本文選題：稀土冶煉廢渣　切入點：活度濃度　出處：《南京航空航天大學》2016年碩士論文

【摘要】：我國稀土礦產(chǎn)資源十分豐富,稀土儲量和稀土產(chǎn)品年出口量均居世界第一位,但稀土礦資源常伴隨高于天然本底水平的放射性核素(如釷、鈾和鐳),且在開采、冶煉、加工和利用的過程中,伴生的放射性物質(zhì)隨之遷移、濃集和擴散,產(chǎn)品和廢棄物都會有不同程度的放射性,對周圍環(huán)境造成了一定的放射性污染,給工作人員和公眾造成了額外的照射劑量。因此,需要尋找出合適的處理處置方案,對稀土廢渣進行妥善處置,消除環(huán)境安全隱患。本論文是以“江蘇省環(huán)�？蒲许椖俊K省稀土冶煉行業(yè)低放廢渣放射性污染控制技術(shù)研究”為依托,對江蘇省稀土冶煉行業(yè)的大物料低放廢渣的放射性解控方法進行研究。主要從平衡與非平衡情況下核素活度對比分析,非平衡情況下γ輻射劑量率與活度濃度研究,稀土冶煉工藝中放射性研究與處理處置建議三個方面進行研究,最后得出如下結(jié)論:(1)稀土廢渣中的放射性平衡已經(jīng)遭到破壞,與實際測量結(jié)果對照表明采用非平衡條件下多個特征核素共同計算放射性活度的方法,與稀土實際的放射性活度更接近。釷系核素在平衡被破壞后的放射性活度隨時間變化情況與母體232Th和228Ra的初始放射性活度濃度有關。鈾系核素在平衡破壞后主要以兩段子體(234Th和226Ra及其子體)的放射性貢獻為主。對于平衡遭到破壞的稀土廢渣,僅測量單一子體的活度濃度并不能保證其它核素的活度濃度不超標,測量特征核素的活度濃度,從而計算得出衰變鏈中各個核素的活度濃度及總放射性活度濃度,為制定相關可操作性強的豁免標準提供了參考,對稀土冶煉廠家申請豁免稀土廢渣具有重要意義。(2)建立了γ劑量率與活度濃度的關系,結(jié)合非平衡情況下的放射系分段理論,得到吸收劑量率與特征核素活度濃度的關系公式,雙重保障了稀土廢渣放射性測量的準確度。參考IAEA對公眾的年有效劑量限值及加拿大對NORM的管理模式及限值,計算得到了基于對公眾年有效劑量為0.3mSv/a和1mSv/a的豁免限值與管理限值。通過第一次和第二次實驗,得到的實測結(jié)果與實驗室分析結(jié)果符合良好,驗證了理論正確性,也修正了現(xiàn)場操作中存在的問題,如樣品尺寸大小、樣品重量、渣樣形態(tài)等對現(xiàn)場實踐的影響。(3)針對稀土冶煉工藝,可以從酸溶工序和最后廢水處理兩個環(huán)節(jié)進行優(yōu)化。酸溶過程中進行的鋇鐳共沉淀,可以實驗確定添加試劑的最優(yōu)配比,也可以使用新的除放射性物質(zhì)的試劑,既有利于放射性核素回收,也有利于減少后續(xù)程序中的放射性水平;中和處理中也可采用新型的除放試劑輔助,降低中和渣中的放射性,使其低于豁免限值。此外,根據(jù)γ光子在稀土渣樣中的有效厚度確定了中和渣模型的形狀與尺寸,提出了可操作的豁免程序。還調(diào)研分析了十家稀土廠酸溶渣和中和渣中的主用成分,提出了廢渣回收再利用建議。
[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 緯 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 緯 dose rate and activity concentration is established, and combined with the segmental theory of radiation system under non-equilibrium conditions, the relationship between 緯 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 緯 -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.
【學位授予單位】：南京航空航天大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：X758

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