Recovery and Resource Utilization of Valuable Metals from Copper Tailings
ZHANG Wenjie1,2
ZHANG Jing1,2
XIE Feng1,2,3
LV Xiangwen1,2,3
XU Anxun1,2
LIANG Yiqiang1,2
1.Kunming Metallurgical Research Institute Co.,Ltd.,Kunming650031,China
2.Yunnan Provincial Key Laboratory of New Technologies in Metallurgy,Kunming650031,China
3.Faculty of Land Resources Engineering,Kunming University of Science and Technology,Kunming650093,China
Citations
ZHANG Wenjie,ZHANG Jing,XIE Feng,LV Xiangwen,XU Anxun,LIANG Yiqiang. Recovery and resource utilization of valuable metals from copper tailings[J]. Copper Engineering,2025(6):110-120.
Abstract
Copper, a non-ferrous metal, is widely used in various industries due to its excellent physical and chemical properties. The main source of copper is from mining, and a large number of tailings are produced after the beneficiation process to enrich copper. The accumulation of tailings in tailings ponds not only occupies land but also causes serious pollution to the surrounding environment due to the residual reagents and heavy metal ions in the tailings. The annual maintenance and management costs of tailings ponds also bring significant economic pressure to enterprises. Improving the comprehensive utilization rate of copper tailings and achieving large-scale consumption of them are important measures to recycle metal resources and eliminate environmental threats. This paper detailed the current status of comprehensive recovery and utilization of resources such as S, Fe, and Cu in copper tailings, and compared the action mechanisms and advantages and disadvantages of different recovery methods. At the same time, it elaborated on the current status of resource utilization of copper tailings in building materials, microcrystalline glass, ceramics, mine filling based on the action mechanisms and application approaches. On this basis, it also summarized the future development direction of comprehensive utilization of copper tailings, providing reference for the development of this field.
铜作为重要的有色金属,被广泛应用于国防工业、电气、机械制造和建筑工业等领域。铜具有优异的理化性质,其消耗量仅次于铝[ ZHANG L M,WANG Y Y,LI Y,et al. Application of copper for sufficient metal extraction from zinc leaching residue:process optimization and copper reuse[J]. Minerals Engineering,2024,214(15):108763. 1]。随着铜需求量不断增加,传统铜矿山被大量开采,贫、细、杂的原矿石逐渐成为铜的主要来源,进而产生大量的尾矿和废石[ ZHANG C H,SU Y H,HE T S,et al. The role of copper ions in improving the flotation of chalcopyrite at low temperatures[J]. Minerals Engineering,2025,220:109091. WANG L,WANG M J,ZOU Y C,et al. Amorphous silica effects on copper flotation:a kinetic and selectivity investigation[J]. Powder Technology,2024,448:120327. 2-3]。
根据资料统计,工业上每生产1 t铜金属,便伴随产生400 t的废石和尾矿。 2021年中国产生的铜尾矿达3.92亿吨,占全国尾矿产量的27.63%,仅次于铁尾矿[ CHEN W,YIN S H,ZHOU G M,et al. Copper recovery from tailings through bioleaching and further application of bioleached tailings residue:comprehensive utilization of tailings[J]. Journal of Cleaner Production,2022,332:130129. 4]。大量的铜尾矿堆存于尾矿库中,不仅占用大量土地,尾矿中残留的药剂和重金属离子还会对周边环境造成严重污染,尾矿库每年的维护管理费用也给企业带来较大经济压力[ PEI T R,ZHENG Y,WANG Y L,et al. Utilization of copper tailings in the preparation of low-calcium Portland cement clinker and carbonation-hardening mechanism[J]. Construction and Building Materials,2024,457:139362. CHEN S C,CAO M Y,LIN W T,et al. Strength and microstructural development in concrete pavements by blended copper tailings powder and copper tailings sand[J]. Materials Today Communications,2024,41:110933. CHEN S H,GAO M C,LIN W T,et al. Study on the performance of highly doped copper tailings sand for concrete pavements using specific grading techniques[J]. Minerals Engineering,2024,216(15):108836. 5-7]。因此,提高尾矿的综合利用率,从源头降低尾矿的堆存量,具有重要的意义。相较于国外,目前国内的尾矿综合利用率较低,国外对铜尾矿的资源化利用技术较成熟,注重“无废、无尾工艺”的应用。随着绿色环保和资源综合利用意识的不断提升,中国对尾矿的综合利用越来越重视,相继出台关于大宗固废利用的政策,加快推进尾矿资源的综合利用[ CHENG Y,QI R F,HOU J H,et al. Feasibility study on utilization of copper tailings as raw meal and addition for low carbon Portland cement production[J]. Construction and Building Materials,2023,382:131275. 8]。
由于不同铜矿山的铜矿成分差异显著,且不同矿山企业的选矿工艺也存在差异,这就导致不同铜尾矿主要成分复杂且差异较大,不同铜矿区尾矿主要成分见表1[ 谭波,张冬冬,宁平,等. 铜尾矿综合利用研究进展[J]. 化工矿物与加工,2021,50(2):46-51. 9]。由表可知,铜尾矿的主要成分为SiO2,Fe2O3,Al2O3,CaO和MgO等,根据成分含量的差异,可分为高硅、高铁、高铝和高钙镁铜尾矿,这种成分差异直接影响其资源化利用途径,使得不同类型铜尾矿适用于制备不同的建筑材料。除此之外,铜尾矿泥化严重,且嵌布粒度细,在前期选矿作业中,磨矿细度的差异导致不同矿物的嵌布关系复杂,结构复杂,这些因素为铜尾矿综合利用增加了一定的难度[ 王璐瑶,刘胜,刘广义,等. 铜矿浮选捕收剂研究进展与展望[J]. 铜业工程,2024(3):69-84. LIU S H,LI Q L,SONG J W. Study on the grinding kinetics of copper tailing powder[J]. Powder Technology,2018,330:105-113. 李天霞,张晓峰,张适合,等. 河北某铜尾矿综合回收铜的选矿试验研究[J]. 有色金属(选矿部分),2019,(2):17-22. 10-12]。
表1 不同矿区的铜尾矿主要成分
Table 1 Main components of copper tailings in different mining areas (%,mass fraction)[ 谭波,张冬冬,宁平,等. 铜尾矿综合利用研究进展[J]. 化工矿物与加工,2021,50(2):46-51. 9]
Fig. 1 Process of flotation of sulfur concentrate from copper tailings[ 郭灵敏,洪建华,曹喜民. 选铜尾矿综合回收铜硫铁试验研究[J]. 铜业工程,2015 (6): 17-21. 19]
在浮选作业中,除了单质硫外,对于易选磁黄铁矿和黄铁矿等硫化矿物,可以通过氧化焙烧将其分解成FeS,进一步氧化后产生SO2,经过催化氧化后制成H2SO4,硫的整体回收率超过95%[ 刘俊,王代军,龚文琪. 从铁尾矿中综合回收铜硫精矿的试验研究[J]. 矿冶工程,2008 (1): 40-42. 20]。Lei等[ LEI C,YAN B,CHEN T,et al. Comprehensive utilization of lead-zinc tailings,Part 1:pollution characteristics and resource recovery of sulfur[J]. Journal of Environmental Chemical Engineering,2015,3(2):862-869. 21]以某铜尾矿为研究对象,通过氧化焙烧脱除尾矿中的硫,研究表明在温度为400 ℃、气固比为1.7 L/g的条件下充分氧化焙烧,最终脱硫率达到99%,产生的SO2能用于制备硫酸。该工艺相较于浮选法能实现尾矿的脱硫和硫资源回收再利用。研究发现,磁黄铁矿在惰性氛围中焙烧,分解速率受产生的SO2扩散速率影响,当温度升到一定高温时,磁黄铁矿能以Fe-O-S低温共融体的形式存在[ 夏飞龙. 高硫高硅铝土矿焙烧脱硫及溶出性能研究[D]. 贵阳:贵州大学,2019. 22]。硫化矿物焙烧物相的转变受温度、反应时间及氧浓度等因素影响,焙烧氛围的改变也会导致反应产物变化,如在CO2氛围中磁黄铁矿能分解成Fe3O4,Fe2O3,CO和SO2等[ 陈文亮,刘占华,丁银贵,等. 某铜冶炼渣综合回收铜、铁工艺研究[J]. 有色金属(选矿部分),2019 (4): 58-62. 23]。孙昊等[ 孙昊,孙体昌,高恩霞,等. 某硫尾矿磁选精矿直接还原同步脱硫时的脱硫机理[J]. 金属矿山,2012 (6):160-164. 24]以褐煤作还原剂、药剂SH作脱硫剂,将黄铁矿和磁黄铁矿还原成S2,COS,Fe和FeS,同时实现硫和铁的回收。
2.2 铜尾矿回收铁
高铁铜尾渣是重要的二次铁资源,一般采用磁选、摇床重选、还原焙烧、焙烧-磁选等工艺回收。焙烧-磁选是高铁铜尾矿中回收铁的主要方法,具有针对性强、铁回收率高等优势,一般以焦炭、活性炭、无烟煤等作为还原剂[ 杨晓峰,刘双安,宋均利. 某尾矿预富集-磁化焙烧-磁选工艺试验研究[J]. 矿冶工程,2019,39(2): 57-60. ZHANG X L,HAN Y X,SUN Y S,et al. An novel method for iron recovery from iron ore tailings with pre-concentration followed by magnetization roasting and magnetic separation[J]. Mineral Processing and Extractive Metallurgy Review,2020,41(2):117-129. 25-26]。邵爽等[ 邵爽,邢鹏,张文娟,等. 从选铜尾矿中选择性还原回收铁[J]. 工程科学学报, 2019,41(6): 741-747. 27]以煤作还原剂,将其与铜尾矿混合均匀后制成球团,在煤添加量为25%、温度为1200 ℃的条件下焙烧120 min,再经过磁选后,铁精矿品位达到90%,回收率超过95%。对于铁分布于硅酸盐中的铜尾矿,需要提高焙烧温度,增加还原剂用量,以提高铁颗粒的融合。Geng等[ GENG C,WANG H J,HU W T,et al. Recovery of iron and copper from copper tailings by coal-based direct reduction and magnetic separation[J]. Journal of Iron and Steel Research International,2017,24(10):991-997. 28]以含铁橄榄石(Fe2SiO4)、钙铁辉石(CaFeSi2O6)的铜尾矿为研究对象,采用还原-磨矿-磁选的工艺进行回收,在煤添加量为30%、石灰添加量为25%的条件下与铜尾矿混合均匀焙烧,最终铁精矿品位达90.1%,回收率达87.3%,涉及的化学反应如式(1~5)所示。
C+2O2=2CO2
式(1)
Fe3O4+CO=3FeO+CO2
式(2)
FeO+CO=Fe+CO2
式(3)
Fe2SiO4+CaCO3+CO=2Fe+CaSiO4+2CO2
式(4)
Fe2SiO4+2CO=2Fe+SiO2+2CO2
式(5)
除了化石原料作焙烧还原剂外,H2和CO等气态还原剂也被用于还原焙烧。H2作还原剂时,铜尾矿中铁的氧化物会由点至面聚集在球团表面,而以H2-CO作还原剂时,颗粒表面会形成气体通道,促进铁氧化物物相的转变[ ZHANG H Q,CHEN G H,CAI X,et al. The leaching behavior of copper and iron recovery from reduction roasting pyrite cinder[J]. Journal of Hazardous Materials,2021,420:126561. 29]。
虽然用火法焙烧+磁选法回收铁效果显著,但能耗较高,易产生SO2等气体,造成二次污染。传统选矿技术依靠矿物的物理性质进行分离,能降低处理成本。Wang等[ WANG L G,CHEN J Z,LI B C,et al. Experimental study on comprehensive recovery of iron from copper flotation tailings[J]. Non-ferrous Metals,2011(4):16-18. 30]从含有赤铁矿和褐铁矿的铜尾矿中回收铁,采用弱磁选赤铁矿,尾矿再磨后经强磁选回收磁性弱的铁矿物,最终从含铁14.5%的铜尾渣中,生产出品位为44.2%的铁精矿,回收率为53%。铜尾矿粒径对磁选富集铁有直接影响,当0.0374~0.075 mm的粒径占比>60%时,磁选无法有效富集铁,需要进行富集预处理[ WANG L G,CHEN J Z,LI B C,et al. Experimental study on comprehensive recovery of iron from copper flotation tailings[J]. Non-ferrous Metals,2011(4):16-18. 30]。
陶恒畅等[ 陶恒畅,郭超华,毛富邦. 内蒙古某铜尾矿再选试验研究[J]. 黄金,2021,42(10):83-86. 32]以内蒙古某铜品位为0.14%的铜尾矿为研究对象,研究发现该尾矿中铜主要分布于+0.045 mm粒级中,并与磁黄铁矿和脉石连生,采用预选脱泥-粗粒再磨-浮选回收的工艺流程(图2),以38号黄药+Y-89作捕收剂、石灰+六偏磷酸钠作调整剂,在最佳工艺条件下,获得铜精矿品位为19.01%、回收率为34.2%。Lü等[ LÜ C C,WANG Y L,QIAN P,et al. Separation of chalcopyrite and pyrite from a copper tailing by ammonium humate[J]. Chinese Journal of Chemical Engineering,2018,26(9): 1814-1821. 33]在铜尾矿浮选试验中,以腐殖酸钠作调整剂,在最佳条件下产出铜精矿品位为19.92%、回收率达84.3%。
图2 尾矿选铜工艺流程
Fig. 2 Process flow of copper separation from tailings[ 陶恒畅,郭超华,毛富邦. 内蒙古某铜尾矿再选试验研究[J]. 黄金,2021,42(10):83-86. 32]
2.4 铜尾矿回收其他金属
铜尾矿中通常含有其他少量有价金属,常见的有W,Ni,Co和Mn等,具有较高的回收价值。
邱显扬等[ 邱显扬,王成行,胡真,等. 从选铜尾矿中综合回收铜铋钨试验研究[J]. 有色金属(选矿部分),2011(4):19-22. 34]对铜尾矿中Cu,Bi和W等金属进行富集回收,通过对有价金属的嵌布关系进行分析,采用全浮选工艺分别回收铜精矿、铋精矿和钨精矿,在最佳工艺条件下,Cu回收率为35.8%、Bi回收率为40.6%、W回收率为53.9%。该项研究已经在实际生产中得到应用,为铜尾矿中复杂低含量有价金属的回收提供了重要参考。除此之外,崔立凤等[ 崔立凤. 从铜尾矿中回收白钨的选矿试验研究[J]. 中国钨业,2014,29(2):8-12. 35]对铜尾矿采用先脱硫再选钨的工艺,在铜尾矿粒径-0.075 mm占比75%的条件下,采用一粗两精两扫的工艺脱硫,产出品位为48.9%、回收率为98.2%的硫精矿,浮选尾矿再经过两粗五精两扫的工艺富集钨,最终钨回收率超过80%。除了传统浮选工艺回收有价金属外,湿法酸浸对嵌布复杂、氧化率高、品位低的铜尾矿效果更佳。Chen等[ CHEN T,LEI C,YAN B,et al. Metal recovery from the copper sulfide tailing with leaching and fractional precipitation technology[J]. Hydrometallurgy,2014,147:178-182. 36]回收低品位硫化铜尾矿中的Cu,Fe,Zn和Mn时,采用硫酸浸出工艺。在硫酸质量浓度为0.24 mg/L、固液比(g/mL)为1∶2的条件下,对铜尾渣进行常温浸出,再分步沉淀回收。Xie等[ XIE Y T,XU Y B,YAN L,et al. Recovery of nickel,copper and cobalt from low-grade Ni-Cu sulfide tailings[J]. Hydrometallurgy,2005,80(1/2):54-58. 37]以硝酸+硫酸在常温常压下浸出含Ni和Co的铜尾矿,在最佳浸出条件下,Ni,Co和Cu的浸出率分别为91.5%,54.6%和85%。湿法浸出后的铜尾矿,有价金属溶解进入浸出液中,再通过萃取剂P204,P507,Cyanex272,P350和N235等实现不同金属的选择性分离。
水泥生产中添加含Si,Ca的脉石矿物作原料,主要成分与铜尾矿相似。 铜尾渣作为水泥原料时,能有效提高水泥强度。Zhang等[ ZHANG C S,ZHOU T T,WU Q S,et al. Mechanical performances and microstructures of cement containing copper tailings[J]. Asian Journal of Chemistry,2014,26(5):1371-1375. 38]对比了不同铜尾矿添加量对水泥强度的影响。试样表面添加铜尾矿,产生C-S-H凝胶与Ca(OH)2胶结在一起,对原本有空隙的浆体进行了有效填充,从而使水泥密度增加,抗压强度和抗弯强度均有明显增加。然而,当铜尾矿添加量超过15%,水泥质量下降,这主要是由于浆体中的空隙有限,一旦填满之后,会影响铜尾矿的抗压强度和抗弯强度。除此之外,铜尾矿的添加还能增加水泥的吸水率和抗酸蚀性。有研究表明,水泥中掺杂5%的铜尾矿时,在高温炉煅烧过程中,能降低烧结成分,更利于生产[ 陈杜娟,王志丰,王婷霞. 某尾矿综合回收选矿实验研究[J]. 矿产综合利用,2021(1):104-108. 39]。
3.1.2 混凝土的生产
除了在水泥生产中的应用,铜尾矿还能替代混凝土中部分砂石,减少生产成本。在控制添加比例的同时,可提升混凝土的抗压强度和透水性。林海威等[ 林海威,张水兵,谢建斌. 铜尾矿粉透水混凝土性能研究[J]. 混凝土,2018(5):157-160. 40]以云南某铜选矿厂的浮选尾矿作混凝土添加剂,发现添加5%细磨后的尾矿,混凝土的抗压强度达24.5 MPa,随着铜尾矿的持续掺入,抗压强度则会下降。铜尾矿提升混凝土的性能主要是由于其粒径小,通过掺杂搅拌均匀后,能改善孔径分布,对混凝土结构的密实度有促进效果。除此之外,铜尾矿还能改良混凝土的机械强度和耐磨性,减缓重金属离子和Cl−的释放、渗透。Onuaguluchi等[ ONUAGULUCHI O,EREN Ö. Cement mixtures containing copper tailings as an additive: durability properties[J]. Materials Research,2012,15(6): 1029-1036. 41]将超细铜尾矿作混凝土添加剂,在添加量为5%时,虽然对混凝土的凝结时间、孔隙率和坍落度等有负影响,但显著提升了抗压强度、耐磨性并抑制了重金属离子的释放。Zhang等[ ZHANG Y X,SHEN W G,WU M M,et al. Experimental study on the utilization of copper tailing as micronized sand to prepare high performance concrete[J]. Construction and Building Materials,2020,244:118312. 42]以铜尾矿作添加剂改性混凝土,研究表明当铜尾矿添加量为20%时,混凝土的抗压强度和抗氯离子渗透能力均有明显提升,并且在毒性浸出实验中发现,原铜尾矿中的重金属离子被固封在混凝土中,难以溶出。铜尾矿中含量较高的SiO2,CaO和Al2O3等物质,经过预处理后,能替代传统钙、硅质矿原料,并且具有高抗拉强度等优势,可减少应用中出现裂缝的问题。
胶状玻璃体自身结构不稳定,需要掺入添加剂改善其网络结构强度,从而提高免烧砖强度。铜尾矿中含有Si,Fe和Al等氧化物,可用于免烧砖的制备。Fang等[ FANG Y H,GU Y M,KANG Q B,et al. Utilization of copper tailing for autoclaved sand-lime brick[J]. Construction and Building Materials,2011,25(2):867-872. 43]以铜尾矿为原料制备免烧砖,对比分析了不同添加量的铜尾矿对砖抗压强度的影响,研究结果表明,未添加铜尾矿时砖的强度为24.3 MPa,在铜尾矿添加量为40%时,砖的强度依然有23.8 MPa,符合国家产品质量要求。冯启明等[ 冯启明,王维清,张博廉,等. 利用四川某铜矿尾矿制作轻质免烧砖的工艺研究[J]. 中国矿业,2010,19(12):90-92,95. 44]将水泥、石灰、废弃聚苯泡沫粒与铜尾矿按一定比例混合均匀后,制备出免烧砖,在铜尾矿用量为70%~80%时,砖的抗压强度为3.6~10.4 MPa,达到应用标准。
尾矿制备微晶玻璃已经成为研究热点,如铁尾矿、粉煤灰、煤矸石、高炉渣等已经被作为制备不同功能微晶玻璃的原料,具有良好的应用前景和经济效益[ 廖力. 利用铜矿尾矿制备微晶玻璃试验研究[J]. 矿产综合利用,2017(6):82-85. DAI W B,LI Y,CANG D Q,et al. Effects of sintering atmosphere on the physical and mechanical properties of modified BOF slag glass[J]. International Journal of Minerals,Metallurgy and Materials,2014,21(5):494-502. 45-46]。铜尾矿中含有的SiO2,CaO,K2O,Na2O和Al2O3等成分与微晶玻璃相似,也可用作制备微晶玻璃的原料。
以铜尾矿为原料制备微晶玻璃的过程中,熔融温度对微晶玻璃黏度和流动性均有显著影响,有研究表明,熔融温度为1180 ℃时,高Ca、低Si铜尾矿熔融法制备的CaO-MgO-Al2O3-SiO2四元系微晶玻璃有更好的流动性,更利于后续晶化[ ZHANG K,LIU J W,LIU W C,et al. Preparation of glass-ceramics from molten steel slag using liquid-liquid mixing method[J]. Chemosphere,2011,85(4):689-692. 47]。此外,高温熔融制备微晶玻璃时,能将铜尾矿中的Fe2SiO4还原成Fe单质,并凭借比重差异实现分离,更利于微晶玻璃表面主晶相的增大。Shi等[ 施麟芸,毛佩林,刘松柏, 等. CaO-MgO-Al2O3-SiO2系铜尾矿微晶玻璃析晶特征研究[J]. 硅酸盐通报,2020,39(5):1645-1649. 48]以硅质量分数为72.4%的铜尾矿作为制备微晶玻璃的原料,将Fe3O4和Cr2O3作为微晶核剂制备CaO-MgO-Al2O3-SiO2四元系微晶玻璃,试验结果表明,通过压延法,在控制温度为900 ℃下进行热处理,最终形成透辉石为主晶相、结构致密的微晶玻璃,具有较高的应用价值。罗冰[ 罗冰. 四川某铜尾矿释硫-选铁-制备微晶玻璃及机理研究[D]. 绵阳:西南科技大学,2021. 49]将释硫、提铁后的铜尾矿制备CaO-SiO2-Fe2O3系磁性微晶玻璃,试验将CaO作添加剂与铜尾矿混合,并在不同温度下烧结,考察不同CaO添加量对磁性微晶玻璃性能的影响。 结果表明,随着焙烧温度升高,磁性微晶玻璃的饱和磁化率(Ms)下降,并且随着CaO的添加量(0%,5%和10%)增加,微晶玻璃的磁化率下降,这主要是由于Ca2+和Fe3+半径较大,更易占据空穴较大的b位,从而导致原子磁矩差降低。不同焙烧温度对磁性微晶玻璃磁化率的影响如图3所示。
图3 不同温度下微晶玻璃的磁化曲线
Fig. 3 Magnetization curves of glass-ceramics at different temperatures: (a) 0% CaO;(b) 5% CaO;(c)10% CaO[ 罗冰. 四川某铜尾矿释硫-选铁-制备微晶玻璃及机理研究[D]. 绵阳:西南科技大学,2021. 49]
铜尾矿充填矿山采空区的方案也被广泛研究和应用,如贵州金川、彝良矿业、云锡等矿区已将铜尾矿用作填充物。在充填过程中,需要添加早强剂、减水剂、纤维材料等物质,以提高膏体的流动性和尾矿充填的强度。影响尾矿充填的因素主要包括:胶凝材料、尾矿颗粒大小、外加剂和周围环境等[ 李翠平,黄振华,阮竹恩,等. 金属矿膏体流变行为的颗粒细观力学作用机理进展分析[J]. 工程科学学报,2022,44(8):1293-1305. ERCIKDI B,KESIMAL A,CIHANGIR F,et al. Cemented paste backfill of sulphide-rich tailings:importance of binder type and dosage[J]. Cement and Concrete Composites,2009,31(4):268-274. 56-57]。常见的凝胶材料包括水泥、石灰、高水材料或硅灰等,与尾矿混合后输送至矿山采空区,经一定时间固结后形成一定强度的胶结体[ LI X B,DU J,GAO L,et al. Immobilization of phosphogypsum for cemented paste backfill and its environmental effect[J]. Journal of Cleaner Production,2017,156:137-146. 58]。对于交通不便和资源相对匮乏的矿山区域,除了考虑凝胶材料的性能,还需要考虑经济成本。实际工业应用中,常将粉煤灰、废玻璃、矿渣等废弃物替代水泥等凝胶材料,以降低处理费用。但对于高硫铜尾矿,需要重视尾矿中硫化物对充填体的腐蚀作用,大量研究发现过高的硫化物会降低充填体强度[ 程绍凯,李文博,韩跃新. 东鞍山浮选尾矿预富集—磁化焙烧—磁选试验研究[J]. 金属矿山,2021 (5): 91-95. 59]。Kesimal等[ KESIMAL A,YILMAZ E,ERCIKDI B. Evaluation of paste backfill mixtures consisting of sulphide-rich mill tailings and varying cement contents[J]. Cement and Concrete Research,2004,34(10):1817-1822. 60]研究发现,尾矿中硫化物易与凝胶材料发生反应,生成CaSO4等,增加充填体间的孔隙率,从而影响强度。对于胶凝时间较长的尾矿,需要添加Na2O·nSiO2,C6H8O7和NaSiO3等外加剂,以加快胶凝材料的水化反应速率,改善充填体孔隙结构。李茂辉等[ 李茂辉,杨志强,王有团,等. 粉煤灰复合胶凝材料充填体强度与水化机理研究[J]. 中国矿业大学学报,2015,44(4):650-655. 61]研究发现,NaSiO3配合适量碱性物质,能减少尾矿中酸性硫化物对充填体的腐蚀,明显改善尾矿充填体的性质。
植被修复铜尾矿的关键在于植物能耐受高浓度重金属离子的恶劣环境。目前用于铜尾矿改良修复的植被包括:紫羊茅、大麦、桉树、印度芥菜、香根草、黑麦草、国槐、红合欢花和紫花豌豆等,均能在贫瘠且重金属离子严重污染的土壤中良好生长[ PADMAVATHIAMMA P K,LI L Y. Phytoremediation technology:hyper-accumulation metals in plants[J]. Water Air and Soil Pollution,2007,184(1):105-126. ASENSIO V,VEGA F A,ANDRADE M L,et al. Tree vegetation and waste amendments to improve the physical condition of copper mine soils[J]. Chemosphere,2013,90(2):603-610. 徐德聪,孙庆业,沈章军,等. 铜尾矿库剑叶金鸡菊根际尾矿和植株的重金属元素含量及相关分析[J]. 植物资源与环境学报,2018,27(1):27-36. 周少燕. 三种豆科植物对铜尾矿矿砂的抗性及修复潜力研究[D]. 南昌:江西财经大学,2017. 马超. 蜀葵、黑心菊对铜尾矿的耐性及铜污染环境的修复研究[D]. 南昌: 江西财经大学,2015. 64-68]。但单独依靠植被改良修复尾矿库效率较低且效果一般,为提高尾矿的改良修复效果,通常添加改良剂至尾矿中,通过吸附、络合、沉淀、氧化还原等反应,改变重金属离子价态或存在形式,降低其有效性和移动性,达到最终的改良目的[ 郝秀珍,周东美,薛艳,等. 天然蒙脱石和沸石改良对黑麦草在铜尾矿砂上生长的影响[J]. 土壤学报,2005,42(3):434-439. 69]。目前,铜尾矿的改良修复多采用植被与改良剂搭配使用,常见的铜尾矿改良剂种类分为:无机型、有机型、复合型。无机改良剂有石灰类、磷酸盐类、黏土矿物和工业废弃物(粉煤灰等),其中石灰类改良剂可提高土壤pH,将重金属离子转变成氢氧化物,磷酸盐类改良剂可通过溶解-沉淀固化Pb。有机改良剂包括农作物秸秆、家禽粪便和污泥等,富含大量腐殖酸,通过络合作用降低有毒重金属离子的活性[ TAPIA Y,CASANOVA M,CASTILLO B,et al. Availability of copper in mine tailings with humic substance addition and uptake by Atriplex halimus[J]. Environmental Monitoring and Assessment,2019,191(11):651. TAN W N,LI Z A,QIU J,et al. Lime and phosphate could reduce cadmium uptake by five vegetables commonly grown in south China[J]. Pedosphere,2011,21(2):223-229. 鲁洪娟,周德林,叶文玲,等. 生物有机肥在土壤改良和重金属污染修复中的研究进展[J]. 环境污染与防治,2019,41(11):1378-1383. 70-72]。Ruben等[ FORJÁN R,ASENSIO V,RODRÍGUEZ-VILA A,et al. Contribution of waste and biochar amendment to the sorption of metals in a copper mine tailing[J]. Catena,2016,137: 120-125. 73]研究发现腐殖酸能促进铜尾矿中Cu2+向香根草根部迁移,但对Zn2+影响较小。复合改良剂一般是将有机和无机改良剂混合使用,如堆肥+生物炭、磷酸氢二铵+石灰石、造纸厂污泥+石灰等,以此来改良铜尾矿中pH,以及TC和TN的含量。
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