烧结协同处置铬渣和含铁粉尘的基础和技术研究

The disposal of chromium slag has always been a worldwide problem. Similarly, a large amount of iron, carbon-bearing dusts are produced in the steel plants but not utilized effectively. The sintering-ironmaking process is always applied to utilize the two kinds of solid wastes, but there still exist some problems hard to overcome, such as incomplete detoxification of hexavalent chromium and low disposal efficiency. In order to solve these problems, a novel technical idea of “co-processing chromium slag and iron, carbon-bearing dusts by sintering process” is proposed. At first, the chromium slag and iron, carbon-bearing dusts are made into composite pellets (as pellet part), and the rest of iron ore fines, fluxes and fuels are granulated into coarse particles (as matrix part). Then, the pellet and matrix parts are mixed and put onto the sintering machine to roast. At high temperature, the chromium-bearing compounds are directly reduced to metallic chromium or chromium carbide by the carbon contained in the pellets during the sintering process, completing the detoxification of chromium slag by one step. In this project, the laws of phase transformation and thermodynamic behavior of Cr, C, Fe components in the composite pellets during the sintering are discovered, and the external field conditions for chromium-containing compounds being directly reduced to metallic chromium are clarified. The technical prototype of coprocessing chromium slag and iron, carbon-bearing dusts via sintering is built based on the above investigations. This project may provide a new method for effectively utilizing the chromium slag and iron, carbon-bearing dusts in a large scale, moreover, new burdens are produced for blast furnace ironmaking chromium-bearing hot metal by this new process.

铬渣的处置利用一直是世界性的难题。与此同时，钢铁厂产生的大量含铁含碳粉尘也未得到高效利用。目前，烧结法是处置这两种固废较常采用的方法，但烧结过程仍存在处理量小、六价铬还原解毒不完全等问题难以克服。为此，申请人提出烧结协同处置铬渣和含铁粉尘的新思路：首先将铬渣和粉尘制成复合球团，其他铁料、焦粉、熔剂等制成基体料，再将复合球团“植入”基体料层，布到烧结机上联合焙烧。本项目巧妙的利用联合焙烧过程中，复合球团内固体碳在高温条件下的还原作用使含铬化合物直接还原为金属铬或碳化铬，一步实现铬的彻底解毒。本项目通过揭示联合焙烧过程复合球团中铬、铁、碳等组分转化的热力学行为和相变规律，确定球团中含铬化合物直接还原为金属铬或碳化铬的外场条件，开发烧结法协同处置铬渣和含铁粉尘的新技术。本项目完成后，可为铬渣和含铁粉尘的清洁、高效利用提供新途径，为高炉冶炼含铬铁水提供新炉料。

铬渣的处置利用一直是世界性难题，钢厂产生的大量含碳粉尘也未得到高效利用。烧结法是处置这两种固废的常用方法，但直接添加到烧结过程仍存在处理量小、六价铬还原解毒不完全等问题难以克服。本项目系统开展了烧结协同处置铬渣和含碳粉尘的理论与新技术研究，获得的主要创新点及结论如下：.（1）查明了模拟烧结条件下铬渣-含碳粉尘复合球团中主要组分还原热力学及相变规律。铬渣中含铬组分碳热还原的优先顺序为：Na2CrO4（或CaCrO4）＞FeCr2O4＞Cr2O3＞CaCr2O4＞MgCr2O4＞NaCrO2。Cr(Ⅲ)组分不能被CO还原，而当温度大于1129 oC，Cr(Ⅲ)可被固体C还原至零价。在C/O摩尔比1.5、焙烧温度1350 oC、时间2min时，铬尖晶石、铬酸钙中的铬被还原为零价铬的占比分别为16.65%和67.01%，而其余铬则以Cr(Ⅲ)形式存在于尖晶石相中。（2）阐明了铬渣-含碳粉尘复合球团对联合焙烧过程的影响规律。采用复合造块工艺，铬渣-含碳粉尘球团配加量不宜超过20%，优化条件下复合烧结矿的转鼓强度比常规烧结矿提高了近10个百分点，烧结固体燃耗降低10%以上。（3）揭示了复合烧结矿的成矿机制及高温冶金性能变化规律。复合烧结矿的基体料以复合铁酸钙（SFCA）液相固结为主，SFCA与尖晶石相形成镶嵌结构；复合球团部分的边缘熔化明显，与基体料紧密连接构成整体。优化条件下，复合烧结矿中2.76%的铬被还原至合金态，其余铬则以(Mg, Fe)(Cr, Al)2O4的形式存在于尖晶石相或以Cr(Ⅲ)存在于液相中。复合烧结矿中铬含量的提高改善了其还原性，但会使高温软熔区间变宽，这对高炉软融带产生一定不利影响。浸出毒性分析表明，复合烧结矿中未发现六价铬，不存在二次污染风险。.新工艺可有效解决铬渣和含碳粉尘的无害化、大规模利用难题，实现Cr、Fe、C等有用组分的资源化利用，市场应用前景广阔。新工艺推广应用后，将对我国钢铁工业和铬工业的持续健康发展意义重大，助力“双碳”战略目标实施。