Magnesium dihydroxide (MDH) recovered from seawater salt production wastewater tested as PIN flame retardant in epoxy. China alone generates some 30 million m3/year of ‘bittern’, the wastewater from salt production from seawater. Over three quarters of this is currently not valorised and discharge can cause environmental problems. In this lab study, sodium hydroxide and MDH seed crystals were added to synthetic bittern, resulting in precipitation of MDH. This was separated by filtration, then heated (80°C) to generate a 40-60 µm hexagonal MDH nanosheet, which was then functionalised with sodium stearate. The resulting PIN flame retardant, at 9% loading in epoxy, reduced heat release rate by over 60% and smoke by around 40%.
“Fast and complete recovery of magnesium from sea bittern to synthesize magnesium hydroxide hexagonal nanosheet for enhanced flame retardancy and mechanical properties of epoxy resin”, B. Sun et al., Desalination 583 (2024) 117716 https://doi.org/10.1016/j.desal.2024.117716