates enter the magnetic‑separation circuit. Three‑disc magnetic separators or vertical‑ring high‑gradient magnetic separators are commonly used. Minerals with different magnetism are separated one by one by precisely adjusting magnetic‑field intensity:
- Low‑intensity magnetic separation: First removes strongly magnetic impurities such as iron filings.
- Medium‑/high‑intensity magnetic separation: Weakly‑magnetic ilmenite is recovered under medium or high magnetic fields.
- Non‑magnetic materials: Non‑magnetic outputs after magnetic separation are mainly zircon, rutile, monazite (rare‑earth mineral) and cassiterite, which proceed to the subsequent electrostatic‑separation process.
4. Electrostatic Purification (Separation by Electrical Conductivity)
This final core procedure for coastal‑placer beneficiation delivers high‑precision separation by utilising differences in mineral electrical conductivity.
High‑voltage electrostatic separator: Non‑magnetic materials from magnetic separation are fed into high‑voltage electrostatic separators (typical operating voltage: 15‑50 kV). Within the high‑voltage electrostatic field, conductive minerals (e.g. rutile) and poorly‑conductive minerals (e.g. zircon, monazite) follow different trajectories due to varying electric‑charge capacity. Accurate separation is realised to produce individual high‑grade concentrate products.
In short, coastal‑placer beneficiation is a standardised production line: washing and desliming ➔ gravity concentration ➔ magnetic separation ➔ electrostatic purification.
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