Sugarcane mill ash has been suggested as having high potential for carbon dioxide removal (CDR) via enhanced weathering (EW), but this had not been quantitatively assessed. The aims of this study were to 1) assess the CDR potential of various sugarcane mill ashes via EW, and 2) investigate the impact of soil conditions and mill ash properties on the CDR. This was done by characterising physical and chemical properties of five mill ashes from Australia and simulating weathering using a one-dimensional reactive transport model. The model was parameterised to simulate weathering of 100 t/ha of wet ash (47–65% water) or crushed basalt for 15 years under various combinations of soil pH and carbon dioxide partial pressure (pCO). A sensitivity analysis was undertaken in a two-level factorial design to test the effect of pH, pH buffering, material surface area, infiltration rate, plant uptake of nutrients, organic matter cation exchange surfaces, and pCO on modelled CDR. The simulated CDR of the mill ashes was significantly less than the basalt (p < 0.001) but mostly did not differ significantly between ashes (p > 0.05). Weathering of mill ash removed 0.0–4.0 t CO/ha (0.00–0.040 t CO/t wet ash) cumulatively, similar to some basalts and olivine modelled in the literature. The theoretical maximum CDR of the mill ashes (based on amount of weatherable material applied) was achieved in around 5 years. The estimate of CDR varied by orders of magnitude depending on conditions. It was least when initial soil solution pH was lowest (4.5, unbuffered), pH was at 6.5 or less with constant buffering, and pCO was low (600 ppm). CDR was also significantly lower when calculated directly from accumulation of carbon in dissolved and solid phases rather than stoichiometrically from cation release. The effects of pH and pH buffering quantified here may explain low measured CDR from EW in field trials on acidic soils and highlight the need for more realistic modelling of pH buffering capacity. Overall, mill ash shows high potential for CDR via EW, especially if lifecycle benefits are considered, although this must be validated in the field.

中文翻译：

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不同土壤条件下甘蔗磨灰风化去除二氧化碳

有人认为甘蔗磨灰具有通过增强风化 (EW) 去除二氧化碳 (CDR) 的巨大潜力，但这尚未得到定量评估。本研究的目的是 1) 通过 EW 评估各种甘蔗磨灰的 CDR 潜力，2) 研究土壤条件和磨灰特性对 CDR 的影响。这是通过表征来自澳大利亚的五种磨灰的物理和化学特性并使用一维反应传输模型模拟风化来完成的。该模型经过参数化，可模拟 100 吨/公顷的湿灰（47-65% 水）或碎玄武岩在不同土壤 pH 值和二氧化碳分压 (pCO) 组合下的风化 15 年。在两级因子设计中进行了敏感性分析，以测试 pH 值、pH 缓冲、材料表面积、渗透率、植物对养分的吸收、有机物阳离子交换表面和 pCO 对建模 CDR 的影响。磨煤灰的模拟 CDR 显着低于玄武岩 (p < 0.001)，但大多数灰烬之间没有显着差异 (p > 0.05)。磨灰的风化累计去除了 0.0–4.0 吨 CO/ha（0.00–0.040 t CO/t 湿灰），与文献中模拟的一些玄武岩和橄榄石类似。磨灰的理论最大 CDR（基于所使用的耐候材料的量）在大约 5 年内实现。根据条件的不同，CDR 的估计值会有几个数量级的变化。当初始土壤溶液 pH 值最低（4.5，无缓冲）、持续缓冲且 pH 值为 6.5 或更低且 pCO 较低（600 ppm）时，该值最低。当直接根据溶解相和固相中的碳积累计算而不是根据阳离子释放的化学计量计算时，CDR 也显着较低。这里量化的 pH 和 pH 缓冲的影响可以解释酸性土壤现场试验中 EW 测得的 CDR 较低，并强调需要对 pH 缓冲能力进行更真实的建模。总体而言，磨煤灰显示出通过 EW 进行 CDR 的巨大潜力，特别是在考虑生命周期效益的情况下，尽管这必须在现场进行验证。