Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands.
Waste Manag. 2011 Nov;31(11):2236-44. doi: 10.1016/j.wasman.2011.05.022. Epub 2011 Jul 8.
Steel slag can be applied as substitute for natural aggregates in construction applications. The material imposes a high pH (typically 12.5) and low redox potential (Eh), which may lead to environmental problems in specific application scenarios. The aim of this study is to investigate the potential of accelerated steel slag carbonation, at relatively low pCO2 pressure (0.2 bar), to improve the environmental pH and the leaching properties of steel slag, with specific focus on the leaching of vanadium. Carbonation experiments are performed in laboratory columns with steel slag under water-saturated and -unsaturated conditions and temperatures between 5 and 90 °C. Two types of steel slag are tested; free lime containing (K3) slag and K1 slag with a very low free lime content. The fresh and carbonated slag samples are investigated using a combination of leaching experiments, geochemical modelling of leaching mechanisms and microscopic/mineralogical analysis, in order to identify the major processes that control the slag pH and resulting V leaching. The major changes in the amount of sequestered CO2 and the resulting pH reduction occurred within 24h, the free lime containing slag (K3-slag) being more prone to carbonation than the slag with lower free lime content (K1-slag). While carbonation at these conditions was found to occur predominantly at the surface of the slag grains, the formation of cracks was observed in carbonated K3 slag, suggesting that free lime in the interior of slag grains had also reacted. The pH of the K3 slag (originally pH±12.5) was reduced by about 1.5 units, while the K1 slag showed a smaller decrease in pH from about 11.7 to 11.1. However, the pH reduction after carbonation of the K3 slag was observed to lead to an increased V-leaching. Vanadium leaching from the K1 slag resulted in levels above the limit values of the Dutch Soil Quality Decree, for both the untreated and carbonated slag. V-leaching from the carbonated K3 slag remained below these limit values at the relatively high pH that remained after carbonation. The V-bearing di-Ca silicate (C2S) phase has been identified as the major source of the V-leaching. It is shown that the dissolution of this mineral is limited in fresh steel slag, but strongly enhanced by carbonation, which causes the observed enhanced release of V from the K3 slag. The obtained insights in the mineral transformation reactions and their effect on pH and V-leaching provide guidance for further improvement of an accelerated carbonation technology.
钢渣可用作建筑应用中的天然骨料替代品。该材料具有高 pH 值（通常为 12.5）和低氧化还原电位（Eh），这可能会在特定应用场景中导致环境问题。本研究的目的是研究在相对较低的 pCO2 压力（0.2 巴）下加速钢渣碳酸化的潜力，以改善钢渣的环境 pH 值和浸出特性，特别关注钒的浸出。碳酸化实验在实验室柱中进行，钢渣在水饱和和不饱和条件下以及 5 至 90°C 的温度下进行。测试了两种类型的钢渣；含游离石灰（K3）渣和游离石灰含量极低的 K1 渣。通过浸出实验、浸出机制的地球化学模型和微观/矿物学分析的组合，对新鲜和碳酸化的炉渣样品进行了研究，以确定控制炉渣 pH 值和由此产生的钒浸出的主要过程。在 24 小时内，被封存的 CO2 量和由此产生的 pH 值降低发生了主要变化，含游离石灰的渣（K3 渣）比游离石灰含量较低的渣（K1 渣）更容易碳酸化。虽然发现这些条件下的碳酸化主要发生在炉渣颗粒的表面，但在碳酸化的 K3 渣中观察到了裂缝的形成，表明炉渣颗粒内部的游离石灰也发生了反应。K3 渣的 pH 值（原始 pH±12.5）降低了约 1.5 个单位，而 K1 渣的 pH 值从约 11.7 降低到 11.1，降低幅度较小。然而，碳酸化后 K3 渣的 pH 值降低被观察到导致钒浸出增加。未经处理和碳酸化的 K1 渣的钒浸出均超过荷兰土壤质量法令的限值。碳酸化后的 K3 渣的 V 浸出仍低于这些限值，因为碳酸化后仍保持相对较高的 pH 值。含钒的二钙硅酸盐（C2S）相已被确定为钒浸出的主要来源。结果表明，这种矿物在新鲜钢渣中的溶解是有限的，但碳酸化强烈增强了这种溶解，从而导致从 K3 渣中观察到的 V 释放增强。对矿物转化反应及其对 pH 值和钒浸出的影响的深入了解为进一步改进加速碳酸化技术提供了指导。
