Abstract: Steel slag and CO2 are the two major wastes emitted by the iron and steel industry. Indirect carbonation of steel slag can achieve the dual benefits of Ca circulation and carbon emission reduction. Effective leaching of Ca from steel slag is a key step in the indirect carbonation process. However, Ca in steel slag exists in different Ca-based phases, and different active phases lead to different leaching efficiency. In order to investigate the dissolution law and reaction mechanism of the Ca-based phase of steel slag in the leaching process and the influence of the leaching process on leaching efficiency, ammonium chloride solution was employed as an extractant to leach steel slag. Furthermore, a thermodynamic calculation method was utilised to predict the dissolution behaviour of the calcium-containing phase of steel slag. The relationship between solid-liquid ratio, extractant concentration and leaching temperature on leaching efficiency was investigated by means of an orthogonal test. In addition, the mineral composition, surface morphology, element distribution and particle size change of steel slag before and after leaching were characterised by XRD, SEM-EDS, and particle size distribution. The results showed that the factors affecting the leaching efficiency of Ca in steel slag were solid-liquid ratio, leaching agent concentration and leaching temperature according to their influence. Under the conditions of solid-liquid ratio of 1:40, leaching temperature of 80℃, and leaching agent concentration of 3 mol/L, the concentration of Ca2+ in the solution was 4689.4 mg/L after leaching for 1 h, and the leaching rate was 63.1%. The results of thermodynamic calculations, XRD, and SEM-EDS analysis indicated that ammonium chloride selectively extracted calcium from the calcium-containing phase, while the iron remained in the slag to form enrichment. In this process, the particle size of the steel slag gradually decreased, and cracks and holes were generated on the surface, which was beneficial to increase the contact area between the steel slag and the ammonium chloride solution.

摘要： 钢渣和CO2是钢铁工业排放的两大废弃物。利用钢渣进行间接碳酸化可实现Ca循环和减少碳排放的双重效益，从钢渣中有效浸出Ca是间接碳酸化过程的关键步骤。然而，钢渣中的Ca存在于不同的Ca基相中，不同活性的相导致其浸出效率不同。为探究钢渣Ca基相在浸出过程的溶解规律和反应机理以及浸出工艺对浸出效率的影响，本工作以NH4Cl溶液作为萃取剂浸出钢渣，采用热力学计算方法预测钢渣含钙相的溶解行为，并通过正交试验研究固液比、萃取剂浓度、浸出温度3个主要工艺参数对浸出效率影响大小的关系，使用X射线衍射(XRD)、扫描电子显微镜-能谱分析(SEM-EDS)和粒度分布等对浸出前后钢渣的矿物组成、表面形貌、元素分布和粒度变化进行表征。结果表明，在常压环境下，影响钢渣Ca浸出效率的因素，按其影响大小依次为固液比、浸出剂浓度和浸出温度，在固液比为1:40、浸出温度为80℃、浸出剂浓度为3 mol/L的条件下，浸出1 h后，溶液中Ca2+浓度为4689.4 mg/L，浸出率达63.1%。热力学计算结果和XRD, SEM-EDS分析都表明，NH4Cl选择性从含钙物相中浸出Ca，而铁则留在渣中形成富集，在此过程中，钢渣颗粒尺寸逐渐减少，其表面产生裂缝和孔洞，有利于增加钢渣与NH4Cl溶液的接触面积。