-
随着中国城市化进程加快,对铁矿石的需求量也不断增加,但中国的铁矿资源多数依靠进口[1-2]。中国是钢铁生产大国,国内铁矿石品位低、结构复杂、难选,导致高品质铁矿石严重短缺。过去几年 (2008-2022年) ,中国铁矿石进口量从4.4×108 t增加到11.7×108 t,外部依赖性逐年增大[3]。铁矿石的长期供应压力,已经成为中国钢铁工业可持续发展的重大隐患。
据统计,中国铁尾矿总堆存量超过1×1010 t[4],每年新增约6×108 t,利用率低,铁尾矿平均总铁品位达11%以上[1],但过去部分矿山采用“粗放式开采、选富弃贫”的方式,使部分尾矿中总铁品位甚至高达30%左右。由于技术限制,铁尾矿一般在尾矿库堆填,这样既造成了大量的土地浪费,也对周围生态环境造成了极大破坏[5-6]。
磁化焙烧技术是指将物料或矿石在一定的气氛条件下加热进行化学反应,选择性地使弱磁性铁矿物转变为强磁性的磁铁矿或磁赤铁矿,而脉石矿物磁性几乎不变。通过磁化焙烧人为地增大铁氧化物与脉石矿物的磁性差异,提高铁矿石的可选性,是难选铁矿分选的最有效方法。同时,焙烧过程还能去除矿石中的结晶水、硫、砷等有害杂质,使矿石结构疏松,有利于提高后续磨矿效率。LI等[7]采用碳作为还原剂对铁尾矿进行磁化焙烧,在750 °C、60 min焙烧条件下,磁选后得到铁品位58.6%,铁回收率68.4%的磁精矿;DENG等[8]采用生物质作为还原剂,在650 °C、20 min焙烧条件下,得到铁品位62.04%,铁回收率95.29%的磁精矿;YUAN等[9]使用纯CO还原铁锰矿,在600 °C、20 min焙烧条件下,得到铁品位为68.31%,铁回收率96.34%的磁精矿。当前磁化焙烧的还原剂主要由煤炭、石油等化石能源制备,具有成本高,碳排放强度大,环保落地困难等不足。
印染行业是我国传统支柱产业,据2021年中国环境统计年鉴[10],2020年全国印染废水量达2.06×109 t,居工业行业第三,并产生5.15×106 t (80%含水率计) 印染污泥。其含有毒有机物质,例如染色剂、表面活性剂、添加剂、多环芳烃(PAHs)、持久性有机污染物(POPs)、芳香胺(AAs)和重金属等[11-13]。目前印染污泥主要是厂内锅炉掺烧以及厂外集中焚烧,少量填埋或者烧砖等[14-15],处理过程中的污染控制是印染污泥无害化处理的关键环节。
中国“十四五”规划中,鼓励污泥在实现稳定化、无害化处置前提下,稳步推进污泥能量资源化回收利用。污泥热解产生的不凝性气体主要由CO、CO2、CH4和H2组成,具有强还原性,可作为铁尾矿磁化焙烧的还原剂,此外印染废水混凝沉淀过程中投加的聚合硫酸铁会产生大量含铁高电荷聚合阳离子,例如[Fe(H2O)6]3+、[Fe(OH)x](3−x)+、[Fem(OH)x]n(3m−x)n+等[16],这些多核络合离子能与水以任意比例互溶,发挥电性中和、吸附架桥作用,当溶液的pH值升高后,单核羟基络离子就会生成羟基桥联的多核络合物[17]。印染污泥含铁多核络合物在焙烧的过程中发生热分解,生成Fe2O3。通过与铁尾矿共同磁化焙烧,可实现印染污泥与铁尾矿中铁的高效协同回收。
本研究利用印染污泥热解产生的还原性气体将印染污泥和铁尾矿中的铁资源还原成四氧化三铁,再通过磁选得到铁精矿,研究了焙烧温度、焙烧时间和印染污泥掺烧量对铁品位和回收率的影响及作用机制。有望开辟以废治废,低碳排放的大宗固体废物资源化利用新途径,具有非常重要的理论价值和实际应用前景。
印染污泥与铁尾矿磁化焙烧回收铁资源
Recovery of iron from iron tailings and textile dyeing sludge with co-magnetization roasting
-
摘要: 我国铁尾矿累计堆存量超1×1010 t,主要为难选的赤铁矿、褐铁矿、菱铁矿等,由于脉石矿物组成复杂,重金属等有害杂质含量高,难以直接资源化利用。利用铁尾矿与印染污泥共同磁化焙烧,回收铁尾矿和印染污泥中铁资源,研究了焙烧温度、焙烧时间和印染污泥掺烧量对铁品位和铁回收率的影响及作用机制。最佳焙烧条件为,800 °C、30 min、印染污泥掺烧量15%,对焙烧产物进行120 mT的湿法磁选,得到铁品位63.78%,回收率92.58%的铁精矿。铁尾矿中的针铁矿失水留下孔隙转化为赤铁矿,进而被还原为磁铁矿,其还原路径为FeO(OH)→Fe2O3→Fe3O4。SEM+MAPPING分析结果表明,磁化焙烧后赤铁矿和铝化合物的连生体被破坏,通过磁选可提升铁精矿品位及回收率。本研究可为印染污泥和铁尾矿的协同处理及资源化利用提供参考。Abstract: The accumulated stockpile of iron tailings in China exceeds 1×1010 t, mainly difficult to select hematite, limonite, and rhodochrosite, etc., which are difficult to resource directly due to the complex composition of vein minerals and high content of heavy metals and other harmful impurities. In this study, iron tailings and textile dyeing sludge were co-magnetized and roasted to recover iron resources from iron tailings and textile dyeing sludge, and the effects of roasting temperature, roasting time and the amount of textile dyeing sludge blending on iron grade and iron recovery and the mechanism of action were investigated. The optimum roasting conditions were: 800 °C, 30 min, 15% textile dyeing sludge blending, 120 mT wet magnetic separation of the roasted product, and the iron concentrate with 63.78% Fe grade and 92.58% recovery was obtained. The goethite in the iron tailings lost water leaving pores transformed into hematite, which was then reduced to magnetite with the reduction path of FeO(OH)→Fe2O3→Fe3O4. SEM+MAPPING analysis showed that the congeners of hematite and aluminum compounds were destroyed after magnetization roasting, and the iron concentrate grade and recovery could be enhanced by magnetic separation. This study provides a scientific basis for the synergistic treatment and resource utilization of textile dyeing sludge and iron tailings.
-
Key words:
- magnetization roasting /
- textile dyeing sludge /
- iron tailings
-
表 1 样品化学及成分分析
Table 1. Chemical analysis of the sample
% 组分 TFe Fe2O3 SiO2 Al2O3 SO3 CaO ZnO MnO K2O CuO 铁尾矿 40.35 52.04 28.90 14.79 3.00 0.12 0.18 0.10 0.51 0.24 印染污泥 20.04 40.31 7.48 5.52 46.71 1.33 0.97 0.24 0.11 0.05 表 2 印染污泥有机元素分析及工业分析
Table 2. Textile dyeing sludge organic elemental analysis and industrial analysis
% 组分 C H N O S Mad Aad Vad FCad 含量 22.09 4.27 2.61 16.75 11.03 6.72 59.06 30.72 3.50 注:Mad为水分;Aad为灰分;Vad为挥发分;FCad为固定碳。 -
[1] LI Q, DAI T, WANG G, et al. Iron material flow analysis for production, consumption, and trade in China from 2010 to 2015[J]. J Clean Prod, 2018, 172: 1807-1813. doi: 10.1016/j.jclepro.2017.12.006 [2] ZHOU W, LIU X, LYU X, et al. Extraction and separation of copper and iron from copper smelting slag: A review[J]. J Clean Prod, 2022, 368: 133095. doi: 10.1016/j.jclepro.2022.133095 [3] SUN Y, ZHU X, HAN Y, et al. Iron recovery from refractory limonite ore using suspension magnetization roasting: A pilot-scale study[J]. J Clean Prod, 2020, 261: 121221. doi: 10.1016/j.jclepro.2020.121221 [4] LV X, SHEN W, WANG L, et al. A comparative study on the practical utilization of iron tailings as a complete replacement of normal aggregates in dam concrete with different gradation[J]. J Clean Prod, 2019, 211: 704-715. doi: 10.1016/j.jclepro.2018.11.107 [5] LI S, WU J, HUO Y, et al. Profiling multiple heavy metal contamination and bacterial communities surrounding an iron tailing pond in Northwest China[J]. Sci Total Environ, 2021, 752: 141827. doi: 10.1016/j.scitotenv.2020.141827 [6] WANG P, SUN Z, HU Y, et al. Leaching of heavy metals from abandoned mine tailings brought by precipitation and the associated environmental impact[J]. Sci Total Environ, 2019, 695: 133893. doi: 10.1016/j.scitotenv.2019.133893 [7] LI M, PENG B, CHAI L, et al. Recovery of iron from zinc leaching residue by selective reduction roasting with carbon[J]. J Hazard Mater, 2012, 237-238: 323-330. doi: 10.1016/j.jhazmat.2012.08.052 [8] DENG J, NING X-A, SHEN J, et al. Biomass waste as a clean reductant for iron recovery of iron tailings by magnetization roasting[J]. J Environ Manage, 2022, 317: 115435. doi: 10.1016/j.jenvman.2022.115435 [9] YUAN S, ZHOU W, HAN Y, et al. Individual enrichment of manganese and iron from complex refractory ferromanganese ore by suspension magnetization roasting and magnetic separation[J]. Powder Technol, 2020, 373: 689-701. doi: 10.1016/j.powtec.2020.07.005 [10] 中华人民共和国国家统计局生态环境部. 2021中国环境统计年鉴 [M]. 北京: 中国统计出版社, 2021. [11] CHEN X, NING X-A, LAI X, et al. Chlorophenols in textile dyeing sludge: Pollution characteristics and environmental risk control[J]. J Hazard Mater, 2021, 416: 125721. doi: 10.1016/j.jhazmat.2021.125721 [12] NING X-A, LIN M-Q, SHEN L-Z, et al. Levels, composition profiles and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in sludge from ten textile dyeing plants[J]. Environ Res, 2014, 132: 112-118. doi: 10.1016/j.envres.2014.03.041 [13] ZHOU W, CHEN X, WANG Y, et al. Anaerobic co-digestion of textile dyeing sludge: Digestion efficiency and heavy metal stability[J]. Sci Total Environ, 2021, 801: 149722. doi: 10.1016/j.scitotenv.2021.149722 [14] HAO X, CHEN Q, VAN LOOSDRECHT M C M, et al. Sustainable disposal of excess sludge: Incineration without anaerobic digestion[J]. Water Res, 2020, 170: 115298. doi: 10.1016/j.watres.2019.115298 [15] LIU J, HUANG L, ZOU H, et al. Do FeCl3 and FeCl3/CaO conditioners change pyrolysis and incineration performances, emissions, and elemental fates of textile dyeing sludge?[J]. J Hazard Mater, 2021, 413: 125334. doi: 10.1016/j.jhazmat.2021.125334 [16] CHENG W P. Hydrolysis characteristic of polyferric sulfate coagulant and its optimal condition of preparation[J]. Colloids Surf Physicochem Eng Aspects, 2001, 182(1): 57-63. [17] LIU X, WU Y, XU Q, et al. Mechanistic insights into the effect of poly ferric sulfate on anaerobic digestion of waste activated sludge[J]. Water Res, 2021, 189: 116645. doi: 10.1016/j.watres.2020.116645 [18] SONG Y, HU J, LIU J, et al. CO2-assisted co-pyrolysis of textile dyeing sludge and hyperaccumulator biomass: Dynamic and comparative analyses of evolved gases, bio-oils, biochars, and reaction mechanisms[J]. J Hazard Mater, 2020, 400: 123190. doi: 10.1016/j.jhazmat.2020.123190 [19] DING Z, LIU J, CHEN H, et al. Co-pyrolysis performances, synergistic mechanisms, and products of textile dyeing sludge and medical plastic wastes[J]. Sci Total Environ, 2021, 799: 149397. doi: 10.1016/j.scitotenv.2021.149397 [20] YUAN S, WANG X, ZHANG H, et al. Experimental and mechanism research of the effects of alkali on the reduction reaction of hematite during roasting reduction reaction[J]. Adv Powder Technol, 2022, 33(6): 103592. doi: 10.1016/j.apt.2022.103592 [21] YU J, LI Y, LV Y, et al. Recovery of iron from high-iron red mud using suspension magnetization roasting and magnetic separation[J]. Miner Eng, 2022, 178: 107394. doi: 10.1016/j.mineng.2022.107394 [22] ZHANG Y, LI H, YU X. Recovery of iron from cyanide tailings with reduction roasting–water leaching followed by magnetic separation[J]. J Hazard Mater, 2012, 213-214: 167-174. doi: 10.1016/j.jhazmat.2012.01.076 [23] QIU G, NING X, SHEN J, WANG Y, ZHANG D, DENG J. Recovery of iron from iron tailings by suspension magnetization roasting with biomass-derived pyrolytic gas[J]. Waste Manage, 2023, 156: 255-263. doi: 10.1016/j.wasman.2022.11.034 [24] LI Y, ZHANG Q, YUAN S, et al. High-efficiency extraction of iron from early iron tailings via the suspension roasting-magnetic separation[J]. Powder Technol, 2021, 379: 466-477. doi: 10.1016/j.powtec.2020.10.005 [25] SALAMA W, EL AREF M, GAUPP R. Spectroscopic characterization of iron ores formed in different geological environments using FTIR, XPS, Mössbauer spectroscopy and thermoanalyses[J]. Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy, 2015, 136: 1816-1826. doi: 10.1016/j.saa.2014.10.090 [26] OMRAN M, FABRITIUS T, ELMAHDY A M, et al. XPS and FTIR spectroscopic study on microwave treated high phosphorus iron ore[J]. Appl Surf Sci, 2015, 345: 127-140. doi: 10.1016/j.apsusc.2015.03.209