What is super gravity separation

Super Gravity Separation is a high-efficiency method used to separate particles based on their specific gravity under elevated centrifugal forces. This technique is a more advanced form of traditional gravity separation, which relies on the differences in density between the materials being processed. By applying significant centrifugal force, much higher than Earth’s gravity, super gravity separation enhances the separation process, making it particularly effective for fine-grained or low-density particles that would otherwise be challenging to separate with conventional methods. The process typically involves the use of specialized equipment, such as a Super Gravity Separator or a high-speed centrifugal concentrator, which increases the gravitational field inside the device. This enhanced force accelerates the settling or stratification of particles, improving the precision of separation, especially for materials with close density differences. Super gravity separation is widely used in industries such as mining, mineral processing, environmental management, and chemical processing, where separating fine particles, precious metals, or even contaminants from a mixture is crucial for obtaining high-purity materials. The technique is particularly beneficial for dealing with ores containing fine gold, rare earth elements, and other minerals with small size distributions.

  • Sustainable recovery of metallic Al and reuse of molten salt in Al dross: Salt flux erosion and super-gravity separation. Zengwu Wang, Jintao Gao, Xi Lan, Zhancheng Guo
  • Supergravity-enhanced liquation crystallization for metal recovery from waste printed circuit boards. Peng Feng, Zhe Wang, Long Meng, Zhancheng Guo

Copper – Bismuth

The non soluble metals – metals system has significant application in low concentrated highly soluble elements removal. In recent work “Rapid removal of copper impurity from bismuth–copper alloy melts via super-gravity separation” the authors reviewed the ultra fast method for the copper purification. The impurities have the segregation coefficient lower than 1, equal or close to 1 and higher. In this study, a green method was developed to enhance the filtration process for removing copper impurities from bismuth-copper alloy melts. This method, called super-gravity separation, helps separate bismuth-rich and copper-rich phases. When the alloy melt was subjected to the super-gravity field, the bismuth-rich liquid phases were mostly filtered in one direction, while the fine copper particles were retained in the opposite direction. The method was optimized with a separation temperature of 280°C, a gravity coefficient of 450, and a separation time of 200 seconds. Under these conditions, the mass of bismuth separated from the Bi–2% Cu and Bi–10% Cu alloys was 96% and 85%, respectively, indicating minimal bismuth loss. At the same time, the impurity copper removal rate reached 88% and 98% for the Bi–2%Cu and Bi–10% Cu alloys, respectively.

The remaining Bismuth is easily purified for the Zinc, Lead, Tin impurities removal. The certain concentration, less than 5% not affecting the process main parameters for the bismuth filtration process.

Gold – Bismuth

Bismuth (Bi) melts and related alloys can effectively capture gold (Au) from gold-poor water, contributing to gold deposits in hydrothermal systems. However, evidence of Au–Bi melts is often hard to find because they are typically altered after they form. This makes it difficult to study how liquid bismuth collects gold in hydrothermal gold deposits. In this study, we provide clear evidence of Au–Bi melts in hydrothermal systems by examining gold and bismuth phases at the Baolun gold deposit on Hainan Island. Our research shows that after native gold forms, various Au–Bi phases appear, including maldonite, native bismuth, Au–Bi symplectite, and Au–Bi melt droplets. The key finding is that large Au–Bi droplets were well-preserved in nature due to the rapid cooling of the fluids. We also observed that the minerals and the conditions of the fluids suggest that the ore fluids at Baolun evolved with a steady decrease in both gold and bismuth concentrations, as well as lower temperatures and sulfur levels. This provides direct evidence that bismuth melts can scavenge gold in a specific type of hydrothermal system, characterized by medium temperatures (275–450°C) and low sulfur. As the fluids cooled further, the gold-bismuth phases were later altered by fluids rich in tellurium (Te) and sulfur (S), which formed new minerals like bismuthinite and jonassonite around the original gold-bismuth phases. Our findings reveal that the Baolun gold deposit is part of a unique Au–Bi–Te hydrothermal system, with the local metamorphic rocks being the primary source of gold, bismuth, and tellurium.

Gold – Bismuth – Tin

To create a stronger joint with a higher melting point while bonding at a lower temperature, the bonding characteristics of Au/Cu joints using Sn-57Bi-1Ag solder were examined. These were compared to Cu/Cu joints for reference. In the Au/Cu joint bonded at 170°C for 1 minute, a large scallop-shaped AuSn4 layer formed at the interface between the gold (Au) and the solder. An Au-diffused layer appeared at the tip of the AuSn4 layer, while a Sn-Cu-Au layer formed at the Cu/solder interface, with about 20% gold content. Over longer bonding times, the eutectic microstructure with β-Sn and Bi disappeared, and the solder structure changed to phases of Bi, AuSn4, and Ag3Sn after 30 minutes. However, in the Cu/Cu joint, the eutectic microstructure remained stable regardless of bonding time. The bond strength of the Au/Cu joint was about one-third of the Cu/Cu joint, and both joints experienced a decrease in bond strength with increased bonding time due to changes in fracture mode. In this study, a Cu electrode electroplated with gold was bonded to a Cu plate using Sn-57Bi-1Ag solder to create a higher melting point joint while bonding at a low temperature. The study looked at the melting properties, microstructure, and bond strength of the joints, including a comparison with Cu/Cu joints. The key findings were as follows:

  1. In the Au/Cu joint bonded at 170°C for 1 minute, a large scallop-shaped AuSn4 layer formed between the gold and solder. An Au-diffused layer formed at the tip of the AuSn4 layer, while a Sn-Cu-Au layer formed at the Cu interface. After 30 minutes, the eutectic microstructure (β-Sn and Bi phases) disappeared, and the solder area changed to Bi phases, including AuSn4 and Ag3Sn, as seen in changes in melting properties on DSC curves.
  2. In the Cu/Cu joint, a typical eutectic microstructure with β-Sn and Bi phases remained in the solder area throughout the bonding time, although a scallop-shaped Cu6Sn5 layer formed at the interface.
  3. The bond strength of the Cu/Cu joint was about three times stronger than the Au/Cu joint. In both cases, bond strength decreased as bonding time increased, due to changes in the fracture mode. In the Cu/Cu joint, the fracture initially occurred in the solder but shifted to the Cu6Sn5/solder interface or within the Cu6Sn5 layer over time. In the Au/Cu joint bonded for 1 minute, fractures mainly occurred at the Bi/Au-diffused layer interface or within the Au-diffused layer, and after longer bonding times, fractures shifted to the Bi/AuSn4 interface.

Additionally, the solubility of gold (Au) in the solder was found to be very low—less than 1%, indicating that gold does not dissolve significantly into the solder at these bonding conditions.

Bismuth – Tin – Lead – In – Cd

Low melting point alloys are materials that have a relatively low melting temperature, typically below 300°C. These alloys are often composed of elements such as bismuth (Bi), tin (Sn), lead (Pb), and indium (In).

Separation – Iron – Nickel – Bronze – Brass

Waste printed circuit boards (WPCBs) are a significant environmental threat but also contain valuable metals such as iron, copper, zinc, tin, and lead, which can be recovered through recycling. This study explores an efficient and cost-effective method to recycle these metals by combining liquation crystallization with supergravity technology. The WPCB particles are first melted to form an alloy, and as the temperature decreases, the different metal components separate due to their varying melting points and densities. These components stratify into layers, with heavier metals like iron settling at the bottom and lighter metals such as copper and lead forming distinct layers. The supergravity field plays a crucial role in accelerating the separation process by enhancing the effects of gravity. By applying centrifugal force, the metals are effectively separated, with iron-rich, copper-zinc, copper-tin, and lead-rich alloys layering from top to bottom. This supergravity-enhanced liquation crystallization method ensures that the metals are isolated with high efficiency and purity, improving the quality of the recovered materials. At temperatures of 1100°C, 850°C, and 500°C, the metal phases separate progressively, and the purity of each metal is notably high—iron (81.8%), copper-zinc (92.9%), copper-tin (91.2%), and lead (94.6%).

The overall recovery rates of iron, copper, zinc, tin, and lead after the three separation stages are impressive, reaching 98.8%, 97.8%, 94.1%, 96.9%, and 97.4%, respectively. This method not only improves the purity of the recovered metals but also offers an efficient way to recycle WPCBs, addressing both economic and environmental concerns. By efficiently separating the metals into distinct layers based on their densities, this process provides a sustainable and cost-effective solution for recovering valuable metals from electronic waste.

Silicon – Tin – Copper – Zirconium

Recycling silicon from waste powder is important for boosting production profits and reducing environmental harm. One effective method for reprocessing silicon powder into high-quality solar-grade silicon (SoG–Si) is solvent refining. In this study, a new approach using a Si–Sn–Cu solvent with Zr assistance was proposed to take advantage of the strong bonding of boron (B) with Zr. The study first measured the activity of boron in the Si–Sn–Cu solvent at different compositions, helping to optimize the process for better boron removal. By controlling the temperature carefully, large amounts of high-purity silicon were obtained, with a 99.2% recovery rate. Compared to simpler solvents, this method reduced the boron content in the silicon to 4.7 parts per million after further processing, achieving a 95.3% boron removal rate. This research offers valuable insights and experimental evidence for more efficient separation and purification of silicon in recycling processes.

  • Efficient separation of bulk Si and enhanced B removal by Si–Sn–Cu ternary solvent refining with Zr addition Yongsheng Ren, Hui Chen

At Alcoa, large-scale fractional crystallization is used to create ultra-pure aluminum (99.999%+). The main use for this high-purity aluminum is in making sputtering targets for integrated circuits. For some applications, impurities like uranium and thorium need to be reduced to very low levels to prevent “soft errors” caused by particle emissions. The crystallization process effectively removes these impurities, producing aluminum with nearly perfect purity.

The same method is used to purify silicon, where silicon is crystallized from molten aluminum alloys with about 30% silicon content. Afterward, the crystallized material is treated to remove any remaining aluminum, resulting in extremely pure silicon suitable for making high-quality photovoltaic cells and certain types of semiconductor components. In both aluminum and silicon production, the crystallization process pushes impurities into the remaining molten material, which is then removed. The ability to purify this leftover material is also important for maximizing the recovery of valuable materials.

  • PRODUCTION OF EXTREME-PURITY ALUMINUM AND SILICON BY FRACTIONAL CRYSTALLIZATION PROCESSING R.K. DAWLESS and R.L. TROUP