(TSE03-O) Bauxite Residue (Red Mud) Neutralization/Treatment Using Fly Ash and Direct Carbonization

安全处理和储存大量工业废物流对废物管理提出了独特的挑战。在土地上处理这些材料往往会对环境产生负面影响，如污染土壤和地下水，并消耗大片土地。铝生产中的铝土矿渣（红泥）、煤燃烧产生的粉煤灰和污水处理厂（WWTP）的生物固体是高容量废物流的三个例子。美国每年生产大约300万吨赤泥（全球每年生产30万吨），这些赤泥被处理在陆上蓄水库中。美国每年分别产生约6300万吨和700万吨粉煤灰和生物固体，其中大部分被填埋。另一个对环境有严重影响的高容量（亿吨/年）废物流是二氧化碳。安全处置这些废物是必要的。迫切需要可持续管理的新方法和为这些废物找到有益用途的途径。赤泥的处理方法通常是将其排入工程水库或天然蓄水池，然后通过重力固结进行脱水，有时用封顶封堵。脱水后的赤泥由于pH值高、盐度高、缺乏营养和有机成分，不添加改剂剂是不可能恢复植被的。本提案探讨了利用大量废弃物，特别是二氧化碳和酸性粉煤灰来中和赤泥的潜力，以达到土壤建设和植被恢复的目的。赤泥安全隔离二氧化碳的潜力也将被确定。通过与稀释的二氧化碳废物流接触和添加酸性粉煤灰，将采用台架规模的间歇式实验来评估赤泥中和的速度和程度。将评估所得混合物的性质，包括pH值、重金属浸出潜力、碳酸盐矿物含量、质地、体积密度和持水量。还将确定污水处理厂生物固体所提供的额外中和能力和减少重金属浸出，这是一种常见的有机土壤改良剂，需要帮助表面中和的红泥恢复植被。各种赤泥灰比、二氧化碳浓度和有机改良剂浓度将被用来确定哪种比例能为植被恢复提供最佳的土壤特性。最后，将对实施该技术的工程方案进行评估，以进行可能的第二阶段现场演示。预期效益和更广泛的影响。该项目将提供中和红泥的新方法，红泥是铝土矿开采产生的高容量、高碱性残留物，与其他高容量废物（二氧化碳、酸性粉煤灰、生物固体）。对赤泥的处理将使美国和其他地方的大片赤泥处置区域的植被和环境恢复成为可能。为此目的有益地利用二氧化碳、粉煤灰和生物固体将降低几个工业对环境的影响。在赤泥中和中使用数百万吨二氧化碳或飞灰的可能性是存在的，而不是分别排放到大气中或在垃圾填埋场处理。在中和目前储存的赤泥的过程中，铝冶炼每年排放的二氧化碳中有多达785%可能被隔离。该项目还将为可持续环境管理领域的研究生和本科生提供独特的培训机会。

Safe treatment and storage of high volume industrial waste streams pose unique waste management challenges. Land disposal of these materials often has negative environmental impacts such as contamination of soil and groundwater, and consumes vast areas of land. Bauxite residue (Red Mud) from aluminum production, fly ash from coal combustion, and waste water treatment plant (WWTP) biosolids are three examples of high volume waste streams. Approximately 3 million tons of Red Mud are produced in the U.S. each year (30 M/yr globally), and are disposed in land-based impoundment reservoirs. Approximately 63 million and 7 million tons of fly ash and biosolids are generated annually in the U.S., respectively, much of which is disposed of in landfills. Another high volume (Gigatons/yr) waste stream with serious environmental impacts is CO2. Safe disposal of these wastes are a requisite. New methods for sustainable management and ways to find beneficial use for these wastes are highly desirable. Red Mud is usually managed by discharge into engineered or natural impoundment reservoirs, with subsequent dewatering by gravity consolidation and sometimes with capping for closure. Revegetation of dewatered Red Mud is not possible without addition of amendments because of the high pH, high salinity, and absence of nutrients and organic constituents.This proposal investigates the potential of using high volume waste materials, specifically CO2 and acidic fly ash, to neutralize Red Mud for the purpose of soil building and revegetation. The potential of Red Mud to safely sequester CO2 will also be determined. Bench scale batch experiments will be used to evaluate the rate and extent of Red Mud neutralization by contacting with dilute carbon dioxide waste streams, and by addition of acidic fly ash. The properties of the resulting mixture will be evaluated including pH, heavy metal leaching potential, carbonate mineral content, texture, bulk density, and water holding capacity. The additional neutralization capacity and reduction in heavy metal leaching afforded by WWTP biosolids, a common organic soil amendment needed to aid revegetation of surficial neutralized Red Mud, will also be determined. Various Red Mud to ash ratios, CO2 concentrations, and organic amendment concentrations will be used to determine which ratio provides optimal soil properties for revegetation. Lastly, engineering schemes to implement this technology will be evaluated for a possible Phase II field demonstration.Expected benefits and broader impacts. This project will provide new methods for neutralizing Red Mud, a high volume, highly alkaline residue from bauxite mining, with other high volume waste materials (CO2, acidic fly ash, biosolids). Treatment of Red Mud will make possible revegetation and environmental restoration of the large Red Mud disposal areas in the U.S. and elsewhere. The beneficial use of CO2, fly ash, and biosolids for this purpose will lower the environment impact of several industries. The potential exists to use millions of tons of CO2 or fly ash in Red Mud neutralization rather than emission to the atmosphere or disposal in a landfill, respectively. As much as 785% of the annual CO2 emissions from aluminum smelting can potentially be sequestered in the process of neutralizing Red Mud currently in storage. This project will also provide unique training opportunities for graduate and undergraduate students in the area of sustainable environmental management.