Developing a new method in brine purification and reducing salinity using recycled carbon fibers

The growing dependence on desalination for freshwater production has led to a significant increase in rejected brine generation, creating critical environmental concerns due to its high salinity and temperature. Discharging such brine into marine environments disrupts osmotic balance, leading to cell dehydration and ecological damage. Conventional disposal methods, including deep-well injection, evaporation ponds, and sewage discharge, remain costly and environmentally unsustainable. Meanwhile, the global demand for carbon fiber–reinforced plastics (CFRPs) has expanded rapidly owing to their superior strength-to-weight ratio, corrosion resistance, and thermal stability, resulting in large volumes of non-biodegradable carbon fiber waste. This study introduces an innovative approach that simultaneously addresses brine management, carbon fiber waste utilization, and CO₂ capture. Waste carbon fibers were recycled through pyrolysis, followed by mechanical and chemical activation using alkaline and acidic treatments to enhance surface area and adsorption performance. The treated fibers were applied in a bubble reactor containing a brine–air mixture, enabling efficient salt adsorption and recovery. Mechanical cryogenic grinding increased surface roughness and adsorption capacity, while chemical treatment introduced new functional groups that improved ion affinity. Salt recovery efficiency was determined based on the fiber mass change before and after treatment, achieving a maximum recovery of 92.9% for NaOH-treated fibers and a minimum of 36.4% for untreated samples. Overall, the developed process demonstrates a promising and sustainable pathway for utilizing waste carbon fibers in effective brine treatment and CO₂ sequestration applications.