Treatment of Spent Dry Barrier from Aluminum Electrolysis by Alkali-Acid Method

doi:10.12068/j.issn.1005-3026.2025.20230344

Abstract

Abstract:

The process of treating spent dry barrier from aluminum electrolysis with alkali and acid is proposed. Spent dry barrier sample from an aluminum company was taken as the raw material， and its main phases are NaF， NaAlSiO₄， CaF₂， α-Al₂O₃， Na₃AlF₆， Si and β-Al₂O₃. Firstly， the NaF with mass fraction of 98.84% is obtained by water leaching separation of the raw materials. Secondly， the optimal process condition for alkali leaching treatment of water leaching residue were obtained by single factor method as follows： temperature of 90 ℃， liquid-solid ratio of 5 cm³/g， alkali-slag mass ratio of 0.25， and reaction time of 100 min， and under this condition， the leaching rate of Na₃AlF₆ was 94.04%. After that， the optimal process conditions for acid leaching treatment of alkali leaching residue were obtained by single factor method as follows： temperature of 58 ℃， reaction time of 45 min， acid concentration of 0.6 mol/L， and liquid-solid ratio of 12 cm³/g， and under this condition， NaAlSiO₄ and CaF₂ can be leached. Subsequently， the alkali leaching solution was dropped into the acid leaching solution to remove silicon in the acid leaching solution. It was found that when the pH was about 3， the precipitation effect of silica sol in the acid leaching solution was the best， and the product obtained by heating the silica sol which was obtained through filtering was mainly SiO₂·0.2Al₂O₃， with a mass fraction of 97.20%. The acid leaching solution after filtering to remove the silica sol was added to the alkali leaching solution to precipitate and recover the fluoride salts， and it was found that when the pH was 9， the recovery rates of CaF₂ and Na₃AlF₆ were the highest， which were 95.91% and 92.44%， respectively， and the mass fractions were 48.41% and 25.14%， respectively. In addition， the precipitate contains 25.32% （mass fraction） of Al（OH）_3.

Key words: aluminum electrolysis, spent dry barrier, alkali-acid method, silica sol, resource utilization

CLC Number:

TF 09

Ke-jian SU, Xian-wei HU, Jun-yu ZHANG, Zhao-wen WANG. Treatment of Spent Dry Barrier from Aluminum Electrolysis by Alkali-Acid Method[J]. Journal of Northeastern University(Natural Science), 2025, 46(6): 40-49.

Figures/Tables 24

Table 1 Analytical instruments used in the experiment

仪器	生产厂家	型号
X射线衍射仪	日本理学(Rigaku)公司	Smartlab SE
高频燃烧红外碳硫分析仪	美国LECO(力可)公司	CS244
原子吸收分光光度计	日本日立公司	180-80
电感耦合等离子体发射光谱仪	美国Perkin Elmer公司	Optima 4300D
扫描电子显微镜	德国蔡司显微镜有限公司	ULTRA PLUS

Fig.1 XRD pattern of spent dry barrier from aluminum electrolysis

Table 2 Element content of spent dry barrier from aluminum electrolysis (mass fraction)

Na	F	Ca	Al	Fe	Li	C	Si	O	余量
25.63	22.90	5.73	10.46	0.96	0.18	0.30	15.06	17.02	1.76

Fig.2 XRD pattern of soluble components in spent dry barrier form aluminum electrolysis

Fig.3 XRD pattern of the remaining solid phase after water leaching

Table 3 Parameter settings for alkali and acid leaching experiments

浸出步骤	温度/℃	时间/min	碱渣质量比	浸出液浓度	液固比	搅拌速率
浸出步骤	温度/℃	时间/min	碱渣质量比	mol·L^-1	cm³·g ^-1	r·min^-1
碱浸	40⁓100	20⁓140	0.1⁓0.35	—	2⁓6	300
酸浸	室温⁓70	15⁓60	—	0.375⁓0.675	8⁓14	300
浸出液处理	室温	实时反应	—	—	—	200

Fig.4 Effect of temperature on leaching rate of Na3AlF6

Fig.5 Effect of leaching time on leaching rate of Na3AlF6

Fig.6 Effect of alkali-slag mass ratio on leaching rate of Na3AlF6

Fig.7 Effect of liquid-solid ratio on leaching rate of Na3AlF6

Fig.8 XRD pattern of typical residue after alkaline leaching

Fig.9 Effect of temperature on leaching rates of CaF2 and NaAlSiO4

Fig.10 Modeling of linear growth and cross-linking process of silica sols

Fig.11 Effect of leaching time on leaching rates of CaF2 and NaAlSiO4

Fig.12 Effect of acid concentration on leaching rates of CaF2 and NaAlSiO4

Fig.13 Effect of liquid-solid ratio on leaching rates of CaF2 and NaAlSiO4

Fig.14 XRD pattern of typical residue after acid leaching

Table 4 Variation of precipitation rate of silicon element in acid leaching solution with pH

pH	2.02	2.29	2.44	2.58	2.71	2.83	2.92	3.03	3.09
Si沉淀率/%	0	19.23	40.77	72.33	84.92	89.65	95.41	98.06	98.11

Fig.15 XRD pattern of product obtained after solution gelation

Fig.16 Morphology of silica coagulation precipitate in acid leaching solution

Fig.17 XRD pattern of precipitate obtained by adding alkali leaching solution to acid leaching solution after silica sol removal

Table 5 Mass fraction of Si and Al in silica coagulation precipitation products in acid leaching solution measured by EDS and ICP %

元素	EDS		ICP
元素	点1	点2	ICP
Al	8.44	9.06	8.76
Si	38.95	37.45	37.69

Fig.18 Variation of fluoride salts (CaF2，Na3AlF6) recovery rate with pH in precipitate

Table 6 Solubility products of CaF2， Na3AlF6 and

种类	溶度积 $K s p$
CaF₂	3.90×10^-10
Na₃AlF₆	4.22×10^-10
Al(OH)₃	1.30×10^-33

Table 6 Solubility products of CaF2， Na3AlF6 and

种类	溶度积 $K s p$
CaF₂	3.90×10^-10
Na₃AlF₆	4.22×10^-10
Al(OH)₃	1.30×10^-33

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