高镁磷尾矿回收利用磷、镁的应用基础研究

【作者】 黄芳；

【导师】 王华； 李军旗；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2010， 博士

【摘要】 目前,随着世界磷矿资源的贫化和枯竭,各国都在寻求新技术以进一步开发利用贫矿资源。我国中、低品位磷矿资源相当丰富,大多属杂质含量高、难选的胶磷矿,采用常规工艺很难获得优质磷酸,必须经过经济有效的选矿富集才能满足磷酸和高浓度磷复肥生产需求,由此产生的大量尾矿尚未得到开发利用。该尾矿属高镁磷尾矿,应该成为可利用的二次资源。因此,开展对该高镁磷尾矿综合利用的基础研究和技术开发工作,是化肥工业、化学工业,乃至国民经济可持续发展的迫切要求。面对这一挑战,本文选择了我国重要磷矿生产基地——瓮福磷矿浮选尾矿为代表,对其中镁和磷的综合开发利用若干重要理论问题,如尾矿的矿物结构、物理化学性质,水溶液热力学,各种杂质对尾矿酸解过程产生的复杂效应,镁、磷的酸解动力学,液固相复杂体系的反应机理等进行比较系统和深入的研究,获得了若干重要的结论,从而为胶磷矿与白云石的分离、高镁磷尾矿的综合利用提供理论依据,同时也对极低品位磷矿及高镁矿的综合利用具有一定借鉴意义。作者采用x射线衍射仪、电子探针、透射电子显微镜、能谱仪、扫描电镜、电子显微镜、分析电镜和常规化学分析等手段测定了尾矿矿物学结构、形貌,镁、磷赋存状态等重要特征,获得了反应活性、抗阻缓性、发泡特性、煅烧特性等矿石工艺方面的重要物性参数,发现了尾矿及其原矿共性和异性之间的关系。研究表明：高镁磷尾矿主要由8.56%氟磷灰石、87.14%白云石组成,属高镁极低品位磷矿；尾矿中镁、磷在细粒级中相对富集,分别为65.66%和66.96%,其中镁主要集中在颗粒内部；依据不同颗粒矿物组成以及内部结构,尾矿类型含量从高到低依次划分为白云石质、白云石磷灰石质、磷灰石白云石石英质、石英质、磷灰石质、褐铁矿质；尾矿中镁多数以独立矿物白云石颗粒形式存在,磷主要以具有相当数量的磷灰石与白云石形成的矿物连生体形式存在,极少数以独立矿物磷灰石形式存在；尾矿反应活性好(反应活性99.65%),有一定的抗阻缓性(抗阻缓系数为12.3),发泡能力强(泡沫稳定指数1780.7ml-min);煅烧温度在900℃时,主要含镁矿物白云石分解完全,而含磷矿物氟磷灰石需在高温时才发生分解。作者利用可靠的热力学数据和大量的热力学理论,首次以Mg2+-Ca2+-H2CO3-H2O、CaCO3·MgCO3-SO42--H2O、Ca2+-F--H3PO4-H2O、Ca5(PO4)3F-SO42--H2O、Mg2+-H3PO4-H2O体系在常温下的热力学平衡分析出发,讨论了Ca-Mg-P-H2SO4体系在常温和高温下的溶液-矿物溶解、沉积现象。结果表明,镁、磷的主要溶出反应的pH0随温度的升高而降低,并在较强酸性条件下分别以Ca2+、Mg2+、H3PO4形式存在于溶液中；用H2SO4作为浸出剂时,会促进钙、镁、磷的反应,它们分别以CaSO4结晶体水合物、Mg2+、H3PO4存在。作者研究了磷尾矿硫酸复杂体系的液固相反应动力学过程,用扫描电镜、等离子发射光谱、常规化学分析等进行了测试与监控,系统测定了尾矿颗粒中镁、磷及铁、铝杂质的反应动力学曲线。研究表明,镁、磷溶出规律相似,不存在选择性溶解。矿石颗粒表面形成的固体膜对反应有重要影响,表现出较大阻缓性,阻缓系数均大于1.6,方程t/1ln1-x/1-βt/x=k可以很好地描述尾矿中镁、磷的反应动力学,活化能分别为14.881kJ/mol和11.908kJ/mol,尾矿酸解反应为固态膜扩散控制过程。因此,作者进一步对表面固态膜进行了细致而深入的研究,发现随着酸解反应的进行,尾矿颗粒表面由致密、平整变得疏松、多孔,表面结晶体逐渐由细碎短小的针状变为粗大的短柱状,表面固态膜先后形成为烧石膏、石膏、硬石膏。这些研究对控制固相产物形态,从而为提高固液相的过滤性能提供了良好的理论依据。以上研究揭示了以磷尾矿为代表的液固相反应机理。尾矿颗粒酸解过程是从外表层到内层逐步深入的,己反应完毕的区域与尚未反应的区域之间的反应界面不是一个面,而是一些硅骨架孔洞。随着反应的进行,这一反应区域逐步向颗粒中心移动,直至反应完全,最后剩下充满复杂孔洞的硅质残骸及钙质覆盖膜。这一进程可描绘为：处于湍流状态的、具有一定浓度的液相主体包围着尾矿颗粒,反应从颗粒外表面的渗透开始,逐渐形成硅骨架孔洞和钙质覆盖膜。进一步反应时扩散过程和化学反应过程同时存在,液相一边沿孔隙扩散,一边与孔壁上的物质进行反应,反应后的液相产物将扩散至液相主体,固相产物沉积、阻塞孔洞、随局部过饱和度的变化发生CaSO4·0.5H2O到CaSO4·2H2O、CaSO4的转化,从而阻碍物流的进一步扩散。作者在研究尾矿酸解动力学的基础上,提出了用循环浸出-净化-萃取(反萃)法从尾矿酸浸液中制取磷酸的方法,所得磷酸可满足工业生产要求。酸解产物石膏可直接作为石膏板的原料,消除了磷石膏的污染。更多还原

【Abstract】 To deal with crisis that high-quality phosphate rocks of the whole world are depleted, the plans to employ low-grade phosphate ores are already in full swing in some of countries presently. Though plenty of phosphate reserve exsist in our country, mainly are middle and low grade and high content impurities and difficult to beneficiat, which need to be beneficiated economically and efficiently to meet demand of phosphorous produces. Result of that, there are large quanlity of tailings to be discarded and not to be recoveried. The tailings belong to phosphorite tailings with high magnesium content and should become available secondary resource. Therefore, it is urgently important to engage in researching and developing to comprehensively utilize tailings in order to satisfy with chemical industry as well as fertilizers. Facing this chanllenge, we chose the floated tailings from Wengfu phosphate ores and made extensive study about some important theories involving in their recovery such as mineralogical structure and physical and chemical characteristics of the tailings, aqueous thermodynamic, effects of impurities in digesting process, complicated reactive mechanism and reaction kinetics, and then obtained significant results, which can provide some theretical basis and reference for cellophane and dolomite separation, comprehensive recovery on phosphorite tailing with high magnesium content, even on low grade phosphorite and high magnesium content ores.The important characteristics such as mineralogical structure, appearance, exsist state of Mg and P of the phosphate tailings were detected by using X ray diffraction (XRD), electron probe, transmission electron micrograph (TEM), spectrometer, scanning electron microscope (SEM), electron microscope (EMS), analytical electron microscope (AEM) and chemical analysis. It is obtained that the key physical and chemical behavior parameters including reactive activity, resistance to retardancy, foaming characteristic and it is discovered that the relation between tailings and their originals. The results indicate that tailings are mainly made of dolomite and phosphorite, accounting for 87.14%and 8.56% respectively, which belong to low grade phosphorite rock with high magnesium content. P2O5 and MgO comparably enriched in fine particle size, accounting for 65.66% and 66.96% respectively, and MgO mainly concentrated to the internal tailing’s particle. On the basis of mineralogical components and internal structure of phosphorite tailing, its brand of tailing is successively divided into dolomite based tailings, dolomite and phosphorite based tailings, dolomite and phosphorite and quartz based tailings, quartz based tailings, phosphorite based tailings and brown iron ore based according to their content’s amount. The existing state of Mg and P is respectively independent dolomite particle and intergrowth of phosphorite and dolomite, and amount of independent phosphorite is very low. Compared with the original phosphate ores, the phosphate tailings’reactivity is higher, resistance to retardancy is lower and the foaming ability is stronger. When calcination temperature is up to 900℃, dolomite decomposed completely.The phenomena of solution-mineral dissolution and precipitatation are discussed through the analyses on thermodynamic equilibriums of Mg2+-Ca2+-H2CO3-H2O, CaCO3·MgCO3-SO42--H2O, Ca2+-F--H3PO4-H2O, Ca5(PO4)3F-SO42--H2O and Mg2+-H3PO4-H2O systems at normal temperature. It is dicovered that the pH0 values of digestion reactions of Mg and P decrease with increasing temperature, and they exsist in the forms of Mg2+、H3PO4 in strong-acid solution respectively. While H2SO4 is as acid solvent, the digestion of Ca, Mg and P will accelerate, exsisting in the forms of CaSO4 crystallines, Mg2+ and H3PO4 in solution, respectively.Based on the above work, the reacting kinetic processes are investigated in a specially designed reactor system by using SEM, plasma emission spectroscopy (PES) analysis. As important results, the digesting behavior of Mg is similar to P’s, not selective dissolution and the negative temperature effect of the digestion of Fe and Al are revealed in the reaction system, which will be of benefit to restrain impurities dissolution from ore particles to acid solution. The strong effects of solid film forming on the surface of tailing particle on acidolysis reaction show stronger retardancy property. It is also noticed that the Drozdov equation (1/tln1/(1-x)-βx/t=k), which took into account the self-impeding effect, can describe the dissolution process of P2O5 and MgO quite well. The result of apparent reaction activation energy of P2O5 and MgO is 14.881 and 11.908 kJ·mol-1 respectively indicates that the main reactions of tailing dissolution are solid film diffusion control process. The detailed investigations on solid film are found that the particle surface turns densy and smoothy into loosy and porus, get thick and bulky, turns finely, and the appearant form turn short, small and needle shapes into big, rough and short column shapes, and the surface materials successively form assanite, plaster and anhydrite.From above results, the reacting mechanism is explored that the reactive components can diffuse in the tailing particle through a large amount of mico pores. With the reaction proceeding, the penetration and the reaction region will move towards the center of the particle, finally remain siliceous survival and calcareous coating. There are three regions in the system, which include penetration region where liquid diffuse in the surface of paticle, reaction region where reaction and diffusion phenomena exist at the same time, and unreacted region.Besides these, cyclic leaching-extraction-stripping method recovering P2O5 in form of high quality phosphoric acid from phosphorite tailing with high magnesium content is already proved to be available.更多还原