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含铜原料在熔炼过程中会释放大量重金属,熔炼原料中所含的锌、铜、铅、锰等重金属在氧化气氛和高温环境中,加上烟气中SO2的作用,容易形成ZnO、CuO、PbO、MnO等氧化物,并以大气为介质迁移到地下水和土壤等,对周边环境造成威胁[1-2]。国务院办公厅印发了《禁止洋垃圾入境推进固体废物进口管理制度改革实施方案》[3],其中包括限制铜精矿、铜锍和废铜的进口,禁止铜冶炼渣、冶炼烟尘、含铜污泥等的进口。为引导进口高品质含铜原料,研究进口含铜原料熔炼过程污染物释放特征变得尤为重要。
目前,国内对于进口含铜原料的处理方式多为在高温还原气氛下火法熔炼。火法熔炼是炼铜最重要的过程,即在1 000~1 250 ℃高温下,使铜原料和熔剂在熔炼炉内进行熔炼,炉料中的铜、硫及未氧化的铁形成硫铁铜共熔体,炉料中的SiO2、Al2O3、CaO、FeO一起形成液态炉渣[4]。其中,温度和熔剂是影响含铜原料熔炼过程重金属释放的2个重要因素[5-6]。温度主要通过改变重金属的饱和蒸汽压力影响其挥发迁移,重金属的蒸汽压随温度的升高而增大,从而提高其挥发效率[7-9]。柴桢[10]提出,废杂铜熔炼过程保持炉内温度在1 250 ℃左右,可在保证铜的回收率的同时提高杂质元素的去除效率。周凯等[11]研究了进口再生铜材冶炼烟气中的重金属,控制冶炼温度在1 200 ℃以下可有效控制烟气中杂质元素的挥发。另外,熔炼等高温状态下的重金属的挥发行为也受气体组分的影响,石英熔剂的添加能与重金属元素形成不同化合价态的硅酸盐等不易挥发物,从而能够在去除含铜原料中杂质的同时降低熔炼烟气中各类重金属的产生[12-13]。熔炼过程中,Fe/SiO2的含量对炉渣性质起决定作用,通过提高炼铜弃渣的SiO2含量和熔炼温度会降低铜氧化物在炉渣中的溶解度[14]。
目前,全面禁止进口废物政策实施后,尚缺乏基于进口含铜原料特性及熔炼工艺等对于熔炼过程重金属释放特征的相关研究。本研究将从不同温度和不同熔剂条件出发,在实验室采用高温管式炉模拟进口铜精矿、铜硫、铜转炉渣和含铜污泥的熔炼过程,比较其熔炼烟气中重金属的释放特性,以探寻进口含铜原料熔炼的最佳温度和熔剂添加比例,以期为我国进口含铜原料熔炼烟气中重金属污染源控制以及海关对于含铜原料的高效监管提供基础数据支撑。
典型进口含铜原料熔炼烟气中重金属的释放特性
Release characteristics of heavy metals in smelting flue gas of typical imported copper-bearing raw materials
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摘要: 为了解我国进口含铜原料熔炼烟气中重金属的释放特性,以近年进口申报的铜精矿、铜锍、铜转炉渣和含铜污泥4种典型含铜原料为研究对象,通过高温管式炉模拟研究不同含铜物料、熔炼温度、熔剂添加比例等条件下,熔炼烟气中重金属的释放特性。结果表明,4种进口含铜原料熔炼烟气中As、Pb质量分数较高,进口铜精矿和含铜污泥熔炼烟气重金属质量分数高于进口铜锍和铜转炉渣;熔炼温度从1 000 ℃升至1 300 ℃时,铜精矿和铜锍熔炼烟气中Zn、Cu、As、Pb等重金属的质量分数随着温度的升高而增加,Mn的质量分数随温度升高变化不大;熔剂添加比例由0增至18%时,铜精矿熔炼烟气中Zn、As的质量分数分别降低了28%、44%,Mn、Cu和Pb质量分数变化不大,进口铜锍熔炼烟气中Zn质量分数减少了85.2%,As的质量分数则随熔剂添加比例的增加而增加。本研究结果可为进口含铜原料熔炼烟气中重金属减排提供参考。Abstract: To understand the release characteristics of heavy metals in the melting flue gas of imported copper-bearing raw materials in China, four typical copper-containing materials, namely copper concentrate, copper matte, copper converter slag, and copper-bearing sludge, were imported in recent years as research objects, and the distribution characteristics of heavy metals in the melting flue gas was studied by high-temperature tube furnace simulation under the conditions of different copper-containing materials, melting temperatures and melt addition ratios. The results showed that the four imported copper-bearing raw materials contain high As and Pb mass fractions in smelting flue gas, imported copper concentrate and copper-containing sludge smelting flue gas has a higher concentration of heavy metals than imported copper matte and copper converter slag; the mass fractions of Zn, Cu, As and Pb in the melting flue gas of copper concentrate and copper matte increased with the increase of temperature when the melting temperature increased from 1 000 ℃ to 1 300 ℃, and the mass fractions of Mn did not change significantly with the increase of temperature; when the flux addition ratio is increased from 0 to 18%, the mass fractions of Zn and As in copper concentrate and copper matte smelting flue gas decreased by 28% and 44% respectively, while the mass fractions of Mn, Cu and Pb does not change much, the mass fractions of Zn in the flue gas of imported copper matte smelting decreased by 85.2%, while the mass fractions of As increased with the increase of flux addition ratio. This study can provide a reference for the reduction of heavy metals in the smelting flue gas of imported copper-bearing raw materials.
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表 1 进口含铜样品的元素组成
Table 1. Elemental analysis of imported copper samples
%(质量分数) 供试样品 Cu Fe S Si As Zn Pb Ca Al Mn 其他 铜精矿 30.10 23.49 14.84 2.56 1.33 1.08 1.15 0.81 0.68 0.09 23.94 铜锍 33.38 15.15 12.46 8.37 4.79 1.59 0.61 0.31 0.41 0.13 22.90 铜转炉渣 16.70 39.39 5.21 4.72 - 1.87 0.47 - 0.64 0.05 30.95 含铜污泥 29.71 21.48 1.81 1.48 - 1.03 0.25 4.97 2.55 - 36.72 -
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