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

大量工业废流的安全处理和储存带来了独特的废物管理挑战。这些材料的土地处置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。铝生产产生的铝土矿残渣(赤泥)、燃煤飞灰和废水处理厂(WWTP)生物固体是三个高容量废物流的例子。美国每年产生约300万吨赤泥(全球每年3000万吨)，并被处置在陆上蓄水池中。美国每年分别产生约6300万吨和700万吨的飞灰和生物固体，其中大部分被丢弃在垃圾填埋场。另一个对环境有严重影响的高容量(十亿吨/年)废流是二氧化碳。安全处置这些废物是必要的。非常需要可持续管理的新方法和为这些废物找到有益利用的途径。赤泥通常通过排放到工程水库或自然蓄水池中进行管理，然后通过重力固结进行降水，有时还会封堵。由于赤泥的高pH、高盐度以及缺乏营养物质和有机成分，不添加改良剂就不可能恢复赤泥的植被。本建议研究了使用大量废物，特别是二氧化碳和酸性飞灰来中和赤泥的可能性，以达到土壤建设和恢复植被的目的。赤泥安全封存二氧化碳的潜力也将被确定。采用小试间歇实验方法，考察赤泥与稀释二氧化碳废液接触和添加酸性飞灰的中和速度和程度。将对所得混合物的性能进行评估，包括pH值、重金属浸出潜力、碳酸盐矿物含量、质地、体积密度和持水能力。还将确定污水处理厂生物固体提供的额外中和能力和减少重金属淋失的能力。污水处理厂生物固体是一种常见的有机土壤改良剂，用于帮助表面中和赤泥恢复植被。不同的赤泥灰比、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恢复植被提供最佳的土壤性质。最后，将对实施这项技术的工程方案进行评估，以进行第二阶段的现场演示。预期的好处和更广泛的影响。该项目将提供中和赤泥的新方法，赤泥是铝土矿开采产生的高容量、高碱性残渣，与其他高容量废物(二氧化碳、酸性飞灰、生物固体)一起中和。赤泥的处理将使美国和其他地方的大型赤泥处理区重新植被和环境恢复成为可能。为此目的有益地利用二氧化碳、飞灰和生物固体将降低几个行业对环境的影响。存在使用数百万吨二氧化碳或飞灰中和赤泥的可能性，而不是排放到大气中或在垃圾填埋场处置。铝冶炼每年排放的高达785%的二氧化碳可能会在中和目前储存的赤泥的过程中被隔离。该项目还将在可持续环境管理领域为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.