Reducing the Environmental Impacts of Desalination Reject Brine Using Modified Solvay Process Based on Calcium Oxide

Abstract

In this research, the influence of a variety of operational factors such as the temperature of the reaction, gas flow rate, concentration of NaCl, and the amount of Ca(OH)2 for reducing the environmental impacts of desalination reject brine using the calcium oxide-based modified Solvay process were investigated. For this purpose, response surface modeling (RSM) and central composite design (CCD) were applied. The significance of these factors and their interactions was assessed using an analysis of variance (ANOVA) technique with a 95% degree of certainty (p < 0.05). Optimal conditions for this process included: a temperature of 10 °C, a Ca(OH)2/NaCl concentration ratio of 0.36, and a gas flow rate of 800 mL/min. Under these conditions, the maximum sodium removal efficiency from the synthetic sodium chloride solution was 53.51%. Subsequently, by employing the real brine rejected from the desalination unit with a 63 g/L salinity level under optimal conditions, the removal rate of sodium up to 43% was achieved. To investigate the process’s kinetics of Na elimination, three different kinds of kinetics models were applied from zero to second order. R squared values of 0.9101, 0.915, and 0.9141 were obtained in this investigation for zero-, first-, and second-degree kinetic models, respectively, when synthetic reject saline reacted. In contrast, according to R squared’s results with utilizing real rejected brine, the results for the model of kinetics were: R squared = 0.9115, 0.9324, and 0.9532, correspondingly. As a result, the elimination of sodium from real reject brine is consistent with the second-order kinetic model. According to the findings, the calcium oxide-based modified Solvay method offers a great deal of promise for desalination of brine rejected from desalination units and reducing their environmental impacts. The primary benefit of this technology is producing a usable solid product (sodium bicarbonate) from sodium chloride in the brine solution.