Preparation and growth mechanism of aluminium hydroxide by precipitation method with sodium carbonate

doi:10.16085/j.issn.1000-6613.2017.03.047

Abstract

Abstract:

Aluminum hydroxide was synthesized by one-pot precipitation method using sodium carbonate (Na₂CO₃) and aluminum sulfate[Al₂(SO₄)₃·18H₂O] as precipitator and precipitate precursor agents, respectively. Simultaneously,the growth mechanism was investigated by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),thermo gravimetric analysis(TGA) and scanning electron microscopy(SEM). The results showed that the hydrolysis ratio of aluminum sulfate solution(0.02mol/L) was 1.98% and 100% under pH=2.50 and 3.80 at 75℃,respectively. The results of XRD,FTIR,TG-DTG and SEM showed that pH played an important role in the preparation of aluminum hydroxide by the dropwise addition of Na₂CO₃ in Al₂(SO₄)₃. When pH was less than 3,Al³⁺ kept a stable state as[Al(OH₂)₆]³⁺. With the gradual increase of pH,[Al(OH)₄(OH₂)₂]^- was generated hydrolyzed from[Al(OH₂)₆]³⁺ and subsequently dehydrated-condensed into[Al₂(OH)₈(OH₂)₂]^2- under the effect of hydration. Then,[Al₂(OH)₈(OH₂)₂]^2- transformed into[Al₂O(OH)₆]^2-with the increase of alkalinity. Finally,aluminum hydroxide was generated. Aggregated and amorphous aluminum hydroxide could be obtained when pH was 3,5 and 7. Under the pH of 9 and 11,amorphous aluminum hydroxide transformed into crystalline state of boehmite(γ-AlOOH) and a little bayerite[α-Al(OH)₃]. Meanwhile,the crystal form of aluminum hydroxide at pH=11 was better than pH=9.

Key words: aluminum hydroxide, precipitation method, boehmite, bayerite

摘要：

以十八水硫酸铝[Al₂（SO₄）₃·18H₂O]为沉淀前驱剂，碳酸钠（Na₂CO₃）为沉淀剂制备氢氧化铝，采用X射线衍射（XRD）、傅里叶变换红外光谱（FTIR）、热重分析（TGA）和扫描电子显微镜（SEM）探究硫酸铝水解反应机理。研究结果表明，75℃下0.02 mol/L的硫酸铝溶液在pH=2.50时水解率为1.98%，pH=3.80时水解率为100%。XRD、FTIR、TG-DTG和SEM结果表明，在Al₂（SO₄）₃溶液中滴加Na₂CO₃沉淀剂制备氢氧化铝的过程中，pH起着重要作用。当溶液pH<3时，Al³⁺以[Al（OH₂）₆]³⁺形式存在，随着溶液pH的增加，[Al（OH₂）₆]³⁺水解生成[Al（OH）₄（OH₂）₂]^-，[Al（OH）₄（OH₂）₂]^-在水化作用下脱水缩合为[Al₂（OH）₈（OH₂）₂]^2-，碱性增强，[Al₂（OH）₈（OH₂）₂]^2-转化为[Al₂O（OH）₆]^2-，最终形成氢氧化铝沉淀。pH=3、5、7时，Al₂（SO₄）₃水解所得产物为无规则团聚的非晶态氢氧化铝；pH=9、11时，氢氧化铝从非晶态转变为晶态的勃姆石（γ-AlOOH）及少量拜尔石[α-Al（OH）₃]，且pH=11时硫酸铝水解所得氢氧化铝结晶晶型较pH=9时好。

关键词: 氢氧化铝, 沉淀法, 勃姆石, 拜尔石

CLC Number:

TQ133.1

HUANG Jing, XIA Jupei, LUO Zhongqiu. Preparation and growth mechanism of aluminium hydroxide by precipitation method with sodium carbonate[J]. Chemical Industry and Engineering Progress, 2017, 36(03): 1120-1125.

黄静, 夏举佩, 罗中秋. 碳酸钠沉淀法制备氢氧化铝及其形成机理探讨[J]. 化工进展, 2017, 36(03): 1120-1125.

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