Technology Principle of Extracting Aluminum from Coal Gangue

Coal gangue, a byproduct of the coal mining process, is the primary solid waste generated in coal-based industries. Large piles of coal gangue are commonly found around mines, causing significant environmental pollution and occupying vast areas of land. The total stockpile of coal gangue in China is estimated to be about 4.5 billion tons [1-2]. This not only poses serious environmental challenges but also represents a major waste of valuable resources. Notably, coal gangue contains a considerable amount of aluminum, with alumina accounting for approximately 25% of its composition [3-4], making it a potential resource for recovery. By utilizing coal gangue, we can address both environmental concerns and resource wastage, transforming waste into a valuable commodity and generating additional economic value [2,6-8]. In this study, coal gangue from a mine in the Zhengzhou area was analyzed and processed. Through multiple experimental trials, an aluminum dissolution rate of up to 89.6% was achieved under optimal conditions, and the purity of the resulting aluminum sulfate reached 95%. These results offer new insights into the development and utilization of coal gangue. The experiment involved several key steps. First, the coal gangue sample, crushed to 40 mesh, was characterized (see Table 1). The equipment used included a muffle furnace, pH meter, electronic balance, grinder, and mixer. The reagents included 1:1 hydrochloric acid, 1:2 sulfuric acid, and aqua regia, as well as reagents for aluminum determination such as 10% sulfosalicylic acid, 0.02 mol/L EDTA, and buffer solutions. The experimental method involved roasting the coal gangue at various temperatures before leaching it with sulfuric acid. Factors such as roasting temperature, leaching time, and acid concentration were tested to optimize the leaching process. Aluminum content was determined using the EDTA titration method. Results showed that the leaching efficiency increased significantly after activation. At temperatures above 500°C, the structure of the gangue changed, leading to improved leaching performance. However, at 1000°C, the formation of new phases reduced the solubility of aluminum. Leaching time also played a crucial role—too short or too long a time resulted in lower dissolution rates. Finally, comparing different acids, sulfuric acid proved more effective than hydrochloric acid, with a higher dissolution rate and lower cost, making it a more economically viable option for industrial use.

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