预加热-碳热还原-磁选法提取煤矸石中的铁

Extraction of Iron from Coal Gangue by Preheating， Carbon Thermal Reduction and Magnetic Separation

摘要:

中国是全球最大的煤炭生产与消费国之一，每年的煤炭生产及消费总量平均达到3×10⁸ t。目前，我国累计堆积煤矸石总量已达5×10⁹ t，其中规模较大的矸石山有1 900座，占用土地15×10⁷ m²，并且每年以1.5×10⁸—2.0×10⁸ t的速度递增。如果能找到科学的利用方法，将这些大量存在的煤矸石变废为宝，则会产生重大的经济效益。煤矸石资源综合利用在中国尚处于发展阶段，主要集中在建筑材料领域方面，如制砖、生产水泥和其他建筑材料。此外，煤矸石也被用于发电和化工领域，如提取氧化铝和白炭黑等，但提取技术和利用率有限。目前，亟需开发煤矸石高值化的应用技术，以进一步提高其利用价值。煤矸石中除了含有大量硅铝外，还含有一定量的硫铁矿。考虑到铁的市场价值，可以采用碳热还原的方法还原出铁单质。然而，煤矸石中的碳大多以有机物的形式存在，不仅还原无法起到作用，还会在加热过程中导致煤矸石粉末黏连，以至于影响到铁的回收率。因此，提出先在空气气氛中焙烧煤矸石，以去除其中的有机物并将硫铁矿氧化为氧化铁，然后在焙烧后的物料中加入适量的碳，在氮气气氛中高温焙烧还原出铁粉，最后采用磁选法提取磁性铁。最佳还原条件为空气氛围中1 000 ℃下预焙烧1 h，再在氮气气氛中1 100 ℃下碳热还原1.5 h，其中碳氧摩尔比为2.0，煤矸石粒度为48 μm。经过碳热还原后，TFe的回收率达到71.3%。除铁后的煤矸石含铁量低，适合做分子筛，以及掺杂于水泥、砖瓦、路基填料等，增加这些材料的强度。

Abstract:

China is a major producer and consumer of coal， with an average annual total coal production and consumption of around 300 million tons. China has accumulated a total of 5 billion tons of accumulated gangue， including more than 1 900 large-scale gangue hills， occupying 15 000 hectares of land， and this amount is increasing at a rate of 150 million to 200 million tons per year. If this vast amount of coal gangue can be scientifically utilized， it will thansform waste into valuable resources， generating significant economic benefits. The resource utilization of coal gangue is currently in the development stage in China. Its comprehensive utilization of coal gangue mainly focuses on its use as a raw material for building materials， such as brick making， cement production， and other building materials. Coal gangue is also used in power generation and chemical industries， such as extracting alumina and white carbon black， but the technology and utilization rate are limited. It is necessary to develop and apply high-value technology for coal gangue to further enhance its utilization value. Besides containing a large amount of silicon aluminum phase， coal gangue also contains some pyrite. Considering the market value of iron， carbon thermal reduction can be used to reduce the elemental iron. The carbon in coal gangue mostly exists in the form of organic matter， which not only fails to play a reducing role， but also causes the coal gangue powder to adhere during the heating process， thereby affecting the iron recovery rate. Therefore， this article first calcines coal gangue in an air atmosphere to remove organic matter and oxidize pyrite to iron oxide. Then， an appropriate amount of carbon is added to the calcined material， and nitrogen is used as a protective gas for high-temperature calcination to reduce iron powder. Finally， magnetic iron is selected by magnetic separation. The optimal reduction condition is： 48 μm coal gangue is used， air calcination temperature is 1 000 ℃， holding time is 1 h， carbon oxygen molar ratio is 2.0， N₂ atmosphere carbon thermal reduction calcination temperature is 1 100 ℃， calcination time is 1.5 h， after carbon thermal reduction， the recovery rate of TFe reached 71.3%. Due to its low iron content， the coal gangue after iron removal is suitable for use as molecular sieve， cement， brick and tile， roadbed filler， etc.， which increases the strength of the material.