This Project integrates a number of chemical processes in which are included different technologies, most of them based on membranes, in order to treat brines from seawater desalination plants. These processes have a dual function. On the one hand these allow to reduce the quantity and concentration of brines, and in turn, by products can be obtained and make the treatments more attractive from an economic point of view. It has been done a review of state of the art of water desalination technologies, and also the more typical brine disposals have been studied. Moreover, it has been identified and developed the most used technologies for the recovery of by products through these brines. Design of these processes includes its mathematical modeling through equations and mass balances with the goal of foreseeing and predict brine’s behavior. This simulation facilitates the comprehension of technologies as well as time saving. For this, previous models have been collected and studied. Once the operations have been modelled, they were represented through a known brine with the purpose of simulating its behavior and to analyze by products obtained as a result of these technologies. To that end, mass balances have been implemented in Excel, and in turn, software Hydra/Medusa has been use to predict the solubility of brines at certain points of the processes. Moreover, an economic evaluation of recovered by products has been done, taking into account the associated chemical costs to evaluate its economic viability. Application of these technologies are very positive from an environmental point of view, due to they allow to reduce volume and concentration of brines that come from desalination plants. Mathematical modeling of these processes is a useful tool because it enables to reproduce the conduct of brines and allows to reduce experimental tests, which don’t stop being necessary to certify the behaviors obtained through these models.