Enhanced Sulfur Fixation Efficiency of Calcium Hydroxide by Fe3+: Dual Mechanisms of Oxidation and Catalysis

doi:10.15541/jim20250348

Abstract

Abstract:

Sulfur dioxide (SO₂) is a major air pollutant that poses severe hazards to environment and human health. Currently, calcium hydroxide (Ca(OH)₂) is widely used as a common desulfurizing agent due to its simple preparation process, low cost and relatively good desulfurization performance. However, how to further improve its sulfur fixation efficiency remains unknown. Here, a novel calcium-iron desulfurizing agent was prepared in a stepwise manner by incorporating ferric hydroxide during hydration process of calcium oxide (CaO), and then its desulfurization performance was investigated. The results demonstrated that sulfur fixation efficiency of the calcium-iron desulfurizing agent was significantly enhanced, increasing by 26.16% compared to the maximum sulfur fixation efficiency of pure Ca(OH)₂. Addition of Fe³⁺ modified the morphology of Ca(OH)₂, rendering its surface much rougher with an increasing of pores and cracks. This morphological change provided more active sites for the desulfurization reaction. X-ray photoelectron spectroscopy analysis revealed that after desulfurization the proportion of hexavalent sulfur (S⁶⁺) in the sample increased from 9.71% (pure Ca(OH)₂) to 33.33% (calcium-iron desulfurizing agent). Experiment study revealed that before desulfurization, all iron in the calcium-iron desulfurizing agent was in the form of Fe³⁺, but after desulfurization, Fe²⁺ amazingly accounted for 68.42% while Fe³⁺ only accounted for 31.58% of the total calcium-iron agent. Calculations based on these data indicated that 35.56% sulfur was oxidized while 64.44% was catalyzed. These calculation findings confirmed that oxidation and catalytic effects of the iron promoted the conversion of tetravalent sulfur (S⁴⁺) to S⁶⁺, thereby further improving the sulfur fixation efficiency. This study provides a promising approach to enhance the sulfur fixation efficiency of Ca(OH)₂ and an effective material for removing sulfur dioxide from industrial flue gas.

Key words: sulfur dioxide, calcium hydroxide, calcium-iron desulfurizer, sulfur fixation efficiency, oxidation, catalysis

CLC Number:

TB321

LI Zhongyi, LIU Biao, CHEN Xi, LI Chunzhong, JIANG Haibo. Enhanced Sulfur Fixation Efficiency of Calcium Hydroxide by Fe³⁺: Dual Mechanisms of Oxidation and Catalysis[J]. Journal of Inorganic Materials, 2026, 41(5): 637-644.

Figures/Tables 11

Table 1 Preparation of pure calcium hydroxide

CaO/g	Deionized water/g	H₂O/CaO
10	6	0.6
10	7	0.7
10	8	0.8
10	9	0.9
10	10	1.0
10	11	1.1

Table 2 Preparation of calcium-iron desulfurizer

CaO/g	Deionized water/g	Fe(OH)₃/g	H₂O/CaO
10	6	6.25	0.6
10	7	6.25	0.7
10	8	6.25	0.8
10	9	6.25	0.9
10	10	6.25	1.0
10	11	6.25	1.1

Fig. 1 Desulfurization experimental device

Table 3 Composition analysis of quicklime sample

Composition	Content/% (in mass)	Composition	Content/% (in mass)
CaO	96.05	SO₃	0.16
MgO	2.1	K₂O	0.086
Al₂O₃	0.33	Fe₂O₃	0.426
SiO₂	0.757	SrO	0.09

Fig. 2 Desulfurization efficiency of calcium-iron desulfurizer and Ca(OH)2 under different water cement ratios

Fig. 3 SEM images of Ca(OH)2 (a-c) and calcium-iron desulfurizer (d-f) after lime digestion reaction

Table 4 Specific surface areas and pore volumes of calcium-iron desulfurizers

H₂O/CaO	Specific surface area/(m²·g^-1)	Pore volume/(cm³·g^-1)
0.6	25.596	0.116
0.7	25.419	0.122
0.8	27.256	0.130
0.9	26.214	0.127
1.0	26.646	0.135
1.1	31.694	0.182

Fig. 4 XRD patterns of desulfurizers before and after desulfurization (a) Pure Ca(OH)2 with water cement ratio of 0.6-1.1; (b) Calcium-iron desulfurizers with water cement ratio of 0.6-1.1; (c, d) Comparison of pure Ca(OH)2 and calcium-iron desulfurizer with water cement ratio of 1.0 before (c) and after (d) desulfurization

Fig. 5 FT-IR spectra of pure Ca(OH)2 and calcium-iron desulfurizer with water cement ratio of 1.0 before (a) and after (b) desulfurization

Fig. 6 XPS spectra of pure Ca(OH)2 and calcium-iron desulfurizer with water cement ratio of 1.0 before and after desulfurization (a) S2p of pure Ca(OH)2 after desulfurization; (b) S2p of calcium-iron desulfurizer after desulfurization; (c) Fe2p of calcium-iron desulfurizer before desulfurization; (d) Fe2p of calcium-iron desulfurizer after desulfurization

Table 5 Comparison of sulfur fixation efficiency between calcium-iron desulfurizer and other desulfurizers

Desulfurizer	Sulfur fixation efficiency/%
Calcium-iron desulfurizer	17.07
Yan et al.^[11]	1.95
Li et al.^[19]	6.4

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Enhanced Sulfur Fixation Efficiency of Calcium Hydroxide by Fe³⁺: Dual Mechanisms of Oxidation and Catalysis

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