Dal Poggetto Giovanni, Douwe Philippe, Stroscio Antonio, Kamseu Elie, Lancellotti Isabella, Elimbi Antoine, Leonelli Cristina
Department of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Via P. Vivarelli 10, 41125 Modena, Italy.
Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, NC 27695-7908, USA.
Materials (Basel). 2024 Oct 17;17(20):5068. doi: 10.3390/ma17205068.
A systematic study on the dissolution in concentrated alkali of two volcanic ashes from Cameroon, denoted as DAR and VN, is presented here. One volcanic ash, DAR, was 2 wt% richer in Fe and Ca and 4 wt% lower in Si than the other, designated as VN. Such natural raw materials are complex mixtures of aluminosilicate minerals (kaersutite, plagioclase, magnetite, diopside, thenardite, forsterite, hematite, and goethite) with a good proportion of amorphous phase (52 and 74 wt% for DAR and VN, respectively), which is more reactive than the crystalline phase in alkaline environments. Dissolution in NaOH + sodium silicate solution is the first step in the geopolymerisation process, which, after hardening at room temperature, results in solid and resistant building blocks. According to XRD, the VN finer ash powders showed a higher reactivity of Al-bearing soluble amorphous phases, releasing Al cations in NaOH, as indicated by IPC-MS. In general, dissolution in a strong alkaline environment did not seem to be affected by the NaOH concentration, provided that it was kept higher than 8 M, or by the powder size, remaining below 75 µm, while it was affected by time. However, in the time range studied, 1-120 min, the maximum element release was reached at about 100 min, when an equilibrium was reached. The hardened alkali activated materials show a good reticulation, as indicated by the low weight loss in water (10 wt%) when a hardening temperature of 25 °C was assumed. The same advantage was found for of the room-temperature consolidated specimens' mechanical performance in terms of resistance to compression (4-6 MPa). The study of the alkaline dissolution of volcanic ash is, therefore, an interesting way of predicting and optimising the reactivity of the phases of which it is composed, especially the amorphous ones.
本文介绍了对喀麦隆两种火山灰（分别记为DAR和VN）在浓碱中溶解情况的系统研究。一种火山灰DAR的铁和钙含量比另一种（记为VN）高2 wt%，硅含量低4 wt%。这类天然原料是铝硅酸盐矿物（钛闪石、斜长石、磁铁矿、透辉石、无水芒硝、镁橄榄石、赤铁矿和针铁矿）的复杂混合物，且含有相当比例的非晶相（DAR和VN分别为52 wt%和74 wt%），在碱性环境中，非晶相比结晶相更具反应活性。在氢氧化钠 + 硅酸钠溶液中的溶解是地质聚合过程的第一步，该过程在室温下硬化后会生成坚固耐用的建筑块体。根据X射线衍射分析（XRD），较细的VN火山灰粉末显示出含铝可溶性非晶相具有更高的反应活性，如电感耦合等离子体质谱（IPC-MS）所示，其在氢氧化钠中会释放铝阳离子。一般来说，在强碱性环境中的溶解似乎不受氢氧化钠浓度（只要保持高于8 M）或粉末尺寸（保持在75 µm以下）的影响，但受时间影响。然而，在所研究的1 - 120分钟时间范围内，大约在100分钟达到平衡时，元素释放量达到最大。假设硬化温度为25 °C时，硬化后的碱激发材料在水中的失重较低（10 wt%），这表明其具有良好的网状结构。在室温固结试样的抗压性能（4 - 6 MPa）方面也发现了同样的优势。因此，对火山灰碱性溶解的研究是预测和优化其组成相尤其是非晶相反应活性的一种有趣方法。
