Leão Adriano, Collin Marie, Ghodkhande Swarali, Bouissonnié Arnaud, Chen Xin, Malin Benjamin, Liu Yiming, Hovey Geanna, Govindhakannan Jagannathan, Plante Erika La, Jassby David, Gädt Torben, Corsini Lorenzo, Simonetti Dante, Rosner Fabian, Sant Gaurav
Laboratory for the Chemistry of Construction Materials (LC2), Department of Civil and Environmental Engineering, University of California, Los Angeles, California 90095, United States.
Institute for Carbon Management (ICM), University of California, Los Angeles, California 90095, United States.
ACS Sustain Chem Eng. 2024 Oct 10;12(43):15762-15787. doi: 10.1021/acssuschemeng.4c03193. eCollection 2024 Oct 28.
Limestone (calcite, CaCO) is an abundant and cost-effective source of calcium oxide (CaO) for cement and lime production. However, the thermochemical decomposition of limestone (∼800 °C, 1 bar) to produce lime (CaO) results in substantial carbon dioxide (CO) emissions and energy use, i.e., ∼1 tonne [t] of CO and ∼1.4 MWh per t of CaO produced. Here, we describe a new pathway to use CaCO as a Ca source to make hydrated lime (portlandite, Ca(OH)) at ambient conditions (, )-while nearly eliminating process CO emissions (as low as 1.5 mol. % of the CO in the precursor CaCO, equivalent to 9 kg of CO per t of Ca(OH))-within an aqueous flow-electrolysis/pH-swing process that coproduces hydrogen (H) and oxygen (O). Because Ca(OH) is a zero-carbon precursor for cement and lime production, this approach represents a significant advancement in the production of zero-carbon cement. The rbon ime (ZeroCAL) process includes dissolution, separation/recovery, and electrolysis stages according to the following steps: (Step 1) chelator (e.g., ethylenediaminetetraacetic acid, EDTA)-promoted dissolution of CaCO and complexation of Ca under basic (>pH 9) conditions, (Step 2a) Ca enrichment and separation using nanofiltration (NF), which allows separation of the Ca-EDTA complex from the accompanying bicarbonate (HCO ) species, (Step 2b) acidity-promoted decomplexation of Ca from EDTA, which allows near-complete chelator recovery and the formation of a Ca-enriched stream, and (Step 3) rapid precipitation of Ca(OH) from the Ca-enriched stream using electrolytically produced alkalinity. These reactions can be conducted in a seawater matrix yielding coproducts including hydrochloric acid (HCl) and sodium bicarbonate (NaHCO), resulting from electrolysis and limestone dissolution, respectively. Careful analysis of the reaction stoichiometries and energy balances indicates that approximately 1.35 t of CaCO, 1.09 t of water, 0.79 t of sodium chloride (NaCl), and ∼2 MWh of electrical energy are required to produce 1 t of Ca(OH), with significant opportunity for process intensification. This approach has major implications for decarbonizing cement production within a paradigm that emphasizes the use of existing cement plants and electrification of industrial operations, while also creating approaches for alkalinity production that enable cost-effective and scalable CO mineralization via Ca(OH) carbonation.
石灰石（方解石，CaCO₃）是用于水泥和石灰生产的氧化钙（CaO）的丰富且具成本效益的来源。然而，石灰石在约800℃、1巴的条件下进行热化学分解以生产石灰（CaO）会导致大量二氧化碳（CO₂）排放和能源消耗，即每生产1吨CaO会产生约1吨CO₂和约1.4兆瓦时的能量。在此，我们描述了一种新途径，即在环境条件下（常温、常压）将CaCO₃用作钙源来制备熟石灰（氢氧化钙，Ca(OH)₂），同时在一个联产氢气（H₂）和氧气（O₂）的水流电解/变pH过程中几乎消除工艺CO₂排放（低至前驱体CaCO₃中CO₂的1.5摩尔%，相当于每生产1吨Ca(OH)₂产生9千克CO₂）。由于Ca(OH)₂是水泥和石灰生产的零碳前驱体，这种方法代表了零碳水泥生产的重大进展。零碳石灰（ZeroCAL）工艺根据以下步骤包括溶解、分离/回收和电解阶段：（步骤1）螯合剂（如乙二胺四乙酸，EDTA）促进CaCO₃在碱性（pH＞9）条件下溶解并使Ca络合，（步骤2a）使用纳滤（NF）进行Ca富集和分离，这使得Ca - EDTA络合物能与伴随的碳酸氢根（HCO₃⁻）物种分离，（步骤2b）通过酸度促进Ca从EDTA中解络合，这使得螯合剂近乎完全回收并形成富含Ca的物流，以及（步骤3）利用电解产生的碱度使富含Ca的物流快速沉淀出Ca(OH)₂。这些反应可以在海水基质中进行，分别产生电解和石灰石溶解的副产物盐酸（HCl）和碳酸氢钠（NaHCO₃）。对反应化学计量和能量平衡的仔细分析表明，生产1吨Ca(OH)₂大约需要1.35吨CaCO₃、1.09吨水、0.79吨氯化钠（NaCl）和约2兆瓦时的电能，且有显著的工艺强化机会。这种方法对于在强调利用现有水泥厂和工业运营电气化的模式下使水泥生产脱碳具有重大意义，同时还创造了碱度生产方法，通过Ca(OH)₂碳酸化实现具有成本效益且可扩展的CO₂矿化。
