Green Valorization of Seawater via Homogeneous Nucleation Electrochemistry: Synthesis of Nano-CaCO3 and Mg(OH)2 Adsorbents for Heavy Metal Removal

Rapid industrialization posed a serious threat to water safety due to heavy metal pollution, creating an urgent need for a green and efficient remediation solution. This research, leveraging electrocatalytic technology, innovatively proposes an electrochemical homogeneous nucleation strategy for the selective recovery of Ca2+ and Mg2+ from seawater. Through employing pH-controlled sequential precipitation, this strategy enables the synthesis of nano-CaCO3 (BET surface area: 50.4 m2/g) and nano-Mg(OH)2 (109.8 m2/g), which serve as high-performance adsorbents for efficient heavy metal removal. Both adsorbents demonstrated adsorption behaviors well-fitted to the Langmuir model, exhibiting exceptional maximum adsorption capacities for Cu(II) (838.2–1331.0 mg/g), Pb(II) (2180.5–3696.8 mg/g), Cd(II) (1065.3–1997.4 mg/g), and Cr(III) (424.1–637.5 mg/g). When configured as fixed-bed columns, the adsorbents reduced effluent concentrations of Cu(II), Pb(II), Cd(II), and Cr(III) to below 0.7 μg/L, meeting World Health Organization drinking water standards. Life cycle assessment revealed the electrochemical strategy reduced carbon emissions by 50–80% compared to conventional methods, achieving net-negative emissions (−10.428 kg CO2eq per ton of water) when incorporating resource recovery benefits. This approach represents a synergistic solution for both resource utilization and environmental remediation, demonstrating significant potential for sustainable water treatment and circular economy development.