二次酸浸法提取煤灰中的氧化铝(英文)

Aluminum extraction from coal ash by a two-step acid leaching method

目的:煤灰渣酸浸提铝通常效率不高,主要因为灰渣中存在含铝晶体矿物(如莫来石、尖晶石和长石等)。为解决含铝晶体不易与硫酸反应的问题,本文提出二次酸浸提铝法。创新点:基本实现铝硅分离,第一步酸浸实现非晶态铝的浸出,残渣经焙烧和水浸后,第二步酸浸实现剩余铝的浸出。方法:1.一次酸浸时,硫酸直接与煤灰渣反应浸出部分氧化铝,提铝残渣加碳酸钠焙烧后,含铝晶体遭到破坏;2.焙烧产物经水浸溶解出硅酸钠,水浸残渣做X射线衍射分析表明其主要为铝硅非晶体活性物质,此时可用硫酸在温和条件下浸出剩余的铝。结论:1.一次酸浸提铝在10 mol/L硫酸、120°C、2 h和1:2固液比的条件下,铝浸出率为81.72%;2.用5 mol/L硫酸二次酸浸时,20°C下铝浸出率已经达到87.31%,100°C下更是达到99.06%;3.综合两次酸浸结果,铝的浸出总效率在97%以上。

To improve aluminum extraction efficiency, a two-step acid leaching process was proposed to dissolve aluminum and aluminum-bearing crystals with sulfuric acid. The first leaching residue （FLR） was obtained through direct leaching of coal ash with sulfuric acid. After roasting a mixture of the FLR and sodium carbonate, the aluminum-bearing crystals in FLR were com- pletely destroyed while sodium silicate was generated. Then the roasted products were leached with water to dissolve the sodium carbonate. X-ray diffraction （XRD） analysis indicated that the water leaching residues （WLR） mainly contained the amorphous phase, which allowed easy aluminum extraction in the second leaching step. In the first leaching test with 10 mol/L sulfuric acid at 120℃ in 2 h and a solid to liquid ratio （S/L） of 1：2, aluminum dissolution from raw coal ash reached 81.72%. In the second leaching step with 5 mol/L sulfuric acid, the aluminum dissolutions from WLR were 87.31% at 20 ℃ and 99.06% at 100℃. Total aluminum dissolutions were more than 97%. Moreover, the leaching process produced two by-products, sodium silicate solution and amorphous silicon dioxide, which contained nearly all the silicon from the coal ash.