Sustainable potassium chloride production from concentrated KCl brine via a membrane-promoted crystallization process

Potassium chloride (KCl) is a vital fertilizer to boost the global crop yield. However, current technologies for KCl production suffer from high energy consumption and complicated operations. Herein, we demonstrate a novel membrane-promoted crystallization (MPC) process for the sustainable production of KCl from concentrated KCl brine, together with water recovery . The MPC process reduces the capital expenditure and simplifies the complex operations by taking advantage of low-grade heat and a tubular hierarchical membrane (macroporous α -Al 2 O 3 substrate, γ -Al 2 O 3 interlayer and mesoporous hydrophilic ZrO 2 top layer). The presence of template-directing molecules P123 is vital in obtaining the mesoporous structure of ZrO 2 top layer by acting as a scaffold during the sol-gel process and preventing the meso-structural shrinkage in the annealing stage. The hierarchical membrane provides capillary forces to drive KCl brine transport from the inner shell of the membrane towards the outer surface. The continuous supply of KCl brine and water evaporation result in heterogenous nucleation and subsequent KCl crystal growth via a tip-growth mechanism, leading to abundant needle-shaped KCl whiskers on the outer surface based on the in-situ optical observation. The obtained KCl whiskers have a very small contact area with the membrane, thereby endowing facile KCl removal from the membrane surface to allow for the consecutive cycles. The MPC process exhibits a high KCl production of 134.3 g/m 2 and excellent water recovery of 738.7 g/m 2 for KCl brine (15 wt%) at 60 °C. Moreover, high performance and structural integrity of the membrane are retained after five cycles. The MPC process provides a new and promising approach for the sustainable production of KCl from KCl brine.