碱在赤泥中的存在方式及固定方法研究

发布时间：2018-03-06 06:09

  本文选题：赤泥　切入点：活化　出处：《中北大学》2015年硕士论文　论文类型：学位论文

【摘要】：赤泥是生产氧化铝时所排出的固体废弃物，排放量大，因其碱含量高、活性低，难以有效利用。目前主要的处置方式是露天堆存，会占用大量土地、引起地下水和空气污染，亟待处理。 本论文针对拜耳法赤泥含碱量高，用在建筑材料中会引起碱集料反应、泛白的问题，利用XRD、火焰光度计等检测手段研究了碱在赤泥中的存在形式（可溶碱、非可溶碱）及比例。同时以碱溶出率、净浆强度为控制目标，研究了赤泥在活化（热活化及加钙热活化）过程中可溶碱和不可溶碱的变化规律及其对赤泥活性的影响。利用物相耦合原理，研究了利用粉煤灰高温吸收赤泥可溶碱降低赤泥可溶碱新技术，并在系统研究粉煤灰掺量、细度、养护时间对粉煤灰固结赤泥可溶碱效果影响的基础上，研究了粉煤灰固碱机理。主要结论如下： （1）拜耳法赤泥中的碱主要分为两部分：一部分是可溶性碱，是在溶出铝土矿过程中带入的附着碱液，一部分是不可溶性碱，是铝土矿中的SiO2与铝酸钠溶液反应生成的不溶性水合铝硅酸钠，主要以钙霞石的形式存在。其中赤泥中可溶碱含量占总碱量的54%，非可溶碱占总碱量的46%。 （2）在赤泥活化过程中，其可溶碱含量随温度的升高先升高后降低，在700℃时达到最大值，表明此时水合铝硅酸钠的结合度低，离子溶出率大，故活性较高。在煅烧温度升高的过程中，赤泥中的一些含水矿物在500℃之前分解，并且钙霞石的衍射峰强度开始降低，所以可溶碱含量逐渐增大，在800℃开始出现结构稳定的钙铝黄长石和钠铝黄长石，Na2O被固结在稳定的钠铝黄长石中，所以可溶碱含量有所降低，900℃时结晶度进一步增大，更多活性物质被固结，离子溶出率减少，故可溶碱含量进一步降低。不同温度下可溶碱含量的变化与净浆试块的早期强度变化一致，但随着龄期的增长，在900℃以下时，试样的抗压强度逐步增长，在900℃出现下降。并且在煅烧过程中，赤泥中的碱含量随着温度的升高而有所挥发，，800℃之前挥发量较大，800℃之后，Na2O被固结，挥发量减小。 （3）赤泥中加入不同比例的石灰并在1200℃下煅烧，生成具有水化活性的C2S及可溶出的铝酸钠，提高了赤泥的活性，最高碱溶出率可达82.55%。在低龄期时，净浆试块的强度与碱的溶出率一致，但龄期增长后，C2S水化程度增大，提高了净浆试块的强度。 （4）利用粉煤灰在高温养护下与赤泥作用可以降低可溶碱的含量。赤泥与粉煤灰比例为1:2.5时，赤泥的碱溶出率最低；粉煤灰细度越大，赤泥可溶碱的含量越低；随着养护时间的增加，粉煤灰-赤泥材料中的可溶碱含量降低。经XRD检测可知，钠与粉煤灰溶出的Al2O3、SiO2反应生成了不溶的钠系菱沸石。
[Abstract]:Red mud is a solid waste discharged from the production of alumina. It has a large amount of discharge, because of its high alkali content and low activity, it is difficult to be effectively utilized. At present, the main disposal method is open storage, which will occupy a large amount of land and cause groundwater and air pollution. There is a great deal to be done. Aiming at the problem of high alkali content in Bayer red mud, which can cause alkali aggregate reaction and widespread whitening in building materials, the existing forms of alkali in red mud were studied by means of XRD, flame photometer, etc. Insoluble alkali) and proportion. At the same time, with alkali dissolution rate, pulp strength as the control target, The changes of soluble and insoluble alkali and their effects on the activity of red mud during the process of activation (thermal activation and thermal activation with calcium) were studied. The new technology of reducing the soluble alkali of red mud by high temperature absorption of red mud by fly ash was studied, and the effects of fly ash content, fineness and curing time on the effect of soluble alkali of fly ash consolidation red mud were studied systematically. The alkali-solid mechanism of fly ash is studied. The main conclusions are as follows:. 1) the alkali in Bayer red mud is mainly divided into two parts: one is soluble alkali, the other is the attached lye brought in during the dissolution of bauxite, and the other is insoluble alkali. It is an insoluble sodium aluminosilicate formed by the reaction of SiO2 in bauxite with sodium aluminate solution, mainly in the form of calcium nepheline. The soluble alkali content in red mud accounts for 54% of the total alkali content, and the non-soluble alkali content accounts for 46% of the total alkali content. (2) during the activation of red mud, the soluble alkali content increased first and then decreased with the increase of temperature, and reached the maximum value at 700 鈩

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