Assessment of the influence of temperature and pressure on the prediction of the precipitation of minerals during the desalination process

The results of research designed to examine the influence of the temperature of geothermal water and transmembrane pressure on the precipitation of selected minerals during the desalination process are presented. The geothermal water used in tests was characterised by a high conductivity value, high total hardness and elevated concentrations of sulphates, silicates, calcium, magnesium, and macro and micronutrients, which can cause scaling phenomena to occur. Based on the physicochemical composition of the water, an estimate was made of the extent of the scaling phenomena for all the processes examined. For these analyses, two parameters of the desalination process: 1) the temperature of feed water (T) and 2) the transmembrane pressure (p) were chosen and tested in different value ranges. The research results demonstrate the existence of reactions determined both by hydrogeochemical modelling and from the results obtained during real laboratory tests. It was found that in the case of carbonate (aragonite and calcite) and all silicate minerals, an increase in the pressure value to 40 bar slightly decreases the Saturation Index for each mineral. A reverse relationship was reported with gypsum. Increasing transmembrane pressure to 40 bar increases the tendency of the mineral form studied to precipitate.