【作者】 刘万超；

【导师】 杨家宽； Sharif Jahanshahi；

【作者基本信息】 华中科技大学 ， 环境工程， 2010， 博士

【摘要】 赤泥是从铝土矿中提取氧化铝之后的废渣。赤泥产量大、颗粒小、碱度高,目前以筑坝堆存为主,容易造成环境污染及安全事故。赤泥综合利用是一项世界性难题。本文以中国铝业公司山东企业第二氧化铝厂产生的拜耳法赤泥为研究对象,在详细分析赤泥样品基本性质的基础上,提出了先粒径分级预处理然后回收利用的技术路线,重点针对分级后细赤泥的利用问题展开了研究。论文在两种不同还原气氛下制得海绵铁与磁铁矿,并在这两种还原气氛下分别开展了碱石灰烧结实验研究。对拜耳法赤泥高温烧结过程进行了模拟和实验分析,探讨了烧结气氛、体系组成对体系相产物及铁铝钠回收率的影响规律。(1)在系统分析了赤泥中主要元素和矿物在不同粒径颗粒中的分布规律后,提出了赤泥可以分为两部分进行回收利用：粒径大于0.075 mm的粗赤泥,粒径小于0.075mm的细赤泥。其中,粗赤泥可以通过磁选或重选工艺富集赤铁矿,粗砂用作建材；细赤泥可用于回收铁、铝、钠,残渣用于建材生产。(2)拜耳法赤泥单独回收海绵铁的初步探索实验表明,焙烧温度1300℃,炭粉：赤泥为18：100,添加剂：赤泥为6：100,焙烧时间110 min时,磁选精矿中总铁含量达到89.05%,金属化率96.98%,回收率81.40%。细赤泥联合回收铁铝的初步探索实验表明,在1100℃左右的焙烧条件下,Al的回收率可以达到80%,但精矿中铁的含量和铁的回收率仅为34.46%和45.83%。烧结温度的提高有利于获得较高的铁回收率和铁矿质量,但过高的温度不利于铝钠的回收。(3)以磁铁矿为目标产物的拜耳法赤泥还原烧结实验表明,以煤焦为还原剂,煤焦用量为赤泥质量的0.4%-0.5%,1000℃焙烧1h,可以得到磁铁矿为主的尖晶石结构固溶体。在该还原条件下,碱石灰焙烧后Al和Na的溶出率分别为75.74%和88.42%,赤泥中钠回收率为80.70%。残渣经磁选后,铁回收率和精矿总铁分别为50.01%,50.29%。溶出渣中的Na2O含量较低(1.55%),有利于后续资源化利用。(4)应用MPE (Multi Phase Equlibrium)热力学模拟计算软件对拜耳法赤泥高温烧结过程进行了模拟分析,并对模拟数据进行了实验验证。不同还原气氛下的赤泥焙烧过程的模拟结果表明,体系的平衡产物主要包括铝硅酸钠(Na2Al(Al,Si)O4)、黄长石((Ca, Na)2(Al, Mg, Fe2+)[(Al, Si)SiO7])、尖晶石(包括磁铁矿(Fe3O4)和铝尖晶石(FeAl2O4)及其固溶体)、赤铁矿(Fe2O3)、方铁矿(FeO)及单质铁(Fe)等,其中尖晶石、赤铁矿、方铁矿及单质铁的产生有赖于体系的还原气氛。1000℃时,氧分压在1×10-5atm至1×10-13 atm之间时,可以保持尖晶石的稳定。实验结果表明,样品中的尖晶石为磁铁矿(Fe304)、铝尖晶石(Fe(Fe,Al)2O4)和钛铁尖晶石(Fe(Fe,Ti)2O4或(Ti,Fe)Fe2O4)的固溶体,可以验证模拟结果。模拟和实验分析表明,氧化钙和氧化钠的适量加入将降低尖晶石类矿物的稳定性,还原气氛有利于铝的回收。体系中的钙硅比与铝硅酸钠体系中的硅含量及铝硅酸钠中铝和钠的溶出性能之间存在相关性,体系中CaO的加入可以降低铝硅酸钠体系中的硅含量,提高铝和钠的溶出率；Na2O的增加可以降低尖晶石固溶体中铝尖晶石的含量,从而有利于提高铝的溶出率和铁精矿的质量。850℃-1000℃温度范围内时,体系的平衡产物为铝硅酸钠、斜硅钙石、尖晶石等。拜耳法赤泥先经粒径分级预处理,粗赤泥经物理处理分离铁矿和粗砂,细颗粒采用还原碱石灰烧结联合回收铁、铝、钠,低碱残渣用于生产建材,可以实现赤泥的零排放。反应气氛及体系组成对赤泥碱石灰烧结体系相转变及铁铝钠回收影响的研究将为实现拜耳法赤泥的零排放奠定一定的理论基础。更多还原

【Abstract】 Bauxite residue, or red mud, is the largest environmental concern of alumina refineries mainly because of the fine particle sizes of this waste stream and its caustic nature. This waste presents serious problems for storage and potential environmental pollution. The treatment and utilization of high volume red mud waste has been a major challenge for the alumina industry.For this study, the Bayer red mud sample was supplied by the No.2 alumina plant of Shandong Aluminum Company, a branch of Chinalco. Based on analysis on elements and mineral phase distributions in red mud particles with different sizes, the thesis proposed that, the separation pretreatment of red mud by particle sizes was beneficial to red mud utilization. The study focused on the recovery of Al, Na and Fe from fine red mud with soda-lime roasting under reductive atmosphere. Both of direct reductive iron (DRI) and magnetite were considered as desirable products in different reductive atmospheres. Optimizing experiments for soda-lime roasting and leaching processes were carried out. The reductive soda-lime roasting process of Bayer red mud at high temperature was modeled, and the effect of PO2 and composition of the system on phase transformation and recovery of Fe, Al and Na were discussed.(1) Based on the distributions of elements and mineral phases in red mud particles with different sizes, the thesis proposed that, the red mud sample can be divided into two parts, i.e. bulk red mud particles, with particle sizes above 0.075 mm, and fine red mud particles, with sizes below 0.075 mm. Iron ore and sand can be separated out from the bulk red mud with physical beneficial technologies. Fe, Al and Na can be recovered from fine red mud particles.(2) The optised conditions for DRI recovery from red mud are sintering temperature of 1300℃,110 min, with 18 g carbon and 6 g addition for 100 g red md. Under these conditions,81.40% Fe was recovered from red mud with 89.05% of total Fe contents (TFe). When the samples were roasted at 1100℃, over 80% Al were concentrated into the solution, however, the TFe and recovery ratio of Fe were 34.46% and 45.83%, respectively. A serial of experimental results showed that, the temperature requirements of recovery of Fe and Al were much different.(3) For recovery of magnetite from the fine red mud, the coal char was used as reductive agent. When the fine red md was roasted with coal char (0.4-0.5 g/100 g red mud) at 1000℃for 1h, spinel can be obtained as one of main phases. Under optimized soda-lime roasting and leaching conditions, the extraction of Al and Na were 75.74% and 88.42%, respectively. And 80.70% of Na in raw red mud was recovered. After magnetic separation of leached residue,50.01% of Fe was concentrated with TFe of 50.29% in concentrate. In separated residue, the content of Na was 1.55%, which would be available for production of building materials.(4) The roasting process was modeled with MPE (Multiphase Equilibrium), a thermodynamics modeling software. Some experiments were carried out to verify the modeling results. The modeling results showed that, the equilibrium phases in reductive roasting system are sodium aluminosilicate (NaAl(Al, Si)O4), melilite ((Ca, Na)2 (Al, Mg, Fe2+) [(Al, Si)SiO7]), spinel (including the solid solution of Fe3O4 and FeAl2O4), hematite (Fe2O3), wustite (FeO) and metallic Fe. The existing of iron containing phases depends on the atmospheres of the system. The PO2 (Partial Pressure of O2) should be kept between 1.0 x 10-5 atm and 1.0×10-13 atm to make the spinel phase stable in the system. Experiments proved that the spinel phase in samples were solid solution of aluminous spinel (Fe (Fe, Al)2 O4), ulvite ((Fe (Fe, Ti)2O4, or (Ti, Fe) Fe2O4)), as well as magnetite (Fe3O4). The results were agreed with MPE results.The soda-lime roasting processes of the Bayer red mud were also modeled. The calculated results showed that, the addition of CaO and Na2O in limited ranges can decrease the stability of spinel phase. And the addition of CaO may decrease the Si contents in sodium aluminosilicate, as well as the addition of Na2O decrease the Al content in spinel. The temperature range of 850℃-1000℃is suitable for the formation of desirable phases i.e. sodium aluminosilicate, larnite and spinel. However, the reaction velocity will be slow.After pretreating of Bayer red mud, iron ore and sand can be separated from the bulk red mud. Fe, Al and Na can be recovered from the fine red mud, and the residue can be used for producing building materials. The study on effects of reaction atmospheres and compositions of the system on phase transformation and recovery of Fe, Al and Na will be a theory foundation for realization of zero waste of Bayer red mud.更多还原