【作者】 招国栋；

【导师】 吴超； 赵由才；

【作者基本信息】 中南大学 ， 安全技术及工程， 2011， 博士

【摘要】 氧化型含锌危险废物会对环境造成严重的危害,因此无害化、资源化处理氧化型含锌危险废物势在必行,本着改善环境质量,缓解锌需求量急剧增加与锌精矿资源日趋枯竭的矛盾、克服传统湿法提锌工艺的缺陷目的,本论文基于锌的强碱介质选择性浸出、低电解能耗优势,对氧化型含锌危险废物的碱浸—净化—电解—苛化生产金属锌粉技术展开了系统地研究。通过优化浸取条件、彻底净化杂质、高值化电积回收等技术,使碱浸—电解工艺的工业化应用取得良好环境和经济效益,并得到以下主要结论：(1)构建了Zn(Ⅱ)-NaOH-H2O体系热力学模型,在强碱性溶液中,锌是以zn(OH)42-和ZnO22-形式存在的,并确定了锌的平衡浓度与碱浓度的关系,用实验进行验证,测得在不同碱浓度下,锌的平衡浓度计算值和实验值相对偏差的绝对平均值为0.1298%,说明热力学模型是正确的。(2)氧化型含锌废料强碱浸取时,含锌烟灰原料最佳浸出条件为：NaOH浓度6mol/L、温度90℃、浸出时间120min、液固比10：1、颗粒直径100～160目、搅拌速率为300r/min,锌浸出率可达90%以上：ZnCO3原料最佳浸取条件为：NaOH浓度6mol/L、温度90℃、浸出时间120min、液固比10：1、颗粒直径100～160目、搅拌速率450r/min,锌浸出率超过90%；Zn2Si04原料最佳浸取条件为：NaOH浓度8mol/L、温度90℃、浸出时间240min、液固比8：1、颗粒直径100-160目、搅拌速率450r/min,锌浸出率接近85%。浸取参数对锌浸出影响大小的顺序分别为：ZnO原料,R>T>CNaOH>D>t>V；ZnC03原料,R>T>V>D>CNaOH>t；Zn2Si04原料,t>V>T>R>CNaOH>D。(3)含锌烟灰在强碱性溶液中的活化能为42.00kJ/mol、碳酸锌矿的活化能为43.15kJ/mol,表明碱浸取含锌烟尘和碳酸锌矿过程主要受化学反应控制；硅酸锌矿在碱溶液中的浸出过程分为两段,在0～10min内其活化能为13.59kJ/mol,表明在浸取开始段内是受内扩散控制,浸出后端其活化能为31.86kJ/mol,表明浸取后段的过程是受化学反应和内扩散共同控制。(4)硫化钠可选择性定量分离强碱性溶液中的铅锌,并发现硫酸铁、硫酸钠、氧化钙对强碱性溶液中的砷、铝等杂质具有一定的净化作用,以此提出了浸出液深度净化工艺：将浸取液升温到70℃,加入硫化钠,硫化钠的加入量为浸取液中铅含量的1.8倍(质量比),搅拌1.5h；加入硅酸钠,硅酸钠的加入量为每升浸取液1.5g,搅拌1h；加入硫酸铁,硫酸铁的加入量为每升浸取液1g,搅拌1h；再加入石灰,石灰的加入量为硫化钠加入量的0.8倍,搅拌1h；静置4h,过滤,输送入陈化池陈化48小时后电解。(5)对Zn(Ⅱ)-NaOH-H2O体系中锌电积理论分解电压进行了计算,在强碱性溶液中锌电积的理论分解电压为1.728V,比传统硫酸锌溶液锌电积分解电压低0.352V；其锌电积的最佳工艺条件为：电流密度800～1000A/m2,碱浓度180～200g/L,电解温度30-50℃,锌浓度30-40g/L,电流效率可达99%以上,电能耗为2.38kWh/kg锌粉；锌在阴极板上析出时,增加电流密度、降低溶液温度,锌粉从麦穗状向具有更大比表面积的薄片状转变；增大电解液碱浓度,锌粉从薄片状向层状、石块状转变；电解液锌浓度越大,越易形成粒径较大的锌粉。(6)研究了As、Cl-、SiO32-、SO42、CO32-、F-、Al、Pb、 Mg、Fe、Ni、Mn、Ca、Cd、Cr、Cu等对电解金属锌粉的影响,确定电解液中杂质许可的浓度范围。(7)提出了废电解液的苛化处理工艺：在废电解液中加入碱,使碱浓度达到350g/L,通过提高碱浓度使碳酸钠和一些杂质结晶生成沉淀。在沉淀中加入洗渣水等废水,控制苛化液的碱浓度在80-100g/L范围内,碳酸钠的浓度在40g/L以上。苛化工艺参数确定为：氧化钙的加入量为理论值的1.5～1.8倍；温度为90℃；苛化时间为30min；废电解液经过苛化处理后,1m3的废电解液可苛化出约28kg碱,废电解液在经过苛化处理后,废液中的铁、铜、镁、锰、镉、铬等重金属的去除率在10-40%左右,对砷的去除率达到62%,废电解液苛化工艺具有较好的除杂效果。(8)设计了年处理1万吨氧化型含锌危险废料再生加工厂,对磨矿、浸取、净化、电解、锌粉清洗干燥粉碎工艺段的设备进行了最优化设计。根据设计建成的某锌废料再生加工厂锌浸取率达到90%以上,生产的金属锌粉能达到国家锌粉二级标准,运营状况良好。(9)经过碱浸处理的氧化型含锌危险废料变为一般固体废弃物,实现了无害化,对环境的危害大大降低。总之,无论从经济效益、环境效益还是社会效益方面含锌危险废物的碱浸—电解—制备金属锌粉工艺比传统锌粉生产方法更具有竞争优势,它可以利用酸法炼锌不能利用的含氟、氯、硅的贫杂氧化锌矿和含锌废料,是氧化型含锌危险废料的全湿法清洁工艺,具有广阔的工业化应用前景。更多还原

【Abstract】 Zinc oxidation hazardous wastes will be harmful to the environment, so harmless and resource treatment on these materials is necessary.In order to improve the environmental quality,alleviate the demand for increased sharply of zinc resource,overcome the defect of tradition wet mention,so processing zinc oxidation hazardous wastes for zinc production is becoming more attractive. Among possible alternative technologies, the alkaline leaching and electrolysis process deserves attention. The Zn in zinc oxide wastes and ores can be leached selectively in NaOH solution, and then be recovered as metallic zinc by electrowinning which offering a significant energy saving over the conventional sulfate process.In this work, the alkaline leaching and electrolysis process was in-depth studied. The leaching parameters were observed and optimized, the impurities in leach solution were removed, Zn recovered as high-value-added metallic zinc powder, and the integrated alkaline process was thus developed, using the oxidized zinc wastes and ores at industrial scale, with a good economic and environmental benefits. The main conclusions were as follows:(1) A thermodynamic model of the system of Zn(Ⅱ)-NaOH-H2O was set up, Zn(Ⅱ) is existed as Zn(OH)42-and ZnO22-in the Zn(Ⅱ)-NaOH-H2O system, the molde between the zinc equilibrium concentration of zinc and the concentration of alkaline was constructed. The absolutely average error between experimental values and theoretically calculated values of zinc equilibrium concentration was found to be0.1298%using the solubility test of ZnO in the alkaline solution, showing the model developed should be reliable.(2) The effects of sodium hydroxide concentration, phase ratios (v/w), reaction, temperature, leaching time, particle size, stirring speed on leaching rate of zinc in sodium hydroxide solution were investigated. The optimum conditions varied for different raw materials. For the wastes bearing zinc, the optimum conditions were found to be a temperature of90℃, NaOH concentration of6mol/L, phase ratios (v/w) of10:1, and leaching time of120minutes, stirring speed of300r/min; and for smithsonite, to be a temperature of90℃, NaOH concentration of6mol/L, phase ratios (v/w) of10:1, and leaching time of120min, less than0.125mm of particle size, stirring speed of450r/min; while for willemite, to be a temperature of90℃, NaOH concentration of8mol/L, phase ratios (v/w) of8:1, and leaching time of240min, less than0.125mm of particle size, stirring speed of450r/min.(3) The leaching reaction kinetics of waste bearing zinc, smithsonite, and willemite in alkaline solution were studied. For waste bearing zinc and smithsonite, the apparent activation energy was obtained to be42kJ/mol and43.15kJ/mol from an Arrhenius plot. For willemite, during the early stage of leaching reaction the apparent activation energy of13.59kJ/mol; while in the later stage, the apparent activation energy of31.86kJ/mol. Thus, it indicated that the leaching mechanism of willemitethe changes from inner diffusion control to mixed control, during the leaching process in alkaline solution.(4) In depth purification of leach solution was explored. Sodium sulphide, sodium silicate, ferric sulfate and lime were used as purification agents. When the weight ratio of sodium sulphide/Pb was1.8,1.5g/L sodium silicate,1g/L ferric sulfate and weight ratio of lime/sodium sulphide of0.8were used, a high purity of zinc powder can be electrowon.(5) The theoretical voltage of alkaline zinc electrowinning is much lower than acidic electrowinning process. The optimum conditions of electrodeposition was that Current density of800-1000A/m2, NaOH concentration of180-240g/L, temperature of30-50℃, Zn concentration of30-40g/L. The current efficiency was99%and consumption of Power was only2.38kWh/kg Zn under the optimum conditions. The morphology of Zn on cathode changed from grain shape to thin slice if increasing current density and reducing solution temperature, the morphology of Zn changed from thin slice to Layered if increasing alkaline concentration.(6) The effects of various cation metal ions and anion ions on the electrowinning of metallic zinc powder from the alkaline solution was studied in detail. It was found that top impurities contents in the electrowinning solution should be controlled so that a high quality of zinc powder can be obtained.(7) Causticization of spent zinc electrolyte was conducted, by adding caustic soda into the spent electrolyte to make the concentration of caustic soda to350g/L so that the sodium carbonate and impurity ions can be thus separated from the solution. The precipitates separated from the process was then dissolved using the zinc-powder-washing wastewaters, with the concentrations of NaOH and sodium carbonate in the solution at80-100g/L and above40g/L, as well as at the conditions of temperature of90℃, reaction time of30min, lime1.5-1.8times of the theoretical value. As a result,28kg NaOH can be re-generated from each cubic meter solution, while some Fe、Cu、Mn、Mg、Cr、Cd and As can be removed simultaneously.(8) The process developed has been successfully at several plants with a scale of2000tons of metallic zinc powder annually. The long-term industrial operations have been shown that the process can use any raw materials containing Cl, F, Si, Fe, As, Cu, etc., except for zinc sulfides. Hence, the process is quite different to the acidic process and can apply the raw materials that the acidic process is unable to apply.(9) Zinc oxidation hazardous wastes change into general solid wastes after alkali extraction and it fulfils the requirement of waste disposal in harmlessness and reuse.In a word, whether from the economic benefits, environmental benefits or social benefit the process of alkaline leaching-electrowinning-preparation zinc powder has more competitive advantagea than traditional Zinc powder production methods, it can deal with the materials containing fluorine, chlorine, silicon which acid method can’t deal with, it is a wet-cleaner process and has a bright prospects for industrial application.更多还原