江苏省稀土冶炼行业放射性废渣污染控制研究

发布时间：2018-03-26 04:24

本文选题：稀土冶炼废渣　切入点：活度浓度　出处：《南京航空航天大学》2016年硕士论文

【摘要】：我国稀土矿产资源十分丰富,稀土储量和稀土产品年出口量均居世界第一位,但稀土矿资源常伴随高于天然本底水平的放射性核素(如钍、铀和镭),且在开采、冶炼、加工和利用的过程中,伴生的放射性物质随之迁移、浓集和扩散,产品和废弃物都会有不同程度的放射性,对周围环境造成了一定的放射性污染,给工作人员和公众造成了额外的照射剂量。因此,需要寻找出合适的处理处置方案,对稀土废渣进行妥善处置,消除环境安全隐患。本论文是以“江苏省环保科研项目——江苏省稀土冶炼行业低放废渣放射性污染控制技术研究”为依托,对江苏省稀土冶炼行业的大物料低放废渣的放射性解控方法进行研究。主要从平衡与非平衡情况下核素活度对比分析,非平衡情况下γ辐射剂量率与活度浓度研究,稀土冶炼工艺中放射性研究与处理处置建议三个方面进行研究,最后得出如下结论:(1)稀土废渣中的放射性平衡已经遭到破坏,与实际测量结果对照表明采用非平衡条件下多个特征核素共同计算放射性活度的方法,与稀土实际的放射性活度更接近。钍系核素在平衡被破坏后的放射性活度随时间变化情况与母体232Th和228Ra的初始放射性活度浓度有关。铀系核素在平衡破坏后主要以两段子体(234Th和226Ra及其子体)的放射性贡献为主。对于平衡遭到破坏的稀土废渣,仅测量单一子体的活度浓度并不能保证其它核素的活度浓度不超标,测量特征核素的活度浓度,从而计算得出衰变链中各个核素的活度浓度及总放射性活度浓度,为制定相关可操作性强的豁免标准提供了参考,对稀土冶炼厂家申请豁免稀土废渣具有重要意义。(2)建立了γ剂量率与活度浓度的关系,结合非平衡情况下的放射系分段理论,得到吸收剂量率与特征核素活度浓度的关系公式,双重保障了稀土废渣放射性测量的准确度。参考IAEA对公众的年有效剂量限值及加拿大对NORM的管理模式及限值,计算得到了基于对公众年有效剂量为0.3mSv/a和1mSv/a的豁免限值与管理限值。通过第一次和第二次实验,得到的实测结果与实验室分析结果符合良好,验证了理论正确性,也修正了现场操作中存在的问题,如样品尺寸大小、样品重量、渣样形态等对现场实践的影响。(3)针对稀土冶炼工艺,可以从酸溶工序和最后废水处理两个环节进行优化。酸溶过程中进行的钡镭共沉淀,可以实验确定添加试剂的最优配比,也可以使用新的除放射性物质的试剂,既有利于放射性核素回收,也有利于减少后续程序中的放射性水平;中和处理中也可采用新型的除放试剂辅助,降低中和渣中的放射性,使其低于豁免限值。此外,根据γ光子在稀土渣样中的有效厚度确定了中和渣模型的形状与尺寸,提出了可操作的豁免程序。还调研分析了十家稀土厂酸溶渣和中和渣中的主用成分,提出了废渣回收再利用建议。
[Abstract]:Our country is very rich in rare earth mineral resources, rare earth reserves and rare earth products export amount rank first in the world every year, but rare earth mineral resources are often accompanied by radionuclides (such as thorium, uranium and radium), which are higher than the natural background level, and are being exploited and smelted. During the process of processing and utilization, the accompanying radioactive material is transported, concentrated and diffused, and the products and wastes will have different levels of radioactivity, which has caused certain radioactivity pollution to the surrounding environment. Additional exposure doses to staff and the public. Therefore, there is a need to find appropriate disposal options for the proper disposal of rare earth waste, This paper is based on the project of environmental protection research in Jiangsu Province-study on radioactive pollution control technology of low level waste residue in rare earth smelting industry in Jiangsu Province. In this paper, the radioactive decontamination method of large material and low radioactive waste residue in rare earth smelting industry in Jiangsu Province was studied. The comparison analysis of nuclide activity between equilibrium and non-equilibrium, and the study of 纬 radiation dose rate and activity concentration under non-equilibrium condition were carried out. The radioactive research and disposal suggestion of rare earth smelting process are studied in three aspects. Finally, it is concluded that the radioactive balance in rare earth waste residue has been destroyed. Compared with the actual measurement results, it is shown that the method of calculating radioactivity by using multiple characteristic nuclides under non-equilibrium conditions, The change of radioactivity of thorium nuclides over time is related to the initial activity concentration of parent 232Th and 228Ra. The radioactive contribution of the two-stage daughter (234Th and 226Ra and their daughters) is the main one. For the rare earth waste residue whose balance has been destroyed, Measuring the activity concentration of a single daughter does not guarantee that the activity concentration of other nuclides does not exceed the standard. The activity concentration of the characteristic nuclides is measured, and the activity concentration and the total activity concentration of each nuclide in the decay chain are calculated. This paper provides a reference for the establishment of relevant operational exemption standards, and is of great significance for rare earth smelters to apply for exemption from rare earth waste residue.) the relationship between 纬 dose rate and activity concentration is established, and combined with the segmental theory of radiation system under non-equilibrium conditions, the relationship between 纬 dose rate and activity concentration is established. The formula of relationship between absorption dose rate and characteristic nuclide activity concentration is obtained, which ensures the accuracy of radioactive measurement of rare earth waste residue. Referring to the annual effective dose limit of IAEA to the public and the management mode and limit value of NORM in Canada, Based on the results of the first and second experiments, the experimental results are in good agreement with the results of laboratory analysis, and the theoretical correctness is verified. It also corrects the problems existing in the field operation, such as the influence of sample size, sample weight, slag sample shape, etc., on the field practice. The barium radium coprecipitation in the acid dissolution process and the final wastewater treatment process can be optimized by experiments to determine the optimum ratio of the reagents added, or the new reagent for removing radioactive substances can be used. It is beneficial to the recovery of radionuclides as well as to the reduction of the level of radioactivity in subsequent procedures; the neutralization process can also be supplemented by new removals to reduce the radioactivity in neutralized residues below the exempted limit... in addition, According to the effective thickness of 纬 -photon in rare earth slag sample, the shape and size of neutralizing slag model are determined, and an operational exemption program is proposed. The main components of acid soluble slag and neutralized slag in ten rare earth plants are also investigated and analyzed. The suggestion of recovery and reuse of waste residue is put forward.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X758

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