赤泥堆场土壤化过程及其环境风险

Bauxite residue （red mud）is an alkaline solid waste produced in the process of alumina extraction from bauxite. These residues are usually deposited in impoundments surrounding the refinery. Ideally this residue would be utilized as an industrial by-product for other applications, leading to a zero waste situation. However, little evidence exists of any significant utilization of bauxite residue. Ecological restoration of industrial residues can stabilize the residue surface, decreasing wind and air erosion and improving aesthetics which are issues of concern to alumina producers worldwide. The high alkalinity and salinity as well as the poor nutrient status are considered to be the major constraints of red mud revegetation. A detailed understanding of the complex buffering and neutralization chemistry of bauxite residue remains the key to improved management, both in terms of reduced environmental impact for current storage practices, legacy costs and for the utilization of the material as an industrial by-product for other applications. The key parameters of residue chemistry and its physical properties are considered in the context of what is required for a remediated residue to support a viable eco-system. This chemistry also impacts physical properties e.g. bulk density, sedimentation rates and compaction, hydraulic conductivity, drying rates and dusting behavior, and physical strength after drying. The most promising pathway for an in situ rehabilitated bauxite residue disposal area would appear to be bioremediation based on strategies developed for saline-sodic soils using halophyte plants and alkaliphilic microbes to effectively farmsodium from the system and mitigate pH, respectively. It is proposed that research design for bioremediation should commence with amore rigorous plant, fungi and microbe selection in conjunction with a better understanding of residue chemistry. Vegetation restoration is expected to improve soil microstructure and therefore enhance soil stability and reduce soil erosion. Soil reconstruction of bauxite residue disposal area is a simple way to deal with mass red mud, which can get huge economic, environmental and social benefits with low-cost.

赤泥是氧化铝工业生产过程中产生的高碱性废弃物,综合利用难度大、利用率低，大量外排赤泥以堆存为主，赤泥堆场的环境安全问题正严重威胁我国氧化铝工业可持续发展。赤泥堆场是一种典型的矿业废弃地，堆场碱性强、盐分含量高、营养成份缺乏、持水保肥能力差、金属元素含量高、一般植物难以生长。本项目拟在对不同年代赤泥堆场土壤化发生、演化过程调查的基础上，开展堆场土壤化过程中的物理、化学与生物学特性研究；对赤泥堆场土壤化过程开展物理特性和化学特性调控，通过定向培育，实现赤泥堆场土壤重构；开展赤泥堆场及铝土矿周边区域生态调查，筛选耐性植物，构建堆场植物群落；拟选取广西平果铝有限公司的赤泥堆场为野外示范基地，通过田间试验开展堆场土壤化过程的环境风险评估，探讨赤泥堆场生态重建模式。研究成果将有助于开展赤泥堆场生态重建、解决氧化铝工业生产过程赤泥的减排问题，保障铝土矿冶区的生态安全与氧化铝工业可持续发展。

赤泥是氧化铝工业过程中产生的高碱性废弃物，资源化利用率仅5%，大量外排赤泥以堆存为主。赤泥碱性强、盐分含量高、污染物迁移风险大、金属元素含量高，赤泥堆场的环境安全问题正严重威胁氧化铝工业可持续发展。通过对典型赤泥堆场开展生态调查，筛选了10 种赤泥堆场耐性植物，建立了1000平方米的赤泥土壤化示范工程，对赤泥堆场周边农田土壤开展污染环境风险评估，发现了堆场赤泥碱性的自然衍化现象，分析了赤泥自然风化条件下的土壤发生特征；随着堆存时间的增加，赤泥可溶性碱、电导率、可交换性钠含量、酸性中和能力明显降低，赤泥物理化学性质得到明显改善，钙离子含量增加促进团聚体的形成，赤泥团聚结构由片状结构变为团粒结构；有机质能够促进赤泥颗粒的团聚，有机碳可以提高大团聚体的稳定性，而铁铝氧化物可能是微团聚体稳定性的重要因素；赤泥碱性物质以方解石、钙霞石、水化石榴石、方钠石和铝酸三钙等矿物状态存在，碱性转化过程受矿物赋存状态及矿物表面行为共同控制；柠檬酸促进了碱性转化，主要碱性矿物明显降低，Na介孔尺度空间分布、矿物表面碱性官能团等变得稀散，生物质-真菌-石膏联合能将赤泥pH降至8以下；联合施用石膏和蚯蚓粪肥，赤泥团聚体由片状结构变为团粒结构，微团聚体颗粒由粒状结构变为团粒结构或棱柱结构，促进赤泥土壤化过程。项目实施期间，首次发现了赤泥堆场的土壤发生现象，系统开展了赤泥堆场自然风化过程中团聚体形成过程，提出一种新颖的赤泥团聚体微观结构定量化分析方法；发现了堆场赤泥碱性自然衍化现象，借助同步辐射技术探讨了赤泥碱性调控过程中碱性物质化学形态及Na的微分布，从介孔尺度下揭示了赤泥碱性转化特征；发表SCI/EI论文18篇（ESI 1%论文3篇，中科院1区论文4篇）、CSCD论文4篇；申请发明专利2件。研究成果对实现氧化铝工业赤泥的土壤化处置，经济安全地消除赤泥堆场环境隐患具有重要意义。