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拜耳法赤泥碱介质中相结构转化应用基础研究
其他题名Fundamental applied research on the phase transformation principles of Bayer red mud in hydro-alkali medium
张然
学位类型博士
导师张懿
2012-05-22
学位授予单位中国科学院研究生院
学位专业化学工艺
关键词拜耳法赤泥 碱介质 方钠石 钙石榴石 硅酸钠钙
摘要氧化铝工业产生的赤泥是我国有色行业排放量最大的难处理冶炼固体废弃物,我国每年排放量接近4000万吨,累计已达约2.5亿吨。受拜耳法氧化铝生产工艺的限制,赤泥中铝、碱含量较高,难以利用,目前多以筑坝堆存为主,这不仅占用大量土地资源,而且强碱性赤泥还会对周边生态环境造成严重污染。本论文针对拜耳法赤泥堆存产生的环境污染问题,开展了碱性体系下赤泥各物相结构变化及转化关系的应用基础研究,并研究开发与拜耳法流程相耦合的赤泥处理工艺,大幅度降低赤泥的碱含量,旨在削减高碱赤泥环境污染,并为赤泥的综合利用创造前提条件。论文取得了如下创新性进展:(1)研究了我国高铁赤泥及低铁赤泥两类拜耳法赤泥的物理化学性质。研究发现,高铁赤泥物相主要以方钠石和氧化铁为主,低铁赤泥主要以方钠石/钙霞石和钙铁榴石为主,二者性质上的差异与铝土矿来源和处理工艺直接相关。(2)查明了拜耳法赤泥中方钠石/钙霞石在碱性条件下的分解及物相结构转化规律。研究发现,在低温低碱及水热条件下,方钠石/钙霞石分解为不同端元物相组成的钙石榴石固溶体。在优化条件下,高铁赤泥和低铁赤泥中氧化钠回收率达90%以上,高铁赤泥中氧化铝回收率可达75%。(3)深入研究了钙石榴石中钙铝榴石及钙铁榴石的Fe-Al类质同象替换规律。结果表明,当体系中Fe/Si摩尔比大于0.9,钙石榴石全部由钙铁榴石相组成,此时钙铁榴石中Fe在六配位点的替换率达到75-80%。此外,发现钛对钙铁榴石生成具有显著的促进作用,探讨了钛的作用机理。(4)系统研究了硅酸钠钙在低浓度碱液中分解为硅酸钙类物质(CSH)的分解机理。结果表明,硅酸钠钙在纯氢氧化钠溶液会分解成“有缺陷的雪硅钙石”;在低浓度铝酸钠溶液中,分解产物会有部分钙铝榴石存在。硅酸钠钙在纯氢氧化钠溶液中的分解属于化学反应控制过程。(5)基于本论文研究结果进行了拜耳法赤泥液流内循环处理工艺流程设计,提出了“种分母液深度脱碱”及“洗涤沉降底流脱碱”两种工艺。该工艺使用拜耳法系统本身的碱液,处理赤泥后终渣的Na2O<0.3wt%,具有较好的技术经济效益。
其他摘要Red mud is the residue generated in alumina industry which is the biggest industry of nonferrous metals in China. The amount of red mud discharged every year is above 40 million tonnes, which has accumulated up to 250 million tonnes. Limited by the Bayer process, red mud contains plenty of alumina and alkali. The major method for red mud disposal now is piling only, which would occupy plenty of field and lead to severe environment contamination as the alkali attached in red mud. Therefore, it is urgently required to explore the treatment process for red mud in large scale. This thesis thus considered the Bayer red mud as research object, aimed at exploring effective treatment process for red mud coupled with Bayer process. Based on the purpose, it has systematically researched the phase structure and transformation of red mud in hydro-alkali system, in order to convert the environment-harmful phase into harmless phase and recycle the valued metals simultaneously. In this thesis, the following results and progresses were achieved: (1)The properties of Bayer red mud have been studied systematically. The Bayer red mud were classified into two species as Fe-rich red mud and Fe-lean one, according to the differences of raw resources, technical processes. The phases of Fe-rich red mud were composed of sodalite and hematite, whereas those of Fe-lean red mud were sodalite/cancrinite and grandite. (2)The decomposition principle of sodalite/cancrinite in Bayer red mud has been investigated. It has been found that, in the low temp. & alkai-concentr. and hydrothermal zone, the equilibrium phase of sodalite/cancrinite decomposition was grandite with solid solution of some end-member materials. In optimal condition, the recycling ratio of alkali in both Fe-rich and –lean red mud can be above 90%, and the recycling ratio of alumina in Fe-rich red mud can reach approximately 75%. (3)The isomorph phenomenon of andradite and grossular was researched. The Fe-Al substitution was happened in six-coordination site, and factors which would influence the ratio of Fe substitution for Al were studied. It showed that the grandite would make up by andradite only when the molar ratio of Fe to Si is above 0.9, the ratio of Fe substitution in andradite was about 75-80%. In addition, the promotion effect of Ti in andradite formation was researched. (4)The decomposition principle of NaCaHSiO4 was researched, and the mechanism of converting NaCaHSiO4 to CSH and grossular was discussed respectively. Moreover, the kinetics calculation of NaCaHSiO4 to CSH was carried out. It was deduced that the reaction was controlled by chemical reaction. In pure sodium solution, the end-product of decomposed NaCaHSiO4 is “defected tobermorite”; whereas in sodium aluminate solution, grandite would emerge in end-product. (5)Based on the research results in previous chapters, two treatment processes for Bayer red mud were deduced: de-sodium process by using overflow liquid and de-sodium process by using spent liquor. Alkali in disposal residue was below 0.3wt% Na2O and both the technical processes showed great economic benefits.
语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/1842
专题研究所(批量导入)
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张然. 拜耳法赤泥碱介质中相结构转化应用基础研究[D]. 中国科学院研究生院,2012.
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