China extracts hypersonic weapon fuel from seawater.

According to SCMP, scientists at Northwest Agricultural and Forestry University (China) have developed a new technology that allows for the extraction and collection of boron from seawater.

Boron is a lightweight element used as a solid fuel for scramjet engines on some of China's advanced hypersonic weapons. Additionally, it is a key component in neodymium-iron-boron rare-earth magnets, a material widely used in industry and defense.

Amidst trade tensions related to strategic minerals, the need for a stable supply of boron, along with neodymium and iron, is becoming increasingly important to global supply chains.

Boron plays a crucial role in the production of fuel for China's hypersonic weapons. (Photo: SCMP)

China has the world's largest demand for boron but is not a major producer. The majority of global boron supply comes from Turkey and the United States.

Seawater contains very small amounts of boron that current reverse osmosis desalination technology cannot remove, and may even increase the concentration. Long-term use of filtered water that still contains boron can be harmful to health.

In a study published on November 7th in the journal Science Bulletin, the research team stated that solar-powered interface evaporation (SDIE) technology is being considered as a sustainable solution for freshwater production.

The team stated that the recent integration of selective adsorbents into the SDIE system has opened up the possibility of simultaneously separating freshwater and recovering many valuable elements such as lithium, uranium, and cesium. Building on that foundation, they developed a solar-powered system to both produce freshwater and separate boron from seawater.

The team fabricated a novel gel called MMS, using sodium alginate as a base and supplementing it with two high-tech compounds, MXene and MgO. MXene is a two-dimensional nanomaterial with a graphene-like structure, notable for its efficient photothermal conversion, which accelerates evaporation. Meanwhile, MgO acts as an adsorbent, enabling selective boron capture.

MMS gel is made into thin sheets 2 mm thick. The top layer floats on the water surface to absorb light and exchange air, while the bottom layer is submerged in seawater to carry out the absorption process.

Under sunlight, water evaporates from the gel surface, creating a concentration gradient that draws seawater up through the gel. The portion of the gel in contact with seawater continuously absorbs water and boron, while the MgO particles inside retain the boron.

According to the research team, freshwater is produced through evaporation within the MXene-MgO composite gel, while boron accumulates inside the gel. In laboratory tests, the system achieved a maximum evaporation rate of 2.14 kg of water/m2 of gel per hour and captured 225.52 mg of boron.

The effectiveness of MMS stems from its unique layered porous structure and the combination of MXene and MgO. MXene absorbs light and converts energy into heat, while MgO is an efficient boron adsorbent. Variations in temperature, concentration, and flow within the gel also contribute to the accelerated boron capture rate.

To verify its practical application, the team conducted outdoor tests in Hong Kong. After three hours of operation, condensation appeared on the upper part of the device. Despite the relatively weak March solar radiation, the gel still produced 5.20 kg of water/m2 and captured 122.45 mg of boron/m2. No boron ions were detected in the condensed water.

According to the research team, the MMS gel can be reused multiple times. After seven cycles, the boron adsorption capacity remained above 86%, while the evaporation rate hardly decreased.

“The results show that MMS has great potential in simultaneously producing freshwater and extracting boron from seawater or brackish water,” said Fan Zhimin, the research project leader, adding that the team wants to continue evaluating the cost and scalability of the technology for large-scale applications.

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