Department of Environmental Engineering, Korea Maritime and Ocean University, Busan, 49112, Korea.
Environ Sci Pollut Res Int. 2020 Jun;27(16):20490-20499. doi: 10.1007/s11356-020-08403-1. Epub 2020 Apr 3.
In this study, indirect carbonation was carried out by using cement kiln dust (CKD), an alkaline industrial by-product, and three chelating agents (citrate, malonate, and adipate salts) as solvents at the room temperature and atmospheric pressure. We derived the optimum conditions for eluting Ca from CKD, as well as those for storing CO and producing CaCO through carbonation. The most important factor affecting the Ca elution from CKD was the solvent concentration and that for the carbonation was the end-of-carbonation pH. Under the optimum conditions of Ca elution, the molar ratios of Ca and solvent in eluates were 1:1, 1:2, and 1:2, respectively, using citrate, malonate, and adipate solvents. Based on the results, we propose that one molecule of Ca ion and one molecule citrate that is tridentate are combined to form a complex. The bidentate malonate and adipate, on the other hand, form complexes by combining one molecule of Ca ion and two molecules of each solvent. It is essential to raise the pH while simultaneously minimizing the amount of free chelating agent in solution to produce more CaCO and prevent its dissolution. Besides, it is absolutely necessary to terminate the carbonation reaction at a pH of about 10.5 to improve the reuse efficiency of the chelating agent. CaCO produced through carbonation reaction started to dissolve at pH approximately 10.5. All of the CaCO produced was calcite with a purity of 98%. The efficiency of Ca elution from CKD using three solvents increased significantly with increasing stability constant of a Ca-ligand complex, but the efficiency of carbonation was the same for all solvents.
在这项研究中，使用水泥窑灰（CKD），一种碱性工业副产品，以及三种螯合剂（柠檬酸盐、丙二酸盐和己二酸盐）作为溶剂，在室温常压下进行间接碳酸化。我们得出了从 CKD 洗脱 Ca 的最佳条件，以及通过碳酸化储存 CO 和生产 CaCO 的最佳条件。影响 CKD 中 Ca 洗脱的最重要因素是溶剂浓度，而影响碳酸化的最重要因素是碳酸化结束时的 pH 值。在最佳洗脱条件下，使用柠檬酸盐、丙二酸盐和己二酸盐作为溶剂，洗脱液中 Ca 和溶剂的摩尔比分别为 1:1、1:2 和 1:2。根据这些结果，我们提出一个 Ca 离子和一个三配位的柠檬酸分子结合形成一个配合物。另一方面，二配位的丙二酸盐和己二酸盐通过一个 Ca 离子和两个每个溶剂分子结合形成配合物。为了生成更多的 CaCO 并防止其溶解，提高 pH 值并同时最小化溶液中游离螯合剂的量是至关重要的。此外，必须在 pH 约 10.5 时终止碳酸化反应，以提高螯合剂的重复使用效率。通过碳酸化反应生成的 CaCO 开始在 pH 约 10.5 时溶解。所有生成的 CaCO 均为纯度为 98%的方解石。使用三种溶剂从 CKD 中洗脱 Ca 的效率随着 Ca-配体配合物的稳定性常数的增加而显著提高，但所有溶剂的碳酸化效率是相同的。
