{"title":"Acid leaching of blast furnace slag for enhanced zeolite synthesis","authors":"Nhlanhla Nyembe, Yusuf M. Isa","doi":"10.1016/j.clwas.2025.100207","DOIUrl":null,"url":null,"abstract":"<div><div>The iron- and steelmaking industry generates a substantial amount of waste in the form of blast furnace slag (BFS). Previous studies have highlighted the potential of utilizing BFS, composed of SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub>, for synthesizing zeolitic materials. However, impurities such as Ca and Mg have been found to hinder the hydrothermal synthesis process by inhibiting zeolite crystallization. To address this, acid leaching of BFS has been proposed as a viable pretreatment method. However, the influence of acid-leaching conditions on the hydrothermal synthesis technique remains unclear. Therefore, the study aims to evaluate the effectiveness of leaching conditions in reducing Ca and Mg from BFS, thereby improving zeolite synthesis from BFS. The BFS under investigation contained significant amounts of SiO<sub>2</sub> (35.1 wt%), Al<sub>2</sub>O<sub>3</sub> (16.1 wt%), CaO (30.6 wt%) and MgO (10.5 wt%). The results revealed that the optimal leaching conditions were achieved at a solids concentration of 8 wt%, an HCl concentration of 3 mol/L, and a leaching time of 90 min. Under these conditions, Ca and Mg were successfully solubilized from BFS with a maximum leaching efficiency of 80.4 % and 71.1 %, respectively. X-ray diffraction analysis revealed the mineral phase in the BFS as akermanite, while the products derived from the raw slag and leached slag consisted of augite and zeolite ZSM-5, respectively. It was observed that acid leaching of BFS resulted in a transformation of the mineral phase to augite. The initial composition of CaO and MgO in the starting material significantly influenced the formation of zeolite ZSM-5 during the hydrothermal treatment. With reduced impurities, the leached slag demonstrated successful conversion into zeolite ZSM-5. However, the resultant crystals exhibited a distinctive ball-shaped morphology. The environmental impact of the acidic leachate was minimized by neutralization, ensuring safe disposal and enhancing the sustainability of the leaching process.</div></div>","PeriodicalId":100256,"journal":{"name":"Cleaner Waste Systems","volume":"10 ","pages":"Article 100207"},"PeriodicalIF":0.0000,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Cleaner Waste Systems","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2772912525000053","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
The iron- and steelmaking industry generates a substantial amount of waste in the form of blast furnace slag (BFS). Previous studies have highlighted the potential of utilizing BFS, composed of SiO2 and Al2O3, for synthesizing zeolitic materials. However, impurities such as Ca and Mg have been found to hinder the hydrothermal synthesis process by inhibiting zeolite crystallization. To address this, acid leaching of BFS has been proposed as a viable pretreatment method. However, the influence of acid-leaching conditions on the hydrothermal synthesis technique remains unclear. Therefore, the study aims to evaluate the effectiveness of leaching conditions in reducing Ca and Mg from BFS, thereby improving zeolite synthesis from BFS. The BFS under investigation contained significant amounts of SiO2 (35.1 wt%), Al2O3 (16.1 wt%), CaO (30.6 wt%) and MgO (10.5 wt%). The results revealed that the optimal leaching conditions were achieved at a solids concentration of 8 wt%, an HCl concentration of 3 mol/L, and a leaching time of 90 min. Under these conditions, Ca and Mg were successfully solubilized from BFS with a maximum leaching efficiency of 80.4 % and 71.1 %, respectively. X-ray diffraction analysis revealed the mineral phase in the BFS as akermanite, while the products derived from the raw slag and leached slag consisted of augite and zeolite ZSM-5, respectively. It was observed that acid leaching of BFS resulted in a transformation of the mineral phase to augite. The initial composition of CaO and MgO in the starting material significantly influenced the formation of zeolite ZSM-5 during the hydrothermal treatment. With reduced impurities, the leached slag demonstrated successful conversion into zeolite ZSM-5. However, the resultant crystals exhibited a distinctive ball-shaped morphology. The environmental impact of the acidic leachate was minimized by neutralization, ensuring safe disposal and enhancing the sustainability of the leaching process.
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