Sequestration of CO₂ within stable mineral carbonates (e.g., CaCO₃) represents an attractive emission reduction strategy because it offers a leakage-free alternative to geological storage of CO₂ in an environmentally benign form. However, the pH of aqueous streams equilibrated with gaseous streams containing CO₂ (pH < 4) are typically lower than that which is required for carbonate precipitation (pH > 8). Traditionally, alkalinity is provided by a stoichiometric reagent (e.g., NaOH) which renders these processes environmentally hazardous and economically unfeasible. This work investigates the use of regenerable ion-exchange materials to induce alkalinity in CO₂-saturated aqueous solutions such that the pH shift required for mineralization occurs without the need for stoichiometric reagents. Na⁺-H⁺ exchange isotherms (at [H⁺] = 10⁻⁸–10⁻¹ M) and rates were measured for 13X and 4A zeolites and TP-207 and TP-260 organic exchange resins in batch equilibrium and fixed-bed exchange experiments, respectively. At solutions equilibrated with CO₂ at 1.0 atm (pH = 3.9), H⁺ exchange capacities for the materials were similar (1.7–2.4 mmol H⁺/g material) and resulted in pH increases from 3.9 to greater than 8.0. Multi-component mixtures using Ca²⁺ and Mg²⁺ cations (at 10⁻³–10⁻¹ M) in CO₂-saturated water were used to probe competitive ion exchange. The presence of divalent cations in solution inhibited H⁺ exchange, reducing capacities to as low as 0.2 mmol H⁺/g for both resins and zeolites. Dynamic H⁺ exchange capacities in fixed-bed ion exchange columns were similar to equilibrium values for resins (∼1.5 mmol/g) and zeolites (∼0.8 mmol/g) using inlet solutions that were equilibrated with gaseous streams of CO₂ at 1.0 atm. However, exchange kinetics were limited by intraparticle diffusion as indicated by the increased rate parameters with increasing inlet flow rates (20–160 cm³ min⁻¹). Experimental calcite precipitation from mixing the alkaline CO₃²⁻-rich water solution obtained from the ion-exchange column with a simulated liquid waste stream solution achieved thermodynamic maximum yields. The results from these studies indicate that ion exchange processes can be used as an alternative to the addition of stoichiometric bases to induce alkalinity for the precipitation of CaCO₃, thereby opening a pathway toward sustainable and economic mineralization processes.

在稳定的矿物碳酸盐（例如CaCO ₃）中封存CO ₂代表了一种有吸引力的减排策略，因为它为地质环境中无害于CO ₂提供了无泄漏的替代选择。然而，用含CO _2的气态物流平衡的水流的pH（pH <4）通常低于碳酸盐沉淀所需的pH（pH> 8）。传统上，碱度是由化学计量试剂（例如NaOH）提供的，这使这些过程对环境有害且在经济上不可行。这项工作研究了使用可再生离子交换材料诱导CO _2中的碱度-饱和水溶液，使得不需要化学计量试剂即可发生矿化所需的pH值变化。Na ⁺ -H ⁺交换等温线（在[H ⁺ ] = 10 ^-8 –10 ^-1  M时），并在间歇平衡和固定床中测量13X和4A沸石以及TP-207和TP-260有机交换树脂的速率分别进行交换实验。在以1.0 atm（pH = 3.9）的CO ₂平衡的溶液中，材料的H ⁺交换容量相似（1.7–2.4 mmol H ⁺ / g材料），导致pH从3.9增加到大于8.0。使用Ca ²⁺和Mg ^2+的多组分混合物饱和 CO ₂水中的阳离子（浓度为10 ^-3 –10 ^-1 M）被用来探测竞争性离子交换。溶液中二价阳离子的存在抑制了H ^+的交换，将树脂和沸石的容量降低至低至0.2 mmol H ⁺ / g。固定床离子交换塔中的动态H ⁺交换容量与使用1.0 atm的CO ₂气态流平衡的入口溶液的树脂（〜1.5 mmol / g）和沸石（〜0.8 mmol / g）的平衡值相似。。然而，交换动力学受到颗粒内扩散的限制，如入口流速（20–160 cm ³  min^-1）。通过将从离子交换塔获得的富含碱性CO ₃ ^2-的水溶液与模拟的废液流溶液混合，进行方解石沉淀实验，获得了热力学上的最大产率。这些研究的结果表明，离子交换过程可以用作添加化学计量碱的替代方法，以诱导CaCO ₃沉淀的碱度，从而开辟通往可持续和经济矿化过程的途径。