The core of beach placer sorting lies in utilizing the differences in physicochemical properties such as density, magnetism, electrical properties, and surface wettability of different minerals. Combined with the characteristics of beach placer, which are relatively uniform particle size, low silt content, and good enrichment of heavy minerals, a combined process flow of classification → gravity separation → magnetic separation → electrostatic separation / flotation is adopted. At the same time, auxiliary processes such as desliming, dewatering, and impurity removal are required. The following are standardized sorting processes, key equipment, and operational points, which are suitable for industrial large-scale production and process docking needs in foreign trade business.
I. Pre-treatment before Separation: Raw Material Preparation (the core is to remove impurities and grade to avoid subsequent equipment blockage/low separation efficiency) After seaside placer mining (by boat/onshore), it will contain shells, gravel, silt, and seawater salt. Pre-treatment is the foundation of separation, and the steps are as follows: Coarse screening: Use a vibrating screen (circular vibrating screen/linear screen) to screen out shells and large pieces of gravel larger than 20mm. The product below the screen is 0.074~20mm placer raw material (heavy minerals in seaside placer are mainly concentrated in the 0.074~2mm particle size range); Desliming and Dewatering: Use a spiral classifier/hydrocyclone to remove silt smaller than 0.074mm (muddy substances will adhere to the surface of minerals, affecting subsequent separation), and simultaneously use a dewatering screen to remove excess seawater from the raw material, controlling the moisture content to less than 15%; Grading: Use a high-frequency vibrating screen/grading screen to separate the placer into coarse particles (1~2mm), medium particles (0.25~1mm), and fine particles (0.074~0.25mm) based on particle size. Raw materials of the same particle size enter subsequent separation (the separation efficiency of minerals of different particle sizes varies greatly, and grading can improve the processing accuracy of subsequent equipment).
II. Core Separation Process: Following the principle of "starting with the easier and moving to the harder", the main valuable minerals in beach placer deposits are separated from the most significant differences in physical properties. These include ilmenite, zircon, rutile, monazite, xenotime, quartz sand (associated), etc. Among them, density differences (heavy minerals have a density of 4.0~7.0g/cm³, while quartz has a density of 2.65g/cm³) and magnetic differences are the most easily exploitable properties. Therefore, the separation sequence is gravity concentration → magnetic separation differentiation → electrostatic separation / flotation purification, with each stage filtering out a single concentrate.
(1) Step 1: Reselection - Enrich heavy minerals and discard a large amount of gangue (mainly quartz). The core is to utilize the density difference between heavy minerals and gangue, and through the gravitational field/centrifugal force field, make heavy minerals settle and enrich, discarding more than 80% of quartz sand, to obtain a mixed concentrate of heavy minerals (mixed with ilmenite, zircon, rutile, etc.). This is the key enrichment process for the separation of beach placer deposits. The suitable equipment and its characteristics are as follows:
Trommel Screen
Sprial Chute
shaking table
Operation points: For the gravity separation of coastal placer deposits, it is preferred to use a combination of spiral chutes (coarse separation) and shaking tables (fine separation). The spiral chutes remove a large amount of quartz, while the shaking tables increase the enrichment ratio of heavy minerals to 10-50 times, resulting in a mixed concentrate with a heavy mineral content of >60%. During gravity separation, it is necessary to control the feed concentration (20%-30%) and feed rate to avoid excessive ore flow, which can lead to the loss of heavy minerals.
(2) Step 2: Magnetic Separation - Separating different minerals in beach placer deposits based on their magnetic differences, such as ilmenite and monazite. The magnetic differences among these minerals are significant: strong magnetism (ilmenite), weak magnetism (monazite, biotite), and non-magnetism (zircon, rutile, quartz). Magnetic separation utilizes these differences to separate magnetic concentrate (ilmenite/monazite) from mixed heavy minerals, while discarding non-magnetic minerals (zircon, rutile, etc.). The core equipment is a dry magnetic separator (beach placer deposits have low moisture content after dehydration, making dry magnetic separation more efficient and waste-free compared to wet separation). Common industrial combinations include: strong magnetic roller magnetic separator (magnetic field strength 8000~12000Oe): separates strongly magnetic ilmenite to obtain ilmenite concentrate (TiO₂ content ≥45%, which can be directly exported/further processed); weak magnetic roller magnetic separator (magnetic field strength 2000~6000Oe): separates weakly magnetic monazite (a rare earth mineral) from the tailings of strong magnetic separation to obtain monazite concentrate; magnetic separation column/wet magnetic separator: if the raw material has a high moisture content, wet magnetic separation is used for supplementary separation to avoid loss of magnetic minerals.
Operation points: For magnetic separation, the magnetic field strength should be adjusted according to the magnetic properties of the minerals to avoid adsorbing non-magnetic minerals due to an excessively strong magnetic field or losing magnetic minerals due to an excessively weak magnetic field. For dry magnetic separation, the feeding speed should be controlled evenly to prevent the ore layer from being too thick, which may affect magnetic separation.
(III) Step 3: Electro-separation / Flotation - Purification of Non-magnetic Valuable Minerals such as Zircon and Rutile. The tailings after magnetic separation of non-magnetic valuable minerals such as zircon and rutile are non-magnetic mixed minerals (including zircon, rutile, quartz, feldspar, etc.). These minerals have small differences in density and magnetism, and require separation based on electrical properties (permittivity) or surface wettability to obtain high-purity zircon and rutile concentrates. This is the purification process for beach placer ore separation. The two processes are suitable for different scenarios: 1. Electro-separation (the mainstream process, suitable for beach placer ore) utilizes the differences in dielectric constant and conductivity of minerals. In a high-voltage electric field, conductive minerals (rutile, ilmenite residuals) are adsorbed onto the electrodes, while non-conductive minerals (zircon, quartz) are thrown out by centrifugal force. The core equipment is a high-pressure roller electro-separator (an industrial standard equipment). The operation process is as follows: roughing: separating rutile (conductive) from zircon (non-conductive) to obtain rutile rough concentrate; cleaning: multiple electro-separation purifications to increase the TiO₂ content of rutile concentrate to ≥95%, and the ZrO₂・SiO₂ content of zircon concentrate to ≥65% (industry standard product).
