In a previous work, the overall performance of modified Solvay process was investigated in the absence of ammonia, where carbon dioxide and brine treatments were accomplished in a single reaction and in the presence of calcium hydroxide (Ca(OH)₂). In this study, the impact of alkaline and amphoteric oxides, namely potassium hydroxide (KOH) and aluminum oxide (Al₂O₃), on the pH level, CO₂ capture capacity, ions reduction, and type of produced solids was investigated at a temperature of 20°C and a gas flow rate of 1 L/min. At the stoichiometric ratio and less than the solubility limit, the KOH/brine mixture achieved a CO₂ uptake of 0.31 g CO₂/g KOH. In comparison, about 0.92 g of CO₂ was captured by 1 g of CaO when CaO was added to the brine in an amount that was more than the solubility limit but less than the stoichiometric ratio. Moreover, the percentage of the ions reduction for the KOH and CaO was almost the same except for the sulfate ions, as the best removal was for the CaO. The poorest CO₂ capture and ions removal occurred with the Al₂O₃. X‐ray diffraction was used to identify most of the solid products, and the obtained results proved that KOH is a promising alkaline for the combined process. In addition, potassium chloride crystals were produced when KOH was utilized, which is a very valuable product, and it can also be easily separated. Although Al₂O₃ showed no reactivity, it revealed good results in terms of magnesium ions recovery and could be considered as a coagulant for recovering magnesium ions in the reject brine solution.

The traditional Solvay process and other modifications that are based on different types of alkaline material and waste promise to be effective in the reduction of reject brine salinity and the capture of CO₂. These processes, however, require low temperatures (10–20 °C) to increase the solubility of CO₂ and enhance the precipitation of metallic salts, while reject brine is usually discharged from desalination plants at relatively high temperatures (40–55 °C). A modified Solvay process based on potassium hydroxide (KOH) has emerged as a promising technique for simultaneously capturing carbon dioxide (CO₂) and reducing ions from reject brine in a combined reaction. In this study, the ability of the KOH-based Solvay process to reduce brine salinity at relatively high temperatures was investigated. The impact of different operating conditions, including pressure, KOH concentration, temperature, and CO₂ gas flowrate, on CO₂ uptake and ion removal was investigated and optimized. The optimization was performed using the response surface methodology based on a central composite design. A CO₂ uptake of 0.50 g CO₂/g KOH and maximum removal rates of sodium (Na⁺), chloride (Cl⁻), calcium (Ca²⁺), and magnesium (Mg²⁺) of 45.6%, 29.8%, 100%, and 91.2%, respectively, were obtained at a gauge pressure, gas flowrate, and KOH concentration of 2 bar, 776 mL/min, and 30 g/L, respectively, and at high temperature of 50 °C. These results confirm the effectiveness of the process in salinity reduction at a relatively high temperature that is near the actual reject brine temperature without prior cooling. The structural and chemical characteristics of the produced solids were investigated, confirming the presence of valuable products such as sodium bicarbonate (NaHCO₃), potassium bicarbonate (KHCO₃) and potassium chloride (KCl).

Effective gas dispersion and liquid mixing are significant parameters in the design of an inert-particle spouted-bed reactor (IPSBR) system. Solid particles can be used to ensure good mixing and an efficient rate of mass and heat transfer between the gas and liquid. In this study, computational fluid dynamics (CFD) coupled with the discrete phase model (DPM) were developed to investigate the effect of the feed gas velocity (0.5–1.5 m/s), orifice diameter (0.001–0.005 m), gas head (0.15–0.35 m), particle diameter (0.009–0.0225 m), and mixing-particle-to-reactor-volume fraction (2.0–10.0 vol.%) on the solid mass concentration, average solid velocity, and average solid volume fraction in the upper, middle, and conical regions of the reactor. Statistical analysis was performed using a second-order response surface methodology (RSM) with central composite design (CCD) to obtain the optimal operating conditions. Selected parameters were optimized to maximize the responses in the middle and upper regions, and minimize them in the conical region. Such conditions produced a high interfacial area and fewer dead zones owing to good particle dispersion. The optimal process variables were feed gas velocity of 1.5 m/s, orifice diameter of 0.001 m, gas head of 0.2025 m, a particle diameter of 0.01 m, and a particle load of 0.02 kg. The minimum average air velocity and maximum air volume fraction were observed under the same operating conditions. This confirmed the novelty of the reactor, which could work at a high feed gas velocity while maintaining a high residence time and gas volume fraction.

Soda ash (Na₂CO₃) is produced using the traditional Solvay process. It entails the reaction of CO₂ with high-salinity water in the presence of ammonia (NH₃), which produces insoluble sodium bicarbonate (NaHCO₃) and soluble ammonium chloride (NH₄Cl). In the current work, a newly combined approach has been developed to effectively manage the removal of ammonia and sulfate from the effluent of the Solvay process. The devised technique centers on an electrochemical coagulation process, complemented with the utilization of calcium oxide (CaO) as a buffering reagent. This innovative approach excels at achieving high recovery rates for both ammonia and sulfate. The recovered ammonia holds the potential for recycling, thereby contributing to the sustainability of the Solvay process by reusing ammonia in its initial stages. Furthermore, sulfate ions are recuperated in the form of calcium sulfate, a value-added product boasting various industrial applications. The results gleaned from this study underscore the efficacy of the ammonia recovery process, particularly when operating at elevated current densities and with higher calcium oxide concentrations. On the other hand, sulfate recovery demonstrates superior performance when exposed to moderate current densities and limited calcium oxide concentrations. Consequently, the integration of both stages within a single, cohesive process necessitates the development of an optimization methodology to cater to varying operational conditions. To address this need, second-order polynomial equations were formulated and employed to anticipate ammonia and sulfate removal rates in the integrated approach. Four independent variables come into play: calcium oxide concentration, current density, temperature, and mixing rate. The findings reveal that most of these variables exert substantial influences on both ammonia and sulfate removal rates, underscoring the need for careful consideration and fine-tuning to optimize the overall process. The maximum ammonia and sulfate removal were found to reach 99.50% and 96.03%, respectively, at a calcium oxide concentration of 3.5 g/100 mL, a current density of 19.95 mA/cm², a temperature of 35 °C, and a mixing rate of 0.76 R/s. The results are promising, and the developed process is also suitable for recovering high concentrations of sulfate and ammonia from various wastewater sources.