Brine disposal poses a major environmental challenge in the desalination sector due to its high concentrations of salts and chemical additives. This study investigates magnesium recovery from brine through the precipitation of Mg²⁺ as Mg(OH)₂ and its subsequent conversion to MgO. A systematic experimental design using Response Surface Methodology (RSM) with a central composite design was applied to evaluate the effects of NaOH concentration (5–10 g/L) and precipitation temperature (60–90 °C) on magnesium precipitation efficiency. Analysis of variance (ANOVA) confirmed that NaOH concentration has a statistically significant effect on magnesium precipitation, while temperature and interaction terms were negligible. Aspen Plus simulations quantified the effects of feed flow rate, precipitation temperature, and NaOH concentration on NaOH consumption, product yields, energy demand, water generation, and economic analysis. Increasing feed flow rate from 50,000 m³/day to 100,000 m³/day doubled Mg(OH)₂ production (131–263 t/day), MgO production (91–182 t/day), and water generation (150–300 m³/day), while NaOH consumption rose from 375 t/day to 750 t/day, and energy demand increased from 12,000 kW to 44,000 kW. Raising the precipitation temperature from 60 °C to 90 °C keeps Mg(OH)₂ and MgO production almost stable but increases energy demand by approximately 2.3 times. Increasing NaOH concentration from 5 g/L to 10 g/L doubled Mg(OH)₂ and MgO production, increased revenue by 117%, and slightly decreased net energy consumption (~3.7%). Economic analysis showed that maximum feed flow rate, high NaOH concentration, and low precipitation temperature (60°C) yielded the highest net annual profit (~133 million USD).