Cement production is a major contributor to CO2 emissions, while the steel industry generates large amounts of non-recyclable iron waste. This study develops an iron carbonate binder as a sustainable alternative to cement by utilizing waste iron powder, which reacts with CO2 during carbonation curing. The binder consists of iron powder, fly ash, metakaolin, limestone powder, and oxalic acid, with water playing a key role in reaction efficiency. The research optimizes CO2 curing duration, pressure (1.5 and 3 bar), and water type (distilled and saline water) to enhance mechanical properties and CO2 sequestration potential. Cylindrical specimens (38 × 76 mm) were subjected to CO2 curing for 1 to 15 days, with compressive strength measured after an additional 3 days of air curing. Carbonation depth was analyzed immediately after CO2 curing by sealing all but one surface with epoxy and measuring CO2 penetration. Experimental results showed that higher CO2 pressure accelerated carbonation and strength development, with saline water specimens exhibiting slightly lower carbonation efficiency than those mixed with distilled water. By refining carbonation curing conditions, this study highlights the potential of iron carbonate binders as a low-carbon, high-strength alternative to cement, promoting sustainable construction and industrial waste valorization.