Preparation of battery-grade iron phosphate using the by-product ferrous sulfate of titanium dioxide

doi:10.16085/j.issn.1000-6613.2024-0152

Abstract

Abstract:

Battery-grade iron phosphate was synthesized by liquid-phase precipitation using ferric sulphate as the source of iron, which was obtained from purification of by-product ferrous sulfate of titanium dioxide. The effects of iron to phosphorus feed ratio (Fe/P feed ratio), reaction temperature, pH, CTAB addition on Fe/P, grain size and yield of iron phosphate were investigated. The optimal synthesis conditions for high-yield iron phosphate obtained by response surface methodology were Fe/P feed ratio of 1.33, 80℃, pH of 1.6 and CTAB addition of 2%. Through the response surface optimization experiment, the feed ratio of raw materials was reduced and the cost of materials decreased while ensuring the high yield of 90.98%. The product obtained was determined to be amorphous iron phosphate dehydrate, which was transformed into α-quartz type after calcination. The primary particle size of iron phosphate dihydrate was about 100nm and the average particle size D₅₀ of secondary particles was 8.4μm. The formation mechanism of amorphous iron phosphate was analyzed according to the theory of crystal nucleus formation and crystal growth. The nucleation rate of iron phosphate was much higher than its growth rate and a large number of micro-nuclei were formed in the system. These micro-nuclei were irregularly aggregated because their radius was less than the critical nucleus radius and then amorphous iron phosphate was formed. The element content of the product (FePO₄·2H₂O) was determined to meet the technical index of battery grade iron phosphate.

Key words: ferrous sulfate, titanium dioxide, precipitation, iron phosphate, response surface analysis

摘要：

以钛白副产硫酸亚铁净化除杂所得硫酸铁溶液为铁源，采用液相沉淀法合成电池级磷酸铁，研究了铁磷投料比、反应温度、pH、CTAB添加量对磷酸铁Fe/P、粒径及产率的影响，并通过响应面分析得到高产磷酸铁的较优合成条件为：投料比1.33、温度80℃、pH为1.6、CTAB添加量为2%。通过响应面优化实验，在保证90.98%的高产率的同时，降低了原料投料比，节省了用料成本。所得产物为无定形二水磷酸铁，经煅烧后转变为α-石英型。二水磷酸铁的一次颗粒粒径在100nm左右，二次颗粒平均粒径D₅₀为8.4μm。根据晶核形成与晶体生长理论分析了无定形磷酸铁的形成机理：磷酸铁的成核速率远大于其生长速率，体系中形成大量微小晶核，这些微小晶核因半径小于临界晶核半径而发生无规则的聚集，进而形成无定形磷酸铁。所得二水磷酸铁的元素质量分数符合电池级磷酸铁的技术指标。

关键词: 硫酸亚铁, 钛白, 沉淀法, 磷酸铁, 响应面分析

CLC Number:

TF09

LI Binde, WANG Bixia, YUAN Wenlong, DANG Xiao’e, MA Hongzhou. Preparation of battery-grade iron phosphate using the by-product ferrous sulfate of titanium dioxide[J]. Chemical Industry and Engineering Progress, 2024, 43(8): 4523-4533.

李斌德, 王碧侠, 袁文龙, 党晓娥, 马红周. 钛白副产硫酸亚铁制备电池级磷酸铁[J]. 化工进展, 2024, 43(8): 4523-4533.

Figures/Tables 17

组成	质量分数/%
FeSO₄·7H₂O	≥90
Fe	17.52
Fe(Ⅲ)	1.37
Ti	0.39
Mg	0.48
Mn	0.12
Al	0.0095

因素	代码	水平
因素	代码	-1	0	1
铁磷投料比	A	1.28	1.33	1.38
温度/℃	B	75	80	85
pH	C	1.5	1.6	1.7

序号	铁磷投料比	pH	温度/℃	Fe/%	P/%	Fe/P	产率/%
1	1.28	1.5	80	28.62	16.78	0.9457	86.34
2	1.38	1.6	75	29.73	16.06	1.0261	91.15
3	1.33	1.7	85	30.60	15.80	1.0738	93.65
4	1.33	1.6	80	29.79	16.59	0.9956	90.29
5	1.33	1.7	75	29.91	16.03	1.0348	91.86
6	1.33	1.5	85	30.14	16.24	1.0290	87.79
7	1.28	1.6	75	28.74	16.90	0.9432	87.30
8	1.33	1.6	80	29.68	16.41	1.0032	91.22
9	1.33	1.6	80	29.66	16.52	0.9955	91.43
10	1.33	1.5	75	29.55	16.47	0.9952	86.58
11	1.38	1.5	80	29.67	16.18	1.0169	90.93
12	1.28	1.7	80	29.90	16.56	1.0016	92.45
13	1.38	1.6	85	30.48	15.99	1.0574	92.04
14	1.28	1.6	85	29.69	16.69	0.9862	89.09
15	1.38	1.7	80	30.83	15.79	1.0825	93.68

方差来源	平方和	自由度	均方和	F	P	显著性
模型	80.63	9	8.96	29.49	0.0008	★★
A	19.91	1	19.91	65.54	0.0005	★★
B	4.03	1	4.03	13.28	0.0148	★
C	50.00	1	50.00	164.60	<0.0001	★★
AB	0.20	1	0.20	0.67	0.4514
AC	2.82	1	2.82	9.29	0.0285	★
BC	0.084	1	0.084	0.28	0.6213
A²	0.039	1	0.039	0.13	0.7354
B²	3.56	1	3.56	11.73	0.0187	★
C²	2.792×10^-3	1	2.792×10^-3	9.192×10^-3	0.9273
残差	1.52	5	0.30
失拟差	0.78	3	0.26	0.71	0.6301
净误差	0.74	2	0.37
总误差	82.14	14

序号	铁磷投料比	pH	温度/℃	预测值/%	实验值/%	偏差/%
1	1.33	1.6	80	90.98	91.22	0.24
2	1.33	1.6	80	90.98	90.29	0.69
3	1.33	1.6	80	90.98	91.43	0.45

检验项目	电池级指标要求	产品检验结果
Fe	29.0~30.0	29.66
P	16.2~17.2	16.52
Fe/P	0.97~1.02	0.9955
Ca	≤0.005	0.0048
Mg	≤0.005	0.0039
K	≤0.01	0.0031
Na	≤0.01	0.001
Cu	≤0.005	0.00093
Zn	≤0.005	0.0038
Ni	≤0.005	0.00036
Mn	≤0.01	0.00033
Ti	≤0.005	0.00053
Al	≤0.005	0.0047
SO $4 2 -$	≤0.01	0.0077
Cl^-	≤0.01	未检出
F^-	≤0.01	0.0055

检验项目	电池级指标要求	产品检验结果
Fe	29.0~30.0	29.66
P	16.2~17.2	16.52
Fe/P	0.97~1.02	0.9955
Ca	≤0.005	0.0048
Mg	≤0.005	0.0039
K	≤0.01	0.0031
Na	≤0.01	0.001
Cu	≤0.005	0.00093
Zn	≤0.005	0.0038
Ni	≤0.005	0.00036
Mn	≤0.01	0.00033
Ti	≤0.005	0.00053
Al	≤0.005	0.0047
SO $4 2 -$	≤0.01	0.0077
Cl^-	≤0.01	未检出
F^-	≤0.01	0.0055

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