Magnesium hydroxide (MH), as a potential alkalinity source, is one of the most promising materials for permanent carbon dioxide removal (CDR) via ocean alkalinity enhancement. We present a new method for generating MH in a diaphragm/membrane-separated electrolyzer using magnesium sulfate as a catholyte and sulfuric acid as an anolyte. This approach offers a zero-waste production of MH of desired purity while generating sulfuric acid, hydrogen, and oxygen, concurrently. The acid is used to extract the Mg from mineral deposits as magnesium salt containing leach solution. Hydrogen can be used as a fuel and subsequently oxidized either by combustion or in a fuel cell to regenerate water and release energy. The oxygen can be vented to the atmosphere or used in solution processing and other mining operations. We designed the unit cells for MH production on an evolving basis, with a view to certain operational challenges. The sources of voltage increase on the cell such as accumulation of MH in a system and adhesion of MH deposits on cathodes were addressed by the cathode vibration technique. The diaphragm-divided cell achieved over 90% current efficiency (C.E.) based on MH at the expense of losing the Mg in anolyte. An anion-exchange membrane divided cell minimized the transport of Mg into anolyte, but the C.E/ never exceeded 70–80% C.E. MH. The preoptimized outcome from unit cells was the energy consumption ranging from 4.9 to 6.5 MWh/t MH. The unit cell performance was validated in the scaled-up version of one of the cells to the multi-cell containing five cathodes and four anodes. We tested two process solutions. The first consisted of a magnesium sulfate with certain impurities (manganese, nickel, calcium, and sodium) simulating the process solution of waste asbestos mine tailings. The second test solution originated from an actual nickel laterite operation. The electrolysis was conducted in three stages. The product of the first stage of electrolysis precipitated most of the impurities along with MH. This product can be used for mixed metal hydroxide precipitation circuit (MHP) practiced in nickel laterite and similar operations. The extent of MH precipitation in the first stage of electrolysis was controlled by the applied current. The final stage of electrolysis produced the MH of the desired purity (over 85% MH) suitable for ocean-based CDR. Based on results from the multi-electrode cell studies, a cell stack configuration and electrical system requirements for constructing industrial-scale electrolytic system for MH production were developed. The calculation was based on process solution inflow rate of ~70 L/min and input Mg content of 47 g/L. The modeling outcome indicated that over 2.7 t/year of MH can be generated efficiently and with a specific energy consumption not exceeding 6 MWh/t-MH.