CAS OpenIR
高碱铝酸钠溶液中羟基方钠石脱硅动力学与机理
江小舵
Subtype博士
Thesis Advisor张懿
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工艺
Keyword高碱铝酸钠溶液,羟基方钠石,脱硅动力学,脱硅机理,水合铝酸钠
Abstract

相较于拜耳法,高压水化学法在处理赤泥、粉煤灰、一水硬铝石铝土矿等低品位铝资源时有着较大优势,但在高温高压高碱浓度的环境下,低品位铝资源中的硅杂质也会溶出到溶液中,溶液中的硅酸根离子会对产品的纯度造成影响,同时还会造成管道结疤和增加能耗等问题。拜耳法一般是将资源浸出液稀释到250 g/L以下,再用各种脱硅剂在低浓度碱液中进行脱硅。本论文首次合成了高碱铝酸钠溶液中适用的羟基方钠石型脱硅剂,可在高碱铝酸钠溶液中直接脱硅,使得脱硅液可以较好的析出水合铝酸钠结晶,不再需要像拜耳法一样稀释脱硅再蒸发种分,从而简化工序并节约能耗。高碱铝酸钠溶液在经过脱硅后可以析出水合铝酸钠结晶,本文考察了初始二氧化硅浓度、实验温度、氧化铝浓度等对于高碱铝酸钠溶液中水合铝酸钠SAH结晶析出的影响。实验结果表明,不同初始二氧化硅浓度的铝酸钠溶液中,温度对于二氧化硅浓度变化的影响很不一样。SAH结晶溶液中的二氧化硅含量应优选脱硅至约2.0 g/L或以下。在高碱铝酸钠溶液中脱硅时,脱硅剂的用量不可过低,否则脱硅过程无法进行;同时氧化铝浓度应低于150 g/L,在80 g/L以下更妥当,否则脱硅剂会起到水合铝酸钠结晶晶种的作用。考察了NaCaHSiO4、zeolite、C3AH6、CaO、Ca(OH)2、合成铝硅酸钠等物质在高碱溶液中的脱硅效果。实验结果表明,合成的羟基方钠石型铝硅酸钠(Na8Al6Si6O24(OH)2(H2O)2)在高碱铝酸钠溶液中的脱硅效果最好。借助XRD、FTIR、NMR考察了在不同温度下合成的方钠石型铝硅酸钠的结构信息。考察了搅拌、脱硅剂用量、碱浓度、初始二氧化硅浓度、脱硅温度、合成时间等因素对高碱溶液中羟基方钠石脱硅效果的影响。以铝土矿和粉煤灰为例,利用这两种经济常见的低品位铝资源来合成高碱铝酸钠溶液下适用的脱硅剂,脱硅剂Sod-bauxite和Sod-fly ash的主要物相都被鉴定为方钠石。使用Sod-bauxite和/或Sod-fly ash作为脱硅剂,含有500 g/L Na2O的铝酸盐溶液中的硅酸盐含量在100℃下在16小时内成功降低至约2 g/L。对于合成的羟基方钠石型脱硅剂,研究了其溶解度和实验温度以及Na2O浓度的关系。实验结果表明,溶解度随实验温度以及Na2O浓度的升高而增加。高碱铝酸钠溶液中二氧化硅(σ)的相对过饱和度是脱硅过程中促进方钠石沉淀的驱动力。470 g/L的高碱铝酸钠溶液的脱硅过程的表观活化能Ea为94.04 kJ/mol,其中脱硅级数n = 2.47±0.47。500 g/L的高碱铝酸钠溶液的脱硅过程的表观活化能Ea为144.21 kJ/mol,其中脱硅级数n = 4.27±0.18。反应结晶应是高碱铝酸钠溶液中羟基方钠石脱硅剂的脱硅机理。;AbstractCompared with the Bayer method, high-pressure hydro-chemical method has great advantages in dealing with low-grade aluminum-containing resources such as red mud, fly ash and diaspore bauxite. However, in high-temperature, high-pressure and high-alkali environment, silicon will also be dissolved into the solution, the silicate ions in the solution will affect the purity of the product. At the same time, it will also cause pipeline crusting and increase energy consumption.The Bayer process generally dilutes the leachate to below below 250 g/L, and then desilicate it in a low-alkali solution. In this paper, the hydroxy-sodalite desilication agent for high alkali sodium aluminate solution was synthesized firstly. It can be directly desilicated in high alkali sodium aluminate solution, so that the liquid can precipitate hydrated sodium aluminate better. It is no longer necessary to dilute and then evaporate the solution, which simplifies the process and saves energy.The high-alkali sodium aluminate solution can precipitate sodium aluminate hydrate crystal after desilication. The effect of initial silica concentration, experimental temperature and alumina temperature are investigated for the precipitation of sodium aluminate hydrate SAH in high-alkali sodium aluminate solution. The experimental results show that the temperature has a very different effect on the change of silica concentration in sodium aluminate solution with different initial silica concentration. The silica content in the SAH crystallization solution should preferably be desilicated to about 2.0 g/L or less. When desilication is carried out in high-alkali sodium aluminate solution, the dosage of the desilication agent should not be too low, otherwise the desilication process cannot be carried out; at the same time, the alumina concentration should not be higher than 150 g/L, and should be lower than 80 g/L, otherwise the desilication agent will act as a seed crystal of sodium aluminate hydrate.The desilication effect of NaCaHSiO4, zeolite, C3AH6, CaO, Ca(OH)2, synthetic sodium aluminosilicate and other substances in high-alkali solution was investigated. The experimental results show that the synthetic sodalite-type sodium aluminosilicate has the best desilication effect in the high-alkali sodium aluminate solution. The structure infomation of hydroxy-sodalite type aluminosilicates synthesized at different temperatures were investigated by XRD, FTIR and NMR.The effects of stirring, dosage of desilication agent, alkali concentration, initial silica concentration, desilication temperature and synthesis time on the desilication process of hydroxy-sodalite in high-alkali solution were investigated. Using bauxite and fly ash, two economically common low-grade aluminum resources, to synthesize desilication agent suitable for the high-alkali sodium aluminate solution. The main phases of the desilication agent sod-bauxite and sod-fly ash were both identified as sodalite. Using sod-bauxite and/or sod-fly ash as the desilication agent, the silicate content in the aluminate solution containing 500 g/L Na2O was successfully reduced to about 2 g/L in 16 hours at 100 °C.For the synthesized hydroxy-sodalite desilication agent, the relationship between the solubility and the experimental temperature, and the relationship between the solubility and the Na2O concentration was investigated. The experimental results show that the solubility increases with the experimental temperature and the concentration of Na2O.The relative supersaturation of silica (σ) in a high-alkali sodium aluminate solution is the driving force for the sodalite precipitation that promotes the desilication process. The apparent activation energy Ea of the desilication process in 470 g/L high-alkali sodium aluminate solution is 94.04 kJ/mol, and the order of desilication is n=2.47±0.47. The apparent activation energy Ea of the desilication process in 500 g/L high-alkali sodium aluminate solution is 144.21 kJ/mol, and the order of desilication is n=4.27±0.18. The reaction crystallization should be the desilication mechanism using hydroxy-sodalite desilication agent in a high-alkali sodium aluminate solution.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40661
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
江小舵. 高碱铝酸钠溶液中羟基方钠石脱硅动力学与机理[D]. 中国科学院大学,2019.
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