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Acid leaching of ultramafic rocks to produce Mg²⁺- and Ca²⁺-rich solutions for mineral carbonation may inadvertently leach toxic trace metals. This study investigates the capacity of nesquehonite (MgCO₃·3H₂O), a common product of mineral carbonation at Earth’s surface conditions, to sorb Cr, Ni, Mn, Co and Cu from solution. Our results demonstrate that upon precipitation, nesquehonite rapidly sequesters transition metals present in solution at concentrations from 10 to 100 mg/L. Trace metal uptake appears to occur by substitution for Mg²⁺ in the nesquehonite crystal structure, and also by incorporation into minor, metal-rich phases, such as Fe-oxyhydroxides. This indicates that first row transition metals will likely be trapped and stored within Mg-carbonate minerals produced in industrial mineral carbonation reactors and in landscapes modified to capture atmospheric CO₂ via enhanced weathering. Thus, it is …