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尾矿是世界上最大的工业固体废物之一。钢铁行业的飞速发展产生了大量铁尾矿,截至2013年底,我国累积了5.00×109 t铁尾矿[1]。这些铁尾矿不仅污染了土地和水体,还威胁着人群健康[2]。同时,随着选矿技术的进步和可开发利用矿产资源的减少,铁尾矿的资源化利用已成为缓解铁矿供需矛盾的可行途径。
目前,对铁尾矿大多采取无害化和资源化处理两条路径。一是将重金属从铁尾矿中分离出来。YE等[3]利用生物浸出从铁尾矿中回收Pb(4.12%)和Zn(97.85%);SIRKECI等[4]利用浮选技术从铁尾矿中分离Co(83.1%)、Ni(57.7%)和Cu(59.0%)。另一途径是直接对铁尾矿进行资源化利用。WANG等[5]在铁尾矿中添加高岭土和飞灰制烧结砖;LI等[6]以铁尾矿为原料,采用泡沫凝胶法制备了高孔隙率(89%)、高强度、低导热率(导热系数0.032 W·(m·K)−1)的多孔砖;HU等[7]通过铁尾矿、K2CO3和KOH混合950 ℃烧结制备缓释硅肥,但该方法将重金属固定在了硅肥中。上述方法都会将重金属元素固定在产品中,存在二次暴露的风险,潜在危害性高[8]。生物浸出和浮选也存在微生物生存条件苛刻的难题[3],浮选产生的二次污染处理[4]等会导致工业化管理成本提高。因此,开发出更适合工业化处理铁尾矿重金属污染的技术是十分必要的。
一般来说,金属氯化物的沸点较氧化物的低,因此,氯化焙烧能够在较低焙烧温度下有效分离去除固体废物中的重金属[9]。LI等[10]在添加4% CaCl2、温度1 050 ℃、时间2 h的条件下,通过氯化焙烧回收氰化尾矿中的Au(91.6%)和Ag(54.7%)。YU等[11]以MgCl2·6H2O为氯化剂,在Cl与飞灰质量比为0.15、温度1 000 ℃条件下,对生活垃圾飞灰进行焙烧,结果发现,Cd和Pb挥发率接近100%。氯化焙烧相对于氧化焙烧,能够在较低温度下将重金属挥发[11]。氯化焙烧工艺在固体废物分离回收重金属中具有较好的效果,但目前很少有关于氯化焙烧在回收和安全处理铁尾矿方面的应用研究。铁尾矿作为亟需处理并可资源化的固体废物,在氯化焙烧分离重金属上值得进行深入研究。考虑到固体氯化剂更易控制Cl的添加量从而控制尾气污染,多数学者选择固体氯化剂来进行氯化焙烧。CaCl2的氯含量高、价格低廉[12]、释放HCl的能力比NaCl和KCl强[13],因此,CaCl2是最为常用的氯化剂之一。
本研究以CaCl2为氯化剂对铁尾矿进行氯化焙烧,研究不同焙烧温度和CaCl2添加量对Pb、Cu和Cd挥发率的影响;并利用X射线荧光分析(XRF)、热重分析(TG)、X射线衍射(XRD)和扫描电子显微镜(SEM)探究焙烧前后铁尾矿的基本特性和晶相结构的变化,从而了解在氯化焙烧过程中的物相和元素转变机理。本研究结果可为铁尾矿的无害化处理和资源化利用提供参考。
CaCl2氯化焙烧分离铁尾矿中的重金属铅铜镉
Separation of lead, copper, cadmium in iron tailings by CaCl2 chlorination roasting method
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摘要: 为实现铁尾矿中铅(Pb)、铜(Cu)、镉(Cd)与铁(Fe)、铝(Al)、硅(Si)等氧化物的分离,以CaCl2为氯化剂对铁尾矿进行氯化焙烧,探究焙烧温度和CaCl2添加量对Pb、Cu和Cd挥发率的影响,并采用X射线荧光和X射线衍射等方法研究铁尾矿的基本特性和晶相结构。结果表明,足够的Cl含量是氯化焙烧挥发铁尾矿中Pb、Cd的保证,而Cu的挥发需要更高的温度和CaCl2添加量。最佳氯化焙烧条件为温度1 000 ℃、CaCl2添加量为10%,此时Pb、Cd和Cu的挥发率分别为97.80%、96.57%和79.80%,焙烧渣的主要成分与铁尾矿相比变化不大。铁尾矿中的Ca、S和SiO2经过氯化焙烧后以CaSO4和Ca2SiO4形式残留在焙烧炉渣中,而Cl在焙烧渣中没有观察到。焙烧渣的重金属浸出浓度符合国家标准(GB 5085.3-2007)。Abstract: In order to separate lead, copper and cadmium from iron, aluminum, silicon and other oxides in iron tailings. Using CaCl2 as the chlorinating agent, the influence of temperature and CaCl2 content on the volatilization ratio of hazardous Pb, Cu, and Cd was investigated in the study. The basic characteristics and crystal structure of iron tailings were analyzed using X-ray fluorescence and X-ray diffraction et al. The results show that the contents of Pb, Cd and Cu in iron tailings are 2 230.04, 6.44 and 4 568.00 mg·kg−1, respectively. Sufficient chlorine content is the guarantee for chlorination roasting to remove Pb and Cd from iron tailings. Cu is more dependent on high temperature and CaCl2 addition. With the optimum chlorination roasting conditions at 1 000 °C with 10% of CaCl2, the volatilization ratio of Pb, Cd and Cu were 97.80%, 96.57% and 79.80%, respectively, and the main components of roasted slag have little change compared with iron tailings. Ca, S and SiO2 in iron tailings remain in the roasting slag in the form of CaSO4 and Ca2SiO4 after roasting in chlorination, while Cl hardly observed in the roasting slag. The leaching concentrations of heavy metals in the roasting slag is below the national standards (GB 5085.3-2007).
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Key words:
- iron tailings /
- heavy metal /
- chlorination roasting /
- harmless /
- solid waste
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表 1 铁尾矿的主要化学成分
Table 1. The main chemical composition of iron tailings
化学成分 含量/% 化学成分 含量/% Fe2O3 58.45 P2O5 0.14 SiO2 15.78 PbO 0.13 Al2O3 8.36 CaO 0.09 SO3 3.35 WO3 0.05 K2O 0.40 As2O3 0.05 MgO 0.32 Cr2O3 0.04 CuO 0.38 V2O5 0.01 TiO2 0.23 Bi2O3 0.02 MnO 0.32 ZrO2 0.01 ZnO 0.21 表 2 不同焙烧条件下焙烧渣的浸出毒性
Table 2. Leaching toxicity of the roasting slags under different conditions
mg·L−1 焙烧条件或数据来源 Zn Cu Ni Pb 600 ℃,10%CaCl2 0.017 3 − − − 800 ℃,10%CaCl2 − − − − 1 200 ℃,10%CaCl2 − − − − 1 000 ℃,未添加CaCl2 0.224 0 3.857 6 − 1.146 0 1 000 ℃,5%CaCl2 0.012 1 0.079 1 − − 1 000 ℃,10%CaCl2 − − − − 1 000 ℃,20%CaCl2 − − − − 未处理(铁尾矿原矿) 3.470 0 30.290 0 0.012 0 13.190 0 浸出标准限值a 100 100 5 5 注:“−”表示未检出;a限值来源于GB 5085.3-2007[30]。 -
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