Abstract: With the rapid progress of seawater desalination technology, concentrated brine has not been effectively used due to the lack of mature development and treatment process. Direct emissions of concentrated brine are seriously harmful to the ecological environment. At the same time, massive emissions of carbon dioxide have exacerbated the greenhouse effect. Aiming at the resource utilization of concentrated brine and carbon dioxide, combined with the previous research basis of using calcium hydroxide as the precipitant to prepare magnesium hydroxide, this paper proposes a carbonization technical process to prepare magnesium bicarbonate using magnesium hydroxide as the precursor from low magnesium systems. The research focused on the carbonization process of magnesium hydroxide, investigating the influence of liquid-solid ratio, temperature, carbon dioxide gas velocity, stirring speed, and raw material difference on the carbonization process, and monitoring the change of calcium and magnesium ion concentration and pH value during the carbonization process. It was found that under room temperature and atmospheric pressure, the carbonization effect was the best when the liquid-solid ratio was 40, the carbon dioxide gas velocity was 400 mL/min, and the stirring speed was 300 r/min, the concentration of Mg²⁺ in the carbonization solution from magnesium hydroxide (AR) was 0.315 mol/L and there existed no Ca²⁺, the concentration of Mg²⁺ in the carbonization solution from self-made magnesium hydroxide was 0.203 mol/L, the concentration of Ca²⁺ was 3.2×10⁻⁴ mol/L, calcium impurities were basically separated. The particle size and dispersion of magnesium hydroxide had a significant impact on the carbonization effect, smaller particle size and better dispersion promoted the carbonization process. The shrinking core model of magnesium hydroxide was briefly discussed at the same time, the fits of the carbonization process at different slurry temperatures showed good linearity.