Exploitation of seawater brines for the production of Nesquehonite solids and CO2 utilization

Abstract

The simultaneous utilization of waste CO₂ streams and bivalent rich saline solutions is a crucial opportunity to face climate change challenges. Several authors have investigated desalination seawater brines as promising sources of bivalent solutions for CO₂ utilization technologies. However, the Mg^2 + and Ca²⁺ content in brines affects the purity of the synthesized compounds. In this context, the present work thoroughly assesses, for the first time, the direct and indirect mineral carbonation processes of real highly concentrated Mg²⁺-rich saline solutions (bitterns), the latter being the by-products of the evaporation process of seawater or desalination brines in saltworks or evaporative ponds. For comparison, the indirect carbonation process of real desalination brines was also explored. The bittern had Mg²⁺ and Ca²⁺ concentrations of ∼2.00 mol/L and ∼0.004 mol/L, while ∼0.13 mol/L and ∼0.025 mol/L were those in the desalination brine, respectively. Carbonation tests were conducted at room temperature and atmospheric pressure in a (semi-)batch reactor. The high concentration of Mg²⁺ and the almost absence of Ca²⁺ in the bittern allowed (i) the production of highly pure Nesquehonite solids (purity ∼99 %) and (ii) almost doubling the CO₂ yield (from 23 % to 37 %) through the direct carbonation approach against the indirect one.