【作者】 刘智勇；

【导师】 杨天足； 刘志宏；

【作者基本信息】 中南大学 ， 有色金属冶金， 2012， 博士

【摘要】 低品位氧化锌矿选矿富集困难,碱性脉石含量高,采用火法及酸性体系湿法工艺处理,能耗高、回收率低、废弃物多。氨—铵盐—水体系浸出,因其选择性强,氨与有价金属离子配合而促进浸出,是处理这类资源较为适宜的工艺。本文研究了氧化锌矿,特别是硅酸盐类矿物在NH3-(NH4)2SO4-H2O体系中的浸出机理,研究结果不仅在学术上弥补了这一领域基础研究的不足,也可为实际浸出工艺开发提供理论指导和基础数据。以天然异极矿和人工合成硅锌矿纯矿物为研究对象,综合运用XRD、FT-IR、XPS、SEM、EDS、TGA-DSC、ICP-AES等检测技术,研究了这些矿物在NH3-(NH4)2SO4-H2O体系中的溶解平衡、溶解速率和浸出机理,得到如下主要结论。(1)根据物质守恒、同时平衡及电中性原理,建立了Zn2SiO4-NH3-NH4+-H2O体系的热力学模型,通过对模型计算求解,绘制了体系中各组元浓度变化的热力学关系图。图示结果表明,[NH3]与[NH3]T摩尔比为0.5时,体系中[Zn]T最大,且随总氨浓度的增加而增大。总氨浓度为5mol/L,[NH3]与[NH3]T摩尔比为0.5时,无定形Si02在该体系中的溶解度为0.11g/L,其过饱和析出的pH值范围为7.16～12.68,受无定形Si02溶解度低的限制,在上述条件下体系中[Zn]T只能达到27.88g/L,远低于ZnO在该体系中的溶解度。(2)异极矿在NH3-(NH4)2SO4-H2O体系可以浸出。浸出时Zn-O-Zn键断裂后,Si-O双四面体从异极矿晶体架构中脱离形成无定形Si02。无定形二氧化硅单独形核,并未对异极矿表面形成包裹。(3)实验证实,当[NH3]与[NH3]T摩尔比为0.5时,锌浸出速率最高；在总氨浓度5mol/L,[NH3]与[NH3]T摩尔比0.5,固液比20g/L,温度35℃,搅拌速度350r/min,浸出150min时,锌的浸出率可达95%,而纯氨水和纯硫酸铵溶液中锌的浸出率只有2%；高固液比下,由于溶液中[Zn]T达到饱和,锌浸出率会大幅度下降。(4)在固液比20g／L、总氨浓度5mol/L、[NH3]与[NH3]T摩尔比0.5、搅拌速度350r/min的条件下,研究了-100-+160目的异极矿在NH3-(NH4)2SO4-H2O体系中浸出的动力学。结果表明,异极矿在NH3-(NH4)2SO4溶液中的浸出过程可用Elovich方程进行描述,浸出反应的表观活化能为55.42kJ/mol,属表面化学反应控制,这与浸出机理研究所得结论一致。(5)实验发现,异极矿和湿化学法合成的硅酸锌在不同温度下煅烧2h,均可获得结晶度不同的正交晶系的硅锌矿(β-Zn2SiO4)和三方晶系的菱面体晶硅锌矿(α-Zn2Si04)。硅锌矿的晶体结构及结晶度对其在NH3-(NH4)2SO4-H2O体系中的浸出效果有显著影响。在温度35℃、固液比20g/L、总氨浓度5mol/L、[NH3]与[NH3]T摩尔比0.5、搅拌速度350r/min的条件下浸出120min,β-Zn2SiO4的结晶度为29.88%和60.11%时锌的浸出率分别为86.66%、42.14%,α-Zn2SiO4结晶度为99%和100%时锌的浸出率分别为10.13%、6.4%,β-Zn2SiO4比α-Zn2SiO4容易浸出。(6)a-硅锌矿在浸出时,锌与硅同时溶解进入溶液,但Si02在体系中溶解度较小,过饱和后以无定形水合二氧化硅形态单独形核析出,由于其析出速度缓慢,抑制了锌的浸出。(7)在固液比5g/L、总氨浓度5mol/L、[NH3]与[NH3]T摩尔比0.5、搅拌速度350r/min的条件下,研究了-140～+160目的结晶完整的α-硅锌矿在NH3-(NH4)2SO4-H2O体系中浸出的动力学。其浸出过程特征符合多孔颗粒粒子模型,浸出过程的表观活化能为67.93kJ/mol,表明浸出过程受孔隙扩散控制,这与实验现象是一致的。更多还原

【Abstract】 Low grade zinc oxide ores containing high content of alkaline gangues, which are difficult to concentrate by minerals dressing, are inadequate to be treated by pyro-or acidic hydro-metallurgical process due to its high energy consumption, low recovery and large waste disposal. The combination of ammonia and ammonium salt solutions is a powerful lixiviant to treat this kind of ores. As the high selectivity, as well as the coordination of ammonia with valuable metallic ions is helpful to encourage the leaching process. In this paper, leaching mechanisms in ammoniacal solutions of zinc silicate minerals, such as hemimorphite and willemite, were investigated in NH3-(NH4)2SO4-H2O system, and the results obtained could not only fill the research gaps, but also provide theoretical instructions and basic data for the development of practical leaching processes.Comprehensively using XRD, FT-IR, XPS, SEM, EDS, TGA-DSC and ICP-AES, dissolution equilibrium, leaching mechanism and rates of pure natural hemimorphite and synthetic willemite minerals in NH3-(NH4)2SO4-H2O solution were investigated. The main conclusions were as follows:(1) The thermodynamic model of Zn2SiO4-NH3-NH4+-H2O system was established based on the laws of mass conservation, charge balance and simultaneous equilibrium principle. Then the thermodynamic diagrams regarding concentrate variations of different species in the system were plotted. The results showed that the highest [Zn]T in the system was obtained under the condition of [NH3]/[NH3]t molar ratio equal to0.5, where the higher the [NH3]T, the higher the [Zn]T. Under the conditions of [NH3]T5mol/L,[NH3]/[NH3]T molar ratio0.5, the solubility of amorphous SiO2in the system was as low as0.11g/L, and with the dissolution of zinc silicate, amorphous SiO2would soon supersaturate and precipitate from the solutions in the pH range of7.16～12.68. Owing to the limitation of low solubility of amorphous SiO2,[Zn]T under the conditions mentioned above was merely27.88g/L, which was far bellow that of ZnO in the system.(2) Hemimorphite can leach in NH3-(NH4)2SO4-H2O system. During the leaching process, the Zn-O-Zn bond broke and the Si-O double tetrahedron would detach from the hemimorphite crystal structure to form amorphous SiO2-Amorphous SiO2forms nuclei independently and would not coat the surfaces of hemimorphite.(3) Experimental results showed that the highest leaching rate of hemimorphite was obtained at [NH3]/[NH3]T molar ratio equal to0.5. Under the conditions of [NH3]/[NH3]T molar ratio0.5,[NH3]T5mol/L, S/L ratio20g/L, temperature of35℃and stirring rate350r/min, the leaching efficiency of zinc could reach as high as95%, while that is only2%of leaching hemimorphite in pure ammonia or ammonium salt systems under the same conditions. Zinc leaching efficiency of hemimorphite decreased sharply at high S/L ratio, due to [Zn]T in the system reaching saturation.(4) The leaching kinetics of hemimorphite in NH3-(NH4)2SO4-H2O system was studied under the conditions of S/L20g/L,[NH3]/[NH3]T molar ration0.5,[NH3]T of mol/L and stirring rate350r/min. The results showed that the leaching kinetics can be described by Elovich equation and the activation energy of hemimorphite of-100～+160mesh is55.42kJ/mol, where the controlling step was surface reaction in accordance with the conclusion obtained in the leaching mechanism study.(5) Experimental results showed that both crystal structure and crystallinity have significant effects on the leaching of willemite in NH3-(NH4)2SO4-H2O system. Both hemimorphite and the chemically synthesized willemite can turn to β-Zn2SiO4and a-Zn2Si04with different crystallinity after calcinations for2h at different temperatures. The leaching efficiencies of zinc for β-Zn2Si04with the crystallinity of29.88%and60.11%were86.66%and42.11%, respectively, while the leaching efficiencies of zinc for a-Zn2Si04with the crystallinity of99%and100%were10.13%and6.4%, individually, under the conditions of temperature35℃, S/L ratio50g/L,[NH3]/[NH3]T molar ratio0.5,[NH3]T5mol/L, stirring rate350r/min and leaching time120min. The leaching of β-Zn2SiO4was easier than that of a-Zn2Si04regardless of crystallinity.(6) During the leaching process of a-Zn2SiO4, zinc and silica in willemite were found to be dissolved simultaneously into the solution, which was followed by the precipitation of amorphous silica. The solubility of silica in the NH3-(NH4)2SO4-H2O system was very low with a saturated concentration of0.3g/L. In addition, the precipitation rate of dissolved silica in the leaching solution was found to be significantly slow, which lead to the difficulty of willemite leaching in the NH3-(NH4)2SO4-H2O system, especially at a low liquid/solid ratio.(7) The leaching kinetics of a-Zn2Si04of-100+160mesh with complete crystallinity in NH3-(NH4)2SO4-H2O system was studied under the conditions of S/L ratio5g/L,[NH3]/[NH3]T0.5,[NH3]T5mol/L and stirring rate350r/min. The results showed that the leaching kinetics can be described by porous particle model and the activation energy is67.93kJ/mol, which shows the controlling step is pore diffusion, and this agreed with the experimental phenomenon.更多还原