The evaporative crystallization of minerals in saltworks is one of the oldest industrial processes still in operation and has the potential to achieve high solar energy conversion efficiencies. While salt production from seawater has been extensively studied, the circular economy of brines exploitation is opening new fields of investigation. This article focuses on the design and simulation of a process for selective precipitation and mineral recovery from reverse osmosis brines. The process involves a two-step evaporative system followed by reactive crystallization of magnesium hydroxide. Laboratory tests and simulations using PHREEQC (pH-REdox-Equilibrium C-program) were conducted to validate the thermodynamics of the process and forecast the optimal operative conditions